Has the Legalisation of Medical and Recreational Cannabis Use in the USA Affected the Prevalence of Cannabis Use and Cannabis Use Disorders?

The impact of recreational cannabis legalization on youth: the Colorado experience

Over the past two decades, cannabis policies have liberalized in the United States, culminating in the legalization of recreational cannabis in Colorado and Washington state in 2012. This review will focus on the impact of recreational cannabis legalization in Colorado. While the prevalence of past-year and past-month cannabis use has remained relatively steady among adolescents post-legalization, the prevalence of young adult use has continued to rise. Cannabis products with increased potency have become more prevalent and widely used. There are concerns that the use of products with increased potency will increase risk for cannabis use and comorbid mental health disorders, particularly cannabis-induced psychosis and suicidal behavior, although more research is needed to fully understand the impact of high-potency products. Since the legalization of recreational cannabis, numerous additional public health concerns have emerged: unintentional overdoses requiring acute care visits, electronic vaping-associated lung injury, increased motor vehicle collisions related to cannabis consumption, and higher rates of cannabis use during pregnancy. Lessons learned from the first decade of cannabis legalization emphasize the need for research efforts to provide evidence-based guidelines, inform prevention strategies, and implement selective interventions for at-risk populations including youth, individuals with comorbid mental health disorders, and individuals who are pregnant.

Behavioral economic analysis of legal and illegal cannabis demand in Spanish young adults with hazardous and non-hazardous cannabis use

BACKGROUND

In October 2021, a legal framework that regulates cannabis for recreational purposes in Spain was proposed, but research on its potential impacts on cannabis use is currently limited. This study examined the reliability and discriminant validity of two Marijuana Purchase Tasks (MPTs) for measuring hypothetical legal and illegal cannabis demand, and to examine differences in demand of both commodities in young adults at hazardous vs. non-hazardous cannabis use risk levels.

METHODS

A total of 171 Spanish young adults [Mage = 19.82 (SD = 1.81)] with past-month cannabis use participated in a cross-sectional study from September to November 2021. Two 27-item MPTs were used to estimate hypothetical demand for legal and illegal cannabis independently. The Cannabis Use Disorder Identification Test (CUDIT-R) was used to assess hazardous cannabis use and test for discriminant validity of the MPTs. Reliability analyses were conducted using Classical Test Theory (Cronbach's alpha) and Item Response Theory (Item Information Functions).

RESULTS

The MPT was reliable for measuring legal (α = 0.94) and illegal (α = 0.90) cannabis demand. Breakpoint (price at which demand ceases), and Pmax (price associated with maximum expenditure) were the most sensitive indicators to discriminate participants with different levels of the cannabis reinforcing trait. No significant differences between legal and illegal cannabis demand in the whole sample were observed, but hazardous vs. non-hazardous users showed higher legal and illegal demand, and decreased Breakpoint and Pmax if cannabis were legal vs illegal.

CONCLUSION

The MPT exhibits robust psychometric validity and may be useful to inform on cannabis regulatory science in Spain.

What is the hype on #MedicinalCannabis in the United States? A content analysis of medicinal cannabis tweets

INTRODUCTION

Medicinal cannabis is now legal in 44 US jurisdictions. Between 2020 and 2021 alone, four US jurisdictions legalised medicinal cannabis. The aim of this study is to identify themes in medicinal cannabis tweets from US jurisdictions with different legal statuses of cannabis from January to June 2021.

METHODS

A total of 25,099 historical tweets from 51 US jurisdictions were collected using Python. Content analysis was performed on a random sample of tweets accounting for the population size of each US jurisdictions (n = 750). Results were presented separately by tweets posted from jurisdictions where all cannabis use (non-medicinal and medicinal) is 'fully legalised', 'illegal' and legal for 'medical-only' use.

RESULTS

Four themes were identified: 'Policy', 'Therapeutic value', 'Sales and industry opportunities' and 'Adverse effects'. Most of the tweets were posted by the public. The most common theme was related to 'Policy' (32.5%-61.5% of the tweets). Tweets on 'Therapeutic value' were prevalent in all jurisdictions and accounted for 23.8%-32.1% of the tweets. Sales and promotional activities were prominent even in illegal jurisdictions (12.1%-26.5% of the tweets). Fewer than 10% of tweets were about intoxication and withdrawal symptoms.

DISCUSSION AND CONCLUSION

This study has explored if content themes of medicinal cannabis tweets differed by cannabis legal status. Most tweets were pro-cannabis and they were related to policy, therapeutic value, and sales and industry opportunities. Tweets on unsubstantiated health claims, adverse effects and crime warrants continued surveillance as these conversations could allow us to estimate cannabis-related harms to inform health surveillance.

Health, safety, and socioeconomic impacts of cannabis liberalization laws: An evidence and gap map

Background

Globally, cannabis laws and regulations are rapidly changing. Countries are increasingly permitting access to cannabis under various decriminalization, medicalization, and legalization laws. With strong economic, public health, and social justice incentives driving these domestic cannabis policy reforms, liberalization trends are bound to continue. However, despite a large and growing body of interdisciplinary research addressing the policy-relevant health, safety, and socioeconomic consequences of cannabis liberalization, there is a lack of robust primary and systematic research that comprehensively investigates the consequences of these reforms.

Objectives

This evidence and gap map (EGM) summarizes the empirical evidence on cannabis liberalization policies. Primary objectives were to develop a conceptual framework linking cannabis liberalization policies to relevant outcomes, descriptively summarize the empirical evidence, and identify areas of evidence concentration and gaps.

Search Methods

We comprehensively searched for eligible English-language empirical studies published across 23 academic databases and 11 gray literature sources through August 2020. Additions to the pool of potentially eligible studies from supplemental sources were made through November 2020.

Selection Criteria

The conceptual framework for this EGM draws upon a legal epidemiological perspective highlighting the causal effects of law and policy on population-level outcomes. Eligible interventions include policies that create or expand access to a legal or decriminalized supply of cannabis: comprehensive medical cannabis laws (MCLs), limited medical cannabidiol laws (CBDLs), recreational cannabis laws (RCLs), industrial hemp laws (IHLs), and decriminalization of cultivations laws (DCLs). Eligible outcomes include intermediate responses (i.e., attitudes/behaviors and markets/environments) and longer-term consequences (health, safety, and socioeconomic outcomes) of these laws.

Data Collection and Analysis

Both dual screening and dual data extraction were performed with third person deconfliction. Primary studies were appraised using the Maryland Scientific Methods Scale and systematic reviews were assessed using AMSTAR 2.

