Health Risks

December 12, 2024 - An exploratory study of metabolomics in endogenous and cannabis-use-associated psychotic-like experiences in adolescence. This small-scale study (Kurkinen et al., 2024) focuses on how products of biological metabolism after use of cannabis may be related to the onset of psychosis. The authors’ strategy is to analyze different biological products, a distinction from other studies that evaluate genes, proteins or neurotransmitter receptors. All of these strategies may be methods of finding some of the causes of psychosis. The sample of subjects allowed for examining metabolic associations when participants used cannabis from those who didn’t. 

This study compared cellular metabolites (the organic chemicals produced within cells) such as carbohydrate conjugates, cholesterol and steroid metabolites, choline metabolites, citric acid cycle metabolites, enzyme cofactors etc. These metabolites have important functions such as managing cellular energy and the integrity of the immune system.  

What we learn from the study is that cannabis effects cellular energy metabolism and this influence has been associated with first episode psychosis. Cannabis alters another system called acylcarnitines which alters the way cells use energy, shifting to an alternative molecule called ketones rather than the universal energy source glucose. Cannabis can cause this shift in a special cell in the brain called an astrocyte. Astrocytes play a critical role in the brain including brain damage repair following infection and traumatic injuries and the regulation of brain blood flow. Finally, the amino acid valine has been associated with symptoms of schizophrenia, and cannabis increases levels of valine.  

In summary, cannabis has important effects on metabolic processes and these cellular processes have been associated with severe mental illnesses. 

December 4, 2024 - Epigenetic effects of cannabis: A systematic scoping review of behavioral and emotional symptoms associated with cannabis use and exocannabinoid exposure. This publication by Machado and colleagues (Machado et al., 2024) is a meta-analysis of 37 clinical and preclinical peer reviewed studies, each of which explored the effect of cannabis on epigenetic processes.  

A meta-analysis is a statistical procedure that synthesizes a group of similar studies, all of which measure the same  or similar outcome variable(s).  

Epigenetics is the biological process by which specific genes, or the proteins produced by them, are chemically modified by environmental actions.  This phenomenon provides an explanation for how a person’s experience or exposure to something in the environment (such as drug useP can “get under the skin” and alter downstream health, behavior or both.  These modifications (augmenting/suppressing) of genetic material influence emotions, behavior, aging, cognition and disease. There are four different ways that genes can be modified through epigenetics: 1. DNA methylation which deactivates gene activity. 2. Histone modifications-changing the cells proteins that determine the structure/shape and hence the activity of chromosomes. 3. Changes in the levels of enzymes that are responsible for DNA methylation, Histone modification and others. 4. MicroRNA’s are noncoding pieces of RNA that interfere/silence the activity of target genes.  

The goal of the present study was to determine how cannabinoids affect the epigenetic processes noted above. The studies were stratified by age of cannabis use (exposure). Some of the important study findings include the following: (1) Animal studies found differential methylation of the reward and executive processing centers of the brain, which could lead to increased reward processing and addiction susceptibility, as well as positive psychotic symptoms and cognitive impairments, negative symptoms of schizophrenia and mood disorders. (2) The human based studies did not replicate these effects on genes. (3) A synergistic effect of combined exposure to CBD and THC was observed, and this was different from the effects of either cannabinoid alone. (4)  THC exposure both prenatally and in adulthood was associated with increased opioid vulnerability, which supports the view that use of cannabis increases rather than decreases risk for subsequent opioid dependence.  

In sum, the authors note that while many of their findings have been noted previously in epidemiological and clinical studies, this meta-analysis gives clear genetic biologic affirmation of the consequences of cannabinoid exposure.  

December 2, 2024 - Key insights into cannabis-cancer pathobiology and genotoxicity. The authors of this paper (Reece and Hulse, 2024) have multiple scientific publications that link the cannabinoids with cancer, neurodevelopmental disorders, accelerated aging and congenital anomalies. The current paper conceptually but not yet experimentally, discusses recent research published in Science in 2024 that explains in vivid detail how cannabinoids contribute to cellular DNA disruptions leading to cancer and other toxic effects.  

The putative causality is that cannabinoids contribute to  DNA disruptions. The critical concept explained in the paper is the dissolution of mononuclear envelopes (tiny collections of pieces of DNA produced by various kinds of stress at the organism and cellular level) which when dissolved leads to carcinogenic processes such as chromosomal shattering and chromothripsis (disruption of the standard sequence of chromosomal regions and their subsequent reassembly in ways that result in loss of tumor suppressor processes and the augmentation of newly formed genes from the reassembly that are tumor/cancer producers). The authors refer to two studies that show the link between cannabis and both micronuclear development (the sequestration of DNA bits) and itochondria inhibition (the restraint of the energy producing mechanism of a cell that can lead to cell death). These physiological products of cannabinoids they suggest result in accelerated aging, myocardial infarction, early onset and more severe cancers, cognitive anomalies, urogenital and gastrointestinal system disorders, as well as effects on sperm and egg cells leading to generational toxic effects. The theoretical underpinnings of this hypothesis is intriguing but has yet to be proved.

September 19, 2024 - The long-term relationship between cannabis and heroin use: An 18- to 20-year follow-up of the Australian Treatment Outcome Study (ATOS). One of the arguments that advanced the push to legalize cannabis for medicinal and recreational use was the belief that cannabis was a solution to the opioid crisis. Various research has looked at this issue and both sides of the debate point to supportive findings. 

A recent study (Wilson et al., 2024) provides a strong research design that examines the possible causal relationship between cannabis and opioid use among individuals with opioid use disorder. Based on data from the Australian Treatment Outcome Study, the researchers identified 615 young people with heroin dependence who were interviewed at baseline and subsequently again six times over two decades. The analysis evaluated within-person relationships between cannabis and heroin use over time.  This allowed a look at how heroin use and cannabis use and vice versa changed over time. 

After controlling for a wide range of potential clinical and demographic confounders, the results showed that the level of cannabis use at one-time point was not significantly associated with subsequent heroin use, nor was the level of heroin use at one point in time significantly associated with subsequent cannabis use.  

The commentary piece about the Wilson study (Olfson, 2024) concludes that the pattern of findings argues “against a strong directional association between cannabis and heroin use in this population. Such findings are not consistent with claims that cannabis has a role in the management of opioid use disorder. Moreover, the new results suggest that physicians and other clinicians who care for patients with current or past opioid use disorder should view with healthy skepticism the promotion of cannabis-based interventions for this patient group.” (p. 93). 

A related question about the intersection of cannabis and opioid use is whether cannabis use tends to increase the likelihood of transitioning from non-use to use of opioids or opioid use disorder. That issue is not addressed by the Wilson study.  Yet Olfson notes that other studies suggest that those who use cannabis are more likely to start opioid use, with many transiting from opioid use to opioid use disorder.

September 17, 2024 - Epigenetic effects of cannabis: A systematic scoping review of behavioral and emotional symptoms associated with cannabis use and exocannabinoid exposure (summary assisted by ChatGP). New research suggests that cannabis (THC) may cause long-term changes in behavior, possibly through altering gene expression (epigenetics). This could affect thinking and play a role in the development of psychotic symptoms. 

This review (Machado et al., 2024) looked at studies exploring how THC affects gene expression and its link to behavior and emotions. Researchers searched databases like PubMed and found 178 articles, 43 of which were fully reviewed, and 37 included in the final analysis. 

The studies results were based on a mix of human and animal research, using different methods and doses of cannabis. Some studies looked at the whole genome and found widespread changes in gene activity, especially in genes related to cell survival and brain development. Other studies focused on specific genes and found that THC exposure was linked to changes in how certain genes are "turned on" or "off." 

The authors conclude that exposure to THC seems to cause epigenetic changes that may influence depression, anxiety, psychosis, and addiction. More research is needed to standardize how cannabis is studied and which genes should be looked at as potential markers for mental health conditions.

July 29, 2024 - Prenatal cannabis use and maternal pregnancy outcomes. This is another publication that focuses on the impact of prenatal cannabis use. Yet this research report by Young-Wollf and colleagues (Young-Wolff et al., 2024) looked at maternal health during pregnancy.  The data were drawn from a cohort in Northern California from January 2011 to December 2019 (N= 316,722).  Prenatal cannabis use was defined as any self-reported use during early pregnancy or a positive toxicology test result based on universal screening at entrance to prenatal care. 

Compared to non-cannabis users, the cannabis users showed a significant higher rate of these adverse maternal health outcomes during pregnancy: gestational hypertension, preeclampsia (a serious blood pressure condition to the mother that develops during pregnancy), weight gain either below guidelines or above guidelines, and placental abruption (when the placenta detaches from the uterus during pregnancy).  Please click this link to see chart provided by Smart Approaches to Marijuana.

 Additional note from KCW: This study, as well as several others in the research literature, bring to light the importance that cannabis retail staff not extoll the benefits of cannabis use during pregnancy and that products need to include clear warnings to pregnant customers.

July 8, 2024 - Heavy lifetime cannabis use and mortality by sex. The UK Biobank is a large-scale biomedical database and research resource containing de-identified genetic, lifestyle and health information and biological samples from half a million UK participants.  

This rich dataset was analyzed by Vallee (2024) in order to examine the associations of cumulative lifetime cannabis use with mortality from any cause, cancer and cardiovascular disease. Participant monitoring for mortality began from the point of inclusion in the Biobank between 2006 and 2010 and continued until December 19, 2020.  Cannabis use status was assessed by questionnaire and categorized as heavy, moderate, low, and never. The main outcome data was a hazard ratio (HR), which is a measure in this study for how often mortality happens in one group (level of cannabis use) compared to how often mortality happens in another group (non-cannabis use) over time.  Any HR greater than 1.0 would indicate a higher rate of mortality among cannabis users compared to non-cannabis users. 

At the last follow-up point (2020), after full statistical adjustment (demographic and clinical variables), the HRs for males were 1.28 for any cause mortality, 0.98 for cardiovascular disease mortality, and 1.09 for cancer mortality among heavy cannabis users compared with never users.  Among females, all HRs were much higher: 1.49 for all-cause mortality, 2.67 for cardiovascular disease mortality, and 1.61 for cancer mortality. 

When mortality rates were re-examined for tobacco + cannabis use status, the HRs were predictably higher for both sexes among tobacco + heavy cannabis users compared to non-tobacco + heavy cannabis users. 

The authors concluded that “a positive association between cardiovascular disease mortality and heavy lifetime cannabis use was observed among females.”

