The Impact of Legalizing and Regulating Weed: Issues with Study Design and Emerging Findings in the USA

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.

Evaluation of the Daily Sessions, Frequency, Age of Onset, and Quantity of Cannabis Use Questionnaire and its Relations to Cannabis-Related Problems

Cannabis use and the prevalence of cannabis use disorder (CUD) among emerging adults are on the rise. Several indicators of cannabis use (e.g., quantity, frequency) as they relate to negative outcomes have been posited in the extant literature. Despite research examining links between indicators and cannabis outcomes, few assessments of cannabis use indicators exist. The Daily Sessions, Frequency, Age of Onset, and Quantity of Cannabis Use Inventory (DFAQ-CU) was developed to assess cannabis use across a range of factors. However, the factor structure of the DFAQ-CU has not been replicated. Further, the DFAQ-CU was modeled using reflective strategies despite formative strategies being conceptually appropriate. The present study utilized principal components analyses (PCA) and principal axis factoring (PAF) to evaluate the structure of the DFAQ-CU. PCA yielded a four-component solution; PAF resulted in a five-factor solution. Linear regression found significant relations between PCA components and PAF factors with CUD symptoms and cannabis-related problems; however, effect sizes were larger for the PAF suggesting possible misdisattenuation. The PCA components demonstrated evidence of discriminant and convergent validity with measures of cannabis and alcohol behavior. The study informs research and clinical work through the refinement of cannabis use assessment and enhancing our understanding of the importance of model selection.

The supply-side effects of cannabis legalization

OBJECTIVE

The purpose of this study is to examine how cannabis legalization and corresponding taxation would affect the supply-side of the cannabis market. Specifically, the study considers various scenarios in which Oklahoma legalizes recreational cannabis for adult use and simulates changes in state-level market sales for other legal states and the average grower profits in Oklahoma. We assume that legalizing recreational cannabis in medical-only states would significantly increase the demand quantity in the legalized states and the local government would levy a significant level of tax on recreational cannabis. These assumptions are based on the post-legalization phenomena in other legalized US states.

METHOD

We simulate outcomes in the cannabis industry under the assumption of representative consumers with constant elasticity of substitution demand behavior and profit-maximizing firms with a Cobb-Douglas profit function. All agents are assumed to take exogenous prices as given. We calibrate the model using state-level sales data from 2020 and explore potential policies in Oklahoma and at the federal level.

RESULTS

We find that, under the scenarios we consider, legalization of recreational cannabis in Oklahoma would lead to a decrease in the quantity of cannabis sold in Oklahoma's medical cannabis market as well as decreases in the quantity of cannabis sold in other states on average. Furthermore, we find that as the excise tax rate on recreational cannabis in Oklahoma is increased, the demand quantity in recreational cannabis market would decrease while the other markets' demand quantity would increase on average. As the elasticity of substitution between state-level products increases, the overall demand quantity would increase and the market quantity across states become more sensitive to Oklahoma's tax policies. This pattern could become starker as the elasticity of substitution between recreational and medical cannabis increases. In terms of profit, heavy taxation and price decrease due to legalization would significantly decrease cannabis producers' production and profit levels unless the cost reduction strategies complement legalization.

CONCLUSION

Based on our results, the legalization of recreational cannabis has the potential to generate tax revenue to fund critical government projects and services. However, such legalization would have to be done carefully because heavy excise taxes would decrease the legal cannabis market demand and growers' profit, which would incentivize producers and consumers to move to the illicit cannabis market. Policymakers would have to compromise between the levels of interstate transportation and taxation to ensure that cannabis suppliers also realize some profit within the cannabis supply chain.

A Systematic Review and Narrative Synthesis of the Evolution of Adolescent and Young Adult Cannabis Consumption Before and After Legalization

PURPOSE

To systematically review evidence assessing the evolution of cannabis consumption before and after the implementation of non-medical cannabis legislation.

METHODS

MEDLINE, PubMED, PsycINFO, Scopus, and Web of Science were systematically searched for studies that examined change in cannabis consumption before and after nonmedical cannabis legislation. Data were tabulated by study design, levels of consumption, and individual subgroups. Data were analyzed using a narrative synthesis approach, considering study quality.

RESULTS

32 studies were included (11 higher quality and 21 lower quality). 40% of higher quality evidence supported an increase in postlegalization consumption (55% did not report a change and 5% reported a decrease). The increase was most evident for young adults (42% of higher quality evidence) and in the consumption in the past month (37% of higher quality evidence). There was limited supporting evidence for new users having grown in response to legalization. Based on subgroup analysis, the increase in postlegalization consumption was higher among women and those who engage in binge-drinking.

CONCLUSIONS

Higher quality evidence suggests an increase in adolescent past-month consumption of cannabis following legalization in several geographical jurisdictions. Consumption evolution prelegalization and postlegalization differed by age group and for young women and for binge drinkers. Consumption evolution differences suggest a variety of strategies might be required in efforts to lower public health impacts of cannabis consumption following legalization.

Implications of Medical and Recreational Marijuana Laws for Neuroscience Research: a Review

Purpose of Review

Review of US medical and recreational marijuana laws (MML and RML), their effects on cannabis potency, prevalence of non-medical cannabis use and cannabis use disorder (CUD) in adolescents and adults, and implications for neuroscience research, given what is known about the relationship of cannabis to neurocognitive impairments and underlying brain functioning.

Recent Findings

Cannabis potency may be increasing faster in states with MML or RML than in other states. MML and RML have not impacted prevalence in adolescents but have consistently been shown to increase rates of adult non-medical use and CUD.