Main Results

The EGM includes 447 studies, comprising 438 primary studies and nine systematic reviews. Most research derives from the United States, with little research from other countries. By far, most cannabis liberalization research focuses on the effects of MCLs and RCLs. Studies targeting other laws-including CBDLs, IHLs, and DCLs-are relatively rare. Of the 113 distinct outcomes we documented, cannabis use was the single most frequently investigated. More than half these outcomes were addressed by three or fewer studies, highlighting substantial evidence gaps in the literature. The systematic evidence base is relatively small, comprising just seven completed reviews on cannabis use (3), opioid-related harms (3), and alcohol-related outcomes (1). Moreover, we have limited confidence in the reviews, as five were appraised as minimal quality and two as low quality.

Authors’ Conclusions

More primary and systematic research is needed to better understand the effects of cannabis liberalization laws on longer-term-and arguably more salient-health, safety, and socioeconomic outcomes. Since most research concerns MCLs and RCLs, there is a critical need for research on the societal impacts of industrial hemp production, medical CBD products, and decriminalized cannabis cultivation. Future research should also prioritize understanding the heterogeneous effects of these laws given differences in specific provisions and implementation across jurisdictions.

Association of Anxiety and Gastrointestinal Comorbidities in Repeat Hospital Admissions in Pediatric Cyclic Vomiting Syndrome

INTRODUCTION

Cyclic vomiting syndrome (CVS) is a functional gastrointestinal disorder with recurrent episodes of intense nausea and vomiting and thus may require frequent hospitalizations. There is paucity of data exploring the association of psychiatric and gastrointestinal comorbidities in repeat hospitalizations among pediatric patients with CVS.

METHODS

We analyzed the Pediatric Health Information System database and included all patients up to 18 years of age with a diagnosis of CVS between 2016 and 2020. We excluded patients with chronic conditions, which mimic CVS. The primary outcome variable was 90-day admission rate, which was defined as a visit to emergency department or admission to observation/inpatient unit with a primary diagnosis of CVS within 90 days after an index CVS hospitalization.

RESULTS

We evaluated a total of 2,604 hospitalizations represented by 1,370 unique individuals. The overall 90-day admission rate was 28.5%, which steadily decreased from 35.7% in 2016 to 23% in 2019 ( P < 0.001). Patients in the repeat hospitalization cohort were slightly older and more often men. Patients with repeat admissions had an increased proportion of anxiety and other gastrointestinal disorders. Multivariable logistic regression showed that anxiety, gastroesophageal reflux disease, functional dyspepsia, and abdominal migraine were associated with increased odds of repeat admissions.

DISCUSSION

Ninety-day admission rates in pediatric CVS are decreasing overall, although still contributing to significant healthcare expenditure. Anxiety and gastrointestinal comorbidities were associated with increased risk of repeat admissions. Further prospective studies are needed to better understand the complex interactions of these comorbidities and their management affecting the natural course of CVS.

Outdoor Medical Cannabis Advertising in Oklahoma: Examining Regulatory Compliance and Social Meanings in Billboard Content

Background: Medical cannabis currently dominates the U.S. cannabis advertising landscape. The public is increasingly exposed to outdoor cannabis advertising, which increases positive attitudes about and intentions to use cannabis. Research is lacking regarding outdoor cannabis advertising content. This article characterizes the content of outdoor cannabis advertising in Oklahoma, one of the fastest growing U.S. medical cannabis markets. Methods: We conducted a content analysis of cannabis advertising billboard images (n = 73) from Oklahoma City and Tulsa, photographed May 2019-November 2020. We followed a primarily inductive, iterative team approach to thematically analyze billboard content in NVIVO. We reviewed all images, identified a broad coding taxonomy, and then incorporated emergent codes and those related to advertising regulation (e.g. youth/children). We totaled frequencies of code application across billboards and reexamined billboards for final themes. Results: Major themes were social meanings related to cannabis subculture, formal medical systems, and nature, and the presence of company contact information. Minor themes related to convenience, price promotions, store proximity, U.S. affiliation, product quality, and spirituality. State advertising regulation violations were rare, with the exception of content that may promote curative or therapeutic effects (4%) and misrepresentation of product state of origin (1.4%). Conclusion: Outdoor medical cannabis advertising in Oklahoma blurs boundaries between formal medical discourses and cannabis subculture that is suspicious of messaging from authorities and regards cannabis as harmless and natural. Increased monitoring of advertising regulation compliance and greater understanding of social discourses within emerging markets is needed to promote public health within the context of cannabis advertising.

The international regime of drug control may violate the human right to life and security

Critics of the international regime of drug control have often pointed to its criminogenic effects, maintaining that drug criminalization gives rise to a profitable illicit drugs market which in turn sustains organized crime networks. Here I will expand upon this critique to argue that the violent crime resulting from the drug criminalization regime may constitute a violation of the human right to life and security. To support this argument, I will discuss the extent to which policy makers and the citizens who empower them may stand morally responsible for unintended but foreseeable consequences of the policies they implement. I will note that a north-south imbalance is at play: while the Global North has been the driving force behind the criminalization regime, the violent criminality entailed by the regime of drug control has impacted the Global South most strongly.

Association Between Cannabis and Violence in Community-Dwelling Patients With Severe Mental Disorders: A Cross-sectional Study Using Machine Learning

The objective of this cross-sectional study was to identify cannabis-related features and other characteristics predictive of violence using a data-driven approach in patients with severe mental disorders (SMDs). A Least Absolute Shrinkage and Selection Operator regularization regression model was used on the database consisting of 97 patients with SMD who completed questionnaires measuring substance use and violence. Cannabis use, particularly related to patients' decision to consume or time spent using, was a key predictor associated with violence. Other patterns of substance use and personality traits were identified as strong predictors. Regular patterns of cannabis use and interpersonal issues related to cannabis/stimulant abuse were inversely correlated to violence. This study identified the effect of several predictors correlated to violence in patients with SMD using a regularization regression model. Findings open the door to better identify the profiles of patients that may be more susceptible to perpetrate violent behaviors.

Trends in cannabis use intention around the period of cannabis legalisation in Australia: An age-period-cohort model

INTRODUCTION

This study examines age, time period and birth cohort trends in cannabis use intention and weekly use in Australia over a period in which medicinal cannabis was legalised.

METHODS

Hierarchical age-period-cohort models were used to analyse the National Drug Strategy Household Survey between 2001 and 2019, including 158,395 participants aged 18-79 years.