July 2, 2024 - Cannabis use reported by patients receiving primary care in a large health system. The authors of this study (Gelberg et al., 2024) used a cross-sectional research design to report on the prevalence of, factors associated with, and reasons for past–3 month cannabis use reported by primary care patients.  Data were based on electronic health records from patients aged 18 years and older who had an annual wellness visit between January 2021 and May 2023 from a primary care clinic within a university-based health system in Los Angeles, CA. 

Cannabis use was reported by 17% of the sample, and among them, 35% had a screening score indicative of a moderate to high risk for having a cannabis use disorder (CUD).  The most common modes of use included edibles (62%), smoking (52%) and vaporizing (29%).  A high percentage of cannabis users (76%) reported using to manage symptoms including pain, stress and sleep. 

The authors conclude: “Cannabis use and risk of CUD were common, and more than three-quarters of patients who reported any cannabis use reported doing so to manage a health-related symptom.”

June 27, 2024 - Evaluation of potential drug–drug interactions with medical cannabis. Cannabis–drug interactions are a significant health topic given that many cannabis users may also be taking medications prescribed by their physician.  The authors of this publication (Jia Yi Ho et al., 2024) systematically reviewed the literature of published studies on the potential interactions of cannabis with 21 drug classes.  The authors conclude that “Generally, cannabis–drug interactions result in pharmacokinetic (PK) or pharmacodynamic (PD) changes. Therefore, careful monitoring should be performed to detect any unusual elevations in plasma levels.”

May 28, 2024 - Incident psychotic experiences following self-reported use of high-potency cannabis: Results from a longitudinal cohort study. We have posted several research publications on the association of cannabis use and psychosis.  This report from Hines and colleagues (Hines et al., 2024) adds to this body of work with a longitudinal study.  The U.K. researchers collected self-reported data on cannabis use (yes/no) from a youth sample at ages 16 and 18 (n= 5,570) and a subsample at age 24 (n = 1,560) who reported the type of cannabis they most commonly used in the whole time since first using cannabis. Also assessed at age 24 were psychotic experiences using the semi-structured Psychosis-Like Symptom Interview.  Incidence of psychosis experiences was defined as new-onset occurring between ages 19 and 24 years.  Thus, youth who reported psychosis-related experiences prior to using cannabis were excluded from the analysis. 

The main finding was that self-reported use of high-potency cannabis since beginning use of cannabis at either age 16 or 18 was associated with twice the likelihood of experiencing incident psychotic experiences during ages 19–24 (Odds Ratio = 2.15).  Any use of cannabis, regardless of potency, was associated with a much lower association psychotic experiences (Odds Ratio = 1.45). 

The authors' conclusion: “Use of high-potency cannabis appears to be associated with increased likelihood of psychotic experiences.” 

May 24, 2024 - Edible Cannabis Legalization and Cannabis Poisonings in Older Adults. This retrospective, population-based, cross-sectional study (Stall et al., 2024) tapped  Ontario Ministry of Health administrative data to examine emergency department (ED) visit rates for cannabis poisoning in older adults.  Rates were computed for three Canada cannabis policy periods: prelegalization (January 2015 to September 2018); legalization period 1, which permitted the sale of dried cannabis flowers only (October 2018 to December 2019); and legalization period 2, which also permitted the sale of edible cannabis (January 2020 to December 2022). ED visits were identified where cannabis poisoning was the main or contributing reason and rates per 100,000 person-years for older adults were calculated. 

During the 8-year study period, there were 2,322 ED visits for cannabis poisoning in older adults (women, 45%; median age, 70).  Among these patients, 17% had concomitant alcohol intoxication, 39% cancer, and 6.5% dementia.  The rates were significantly higher after legalization (period 1 and 2).  Prelegalization: there was a yearly average of 117 ED visits for cannabis poisoning; legalization: the yearly average was 394. The largest increases occurred after edible cannabis became legally available for retail sale.  The authors note that a similar pattern of ED data and cannabis poisoning was observed in Canadian children.

May 17, 2024 - Association Between Cannabis Use Disorder and Schizophrenia Stronger in Young Males than in Females. This is another Danish national health registry publication that looks at the possible association of cannabis use and the incidence of schizophrenia. The authors (Hjorthøj et al., 2023) estimated the extent to which Cannabis Use Disorder (CUD) impacted the incidence of schizophrenia with a focus on gender.  The analysis included all individuals aged 16–49 at some point during 1972–2021 (N= approx. 6.9 million). CUD and schizophrenia status were obtained from the registers. The key outcome metric was the population attributable risk fraction (PARF). This is the proportion of cases for an outcome (schizophrenia) that can be attributed to a certain risk factor (CUD) among the entire population. 

The PARF of CUD on the incidence of schizophrenia was elevated for both genders and all age groups, yet males had a significantly greater PARF than females. One highlight finding: During 1972–2021, among males, the annual average percentage change in the PARFs of CUD on the incidence of schizophrenia was 4.8, whereas among females, it was 3.2.  Also, the PARF change over this time period was about twice as high among younger males compared to younger females. 

The authors conclude that the “study finds strong evidence of an association between CUD and schizophrenia among both males and females, and the magnitude of this association appears to be consistently larger among males than females, especially among those aged 16–25.  Importantly, 15% of cases of schizophrenia in males may be preventable if CUD was avoided. Although CUD is not responsible for most schizophrenia cases in Denmark, it appears to contribute to a non-negligible and steadily increasing proportion over the past five decades.”  Another summary statement: “at a population level, assuming causality, one-fifth of cases of schizophrenia among young males might be prevented by averting CUD.” 

The authors address possible confounding factors and other study limitations and there is a detailed description of them (e.g., common genetic factors of both cannabis use and schizophrenia, co-use of other substances, registry limitations). Here is a summary statement regarding confounds: “Finally, although the observational nature of this study does not directly allow for causal inference and we cannot be certain of the proportion of exposed individuals who might have developed schizophrenia even in the absence of CUD, it is unlikely that all of the associations between CUD and schizophrenia would be explained by confounding factors.”

March 23, 2024 - Lifetime Marijuana Use and Epigenetic Age Acceleration: A 17-year Prospective Examination. Epigenetics is the study of how your behaviors and environment can cause changes in the way your genes work. These changes do not alter the biological structure or “code” of your DNA but impact whether genes are turned on or off. One example of epigenetics: It can inform how experiences affect the role of genes in the aging process.

 The present study (Allen et al., 2022) capitalized on epigenetics to address if lifetime cannabis use accelerated epigenetic aging. The basic design of the study was to follow 154 participants annually from age 13 to age 30. They completed annual assessments of cannabis use and other health variables (e.g., history of cigarette smoking, mental health), and provided at age 30 blood samples that yielded two indices of epigenetic aging.

 Lifetime marijuana use significantly predicted accelerated epigenetic aging, with effects remaining after controlling for demographics, health variables and chronological age.  A dose-response was observed: the heavier the cannabis use the greater the epigenetics changes linked to accelerated aging. The authors noted that the “effects appeared to be fully mediated by hypomethylation of a site linked to effects of hydrocarbon inhalation (cg05575921), suggesting that the smoking of cannabis rather than non-smoking consumption is the key risk factor of cannabis-related accelerated aging.” (Note: A predominant epigenetic mechanism is DNA hypomethylation and hypermethylation.)

March 23, 2024 - The Association Between Prenatal Cannabis Use and Congenital Birth Defects in Offspring: A Cumulative Meta-Analysis. This is a meta-analysis study, a type of research we have often highlighted.  A meta-analysis study combines many studies that address a similar topic and share high quality characteristics.  Each study’s findings are pooled to create global or “meta” statistical results.

 Here the authors (Tadese et al., 2024) sought to characterize the association between prenatal cannabis use and structural birth defects in exposed offspring. They located 36 observational studies, consisting of 18 case-control and 18 cohort studies.

 The final analysis indicated that offspring exposed to maternal prenatal cannabis were at greater risks (noted as odds ratio) of a wide range of structural birth defects: cardiovascular/heart (odds ratio = 2.4), gastrointestinal (odds ratio = 2.4), central nervous system (odds ratio = 2.9), genitourinary (odds ratio = 2.4) and any (unclassified) birth defects (odds ratio = 1.3).

The authors concluded: “The findings from the current study suggest that maternal prenatal cannabis exposure is associated with a higher risk of different forms of structural birth defects in offspring.”

March 23, 2024 -Association of Cannabis Use With Cardiovascular Outcomes Among US Adults. The researchers (Jeffers et al., 2024) examined the link between cannabis use and cardiovascular outcomes among the general population. The analyses were based on Behavioral Risk Factor Surveillance Survey data collected 2016 to 2020 from 27 American states and 2 territories.  Specifically, associations were computed between cannabis use (number of days of cannabis use in the past 30 days) and self-reported cardiovascular outcomes (coronary heart disease, myocardial infarction, stroke, and a composite measure of all 3). Statistical adjustments were made for tobacco use and other potentially confounding characteristics (e.g., alcohol use, body mass index, physical activity).

Among the over 400,000 respondents, the prevalence of daily and nondaily cannabis use was 4% and 7.1%, respectively.  

All analyses of the association of cannabis use and adverse cardiovascular outcomes were significant, with odds ratios typically about 1.5 (that is, about one-and-a-half greater likelihood of having an adverse cardiovascular outcome if a person used cannabis compared to those who did not use cannabis).   

Other study conclusions:  1. Relationships between cannabis use and cardiovascular outcomes were similar for men <55 years old and women <65 years old; 2. Heavier cannabis use (more days per month) was associated with higher odds of adverse outcomes; 3. Non-smoking cannabis use was associated with elevated likelihood of adverse outcomes; and 4. Cannabis users who did not use nicotine also had elevated risks for negative cardiovascular outcomes.

March 10, 2024 - The prevalence of cannabis use disorders in people who use medicinal cannabis: A systematic review and meta-analysis. The authors (Dawson et al., 2024) conducted  systematic literature review and subsequent meta-analysis to assess the prevalence of Cannabis Use Disorder (CUD) in people who use medicinal cannabis. Their review identified 14 eligible publications that provided data for 3,681 participants from five different countries. 

 For individuals using medicinal cannabis in the past 6-12 months, the prevalence of CUDs was 29% based on DSM-5 criteria. Similar prevalence was observed with DSM-IV (24%) for the same period.

The authors conclude the following: “The prevalence of CUDs in people who use medicinal cannabis is substantial and comparable to people who use cannabis for recreational reasons, emphasizing the need for ongoing research to monitor the prevalence of CUDs in people who use medicinal cannabis.”

February 16, 2024 - Development of an anxiety disorder following an emergency department visit due to cannabis use: a population-based cohort study. This study (Myran et al., 2024) used health records from Ontario Canada to look at the issue of whether cannabis use increases the risk of later developing an anxiety disorder. 

 The study included 12,099,144 individuals aged 10–105 without prior care for an anxiety disorder in the ED or hospital, between January 2008 and March 2019.  Among this group, 34,822 (less than 1%) had an incident ED visit due to cannabis. 

The primary analysis examined those that had an emergency department (ED) visit due to cannabis and then the likelihood over a subsequent 3-year period of either another ED visit or hospitalization for an anxiety disorder. Within 3-years of an incident ED visit due to cannabis, 12.3% (n = 4294) of individuals had an incident ED visit or hospitalization for an anxiety disorder. In the general population, 1.2% had an incident visit for anxiety disorder.  This represented an adjusted 3.7-fold increased risk relative among those with a prior cannabis incident compared to the general population.  The age and sex analysis showed that the relative risk was highest among young males.

 A secondary analysis excluded those with any history of outpatient treatment for an anxiety disorder.  That analysis yielded an even larger adjusted relative risk – 3.9.

 The authors conclude that “ED visits for cannabis use were associated with an increased risk of having an incident healthcare visit for an anxiety disorder, particularly in young males”.

December 27, 2023 - Prospective, longitudinal study to isolate the impacts of marijuana use on neurocognitive functioning in adolescents. We have summarized in this website the growing number of longitudinal studies focused on the effects of cannabis use during neurodevelopmental period of adolescence.  The present study (Ren and Fishbein, 2023) is one of the better ones from a research design standpoint (albeit the sample size is only modest). Early adolescents who were substance-naïve at baseline (N = 529, aged 10–12) were recruited and tracked into adolescence when a subgroup initiated marijuana use during one of three subsequent waves of data collection, approximately 18 months apart. Several cognitive functioning measures collected at baseline and again repeated at subsequent waves were analyzed.  

The findings “suggest that marijuana use may be specifically related to a decline in verbal learning ability in the short term and in emotion recognition, attention, and inhibition in the longer-term.”   

These results imply that learning and planful decision making can be impaired resulting from cannabis use during adolescence.

December 19, 2023 - Cannabis Exposure and Adverse Pregnancy Outcomes Related to Placental Function. This is report (Metz et al 2023) follows a meta analysis,, a Canadian cross sectional study,  and a study that looked at the timing of cannabis use comparing first trimester compared to controls that points to fetal health compromise due to use.

This study theorizes toxic cannabis effect on the placenta leading to fetal health toxicities. This very large sample study ((10,038) was able to  compare cannabis use in the first trimester only to cannabis for the entire pregnancy and non cannabis use. Cofounds such as nicotine use, SES, maternal body mass index and medical comorbidities, Cannabis use in pregnant women was measured in stored urine samples. A composite outcome indes that included small for gestational age birth, medically indicated preterm birth, stillbirth, and hypertensive disorder was derived. Results showed the negative outcomes were 25.9% in the cannabis group and 17.4%in the non-cannabis group. Cannabis use in the first trimester was not associated with risk while cannabis throughout exposure had anadjusted relative risk of 1.32. These results are consistent with three recently reviewed studies on this topic in 2023.  

November 21, 2023 - Risk for Cannabis Use Disorder in people who use cannabis to cope with internalizing disorders: Implications for policy and practice. This manuscript (Schermitzler et al., 2023) provides a review of the research literature on the intersection of cannabis use and internalizing disorders (anxiety and depression). The authors conclude that there is “little to no evidence” that cannabis use improves symptoms of internalizing disorders over time, in contrast to the marketing of cannabis as a therapeutic for these disorders and the perception of many recreational users who use cannabis to cope with negative emotions associated with anxiety and depression. The authors note that the longitudinal studies examining cannabis use and symptoms of internalizing disorders have “generally reported either no association or that heavier cannabis use predicts increased symptoms”. The manuscript emphasizes the importance of educating the public and policy makers that chronic cannabis use contributes to neurobiological changes that deleteriously affect internalizing disorders. 

November 13, 2023 - Cannabis retailer communication about cannabis products, health benefits and risks: A mystery shopper study of licensed retailers in 5 US cities. Researchers (Romm et al., 2023) enlisted "mystery shoppers" to assess cannabis retail personnel communications regarding product recommendations, health benefits, safety, and/or risks. One-hundred-and-forty established legal, non-medical adult cannabis retail outlets with diverse regulations in 5 cities (Denver, Colorado; Seattle, Washington; Portland, Oregon; Las Vegas, Nevada; Los Angeles, California) were sampled.   

The results indicate that retail staff frequently violated state regulations by expressing medical benefits of THC and CBD. More than 93% and 90% of retailers endorsed THC and CBD use, respectively, for anxiety, insomnia, and/or pain. Other overall findings were the following (there was considerable variance between cities):

1. 54% endorsed use for pregnancy-related nausea.

2. 52% warned against driving after use.

3. 9% offered free/inexpensive ways to sample products. 

 The authors conclude that retail surveillance is a vital tool to ensure compliance of retail staff with state regulations.

November 6, 2023 - Edible Cannabis Legalization and Unintentional Poisonings in Children. Canadian researchers (Myran et al., 2022) conducted a population-based study examining the association between legalization of cannabis in Canada and unintentional cannabis poisonings in children.  They analyzed data on all hospitalizations in children 0 to 9 years of age in four of Canada’s largest provinces - Alberta, British Columbia, Ontario, and Quebec (86% of the Canadian population).  Hospitalization rates were compared over three periods: before legalization (January 2015 through September 2018); the first period of legalization, when the sale of only dried cannabis flower was legalized in all provinces (October 2018 through December 2019); and the second period of legalization, when edibles were permitted in Alberta, British Columbia, and Ontario (exposed provinces) but prohibited in Quebec (control province) (January 2020 through September 2021).

 The data indicate that legalization was associated with marked increases in hospitalizations for cannabis poisoning in children.  Increases were the highest after edibles were legalized.  The hospitalization rate in the three “edible-allowed” provinces was 7.5 times as high as before legalization.  The one “edibles-not-allowed” province also showed an increase in hospitalizations (3.0 times as high as before legalization in other provinces).  These increases occurred “despite strict regulations aimed at reducing poisonings in children, including a maximum of 10 mg of THC per edible package, requirements for plain and child-resistant packaging, and consumer education campaigns.”

October 27, 2023 - The highs and the lows: Recreational marijuana laws and mental health treatment. The author (Ortega, 2023) summarizes the impact of recreational marijuana laws (RMLs) on the short-term effects of changes in admissions into mental health treatment.  The analysis used an event-study within a difference-in-differences framework, a statistical method to compare pre- and post-RML trends. The study results indicate that “shortly after a state adopts an RML, they experience a decrease in the average number of mental health treatment admissions.” Furthermore, the authors found this trend was largely driven by white and Black people, and at Medicaid-funded admissions. There were no differences for male and female admissions.

 Commentary from this reviewer (KCW): As the author notes, a decrease in mental health treatment admissions needs to be considered in light of the possibility that there was an increase in addiction treatment admissions.  That data point was unfortunately not included in the analysis. Another factor to consider when interpreting the study results: The short-term effects of mental health hospitalization admission rates may not hold over time.  The perceived short-term effects of cannabis on a user’s mental health may lead a person to feel temporary emotional and behavioral relief. Yet the research literature reminds us of the sobering finding that mental health in a cannabis user is not reliably improved with continued use of this drug.

October 23, 2023 - Outcomes associated with nonmedical cannabis legalization policy in Canada: taking stock at the 5-year mark. Canada legalized cannabis use for adults in 2018. The authors (Fischer et al., 2023) reviewed Canadian health and legal data in order to examine legalization effects.

 Conclusions related to available health-related evidence suggests that the prevalence of cannabis use, cannabis-related emergency department visits and admissions to hospital, and cannabis impaired driving have mostly increased or remained steady.  Criminal arrests and charges related to cannabis use were found to have substantially declined.

 A summary statement from the publication is the following: “A consideration of the evidence 5 years after implementation suggests that success in meeting policy objectives has been mixed, with social justice benefits appearing to be more tangibly substantive than health benefits.”

October 23, 2023 - Chronic Pain, Cannabis Legalization and Cannabis Use Disorder in Veterans Health Administration Patients, 2005 to 2019. This study examined the effect of the introduction of medical cannabis laws (MCL) and recreational cannabis laws (RCL) on the increase in cannabis use disorder (CUD) among patients in the US Veterans Health Administration (VHA). 

 Nationally recognized epidemiologist Deborah Hasin and colleagues (Hasin et al., 2023) examined electronic health data from VHA patients with one or more primary care, emergency, or mental health visit during 2005–2019. Patients were stratified as either having chronic pain (excluding those in hospice or palliative care) or no chronic pain, using an American Pain Society taxonomy of painful medical conditions. The statistical analysis provided an estimate of the extent to which MCL/RCL enactment was associated with CUD rates.

 Among patients with chronic pain, enacting MCL led to an 8% increase in CUD attributable to MCL; enacting RCL led to a 12% increase attributable to RCL. For patients with no chronic pain, enacting MCL and RCL led to smaller absolute increases in cannabis use disorder prevalence (6% and 6%, respectively).

 The authors concluded: “Overall, associations of MCL and RCL with cannabis use disorder were greater in patients with chronic pain than in patients without chronic pain.”

October 4, 2023 - Transition to Schizophrenia Spectrum Disorder Following Emergency Department Visits Due to Substance Use With and Without Psychosis. Myran and colleagues (2023) quantified the risk of individuals to transition to a schizophrenia spectrum disorder (a broad term reflecting the continuum of full-blown schizophrenia as well as less-severe psychotic-like symptoms) following an emergency department (ED) incident associated with substance use. 