RESULTS

The hierarchical age-period-cohort model demonstrated a decrease in likelihood of intending to try cannabis as age increases. Similar age effects were found in intending to use cannabis as often or less often. There was broad-based shift in attitudes for people wanting to try cannabis (2007: b = -0.51 [-0.82, -0.21]; 2019: b = 0.68 [0.38, 0.98]) or use cannabis more often (2007: b = -0.15 [-0.50, 0.20]; 2019: b = 0.83 [0.49, 1.18]). The population trend of weekly cannabis use decreased in the earlier periods but increased since 2013 (b = -0.13 [-0.25, -0.02] vs 2019: b = 0.06 [-0.09, 0.20]). This suggests that legalisation would increase uptake of cannabis and consumption among current consumers. There were distinctive inter-generation variations: people born between 1950s and 1960s had more liberal views towards cannabis use than people born before or after (p < 0.05). There were indications that young people born in the 1990 s are catching up with the baby boomers in using cannabis more often if it was legal.

DISCUSSION AND CONCLUSIONS

There has been a population-based shift in Australia in favourable attitudes towards cannabis use, more so among those born in the 1950s to 1960s than other generations. Liberal attitudes and more frequent cannabis use may put certain cohorts at higher risks of cannabis dependence and related harms.

El uso terapéutico del cannabis y los cannabinoides

Los cannabinoides se dirigen principalmente al sistema endocannabinoide (ECS), que surge como un objetivo terapéutico potencialmente interesante debido a su importante papel en la modulación de procesos biológicos clave en todo el organismo. Como tal, los cannabinoides ya se han propuesto como, por ejemplo, antieméticos, agentes antiespásticos, estimulantes del apetito, antiepilépticos, analgésicos, depresores de la presión intraocular o como agentes para controlar los trastornos del movimiento en el síndrome de Tourette. Aquí revisamos las pruebas de investigación disponibles sobre el uso del cannabis y los cannabinoides para un conjunto de aplicaciones terapéuticas sugeridas, y abordamos algunos de los riesgos a corto y largo plazo que se han correlacionado con el uso de estas sustancias. Encontramos escasas pruebas científicas que apoyen el uso de productos basados en el cannabis para la mayoría de las aplicaciones sugeridas, así como ninguna necesidad médica no satisfecha que no esté ya abordada por los medicamentos existentes (algunos basados en cannabinoides) en el mercado. En este escenario, los riesgos potenciales asociados al uso crónico de estas sustancias pueden disuadir su uso médico.

Sex Differences in the Association Between Cannabis Use and Diabetes Mellitus among U.S. Adults: The National Health and Nutritional Examination Survey, 2013-2018

Background: Diabetes mellitus is an important public health problem in the United States, accounting for 87,647 deaths in 2019. This study aimed to assess the association between cannabis use and diabetes mellitus by sex among U.S. adults. Methods: Data were abstracted from the National Health and Nutrition Examination Survey (NHANES) from 2013 through 2018. Cannabis use was estimated using exposure status and frequency of use. Diabetes mellitus was assessed based on physician diagnosis or laboratory results, per the American Diabetes Association guidelines. A multivariable survey logistic regression model was fitted to estimate adjusted odds ratios (aOR) and confidence intervals (95% CIs). Results: A total of 15,062 participants were included in this study. The majority were female (n=7845; 51.1%), >40 years of age (n=8564; 56.3%), non-Hispanic white (n=4873; 61.5%), with at least a college-level education (n=8239; 62.5%). Female participants who used cannabis heavily were less likely to be diagnosed with diabetes mellitus than female noncannabis users (aOR=0.49; 95% CI: 0.30-0.81; aOR=0.51; 95% CI: 0.31-0.84). However, no significant association was found for female adults who engaged in light use of cannabis (aOR=0.98; 95% CI: 0.55-1.75; aOR=1.01; 95% CI: 0.57-1.79). Among male adults, cannabis use, irrespective of the degree of exposure, was not significantly associated with diabetes mellitus (heavy users: aOR=0.89; 95% CI=0.56-1.41; light users: aOR=0.53; 95% CI=0.22-1.29). Conclusions: Heavy cannabis use is inversely associated with diabetes mellitus in females but not males. Further studies are needed to explore the sex-based heterogeneity-and individual and contextual factors responsible-in the association between cannabis use and diabetes mellitus.

Association of Recreational Cannabis Legalization With Alcohol Use Among Adults in the US, 2010 to 2019

Importance

In the US, cannabis use has nearly doubled during the past decade, in part because states have implemented recreational cannabis laws (RCLs). However, it is unclear how legalization of adult-use cannabis may affect alcohol consumption.

Objective

To estimate the association between implementation of state RCLs and alcohol use among adults in the US.

Design, Settings, and Participants

This was a cross-sectional study of 4.2 million individuals who responded to the Behavioral Risk Factor Surveillance System in 2010 to 2019. A difference-in-differences approach with demographic and policy controls was used to estimate the association between RCLs and alcohol use, overall and by age, sex, race and ethnicity, and educational level. Data analyses were performed from June 2021 to March 2022.

Exposures

States with RCLs, as reported by the RAND-University of Southern California Schaeffer Opioid Policy Tools and Information Center.

Main Outcomes and Measures

Past-month alcohol use, binge drinking, and heavy drinking.

Results

Of 4.2 million respondents (median age group, 50-64 years; 2 476 984 [51.7%] women; 2 978 467 [58.3%] non-Hispanic White individuals) in 2010 through 2019, 321 921 individuals lived in state-years with recreational cannabis laws. Recreational cannabis laws were associated with a 0.9 percentage point (95% CI, 0.1-1.7; P = .02) increase in any alcohol drinking but were not significantly associated with binge or heavy drinking. Increases in any alcohol use were primarily among younger adults (18-24 years) and men, as well as among non-Hispanic White respondents and those without any college education. A 1.4 percentage point increase (95% CI, 0.4-2.3; P = .006) in binge drinking was also observed among men, although this association diminished over time.

Conclusions and Relevance

This cross-sectional study and difference-in-differences analysis found that recreational cannabis laws in the US may be associated with increased alcohol use, primarily among younger adults and men.

Evidence on the acute and residual neurocognitive effects of cannabis use in adolescents and adults: a systematic meta-review of meta-analyses

BACKGROUND

Cannabis is among the most consumed psychoactive substances world-wide. Considering changing policy trends regarding the substance, it is crucial to understand more clearly its potential acute and residual adverse effects from a public health viewpoint. Cognitive function is one of the targeted areas with conflicting findings. This meta-review measured the magnitude of acute and residual effects of cannabis on cognition in adolescents and adults provided by meta-analyses and evaluated quality of evidence.