This population-based retrospective cohort study (January 2008 to March 2022) involved all individuals aged 14 to 65 years, in Ontario, Canada, with no history of a psychotic disorder, and who had an ED visit due to a substance use incident (N = 407,737).  Among that group of ED visits, 3.4% individuals were recorded as suffering from a substance-induced psychosis; the others were recorded as suffering from acute substance use intoxication. Within a 3-year follow-up period, 19% of those with the ED psychosis record had transitioned to a diagnosis of a schizophrenia spectrum disorder, compared to 0.1% of the general population.  This represents a 163-fold increased risk for those with substance-induced psychosis history. Some individuals with an ED visit for substance use without psychosis also transitioned to a schizophrenia spectrum disorder, but at a much lower relative risk.   

Cannabis use had by far the highest transition risk among ED visits with substance-induced psychosis, and the third-highest risk among visits without psychosis. 

The authors conclude that “The findings of this cohort study suggest that ED visits for substance use were associated with an increased risk of developing a schizophrenia spectrum disorder. Although substance-induced psychoses had a greater relative transition risk, substance use without psychosis was far more prevalent and resulted in a greater absolute number of transitions." 

This reviewer’s (KCW) additional comments: 1. The sample was limited to those without a history of a psychotic disorder, but we do not know individuals' mental health risk factors. 2. Cannabis was the primary culprit in the transition to a psychotic-related disorder. 

September 11, 2023 - Perceptions of Safety of Daily Cannabis vs Tobacco Smoking and Secondhand Smoke Exposure, 2017-2021. This publication (Chambers et al. 2023) addresses the safety perception regarding daily smoking of and exposure to secondhand smoke of cannabis compared to tobacco. A longitudinal survey study of 5, 035 U.S. adults was conducted using a web-based survey administered in 2017, 2020, and 2021.

 Study results indicated that daily cannabis smoking or smoke exposure was perceived to be safer than tobacco.  Trend data indicated that views increasingly favored from 2017 to 2021.  The authors emphasize the importance of public health efforts “to educate the public on potential risks and curb the increasing social acceptance of cannabis smoke exposure, similar to past education about secondhand tobacco smoke.”

September 1, 2023 - Prevalence of Cannabis Use Disorder and Reasons for Use Among Adults in a US State Where Recreational Cannabis Use Is Legal. This cross-sectional study is based on a large adult data set of primary care patients in Washington State.  The authors (Lapham et al., 2023) examined the prevalence of Cannabis Use Disorder (CUD) among clinic patients who use cannabis for medical or non-medical reasons.  Diagnostic interviews were administered to consenting patients who reported a recent use of cannabis (N= 1,463). 

 The results indicated that the prevalence of a CUD, regardless of level of CUD severity (that is, 2 or more of 11 symptoms present) was 21%, and there was no difference in prevalence between the two marijuana-using groups.  But among those who met moderate to severe CUD (that is, 4 or more of 11 symptoms present), there was a significant group difference: 1% for medical users and 7% for recreational users.   The authors concluded: “In this cross-sectional study of primary care patients in a state with legal recreational cannabis use, CUD was common among patients who used cannabis. Moderate to severe CUD was more prevalent among patients who reported any nonmedical use.”

July 16, 2023 - Cannabis Use Disorder and Subsequent Risk of Psychotic and Nonpsychotic Unipolar Depression and Bipolar Disorder. This study by Jefsen et al (2023). examined the intersection of risk for affective disorders and use of cannabis.  Specifically, whether cannabis use disorder was associated with an increased risk of psychotic and nonpsychotic unipolar depression and bipolar disorder was studied.

This prospective, population-based cohort study was based on Danish nationwide registers included all individuals born in Denmark before December 31, 2005, who were alive, aged at least 16 years, and living in Denmark between January 1, 1995, and December 31, 2021.

Main results: Based on data from over 6 million individuals, it was found that having a cannabis use disorder was significantly associated with about a 2- to 3-fold increased risk of also suffering from a psychotic and nonpsychotic bipolar disorder or unipolar depression. 

July 16, 2023 - Association Between Marijuana Laws and Suicide Among 12- to 25-Year-Olds in the United States From 2000 to 2019. This study by Hammond and colleagues (2023) attempts to address the question of whether cannabis legislation such as medical cannabis and recreational cannabis is associated with a quantifiable metric of youth age 12 to 25 mental health, namely suicide related mortality.

Deaths from suicide for youth age 12 to 25 were extracted from the National Center for Health Statistics National vital statistics system from 2000 to 2019.  Because there are multiple causes of suicide besides cannabis the other influences were controlled for. The covariates included per capita income, proportion of ethnic groups, gender, unemployment, poverty status, insurance status on a state by state basis. Public policy variables that impact suicide were also accounted for including taxes on alcohol, intoxicated driving laws, blood alcohol limit, cigarette tax, gun laws, smoke free laws. The number of health providers and mental health clinics and state mental health expenditures was coded.

Analysis took into account suicide trends contrasting before and after a state’s authorized cannabis legalization.

Results showed the lowest rate of suicide in youth was for states with no cannabis authorization and highest for recreational cannabis states. States with recreational legalization had a 16% higher rate of female suicide than states without cannabis legalization. Females age 20-22 had 20% higher suicide rates than same age females in non-authorized cannabis states. 

The relationship of recreational cannabis legalization and male suicide rate was not consistent by age. Combining male and female cases, youth aged 14 to 16 years had higher rates in states with recreational cannabis compared to states with no cannabis authorization. This is important because earlier onset of use acting in concert with great changes in brain development at this age is related to increased psychiatric disorders in life. Increasing use of high potency THC appears to be more deleterious for females of any age and for males aged 14 to 16.

Conclusions and action steps: These results suggest that adolescent and young adults in particular female youth represent vulnerable subgroups at elevated risk for suicide related to legalized cannabis. Active prevention efforts in places with legal cannabis for high school students age 14 to 16 should be considered. Warning labels for all but especially targeting females should be considered at the point of sale. Limitations on high potency products would reduce risks for all ages and genders. 

July 3, 2023 - Toxicity of Synthetic Cannabinoids in K2/Spice: A Systematic Review. Synthetic cannabinoids (SCs) are emerging drugs of abuse sold as ‘K2’, ‘K9’ or ‘Spice’, and their use has been linked to greater health risks than THC.  This systematic review (de Oliveira et al., 2023) focuses on the toxicity of SCs compounds in Spice/K2 drugs. Sixty-four articles reporting the effects of synthetic cannabinoids in humans were included in this review, as well as ten original papers and fifty-four case studies. 

 The authors conclude that SCs may exhibit higher toxicity than THC and longer-lasting effects. “Their use may be harmful, especially in people with epilepsy and schizophrenia, because of the increased risk of the precipitation of psychiatric and neurologic disorders” (p.1), as well SCs potential to trigger a convulsive crisis, tachycardia, and a decline in consciousness.

May 21, 2023 - The Impact of Timing of In Utero Marijuana Exposure on Fetal Growth. This 2023 publication (Dodge et al., 2023) further supports earlier publications that significant risks exist if cannabis is used during pregnancy.  Study participants were cannabis users (N = 109) and a randomly selected control group of biochemically verified non-users (n = 171).  The authors examined the effect of use on three different health outcomes at birth: weight, length, and head circumference of the newborn, and further analyzed if there was an association of these health outcomes and timing of cannabis use during pregnancy.

The study’s main findings were the following: (1) babies born to mothers who used cannabis during pregnancy had significantly lower birth weight and smaller head circumference compared to babies born to non-cannabis using mothers; (2) babies born to mothers who used cannabis throughout pregnancy were negatively impacted the most; and (3) some indications of more negative health outcomes the earlier cannabis use during pregnancy (first and second trimester).

Whereas the study’s sample size is relatively small, a noteworthy research design is that biochemical markers were employed to verify cannabis use and nonuse and to rule out use of other substances.

April 19, 2023 - Marijuana legalization and opioid deaths We have posted studies in years past on the impact of legalization cannabis on opioid death rates.  This 2023 publication replicates and expands upon prior research by examining the issue over a longer period time (1999-2019), including more eligible states, accounting for incomplete reporting on the drugs involved in overdose deaths, better policy data, and accounting for population weights.

 Consistent with the now reliable finding from other studies that have examined this issue, this study found that cannabis legalization was associated with higher opioid death rates, which contradicts the 'cannabis protection hypothesis' (the belief that availability of cannabis will reduce deaths from opioids).  Specifically, one analysis showed that opioid deaths did appear to reduce shortly after medical legalization policies took place, but the trend soon reversed. When the full ten year period was taken into account, medical cannabis laws were associated with an 18% rise in opioid death rates and policies allowing sales through medical cannabis dispensaries were associated with a 28% rise in opioid death rates. A similar pattern of results were found for policies allowing recreational cannabis use and sales through recreational dispensaries.

 April 4, 2023 - Cannabis legalization and cannabis use, daily cannabis use and cannabis-related problems among adults in Ontario, Canada (2001–2019) The authors (Imtiaz et a., 2023) used data from 19 repeated, population-based, cross-sectional surveys of adults in Ontario Canada to compare pre-legalization and post-legalization prevalence rates of cannabis use, daily cannabis use and cannabis-related problems.  All cannabis use patterns showed a significant increase between 2001 and 2019 (Canada legalized cannabis in 2016).  Small prevalence increases in these use patterns began with the formation of the Canada task force on cannabis legalization in 2013, and rates significantly accelerated after passage into law. Of note: The long-standing prevalence rate of 1% daily cannabis use among Ontario adults has risen to a post-legalization prevalence rate of 6%.  Daily use of cannabis forebodes significant health risks for such individuals.  

February 20, 2023 - Prenatal Cannabis Use Disorder and Infant Hospitalization and Death in the First Year of Life (Bandoli et al., 2023). The study authors identified singleton, live-birth deliveries between 2011 and 2018 and if a maternal diagnosis of a cannabis use disorder (CUD) was present or not from a hospital discharge database maintained by the California Office of Statewide Health Planning and Development and linked with vital statistics files.  

Infant outcomes included infant emergency department visits and hospital admissions identified from health records, and infant deaths identified from death records. The statistical analysis adjusted for sociodemographic variables, psychiatric comorbidities and other substance use disorders.

The results indicated that 1% of the births (34,5443) occurred with the presence of a maternal diagnosis of CUD during pregnancy.  After the statistical adjustments, the incidence of infant death in the first year of life was greater among those with a maternal CUD diagnosis than those without (1.0 % vs 0.4 %; adjusted risk ratio about one-and-a-half times greater risk). Specific causes of the increased risk of death were attributable to perinatal conditions and sudden unexpected infant death.

December 6, 2022 - Cannabis use in pregnancy and maternal and infant outcomes: A Canadian cross-jurisdictional population-based cohort study (Luke et al., 2022) We are posting another large-scale study that examined the possible negative health effects of cannabis use in pregnancy.

This Canada population-based study investigated the effects of maternal cannabis use on birth complications and newborn outcomes. The sample included 1,280,447 singleton births from the British Columbia Perinatal Data Registry, the Better Outcomes Registry & Network Ontario, and the Perinatal Program Newfoundland Labrador from April 1st, 2012 to March 31st, 2019. 

 The prevalence of maternal cannabis use during pregnancy in the sample was approximately 2%. Prenatal cannabis exposure was associated with a significant increased risk of 1) spontaneous and medically indicated preterm birth, 2) very preterm birth, 3) low birth weight, 4) small-for-gestational age, 5) any major congenital anomaly, 6)  caesarean section, 7) and gestational diabetes.

 The study authors concluded that prenatal cannabis use increases the likelihood of several birth complications and negative newborn outcomes.

November 30, 2022 - Chest CT Findings in Marijuana Smokers. This retrospective study by Murtha et al. (2022) evaluated results of chest CT (a type of x-ray to create internal images of the chest) examinations (from October 2005 to July 2020) in three groups: marijuana smokers (n=56) , nonsmoker control patients (n=57) , and tobacco-only smokers (n=33). Health outcomes were compared in terms of rates of emphysema, airway changes, gynecomastia, and coronary artery calcification.  Statistical comparisons made several adjustments to control for potential biases.  

 The researchers found that cannabis smokers had significantly higher rates of airway inflammation and emphysema compared to nonsmokers and tobacco-only smokers.  Given the small sample sizes and variable inter-observer agreement when rating the health outcomes, the authors caution that strong conclusions cannot be drawn.

November 22, 2022 - Does cannabidiol make cannabis safer? A randomised, double-blind, cross-over trial of cannabis with four different CBD:THC ratios. This study examined the issue of if more CBD content in a THC cannabis product impacts harmful effects to the user. Forty-six healthy, infrequent cannabis users participated in a double-blind, within-subject, randomized trial of cannabis preparations varying in CBD content. 

 There was an initial baseline visit followed by four drug administration visits, in which each participant inhaled vaporized cannabis containing 10 mg THC and these various combinations of CBD: 0 mg (0:1 CBD:THC), 10 mg (1:1), 20 mg (2:1), or 30 mg (3:1) CBD in a randomized, counter-balanced order.  Several cognitive, behavioral and other measures were collected after each CBD:THC preparation (verbal learning task; other cognitive tests; severity of psychotic symptoms;  and measures of  subjective, pleasurable, pharmacological and physiological effects). 

 All CBD:THC preparations were associated with predicted negative performances on the cognitive tasks, increases in reporting psychotic symptoms, and subjective ratings of intoxication.  But these effects were not significantly modulated by any dose of CBD.  The authors conclude: “The CBD:THC ratios most common in medicinal and recreational cannabis products did not reveal that CBD protects against the acute adverse effects of THC.”

 Note from this reviewer, KCW:  This study was conducted on a very small sample size and participants were  infrequent cannabis users.  Also, higher doses of CBD may have yielded different results.

November 22, 2022 - The Effect of Prenatal Cannabis Exposure on Offspring Preterm birth: A Cumulative Meta-Analysis. We earlier posted research on the observed negative effects to cognitive functions among youth who were exposed to cannabis prenatally.  This research report looks at  the association between prenatal cannabis exposure and preterm birth.

 The authors performed a comprehensive search of the literature in numerous reputable research electronic databases and identified those studies of high quality. A total of 27 observational studies published between 1986 and 2022 were included in the final synthesis review, using meta-analysis statistics to compare studies.  The sample size of the studies ranged from 304 to 4.83 million births.

 The main finding was that prenatal cannabis exposure was associated with a significant increased risk of preterm birth (pooled adjusted OR = 1.35, 95% CI = 1.24–1.48).  That is, there was about a 1.5 greater likelihood of a preterm birth when maternal use of cannabis occurred during pregnancy, compared when there was no maternal use during pregnancy.   The authors concluded: “Offspring exposed to maternal prenatal cannabis use was associated with higher risk of preterm birth, which warrants public health messages to avoid such expo[1]sure, particularly during pregnancy.”

November 22, 2022 - Directional associations between cannabis use and anxiety symptoms from late adolescence through young adulthood. The co-existence of anxiety symptoms and cannabis use and anxiety symptomology is a well-established research finding.  But the temporal sequence of these two domains is not clear.  The authors of this study (Davis et al., 2022) examined data from an ongoing, longitudinal, cohort study of nearly 3,000 youth. For the present  study, five waves of data collected across ages 17-20 through ages 21-24 were analyzed.  The results show a sex difference regarding the relationship of cannabis use and anxiety.  For men,  greater cannabis use predicted greater subsequent increases in anxiety; for women, cannabis use decreased for those who experienced a recent increase in anxiety.  As the author noted, for many women who experienced increased anxiety due to prior cannabis use, continued cannabis use was not viewed as “useful mechanism for symptom relief”.

September 25, 2022 - Establishing risk-thresholds for the association between frequency of cannabis use and development of cannabis use disorder: A systematic review and meta-analysis. This review article examines the question: What are quantifiable risk-thresholds of the frequency of cannabis use for developing a Cannabis Use Disorder (CUD). Six prospective (longitudinal) studies published in the 2000-2022 period were included in the review by virtue of meeting rigorous standards. The meta-analysis led to this conclusion by the study authors: “The risk of CUD as a potential outcome of cannabis use exists even at infrequent levels of use, but significantly increases as frequency of use increases.”  For example, absolute risk is 36 % for daily users; for yearly users it's 3.5%.

Commentary by this writer, K.C. Winters: The authors did not include in the analysis the association of age of initiation of cannabis and risk of CUD.  If they had, it is my view that the absolute risk levels would be higher for early initiators compared to those who initiated use later in life.  Also, THC potency was not available in the six studies and thus could not be included in the meta-analysis.

September 20, 2022 - Changes in Emergency Department Visits for Cannabis Hyperemesis Syndrome Following Recreational Cannabis Legalization and Subsequent Commercialization in Ontario, Canada. Cannabis hyperemesis syndrome (CHS) is a rare but very distressing condition that occurs in some cannabis users. CHS symptoms are recurrent, severe vomiting and nausea. People with CHS often bathe or shower compulsively to try to relieve symptoms. 

Some anecdotal and local reports suggest that the legal commercialization of cannabis has been associated with an increase in CHS emergency department (ED) visits.  The authors of this cross-sectional research study examined changes in the number and characteristics of CHS ED visits from before and after the legal commercial sales of cannabis in Ontario, Canada.  CHS prevalence rates were obtained for three time periods: pre-commercialization (January 2014-September 2018), post-legalization with product and retail store restrictions (October 2018-February 2020), and post2-legaization with new products and expanded stores, which coincided with the COVID-19 pandemic (March 2020-June 2021). Data were obtained from routinely collected and linked health administrative databases.  

The analysis indicated large increases in CHS ED visits during the period of time when the market commercialized cannabis (post-legalization), and when the COVID-19 pandemic occurred (post2-legalization).   

Overall, monthly rates of CHS ED visits increased 13-fold during the 7.5-year study period, from 0.26 visits per 100 000 population in January 2014 to 3.43 visits per 100 000 population in June 2021. The post-legalization period did not show an immediate effect of CHS ED visits, but a significant effect occurred later in that time period (October 2018-February 2020).  An immediate effect of CHS ED visits was observed during the COVID-19 pandemic period. 

The authors conclude: “This cross-sectional study found large increases in CHS ED visits during the period of time when the market commercialized and the COVID-19 pandemic occurred. Greater awareness of CHS symptoms by ED staff in regions where legal commercialized cannabis markets exist is indicated.”

September 17, 2022 - Association of Mental Health Burden with Prenatal Cannabis Exposure from Childhood to early Adolescence: Longitudinal Findings from the Adolescent Brain Cognitive Development (ABCD) Study. This publication, based on longitudinal data from the U.S.- based  Adolescent Brain and Cognitive Development (ABCD) study, examined the possible link between prenatal cannabis exposure and early adolescence (11 and 12 years) behaviors. The research design involved comparing scores on measures of youth behavioral and mental health problems (Child Behavior Checklist and the Prodromal Questionnaire–Brief Child Version) as a function of youth groups defined by prenatal cannabis exposure.  Three youth cannabis exposure groups were identified based on retrospective report of maternal cannabis use during pregnancy: cannabis use only before maternal knowledge of pregnancy (BK-PCE), use before and after maternal knowledge of pregnancy (BAK-PCE), and no cannabis exposure (NE). 

Both prenatal exposure groups (BK-PCE and BAK-PCE) were associated with persisting vulnerability to a wide range of measures or social, behavioral and mental health problems throughout early adolescence.  Significant findings were primarily driven by youth who were exposed  following maternal knowledge of pregnancy (BAK-PCE group).   

The authors note that these adverse effects may put these affected children at elevated risk during adolescence for substance use disorder and other mental health disorders.

September 14, 2022 - Development Over Time of the Population-Attributable Risk Fraction for Cannabis Use Disorder in Schizophrenia in Denmark. The authors analyzed longitudinal data from Denmark’s nationwide, register-based health records to examine the possible link of cannabis use disorder and schizophrenia. Approximately 7.2 million individuals were included in the analysis. The longitudinal analyses showed that the proportion of cases of schizophrenia associated with cannabis use disorder has increased 3- to 4-fold during the past 2 decades in Denmark.  The authors note this finding “is expected given previously described increases in the use and potency of cannabis." 

Additional commentary from this writer, KCW: A related publication from a few years earlier using the same Danish health records (Hjorthøj et al., 2019) showed that Denmark’s incidence rate of cannabis-induced psychosis increased steadily from 2.8 per 100,000 persons  in year 2006 to 6.1 per 100,000 persons in year 2016. The authors of that study concluded that “The increase in cannabis-induced psychosis follows both the increase in the level of THC in cannabis, and the increase in cannabis use.”