METHODS

A systematic search was performed in PubMed, PsycINFO, Web of Science and Google Scholar. Meta-analyses were included if they quantitatively examined the performances of users from the general population on cognitive tasks.

RESULTS

The search retrieved 10 eligible meta-analyses (71 effects sizes, n = 43 761) with evidence ranging from low to moderate quality, which were categorized into domains of cognitive functions: executive functions (k = 7), learning and memory (k = 5), attention (k = 4), processing speed (k = 5), perceptual motor function (k = 2) and language (k = 2). Verbal learning and memory displayed the most robust evidence and were most impaired by acute cannabis intoxication that persisted after intoxication passed. Small-to-moderate acute and residual   adverse effects were reported for executive functioning. Cannabis use led to small deficits in inhibitory processes and flexibility, whereas small-to-moderate deficits were reported for working memory and decision-making. Evidence regarding processing speed and attention has shown that cannabis administration induced small-to-moderate adverse effects and residual neurocognitive deficits were observed in heavy cannabis-using youths. Results showed no significant difference between cannabis users and non-users on language, and small-to-moderate effects for simple motor skills.

CONCLUSION

Meta-analytical data on the acute effects of cannabis use on neurocognitive function have shown that cannabis intoxication leads to small to moderate deficits in several cognitive domains. These acute impairments accord with documented residual effects, suggesting that the detrimental effects of cannabis persist beyond acute intake.

A Systematic Review of Trends in US Attitudes toward Cannabis Legalization

METHODS

A systematic search was conducted for publications in PubMed, EMBASE, and PsycINFO up to October 2019. Six studies with a regionally or nationally representative adult US-based populations were included. A secondary analysis was conducted using data from the National Survey of Drug Use and Health. Hierarchical age-period-cohort analysis assessed the trends in perceived harmfulness and availability of cannabis between 1996 and 2018. Ecological comparisons were made between these perceptions and support for cannabis legalization over time.

RESULTS

A steep growth in support for cannabis legalization began in the 1990s and continued to grow in a relatively linear manner. Most people developed more liberal views, with no evidence that changes within any one sociodemographic group was disproportionately responsible for the overall attitudinal change. Increases in the proportion of people who use cannabis, non-religious population and political liberalism may partially explain the increased support for legalization. The decline in perceived harmfulness of cannabis, as reflected in the media, may have contributed to the increased support for legalization. However, perceptions of the availability of cannabis remained stable despite significant relaxations in cannabis regulations.

CONCLUSIONS

The US population has become more accepting of cannabis legalization. The attitudinal change is related to changes in the perceived risks and benefits of cannabis use, influenced by broader political and cultural changes over the study period.

Associations between Local Jurisdiction Ordinances and Current Use of Cannabis Products in California Adolescents

PURPOSE

Cannabis use among adolescents may have detrimental effects and use among this age group is increasing. It is important to understand how expansion of laws permitting cannabis sales may impact adolescent use. Much of the current research has explored how state-level policy decisions may impact adolescents' use behaviors; however, there is a gap in the understanding of how differences in local jurisdictional policies may also influence underage cannabis use.Procedures: The present study cross-sectionally assesses local variation in cannabis policies to explore the potential effects of local policy on underage use behaviors. Data were collected from (N = 1,573) adolescents representing 120 different localities across California, collected as a part of Project Cal Teens. Linear regression models were used to assess associations between local jurisdiction's allowance of retail sale of cannabis for adult-use and past 30-day use of non-medical (adult use) cannabis and perceived access to cannabis products.

FINDINGS

Local policy allowing cannabis retail was associated with adolescents' significantly higher past 30-day use of cannabis (β = 0.25 95% CI = 0.08, 0.42) and perceived access (β = 0.60 95% CI = 0.27, 0.94).

CONCLUSIONS

Results highlight the impact of local cannabis policies on adolescent cannabis use and perception. Considering the effects of cannabis use on adolescent development, this is an important public health concern because 14 states have already legalized recreational retail sales and growing numbers of local jurisdictions are allowing the retail sale of recreational cannabis.

Policy influence and the legalized cannabis industry: learnings from other addictive consumption industries

BACKGROUND AND AIM

New Zealand has recently legalized medicinal cannabis and has explored the possibility of legalizing large-scale recreational cannabis supply. In the process, concerns have emerged regarding whether corporations involved in the large-scale production and sale of legalized cannabis will invest in tactics of influence with policymakers and the public. This paper aimed to examine the various ways a legalized cannabis industry could seek to influence governments and the public in the New Zealand reform context.

METHOD

Based on the study of industry tactics with alcohol, tobacco and gambling, we applied a three-chain model of industry influence that breaks tactics into the 'public good', 'knowledge' and 'political' chains.

RESULTS

Exploratory analysis of the nascent cannabis industry's activity in New Zealand provided signs of industry influence strategies related to all three chains. The medicinal cannabis industry has associated the establishment of a legal cannabis sector with regional economic development and employment, supported lobbying for recreational law reform, funded NGOs involved in lobbying for law reform, established research partnerships with universities, invited ex-politicians on advisory boards, and participated in government public sector partnerships.

CONCLUSION

There is emerging evidence that the legal cannabis industry is using strategies to influence the regulatory environment in New Zealand.

Development Over Time of the Population-Attributable Risk Fraction for Cannabis Use Disorder in Schizophrenia in Denmark

IMPORTANCE

Cannabis use and potency of cannabis have increased during the past 2 decades. If the association between cannabis use and schizophrenia is causal, this should be reflected in an increase in the proportion of cases of schizophrenia being attributable to cannabis, the population-attributable risk fraction (PARF).

OBJECTIVE

To determine whether the PARF for cannabis use disorder in schizophrenia has increased over time.

DESIGN, SETTING, AND PARTICIPANTS

This nationwide, register-based historical prospective cohort study included all people in Denmark born before December 31, 2000, who were alive and 16 years or older at some point from January 1, 1972, to December 31, 2016. Data analysis was performed from August 2020 to April 2021.

EXPOSURE

Diagnosis of cannabis use disorder.

MAIN OUTCOMES AND MEASURES

Diagnosis of schizophrenia, with estimated PARF of cannabis use disorder in schizophrenia from 1972 to 2016.

RESULTS

A total of 7 186 834 individuals were included in the analysis, including 3 595 910 women (50.0%) and 3 590 924 men (50.0%). The adjusted hazard ratio for schizophrenia fluctuated at approximately 4 (with 95% CIs ranging from approximately 3 to 6) throughout most of the study period when people diagnosed with cannabis use disorder were compared with those without cannabis use disorder. The PARF of cannabis use disorder in schizophrenia also fluctuated, but with clear evidence of an increase from 1995 (when the PARF was relatively stable around 2.0%, with a 95% CI of approximately 0.3% to either side) until reaching some stability around 6.0% to 8.0% (with a 95% CI of approximately 0.5% to either side) since 2010.

CONCLUSIONS AND RELEVANCE

The results from these longitudinal analyses show the proportion of cases of schizophrenia associated with cannabis use disorder has increased 3- to 4-fold during the past 2 decades, which is expected given previously described increases in the use and potency of cannabis. This finding has important ramifications regarding legalization and control of use of cannabis.

Effect of Washington State and Colorado's cannabis legalization on death by suicides

In the U.S., death by suicide is a leading cause of death and was the 2nd leading cause of death for ages 15-to-34 in 2018. Though incomplete, much of the scientific literature has found associations between cannabis use and death by suicide. Several states and the District of Columbia have legalized cannabis for general adult use. We sought to evaluate whether cannabis legalization has impacted suicide rates in Washington State and Colorado, two early adopters. We used a quasi-experimental research design with annual, state-level deaths by suicide to evaluate the legalization of cannabis in Washington State and Colorado. We used synthetic control models to construct policy counterfactuals as our primary method of estimating the effect of legalization, stratified by age, gender, and race/ethnicity. Overall death by suicide rates were not impacted in either state. However, when stratified by age categories, deaths by suicide increased 17.9% among 15-24-year-olds in Washington State, or an additional 2.13 deaths per 100,000 population (p-value ≤0.001). Other age groups did not show similar associations. An ad hoc analysis revealed, when divided into legal and illegal consumption age, 15-20-year olds had an increase in death by suicides of 21.2% (p-value = 0.026) and 21-24-year olds had an increase in death by suicides of 18.6% (p-value ≤0.001) in Washington State. The effect of legalized cannabis on deaths by suicide appears to be heterogeneous. Deaths by suicide among 15-24-year-olds saw significant increases post-implementation in Washington State but not in Colorado.

Public health impacts to date of the legalisation of medical and recreational cannabis use in the USA

The legality of cannabis use has been changing in a number of jurisdictions around the world. In the U.S., it has been legalised for medicinal and/or recreational uses in 34 jurisdictions and counting. This study leverages the decades-long experience of legalisation in the U.S. to provide an overview of the associated changes in public attitudes, cannabis markets and adverse health effects. We found a broad-based warming of public attitudes toward legalisation, potentially influenced by the increasingly positive portrayal of cannabis in media and declines in cannabis risk perceptions. Potency of cannabis products increased significantly while prices fell sharply. Although adults were less responsive to price changes than adolescents, adults who use cannabis regularly were sensitive to prices, with an estimated 10% price reduction leading to about 2.5% increase in the rate of use. Overall, past-year cannabis use has increased in adults since 2002, and adults over 26 years old who resided in states with medicinal cannabis laws were more likely to have used cannabis in the past 30 days, to have used daily, and to have higher rates of cannabis use disorders than adults who resided in states without legalised medicinal cannabis. Traffic fatalities involving cannabis temporarily increased in some states post-legalisation, and there were more presentations to medical services related to chronic regular cannabis use. There is suggestive evidence that adverse health consequences have increased among people who use cannabis regularly since legalisation. More robust research is needed to determine whether these effects of legalisation are temporary or long-term.

Young-adult compared to adolescent onset of regular cannabis use: A 20-year prospective cohort study of later consequences

INTRODUCTION

This paper compares consequences of cannabis use initiated after high school with those of cannabis initiation in adolescence, with estimates of the proportion of adverse consequences accounted for by adult-onset and adolescent-onset cannabis users.

METHODS

A state-representative sample in Victoria, Australia (n = 1792) participated in a 10-wave longitudinal study and was followed from age 15 to 35 years. Exposure variable: Patterns of cannabis use across 20 years. Outcomes at age 35: Alcohol use, smoking, illicit drug use, relationship status, financial hardship, depression, anxiety and employment status.

RESULTS

Substantially more participants (13.6%) initiated regular use after high school (young-adult onset) than in adolescence (7.7%, adolescent onset). By the mid-30s, both young-adult and adolescent-onset regular users were more likely than minimal/non-users (63.5%) to have used other illicit drugs (odds ratio [OR] > 20.4), be a high-risk alcohol drinker (OR > 3.7), smoked daily (OR > 7.2) and less likely to be in relationships (OR < 0.4). As the prevalence of the young-adult-onset group was nearly double of the adolescent-onset group, it accounted for a higher proportion of adverse consequences than the adolescent-onset group.

DISCUSSION AND CONCLUSIONS

Cannabis users who began regular use in their teens had poorer later life outcomes than non-using peers. The larger group who began regular cannabis use after leaving high school accounted for most cannabis-related harms in adulthood. Given the legalisation of cannabis use in an increasing number of jurisdictions, we should increasingly expect harms from cannabis use to lie in those commencing use in young adulthood.

The impact of state cannabis legislation, county-level socioeconomic and dog-level characteristics on reported cannabis poisonings of companion dogs in the USA (2009-2014)

With current trends in cannabis legalization, large efforts are being made to understand the effects of less restricted legislation on human consumption, health, and abuse of these products. Little is known about the effects of cannabis legalization and increased cannabis use on vulnerable populations, such as dogs. The objective of this study was to examine the effects of different state-level cannabis legislation, county-level socioeconomic factors, and dog-level characteristics on dog cannabis poisoning reports to an animal poison control center (APCC). Data were obtained concerning reports of dog poisoning events, county characteristics, and state cannabis legislation from the American Society for the Prevention of Cruelty to Animals’ (ASPCA) APCC, the US Census Bureau, and various public policy-oriented and government websites, respectively. A multilevel logistic regression model with random intercepts for county and state was fitted to investigate the associations between the odds of a call to the APCC being related to a dog being poisoned by a cannabis product and the following types of variables: dog characteristics, county-level socioeconomic characteristics, and the type of state-level cannabis legislation. There were significantly higher odds of a call being related to cannabis in states with lower penalties for cannabis use and possession. The odds of these calls were higher in counties with higher income variability, higher percentage of urban population, and among smaller, male, and intact dogs. These calls increased throughout the study period (2009–2014). Reporting of cannabis poisonings were more likely to come from veterinarians than dog owners. Reported dog poisonings due to cannabis appear to be influenced by dog-level and community-level factors. This study may increase awareness to the public, public health, and veterinary communities of the effects of recreational drug use on dog populations. This study highlights the need to educate dog owners about safeguarding cannabis products from vulnerable populations.