July 29, 2022 - Association of cannabis potency with mental ill health and addiction: a systematic review. Cannabis potency, defined as the concentration of Δ9-tetrahydrocannabinol (THC), has increased internationally, which could increase the risk of adverse health outcomes for cannabis users. We present, to our knowledge, the first systematic review of the association of cannabis potency with mental health and addiction (PROSPERO, CRD42021226447). We searched Embase, PsycINFO, and MEDLINE (from database inception to Jan 14, 2021). Included studies were observational studies of human participants comparing the association of high-potency cannabis (products with a higher concentration of THC) and low-potency cannabis (products with a lower concentration of THC), as defined by the studies included, with depression, anxiety, psychosis, or cannabis use disorder (CUD). Of 4171 articles screened, 20 met the eligibility criteria: eight studies focused on psychosis, eight on anxiety, seven on depression, and six on CUD. Overall, use of higher potency cannabis, relative to lower potency cannabis, was associated with an increased risk of psychosis and CUD. Evidence varied for depression and anxiety. The association of cannabis potency with CUD and psychosis highlights its relevance in health-care settings, and for public health guidelines and policies on cannabis sales. Standardization of exposure measures and longitudinal designs are needed to strengthen the evidence of this association.

July 25, 2022 - Vaping Cannabinoid Acetates Leads to Ketene Formation. This technical paper was published in ChemRxiv (a free submission, distribution, and archive service for unpublished preprints in chemistry and related areas). The authors examined toxins from both dabbing and e-cigarette cartridge vaping of cannabinoid acetates (delta-8 THC, CBD and CBN).  The main finding was that dabbing/vaping these cannabinoids leads to ketene formation.  Ketene is a highly reactive poisonous gas. The paper provides details as to ketene exposure levels as a function of combinations of delivery method and type of cannabinoid. Ketene was consistently observed in vaped/dabbed condensates from  all three cannabinoids (delta-8, CBD, and CBN), which included commercial delta-8 THC acetate products purchased online.  The ketene emission levels observed in the dabbing experiments for CBN were in range of the  "immediately dangerous to life or health value".  For delta-8 and CBD, the ketene emissions were below this "immediate danger" level.

June 5.2022 - Effects of cannabis on visual function and self‑perceived visual quality. Cannabis use has been associated with impacting performance on various motor, spatial and visual tasks.  These researchers focused on the effects of smoking cannabis on several visual functioning variables (static visual acuity, contrast sensitivity, stereoacuity, accommodative response, straylight, night-vision disturbances (halos) and pupil size. The sample was 31 cannabis users. Study results indicated that smoking cannabis had significant adverse effects on all these visual parameters (p < 0.05). Also, about two thirds of the sample rated that smoking cannabis did impair their vision.

May 31, 2022 - United States marijuana legalization and opioid mortality epidemic during 2010–2020 and pandemic implications. We have summarized in the past several studies that examine the issue of cannabis legalization and lethal opioid overdose rates.  Except for the one now outdated study, all subsequent studies in the peer-reviewed research literature have concluded that rates of opioid mortality rates are higher in states that have legalized commercial sales of cannabis compared to non-legalization states.

The present study by Bleyer and colleagues take another look at this issue with more recent data and by examining a longer period of time.  The authors compared the United States opioid mortality rates in states and District of Columbia that had implemented marijuana legalization versus states that had not.  Whereas the same opioid mortality rates were found between these sets of states during 2010–2012, when the full 2010-2020 period is examined, the opioid mortality rate increased more rapidly in marijuana-legalizing than non-legalizing jurisdictions (2010–2020 annual pairwise comparison p = 0.003 for all opioids and p = 0.0004 for fentanyls).

 During this 2010-2020 decade, all four major race/ethnicities in the U.S. had evidence for a statistically-significant greater increase in opioid mortality rates in legalizing than non-legalizing jurisdictions. Among legalizing jurisdictions, the greatest mortality rate increase for all opioids was in non-Hispanic blacks (27%/year, p = 0.0001) and for fentanyls in Hispanics (45%/year, p = 0.0000008).

 Of note is year 2020, the first year of the COVID-19 pandemic and lockdown. That year had the greatest annual opioid mortality increase, with non-Hispanic blacks having the greatest increase in legalizing vs. non-legalizing opioid-death-rate difference, from 32% higher in legalizing jurisdictions in 2019 to more than double in 2020.

 The authors conclude: “Instead of supporting the marijuana protection hypothesis, ecologic associations at the national level suggest that marijuana legalization has contributed to the U.S.’s opioid epidemic in all major races/ethnicities, and especially in blacks. If so, the increased use of marijuana during the 2020–2022 pandemic may thereby worsen the country’s opioid crisis.”

May 11, 2022 - Editorial in a Prominent Psychiatry Journal on the Negative Impacts of Prolonged Cannabis Use. A recent editorial in the Journal of the American Journal of Child and Adolescent Psychiatry by Christopher Hammond M.D. Ph.D.  “Editorial: Early Cannabis Exposure definitions that correspond with high Cumulative Lifetime dose during Adolescence are the strongest predictors of adverse health outcomes” (Vol. 61 #5, May 2022), highlights the significant findings from an important longitudinal study of the health risks of cannabis. (Adult Psychiatric, Substance, and Functional Outcomes of Different Definitions of Early Cannabis Use William E. Copeland,, Sherika N. Hill,, Lilly Shanahan, : Vol, 61, 2022 p. 533-543; a fee is required to access the journal issue that contains the editorial). The research study followed participants measuring how different ways of assessing the quantity and persistence of use of cannabis from age 9 to 30 years influenced health outcomes. The editorial highlights the special contribution of the Copeland research report that confirms previous studies that showed frequency and quantity of use during adolescence conveys a relative risk for negative health outcomes including depression, psychosis, substance use, suicidal ideation and attempts, and poorer academic and vocational outcomes.  

-George Realmuto, M.D.

May 6. 2022 - The Effects of Cannabinoids on Sleep. The authors provide a comprehensive review of the published literature pertaining to the impact of using cannabis products on a range of sleep features, including normal sleep, circadian sleep-wake rhythms, insomnia, excessive daytime sleepiness, sleep apnea, parasomnias, and restless legs syndrome.  Both THC and CBD are included in the review.  Most studies included in this review were observational in nature, although some randomized controlled studies were available. Sleep measures were mostly based on self-report.   The authors conclude the following: “Our comprehensive review of the effects of cannabis products on normal sleep and sleep disorders, relevant to primary care providers and other clinicians evaluating and treating patients who use these types of products, shows that cannabis products have minimal to no effects on sleep disorders and may have deleterious effects in some individuals.”  With respect to helping normal sleep, the authors offer a similar conclusion: Cannabis products do not offer a reliable aid to improve a user’s normal sleep.

April 15, 2022 - Adult Psychiatric, Substance, and Functional Outcomes of Different Definitions of Early Cannabis Use. Research on associations of early cannabis use with adult functioning reports mixed findings. This may be due, in part, to wide variations in the definitions of early cannabis use. In this study, the authors used data from 1,420 participants in the 25-year Great Smoky Mountains Study to test associations of commonly-used definitions of early cannabis use with a broad range of adult psychiatric, substance, and real-world outcomes.  

Whereas all individuals who initiated cannabis during adolescence showed some poor adult outcomes, those early users who used daily and continuously over time were associated with the most severe negative adult outcomes. Cessation of early use did not fully eliminate later risks, but was associated with fewer negative outcomes.  The various adult outcomes including substance use disorder, psychiatric disorder, and several functional domains.

March 27, 2022 - Long-Term Cannabis Use and Cognitive Reserves and Hippocampal Volume in Midlife. This longitudinal study from Dunedin New Zealand has been following and tracking since birth about 1,000 New Zealanders.  The sample was last assessed when they were about 45-years old.  Those in the sample that began using cannabis before age 18 and continued to use regularly throughout adulthood were compared to others in the sample.  Several negative impacts were found, most notably the following:

1.   average IQ decline from childhood to age 45 of 5.5 IQ points  (almost an average of a half a standard deviation decline)

2.   significantly smaller hippocampus volume (the brain region linked to memory and learning) 

3.   worse performance on learning, memory and information processing tasks

4.those who quit their chronic cannabis habit did not show the same level of deficits

The researchers controlled for various confounding variables, leading to this summary statement: "Cognitive deficits among long-term cannabis users could not be explained by persistent tobacco, alcohol, or other illicit drug use, childhood socioeconomic status, low childhood self-control, or family history of substance dependence."

February 1, 2022 - Geographical variation in hospitalization for psychosis associated with cannabis use. A 2017 national database was utilized to investigate the association between cannabis legalization in the United States and hospitalizations for psychosis associated with cannabis use. The main comparison was data from the Pacific census division, where most states have legalized recreational cannabis use, versus the other census divisions. The main finding: The Pacific census division had significantly higher odds of inpatient hospitalization discharges for psychosis than the other census divisions (adjusted odds ratio 1.55; 95% confidence interval 1.25 – 1.93). Also, there was a significant correlation between the cannabis legality score and proportion of hospital discharges for psychosis associated with cannabis use (r = 0.67, p<0.05). The researchers concluded: "we observed a higher proportion of hospital discharges for psychosis associated with cannabis use in areas with more liberal cannabis legalization laws."

February 1, 2022 - Veterans Use of Cannabis This article published in the American Journal of Psychiatry surveyed the recent use of cannabis and the rate of Cannabis Use Disorder (CUD) among veterans. The main finding was that the prevalence of any past-12 month cannabis use and CUD were 7.3% and 1.8%, respectively. Among those that reported recent cannabis use, the prevalence rate of CUD was 25%.  Among several risk factors for a CUD was residing in a state with medical marijuana laws.

January 14, 2022 - Alcohol and Cannabis Use Disorders (special issue of the American Journal of Psychiatry)

A special issue of the American Journal of Psychiatry consists of several papers on the deleterious health impacts of those with either an alcohol use disorder or a cannabis use disorder.  As noted in the editor’s summary, there are several cannabis-related topics covered in this volume: 1) the prevalence of cannabis use and cannabis use disorder in veterans and the factors contributing to use and misuse in this population; 2) the  association between cannabis use or cannabis use disorder and self-reported psychotic disorders; 3) an estimate of the magnitude of the increased prevalence of psychotic disorders conferred by cannabis use; and 4) causal mechanisms underlying both alcohol and cannabis misuse.

January 14, 2022 - Risks and Benefits of Cannabis and Cannabinoids in Psychiatry

This extensive and comprehensive review of the research literature pertaining to cannabinoids and mental illness concludes that “there is considerable evidence that cannabinoids have a potential for harm in vulnerable populations such as adolescents and those with psychotic disorders”.  Also, the authors argue against prescribing cannabinoids for the treatment of psychiatric disorders because of insufficient research support.

November 1, 2021 - Hepatis and Cannabinoid Signaling. This is a very detailed review of the relationship of the endocannabinoid system, its receptors. ligands and external agonists and alcohol and non-alcohol hepatic (liver) diseases. While it was well known that THC had effects on the endocannabinoid system in the CNS we now know that activation of cannabinoid receptor 1 also has effects on other organs in the body including the liver. The endocannabinoid system includes two receptors with distribution to different organs. Cannabinoid receptor 1 is abundant in the central and peripheral nervous system as well as in the liver, lung, gastrointestinal tract, urinary tract, thyroid, pancreas, heart, vascular, fat tissue, reproductive organs, skeletal muscles and immune tissue. Cannabinoid receptor 2 has expression in bone marrow affecting red cell production and cells responsible for infection prevention. This paper explored the endocannabinoid system and just one organ, the liver. In the condition of developing liver disease caused by excessive alcohol use, stimulation of CBR1 exacerbates the disease process. “Cannabinoid receptor 1 activation whether exogenously such as THC or through oxidative stress from excessive alcohol consumption, aggravates inflammation, fatty liver and scarring of the liver through the reduction of fatty acid oxidation with enhanced fatty liver production. The implications for policy makers who would want to replace alcohol with THC should hesitate in that THC may in fact lead to similar liver diseases as alcohol as well as disease in other organs including the lung.

October 28, 2021 - Marijuana and psychosis: This study used national survey data of the U.S. general population to examine if the association of non-medical cannabis use and self-reported psychotic disorders has changed over time.  In 2001–2002, self-reported psychotic disorders were unrelated to either frequent use or daily/near-daily use of nonmedical cannabis. Yet the 2012–2013 data found that compared with nonusers, self-reported psychotic disorders were significantly more common among survey respondents who reported nonmedical cannabis use that was either used frequently, used at a daily/near-daily level, or when use led to meeting a cannabis use disorder diagnosis. One interpretation of the findings: compared to 2001-2002, the much higher potency level of typical cannabis available to users in 2021-2013 contributed to the association of use and psychotic disorders.

October 11, 2021 - Cannabis and Psychosis: The authors of this publication make a strong case that given the very strong evidence of the association between cannabis use and increased susceptibility to psychosis, prevention and intervention efforts need to accelerate. 

September 1, 2021 - Lower-Risk Cannabis Use Guidelines: This 2021 publication, titled “Lower-Risk Cannabis Use Guidelines (LRCUG) for reducing health harms from non-medical cannabis use: A comprehensive evidence and recommendations update”, provides a framework for how to judge the risk to health from cannabis use.  Eleven researchers from various universities and institutions (most from Europe and Canada) weighed-in with their judgement as to the current status of research evidence pertaining to the "riskiness" to health from cannabis use.

 The researchers used the same criteria to grade the strength of the evidence for each recommendation that the National Academies of Sciences, Engineering, and Medicine used in its 2017 report.  These grades are as follows: 

1. "Conclusive: Evidence is based on many supportive, good quality studies, with no credible opposing findings, and firm conclusions can be made.

2. "Substantial: Evidence is based on supportive findings from good quality studies, with few or no opposing findings.

3. "Moderate: Evidence is based on supportive findings from several fair/good quality studies, with few or no opposing findings.

4. "Limited: Evidence is based on findings from fair quality studies or mixed findings, with most favoring the same conclusion.

5. "No or Insufficient: Evidence is based on a single poor-quality study, mixed findings, or non-existent.”

 The report provides three General Precautions and several specific Recommendations.  Here are the three General Precautions:

 1."General Precaution A: People who use cannabis (PWUC) need to know that there is no universally safe level of cannabis use; thus, the only reliable way to avoid any risk for harm from using cannabis is to abstain from its use.
Evidence Grade: Conclusive”

 2. “General Precaution B: Frequent cannabis use, and especially intensive use over longer periods, can lead to a ‘cannabis use disorder’ (CUD) or cannabis dependence, that may require treatment.
Evidence Grade: Substantial”

 3. “General Precaution C: People who use cannabis should exercise social consideration and responsibility in avoiding cannabis use that may result in harm-to-others.
Evidence Grade: Substantial to Limited”

It is this writer’s view that one of the Recommendations will be debated a lot.

“Recommendation #1: The initiation of cannabis use should be delayed until after late adolescence, or the completion of puberty, to reduce development-related vulnerabilities for harm.
Evidence Grade: Moderate”

 My opinion: I would have preferred (1) replacing “delayed until after late adolescence, or the completion of puberty” with “until mid-20’s in age”, and (2) replacing the evidence grade of “Moderate” with “Substantial to Moderate”.

 -Ken Winters, Ph.D.

August 1, 2021 - Children exposed to second-hand marijuana smoke may experience viral respiratory infections - link to article

July 12, 2021 - Acute and long-lasting effects of cannabis use: The authors of this study provide a review of the human literature on the acute and long-lasting effects of cannabis use on cognitive functioning related to poor academic and work performance. The authors included only cross-over randomized controlled trials and prospective designs, which means all studies examined the effects of cannabis exposure at the within-subject level. These three findings were judged to be relatively consistent across the reviewed studies: 1. Cannabis use is associated with acute mild to moderate negative effects on episodic and working memory, processing speed, and executive functions (complex decision making). 2. Residual mild negative effects are also observed in the same cognitive domains, “suggesting that adverse effects following cannabis intoxication persist at least days or weeks following cannabis abstinence.” 3. Cannabis use initiated during adolescence is associated with longer lasting residual effects even in mild users (<weekly).

June 1, 2021 - Prevalence and correlates of daily blunt use among U.S. African American, Hispanic, and White adults. In this study researchers looked at trends of smoking blunts among a national sample of adults in the U.S.  A blunt is a roll with cannabis inside a cigar or blunt wrap. These wraps are often made out of tobacco, which adds a buzz and energy to the effects of cannabis.  Smoking a blunt increases exposure to toxins and carcinogens, as well as increasing the risk for a cannabis use disorder.  African Americans had the greatest prevalence of daily blunt use (24.2%), relative to Whites (9.1%) and Hispanic/Latinos (13.9%) (p < .001). Also, within the African American group, these two factors were associated with a higher rate of daily blunt use: aged 26-34 and living in a cannabis medical state.

May 30, 2021 - Cannabis and synaptic reprogramming of the developing brain. This article can be a difficult read for those not trained as neuroscientist.  But its comprehensiveness of the effects of cannabis exposure on human and rodents is impressive.  Research is reviewed regarding effects prenatally, and during infancy, adolescence and adulthood.  Below is a quote from the article's conclusion: 

"While debates mount regarding the developmental effects of cannabis, accumulating evidence from various lines of research demonstrates that there is potential for exposure during prenatal and adolescent periods to change the trajectory of various neurobiological systems. Importantly, the causal disturbances of neural processes in adulthood by early cannabinoid exposure are linked to behavioral phenotypes predictive of psychiatric and addiction risk."

May 27, 2021 - Cannabis and Calls to US Poison Control Centers. In this study researchers accessed National Poison Data System data on cannabis exposures reported to US poison centers for January 2017 through December 2019. They coded cannabis product type as unprocessed “plant material” or as “manufactured product” (concentrates, edibles or vaporized liquids). Among the total 28,630 exposures recorded during this time period, plant materials were the most commonly involved exposures (66%), followed by edibles (19%), concentrates (10%) and vaporized liquids (4%).  As predicted, among children exposed, manufactured products were the most common, with edibles the most common among manufactured products.  Other findings: (1) manufactured product calls came from a residence nearly twice as often as plant material-based exposure calls; and (2) except for vaping, states allowing legal adult use had greater exposure rates compared to states not allowing legal adult use.

May 11, 2021 - Cannabis Legalization and College Mental Health. Among U.S. age groups, the largest increase in cannabis use following legalization has been among college age population (18–25 years of age). This age group is especially vulnerable to the negative impacts and risks associated with cannabis use, including risk for the onset of major psychiatric illness.  The paper by De Faria and colleagues reviews current understanding of the pharmacological effects of cannabis on the young adult brain and its potential clinical consequences. The authors review the research on the impact of cannabis use in specific clinical disorders and then discuss the importance of training college health providers about the effects and risks of cannabis use in young adults.

May 11, 2021 - Balancing the Neuroprotective Versus Neurotoxic Effects of Cannabis. This book chapter reviews the research literature on the neurotoxic effects of cannabis. The author’s core summary is that activating cannabinoid receptors in the brain can result in a range of pharmacological effects that can have therapeutic benefits, yet cannabinoids also induce severe adverse effects in the central and peripheral nervous systems that can impair cognitive functioning and mental health.

May 2, 2021 - Prenatal exposure to Cannabis. There is growing evidence that prenatal exposure to cannabis may negatively impact the infant. A new California study, based on data from 2001 to 2012, found that babies born to mothers diagnosed with cannabis use disorders at delivery were more likely to experience negative health outcomes, including preterm birth and low birth weight, compared to babies born to mothers without a cannabis use disorder diagnosis.

April 30, 2021 - Racial and Ethnic Differences in Marijuana use. This study reports the prevalence of ever use of marijuana in e-cigarettes among US youth by racial and ethnic groups in in 2020 and changes in prevalence from 2017 to 2020 by racial and ethnic groups.

April 21, 2021 - Can Marijuana treat PTSD. The researchers in this study examined the important medicinal marijuana issue if PTSD can be effectively treated with medical cannabis.  They conducted the first randomized placebo-controlled trial of smoked cannabis to address those with PTSD.  Study participants were US military veterans and all met DSM-5 criteria for PTSD with symptoms of at least six months in duration.  Participants were randomly assigned to three treatment groups: smoked cannabis with high THC level; smoked THC+CBD; and a placebo smoked product.  All treatment groups, including placebo, showed good tolerability and significant improvements in PTSD symptoms during three weeks of treatment. Thus, the two active conditions (THC only and THC+CBD) were not associated with significantly better outcomes than the placebo group.

April 13th, 2021 - Marijuana and self harm. The researchers of this study examined if cannabis legalization laws are related to rates of non-fatal self-harm or assault injuries.  Self-harm included intentional nonsuicidal self-harm (e.g., cutting) and suicide attempts (e.g., intentional drug overdose). Assault included injuries intentionally inflicted by one person on another (e.g., intimate partner violence). Based on health insurance claims data from 75,395,344 beneficiaries between 2003 and 2017, rates of self-harm injuries among males younger than 40 years increased more in states legalizing commercial cannabis sales compared with states without commercial cannabis laws.  Among states with more restrictive legalization approaches (not legal at all; medical marijuana only), no association with self-harm and assault was found. The researchers conclude: “States with recreational cannabis may benefit from monitoring levels of self-harm as a potential consequence of legalization.”