Medical marijuana laws (MMLs) and dispensary provisions not associated with higher odds of adolescent marijuana or heavy marijuana use: A 46 State Analysis, 1991-2015

Background: States are rapidly moving to reverse marijuana prohibition, most frequently through legalization of medical marijuana laws (MMLs), and there is concern that marijuana legalization may affect adolescent marijuana use. Methods: This natural-experimental study used state Youth Risk Behavior Survey (YRBS) data collected from participants in grades 9-12 from 1991 to 2015 in 46 states (N = 1,091,723). Taking advantage of heterogeneity across states in MML status and MML dispensary design, difference-in-difference estimates compared states with enacted MMLs/dispensaries to non-MML/dispensaries states. Multivariable logistic regression modeling was used to adjust for state and year effects, and student demographics. The main outcome assessed was past 30-day adolescent marijuana use ["any" and "heavy" (≥20)]. Results: In the overall sample, the adjusted odds of adolescents reporting any past 30-day marijuana use was lower in states that enacted MMLs at any time during the study period (OR 0.94, 95% CI 0.89 to 0.99; p < .05), and in states with operational dispensaries in 2015 (OR 0.93, 95% CI 0.88 to 0.99; p < .05). Among grade cohorts, only 9th graders showed a significant effect, with lower odds of use with MML enactment. We found no effects on heavy marijuana use. Conclusions: This study found no evidence between 1991 and 2015 of increases in adolescents reporting past 30-day marijuana use or heavy marijuana use associated with state MML enactment or operational MML dispensaries. In a constantly evolving marijuana policy landscape, continued monitoring of adolescent marijuana use is important for assessing policy effects.

Cannabis use and cannabis use disorder

Cannabis use disorder (CUD) is an underappreciated risk of using cannabis that affects ~10% of the 193 million cannabis users worldwide. The individual and public health burdens are less than those of other forms of drug use, but CUD accounts for a substantial proportion of persons seeking treatment for drug use disorders owing to the high global prevalence of cannabis use. Cognitive behavioural therapy, motivational enhancement therapy and contingency management can substantially reduce cannabis use and cannabis-related problems, but enduring abstinence is not a common outcome. No pharmacotherapies have been approved for cannabis use or CUD, although a number of drug classes (such as cannabinoid agonists) have shown promise and require more rigorous evaluation. Treatment of cannabis use and CUD is often complicated by comorbid mental health and other substance use disorders. The legalization of non-medical cannabis use in some high-income countries may increase the prevalence of CUD by making more potent cannabis products more readily available at a lower price. States that legalize medical and non-medical cannabis use should inform users about the risks of CUD and provide information on how to obtain assistance if they develop cannabis-related mental and/or physical health problems.

Acute Δ9-tetrahydrocannabinol prompts rapid changes in cannabinoid CB1 receptor immunolabeling and subcellular structure in CA1 hippocampus of young adult male mice

The use and abuse of cannabis can be associated with significant pathophysiology, however, it remains unclear whether (1) acute administration of Δ-9-tetrahydrocannabinol (THC) during early adulthood alters the cannabinoid type 1 (CB₁ ) receptor localization and expression in cells of the brain, and (2) THC produces structural brain changes. Here we use electron microscopy and a highly sensitive pre-embedding immunogold method to examine CB₁ receptors in the hippocampus cornu ammonis subfield 1 (CA1) 30 min after male mice were exposed to a single THC injection (5 mg/kg). The findings show that acute exposure to THC can significantly decrease the percentage of CB₁ receptor immunopositive terminals making symmetric synapses, mitochondria, and astrocytes. The percentage of CB₁ receptor-labeled terminals forming asymmetric synapses was unaffected. Lastly, CB₁ receptor expression was significantly lower at terminals of symmetric and asymmetric synapses as well as in mitochondria. Structurally, CA1 dendrites were significantly larger, and contained more spines and mitochondria following acute THC administration. The area of the dendritic spines, synaptic terminals, mitochondria, and astrocytes decreased significantly following acute THC exposure. Altogether, these results indicate that even a single THC exposure can have a significant impact on CB₁ receptor expression, and can alter CA1 ultrastructure, within 30 min of drug exposure. These changes may contribute to the behavioral alterations experienced by young individuals shortly after cannabis intoxication.

What is the prevalence and risk of cannabis use disorders among people who use cannabis? a systematic review and meta-analysis

BACKGROUND AND AIMS

We aim to quantify the prevalence and risk of having a cannabis use disorder (CUD), cannabis abuse (CA) or cannabis dependence (CD) among people in the general population who have used cannabis.

METHOD

We conducted a systematic review of epidemiological cross-sectional and longitudinal studies on the prevalence and risks of CUDs among cannabis users. We identified studies published between 2009 and 2019 through PubMed, the Global Burden Disease (GBD) Database, and supplementary searches up to 2020. The outcomes of interest were CUDs based on DSM or ICD criteria. Estimates were synthesized using random-effects meta-analyses, followed by meta-regression of study characteristics on effect sizes.

RESULTS

From 1383 records identified, 21 studies were included. Meta-analyses showed that among people who used cannabis, 22% (18-26%) have CUD, 13% (8-18%) have CA, and 13% (10-15%) have CD. Estimates from cohort studies, showed that the risk of developing CD increased to 33% (22-44%) among young people who engaged in regular (weekly or daily) use of cannabis. There was a lack of data from cohort studies to estimate the risk of CUD or CA among regular cannabis users.

CONCLUSIONS

Cannabis users need to be informed about the risks of developing CUDs and the higher risks among those who initiate early and use frequently during adolescence. Future studies are needed to examine how changes in cannabis policies may affect the risks of CUDs in the population.

Impact evaluations of drug decriminalisation and legal regulation on drug use, health and social harms: a systematic review

OBJECTIVES

To review the metrics and findings of studies evaluating effects of drug decriminalisation or legal regulation on drug availability, use or related health and social harms globally.

DESIGN

Systematic review with narrative synthesis.

DATA SOURCES

We searched MEDLINE, Embase, PsycINFO, Web of Science and six additional databases for publications from 1 January 1970 through 4 October 2018.

INCLUSION CRITERIA

Peer-reviewed articles or published abstracts in any language with quantitative data on drug availability, use or related health and social harms collected before and after implementation of de jure drug decriminalisation or legal regulation.