February 28th, 2021 - Marijuana and Pregnancy: A repeated cross-sectional study examined the association between state recreational cannabis legalization and maternal cannabis use during the preconception, prenatal, and postpartum periods. The authors used data from the Pregnancy Risk Assessment Monitoring System data set, which covered approximately 15 years in four states.  Two “legalization” states, Alaska and Maine (target states) had pre-legalization and post-legalization data. New Hampshire and Vermont (control states), had necessary survey data for roughly the same time period.  The study results concluded that preconception and postpartum maternal cannabis use significantly increased in the legalization, target states (Alaska and Maine) after legalization of recreational cannabis, compared with the non-recreational control states (New Hampshire and Vermont). But prenatal maternal cannabis use was not increased among women in the target states compared with women in the control states. This study improves on prior research, as this study was the first published that assessed associations between recreational cannabis legalization and maternal cannabis use during multiple maternal health periods in more than 1 state.

February 19, 2021 - Increase in teen use: There continues to be rigorous survey studies documenting that when commercial sale of cannabis is legalized, eventually there is an increase in cannabis use teenagers. The latest in a growing set of studies is from California.  Legalizing cannabis for commercial sales was found to be associated with an increase in adolescent marijuana use (lifetime and past 30-day use) in 2017–2018 and 2018–2019. The largest increase as a function of grades were 7th  graders.

January 24, 2021 - Cannabis and self-harm: A study published in the JAMA Pediatrics examined the possible association of cannabis use with self-harm, suicide and overall mortality risk. The authors analyzed a large sample (204,000 youths, aged 10-24 years) drawn from Ohio Medicaid claims that had a diagnosis of a mood disorder.  Then later claims of self-harm and death (suicide, homicide, other) were linked to cannabis use and cannabis use disorder.  Cannabis use disorder was found to be a common comorbidity and risk marker for self-harm, all-cause mortality, death by unintentional overdose and death by homicide among youths with mood disorders.  The authors conclude that “These findings should be considered as states contemplate legalizing medical and recreational marijuana.”

January 18, 2021 - Use of Cannabis and other substances: Based on U.S. data from 2004–2017 National Survey on Drug Use and Health, legalization of cannabis was associated with increases in cannabis-alcohol poly use in the US.  States with recreational/commercialization laws were associated with increases across all demographic groups, while the  impact of  medical marijuana laws was more limited to  certain sociodemographic groups.

January 18, 2021 - Cannabis use and Veterans: Important new study on Cannabis use among veterans. Using a comprehensive search strategy, 86 studies met the authors’ criteria for inclusion in this review. Most of these studies focused on male veterans from the U.S. Nearly all studies were cross-sectional and thus do not permit causal inferences.  Yet the authors conclude that “Overall, the balance of the evidence implicates cannabis use with negative health outcomes in veteran populations……the results at least suggest that cannabis use is a fellow traveler with a wide variety of health ills, psychiatric and physical.”

January 7, 2021 - Developing a CUD: Based on a literature review of recent national health surveys on substance use, the authors concluded that strong and relatively consistent research literature shows associations between cannabis use and developing a Cannabis Use Disorder, as well as a strong association of cannabis use and having a mental or behavioral disorder. 

December 21, 2020 - Marijuana and Depression: A new article in the American Psychiatric Association states that people who use marijuana are three times more likely to develop depressions and anxiety. Click here for a summary.

May 21, 2020: Characterizing psychosis-relevant phenomena and cognitive function in a unique population with isolated, chronic and very heavy cannabis exposure Heavy, chronic, and early cannabis use that is not confounded by other drug use is associated with psychosis-relevant phenomena and cognitive deficits. The findings are relevant to the evolving attitudes and laws about cannabis.

April 30, 2020: The association between legalization of recreational marijuana use and birth outcomes in Colorado and Washington state. There was evidence of an increased birth prevalence of congenital anomalies in both Colorado and Washington State when comparing prevalence before and after legalization.

April 2020: Is there sufficient evidence that cannabis use is a risk factor for psychosis? There is robust evidence for an association between cannabis use and psychosis. Convergent evidence from prospective and experimental studies points in the direction of a causal relationship.

April 8, 2020: Will Legalization and Commercialization of Cannabis Use Increase the Incidence and Prevalence of Psychosis? Numerous prospective studies have shown that cannabis use carries an increased risk of later schizophrenia-like psychosis

March 13, 2020: Adolescent cannabis use, cognition, brain health and educational outcomes: A review of the evidence We assess the available evidence on whether cannabis use adversely affects learning, attention, and decision-making in youth, a group whom we define as between the ages of 14 and 25 years

March 9, 2020: Cannabis Legalization May Be Moving Too Fast There’s plenty we still don’t know about risks and benefits—and lawmakers don’t always take
into account what we do know

March 2020: Trends in alcohol and marijuana detected in homicide victims in 9 US states: 2004–2016. Use of alcohol and other drugs is a major risk factor for assaultive injuries and violent deaths. The purpose of this study was to examine the time trends in the prevalence of alcohol and marijuana detected in homicide victims.

November 21, 2019: Recreational Cannabis Use Impairs Driving Performance in the Absence of Acute Intoxication. Across the nation, growing numbers of individuals are exploring the use of cannabis for medical or recreational purposes, and the proportion of cannabis-positive drivers involved in fatal crashes increased from 8 percent in 2013 to 17 percent in 2014, raising concerns about the impact of cannabis use on driving. Previous studies have demonstrated that cannabis use is associated with impaired driving performance, but thus far, research has primarily focused on the effects of acute intoxication.

November 13, 2019: Association Between Recreational Marijuana Legalization in the United States and Changes in Marijuana Use and Cannabis Use Disorder From 2008 to 2016. This study’s findings suggest that although marijuana
legalization advanced social justice goals, the small post-RML increase in risk for CUD among respondents aged 12 to 17 years and increased frequent use and CUD among adults 26 years or older in this study are a potential public health concern. To undertake prevention efforts, further studies are warranted to assess how these increases occur and to identify subpopulations that may be especially vulnerable.

September 27, 2019: Contribution of Marijuana Legalization to the U.S. Opioid Mortality Epidemic: Individual and Combined Experience of 27 States and District of Columbia. The marijuana protection hypothesis is not supported by recent U.S. data on opioid mortality trends. Instead, legalizing marijuana appears to have contributed to the nation’s opioid mortality epidemic.

August 16, 2019: Incidence of Pediatric Cannabis Exposure Among Children and Teenagers Aged 0 to 19 Years Before and After Medical Marijuana Legalization in Massachusetts. Pediatric cannabis exposure cases increased in Massachusetts
after medical marijuana was legalized in 2012, despite using childproof packaging and warning labels. This study provides additional evidence suggesting that MML may be associated with an increase in cannabis exposure cases among very young children, and extends prior work showing that teenagers are also experiencing increased cannabis-related health system contacts via the RPC.

August 7, 2019: Heavy Cannabis Use, Dependence and the Brain: A Clinical Perspective. Although causality is unclear, heavy and dependent cannabis use is consistently associated with a high prevalence of co-morbid psychiatric disorders and learning and memory impairments that seem to recover after a period of abstinence.

March 19, 2019: The Contribution of Cannabis Use to Variation in the Incidence of Psychotic Disorder. Findings are consistent with previous studies showing that the use of cannabis with a high concentration of THC has more harmful effects on mental health than the use of weaker forms. The study also indicates how cannabis use affects the incidence of psychotic disorder at a population level.

February 13, 2019: Association of Cannabis Use in Adolescence and Risk of Depression, Anxiety, and Suicidality in Young Adulthood. Although individual-level risk remains moderate to low and results from this study should be confirmed in future adequately powered prospective studies, the high prevalence of adolescents consuming cannabis generates a large number of young people who could develop depression and suicidality attributable to cannabis. This is an important public health problem and concern, which should be properly addressed by health care policy.

January 17, 2019: Is Cannabis Good or Bad for Mental Health? The evidence says it can go either way.

January 14, 2019: Is Marijuana as Safe as We Think? Permitting pot is one thing; promoting its use is another.

January 4, 2019: What Advocates of Legalizing Pot Don’t Want You to Know. The wave toward legalization ignores the serious health risks of marijuana.

December 18, 2018: Cannabis: What are the risks for students? Three major risks associated with adolescent cannabis use.

December 17, 2018: Higher average potency across the United States is associated with progression to first cannabis use disorder symptom. This study provides prospective evidence suggesting higher potency cannabis, on average in the U.S., increases risk for onset of first cannabis use disorder symptom.

November/December 2018: The Problem with the Current High Potency THC Marijuana from the Perspective of an Addiction Psychiatrist. Without any clear guidelines or regulations from government officials, the cannabis industry has taken a page from the tobacco and alcohol industries’ play book and developed strains of marijuana and concentrated marijuana products with much higher concentrations of THC, the psychoactive component that causes addiction.

September, 2018: Butane Hash Oil and Dabbing: Insights into Use, Amateur Production Techniques, and Potential Harm Mitigation

August 27, 2018: AAP Raises Concerns About Increasing Marijuana Use During Pregnancy and Breastfeeding. As more states legalize marijuana and social media touts its use for morning sickness, the nation’s pediatricians caution the drug may not be harmless.

June 2018: National Institute on Drug Abuse (NIDA), Marijuana. Changes in marijuana policies across states legalizing marijuana for medical and/or recreational use suggest that marijuana is gaining greater acceptance in our society. Thus, it is particularly important for people to understand what is known about both the adverse health effects and the potential therapeutic benefits linked to marijuana.

October 11, 2016: The impact of adolescent exposure to medical marijuana laws on high school completion, college enrollment and college degree completion There is concern that medical marijuana laws (MMLs) could negatively affect adolescents. To better understand these policies, we assess how adolescent exposure to MMLs is related to educational attainment.

March 2015: Clearing the Smokescreen: The Current Evidence on Cannabis Use. With a growing number
of jurisdictions across the world heeding this call and introducing legislation to decriminalize or legalize cannabis use, it is essential that any changes to legal frameworks and public health policies are based on the best available scientific evidence.