DATA EXTRACTION AND SYNTHESIS

Two independent reviewers screened titles, abstracts and articles for inclusion. Extraction and quality appraisal (modified Downs and Black checklist) were performed by one reviewer and checked by a second, with discrepancies resolved by a third. We coded study-level outcome measures into metric groupings and categorised the estimated direction of association between the legal change and outcomes of interest.

RESULTS

We screened 4860 titles and 221 full-texts and included 114 articles. Most (n=104, 91.2%) were from the USA, evaluated cannabis reform (n=109, 95.6%) and focussed on legal regulation (n=96, 84.2%). 224 study outcome measures were categorised into 32 metrics, most commonly prevalence (39.5% of studies), frequency (14.0%) or perceived harmfulness (10.5%) of use of the decriminalised or regulated drug; or use of tobacco, alcohol or other drugs (12.3%). Across all substance use metrics, legal reform was most often not associated with changes in use.

CONCLUSIONS

Studies evaluating drug decriminalisation and legal regulation are concentrated in the USA and on cannabis legalisation. Despite the range of outcomes potentially impacted by drug law reform, extant research is narrowly focussed, with a particular emphasis on the prevalence of use. Metrics in drug law reform evaluations require improved alignment with relevant health and social outcomes.

The costs and benefits of cannabis control policies

As is the case for most drugs, cannabis use has costs and benefits, and so do the policies that attempt to minimize the first and maximize the second. This article summarizes what we know about the harmful effects of recreational cannabis use and the benefits of medical cannabis use under the policy of prohibition that prevailed in developed countries until 2012. It outlines three broad ways in which cannabis prohibition may be relaxed, namely, the depenalization of personal possession and use, the legalization of medical use, and the legalization of adult recreational use. It reviews evidence to date on the impacts of each of these forms of liberalization on the costs and benefits of cannabis use. It makes some plausible conjectures about the future impacts of the commercialization of cannabis using experience from the commercialization of the alcohol, tobacco, and gambling industries. Cannabis policy entails unavoidable trade-offs between competing social values in the face of considerable uncertainty about the effects that more liberal cannabis policies will have on cannabis use and its consequences for better or worse.
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Regular cannabis use is associated with blunted affective, but not cardiovascular, stress responses

AIMS

To examine the potential impact of regular cannabis use on cardiovascular and subjective responses to acute stress.

DESIGN

We used a quasi-experimental design in which subjective states and cardiovascular measures were obtained during rest and in response to acute stress challenges in a sample of regular cannabis users and non-users.

PARTICIPANTS

Seventy-nine adults (forty-five cannabis users and thirty-four non-users).

MEASUREMENTS

We measured subjective states (positive affect, state stress, state anxiety, cannabis craving) and cardiovascular indicators (blood pressure, heart rate, mean arterial pressure) during baseline rest and in response to public speaking, mental arithmetic, and cold-pressor challenges. Regular cannabis use was established via self-report and was confirmed with a positive urine drug test.

FINDINGS

Regular cannabis use was associated with blunted positive affect (F = 5.67, p = .002), state stress (F = 6.05, p = .002), and state anxiety (F = 6.48, p < .001) in response to acute stress challenges. There was no evidence of an association between cannabis use and cardiovascular responses (Fs ≤ 1.54; Ps ≥ 0.21). Contrary to expectations, cannabis craving decreased in response to stress challenges (F = 8.44, p < .001).

CONCLUSION

Chronic cannabis use is associated with blunted positive and negative (stress, anxiety) affective responses to acute stress, indicating emotional dysregulation in this population.

Facing the option for the legalisation of cannabis use and supply in New Zealand: An overview of relevant evidence, concepts and considerations

ISSUES

Non-medical cannabis policies are changing, including towards legalisation-with-regulation frameworks. New Zealand will hold a public referendum on cannabis legalisation in 2020. We reviewed data on cannabis use and health/social harms; policy reform options; experiences with and outcomes of reforms elsewhere; and other relevant considerations towards informing policy choices in the upcoming referendum.

APPROACH

Relevant epidemiological, health, social, criminal justice and policy studies and data were identified and comprehensively reviewed.

KEY FINDINGS

Cannabis use is common (including in New Zealand) and associated with risks for health and social harms, mainly concentrated in young users; key harms are attributable to criminalisation. 'Decriminalisation' reforms have produced ambivalent results. Existing cannabis legalisation frameworks vary considerably in main parameters. Legalisation offers some distinct advantages, for example regulated use, products and user education, yet outcomes depend on essential regulation parameters, including commercialisation, and policy ecologies. While major changes in use are not observed, legalisation experiences are inconclusive to date, including mixed health and social outcomes, with select harms increasing and resilient illegal markets. It is unclear whether legalisation reduces cannabis exposure or social harms (e.g. from enforcement) for youth.

IMPLICATIONS/CONCLUSIONS

No conclusive overall evidence on the outcomes of legalisation elsewhere exists, nor is evidence easily transferable to other settings. Legalisation offers direct social justice benefits for adults, yet overall public health impacts are uncertain. Legalisation may not categorically improve health or social outcomes for youth. Legalisation remains a well-intended, while experimental policy option towards more measured and sensible cannabis control and overall greater policy coherence, requiring close monitoring and possible adjustments depending on setting-specific outcomes.

Adolescent treatment admissions for marijuana following recreational legalization in Colorado and Washington

INTRODUCTION

There is concern that recreational marijuana legalization (RML) may lead to increased cannabis use disorder (CUD) among youth due to increased marijuana use. This study investigates whether adolescent substance use disorder treatment admissions for marijuana use increased in Colorado and Washington following RML.

METHODS

Annual data on 2008-2017 treatment admissions for marijuana use from the SAMHSA TEDS-A dataset for adolescents age 12-17 were used to model state treatment admissions trends. Difference-in-differences models were used to investigate whether treatment admissions increased following RML in Colorado/Washington compared to non-RML states, after adjusting for socioeconomic characteristics and treatment availability.

RESULTS

Over all states in the analysis, the rate of adolescent treatment admissions for marijuana use declined significantly over the study period (β=-3.375, 95 % CI=-4.842, -1.907), with the mean rate falling nearly in half. The decline in admissions rate was greater in Colorado and Washington compared to non-RML states following RML, though this difference was not significant (β=-7.671, 95 % CI=-38.798, 23.456).

CONCLUSION

Adolescent treatment admissions for marijuana use did not increase in Colorado and Washington following RML. This may be because youth marijuana use did not increase, CUD did not increase (even if use did increase), or treatment seeking behaviors changed due to shifts in attitudes and perceptions of risk towards marijuana use.

Cannabis Surveillance With Twitter Data: Emerging Topics and Social Bots

Objectives. To use publicly accessible data from people who post to Twitter to rapidly capture and describe the public's recent experiences with cannabis.Methods. We obtained Twitter posts containing cannabis-related terms from May 1, 2018, to December 31, 2018. We used methods to distinguish between posts from social bots and nonbots. We used text classifiers to identify topics in posts (n = 60 861).Results. Prevalent topics of posts included using cannabis with mentions of cannabis initiation, processed cannabis products, and health and medical with posts suggesting that cannabis could help with cancer, sleep, pain, anxiety, depression, trauma, and posttraumatic stress disorder. Polysubstance use was a common topic with mentions of cocaine, heroin, ecstasy, LSD, meth, mushrooms, and Xanax along with cannabis. Social bots regularly made health claims about cannabis.Conclusions. Findings suggest that processed cannabis products, unsubstantiated health claims about cannabis products, and the co-use of cannabis with legal and illicit substances warrant considerations by public health researchers in the future.

Trends in the sequence of first alcohol, cannabis and cigarette use in Australia, 2001-2016

BACKGROUND

Recent analyses of data from the US found that young people were increasingly engaging in cannabis use before alcohol and cigarettes. These shifts are important for public health, but it is not clear whether such trends extend beyond the US. The aim of this study is to examine whether and how the age and sequencing of initiation into alcohol, cannabis and cigarette use has changed in Australia since the early 2000s.

METHODS

Data came from six waves of the Australian National Drug Strategy Household Survey, spanning 2001-2016. We used data from 18 to 21 year-olds (n = 6849) and examined trends in the age at first use for each of the three substances plus any changes in the order of initiation.

RESULTS

The mean age of initiation increased steadily for all three substances (e.g. from 14.9 in 2001 to 16.4 in 2016 for alcohol), while the prevalence of any use declined. There were some changes in ordering of use. For example, in 2001, 62 % of respondents who used both cigarettes and cannabis had first used cigarettes at an earlier age than cannabis, compared with 41 % in 2016. Young people who used both alcohol and cannabis remained more likely to try alcohol before cannabis across the study period.

CONCLUSIONS

Our results partly replicated US findings, with differences potentially reflecting the substantially different environment around these substances in the US compared to Australia. The age of initiation for alcohol, cigarette and cannabis use in Australia has increased sharply over the past 15 years.

Violence and Cannabis Use: A Focused Review of a Forgotten Aspect in the Era of Liberalizing Cannabis

There has been a shift surrounding societal and legal perspectives on cannabis reflecting changing public attitudes towards the perceived safety and social acceptability of cannabis use. With cannabis liberalization internationally, the focus of most cannabis-related harms has been on effects with users themselves. Harm-to-others including injuries from violence have nevertheless been unfortunately largely overlooked. While studies remain heterogeneous, there is meta-analytical evidence pointing towards an association. The aims of this focused review are two-fold: (I) review the evidence from meta-analyses on the association between cannabis and violence; and (II) provide an overview of possible mechanisms relating cannabis use to violence. First, evidence from meta-analytical studies in youths, intimate partners, and individuals with severe mental disorders have shown that there is a global moderate association between cannabis use and violence, which is stronger in the latter more at-risk population. Preliminary data has even highlighted a potential dose-response relationship with larger effects in more frequent users. Although of importance, this subject has remained essentially forgotten as a public health concern. While literature remains inconclusive, data has suggested potential increases in cannabis use following liberalization policies. This may increase violent outcomes if the effect is directly related to the use of cannabis by means of its psychophysiological modifications. However, for the moment, the mechanisms associating cannabis use and violence remain to be clearly resolved. Considering the recency of policy changes on cannabis, further methodologically sound research using longitudinal designs should examine the effects that cannabis use may have on different forms of violence and the trends that emerge, while evaluating the effects of possible confounding factors (e.g. other substance use). In addition, as evidence-based research from meta-analyses have shown that cannabis use is associated with violence, measures must be taken to mitigate the risks.

Public health implications of legalising the production and sale of cannabis for medicinal and recreational use

We assess the current and describe possible future public health impacts of the legalisation of cannabis production, sale, and use in the Americas. First, we describe global patterns of cannabis use and their most probable adverse health effects. Second, we summarise evidence regarding the effectiveness of cannabinoids for medicinal use and describe approaches that have been used to regulate the use of medicinal cannabis and how these approaches might have affected medicinal and recreational use and harms (eg, road crashes). Third, we describe how jurisdictions that have legalised recreational use have regulated production and sale of cannabis. Fourth, we evaluate the effects of cannabis legalisation on cannabis use and harms and on the use of alcohol, tobacco, and other drugs. Fifth, we use alcohol and tobacco policy examples to identify possible long-term public health effects of cannabis legalisation. Finally, we outline policy approaches that could minimise harms to public health arising from the legalisation of a commercial cannabis industry.

Early evidence of the impact of cannabis legalization on cannabis use, cannabis use disorder, and the use of other substances: Findings from state policy evaluations

Background: The past decade has seen unprecedented shifts in the cannabis policy environment, and the public health impacts of these changes will hinge on how they affect patterns of cannabis use and the use and harms associated with other substances.Objectives: To review existing research on how state cannabis policy impacts substance use, emphasizing studies using methods for causal inference and highlighting gaps in our understanding of policy impacts on evolving cannabis markets.Methods: Narrative review of quasi-experimental studies for how medical cannabis laws (MCLs) and recreational cannabis laws (RCLs) affect cannabis use and use disorders, as well as the use of or harms from alcohol, opioids, and tobacco.Results: Research suggests MCLs increase adult but not adolescent cannabis use, and provisions of the laws associated with less regulated supply may increase adult cannabis use disorders. These laws may reduce some opioid-related harms, while their impacts on alcohol and tobacco use remain uncertain. Research on RCLs is just emerging, but findings suggest little impact on the prevalence of adolescent cannabis use, potential increases in college student use, and unknown effects on other substance use.Conclusions: Research on how MCLs influence cannabis use has advanced our understanding of the importance of heterogeneity in policies, populations, and market dynamics, but studies of how MCLs relate to other substance use often ignore these factors. Understanding effects of cannabis laws requires greater attention to differences in short- versus long-term effects of the laws, nuances of policies and patterns of consumption, and careful consideration of appropriate control groups.