Summary

Recent neurocognitive or neuroimaging studies may be more impacted by cannabis than studies conducted when MML and RML were less common. Neurocognitive or neuroimaging studies conducted in MML or RML states should carefully test potential participants for recent cannabis use. More research is needed on cannabis and cognition in medical marijuana patients.

Race/Ethnicity Differences in Trends of Marijuana, Cigarette, and Alcohol Use Among 8th, 10th, and 12th Graders in Washington State, 2004-2016

Accurate estimates of substance use in the teenage years by race/ethnicity may help identify when to intervene to prevent long-term substance use disparities. We examined trends in past 30-day use of marijuana, cigarette, and alcohol among 8th, 10th, and 12th graders in Washington State, which passed a recreational marijuana law in 2012 and initiated retail marijuana sales in 2014. Data are from the 2004-2016 Washington Healthy Youth Surveys (n = 161,992). We used time series regression models to assess linear and quadratic trends in substance use for the full sample and stratified on race/ethnicity and grade level and examined relative differences in prevalence of use by race/ethnicity. In Washington, across all racial/ethnic groups, marijuana use peaked in 2012. Although there was not a significant overall change in marijuana use for the full sample across the study period, there was a statistically significant increase in use among 12th graders and a statistically significant decrease among 8th graders. Relative to Whites, Asians had a lower prevalence of marijuana use, whereas all other race/ethnicity groups had a higher prevalence of use. Prevalence of marijuana use is particularly high among American Indian/Alaska Native and Black youth and has increased most rapidly among 12th grade Hispanic/Latinx youth. There were large and statistically significant decreases in alcohol and cigarette use across the study period for the full sample, as well as for each race/ethnicity group. These findings highlight the need for continued monitoring of trends in use among these groups and potentially warrant consideration of selective interventions that specifically focus on students of color and that include developmentally-appropriate strategies relevant to each grade.

A quasi-experimental evaluation of marijuana policies and youth marijuana use

BACKGROUND

Marijuana use carries risks for adolescents' well-being, making it essential to evaluate effects of recent marijuana policies.

OBJECTIVES

This study sought to delineate associations between state-level shifts in decriminalization and medical marijuana laws (MML) and adolescent marijuana use.

METHODS

Using data on 861,082 adolescents (14 to 18+ years; 51% female) drawn from 1999 to 2015 state Youth Risk Behavior Surveys (YRBS), difference-in-differences models assessed how decriminalization and MML policy enactment were associated with adolescent marijuana use, controlling for tobacco and alcohol policy shifts, adolescent characteristics, and state and year trends.

RESULTS

MML enactment was associated with small significant reductions (OR = 0.911, 95% CI [0.850, 0.975]) of 1.1 percentage points in current marijuana use, with larger significant declines for male, Black, and Hispanic (2.7-3.9 percentage points) adolescents. Effects of MML increased significantly with each year of exposure (OR = 0.980, 95% CI [0.968, 0.992]). In contrast, decriminalization was not associated with significant shifts in use for the sample as a whole, but predicted significant declines in marijuana use among 14-year olds and those of Hispanic and other ancestry (1.7-4.4 percentage points), and significant increases among white adolescents (1.6 percentage points). Neither policy was significantly associated with heavy marijuana use or the frequency of use, suggesting that heavy users may be impervious to such policy signals.

CONCLUSION

As the first study to concurrently assess unique effects of multiple marijuana policies, results assuage concerns over potential detrimental effects of more liberal marijuana policies on youth use.

Medical marijuana laws and adolescent marijuana use in the United States: a systematic review and meta-analysis

AIMS

To conduct a systematic review and meta-analysis of studies in order to estimate the effect of US medical marijuana laws (MMLs) on past-month marijuana use prevalence among adolescents.

METHODS

A total of 2999 papers from 17 literature sources were screened systematically. Eleven studies, developed from four ongoing large national surveys, were meta-analyzed. Estimates of MML effects on any past-month marijuana use prevalence from included studies were obtained from comparisons of pre-post MML changes in MML states to changes in non-MML states over comparable time-periods. These estimates were standardized and entered into a meta-analysis model with fixed-effects for each study. Heterogeneity among the study estimates by national data survey was tested with an omnibus F-test. Estimates of effects on additional marijuana outcomes, of MML provisions (e.g. dispensaries) and among demographic subgroups were abstracted and summarized. Key methodological and modeling characteristics were also described. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed.

RESULTS

None of the 11 studies found significant estimates of pre-post MML changes compared with contemporaneous changes in non-MML states for marijuana use prevalence among adolescents. The meta-analysis yielded a non-significant pooled estimate (standardized mean difference) of -0.003 (95% confidence interval = -0.012, +0.007). Four studies compared MML with non-MML states on pre-MML differences and all found higher rates of past-month marijuana use in MML states pre-MML passage. Additional tests of specific MML provisions, of MML effects on additional marijuana outcomes and among subgroups generally yielded non-significant results, although limited heterogeneity may warrant further study.

CONCLUSIONS

Synthesis of the current evidence does not support the hypothesis that US medical marijuana laws (MMLs) until 2014 have led to increases in adolescent marijuana use prevalence. Limited heterogeneity exists among estimates of effects of MMLs on other patterns of marijuana use, of effects within particular population subgroups and of effects of specific MML provisions.

Medical Marijuana and Marijuana Legalization

State-level marijuana liberalization policies have been evolving for the past five decades, and yet the overall scientific evidence of the impact of these policies is widely believed to be inconclusive. In this review we summarize some of the key limitations of the studies evaluating the effects of decriminalization and medical marijuana laws on marijuana use, highlighting their inconsistencies in terms of the heterogeneity of policies, the timing of the evaluations, and the measures of use being considered. We suggest that the heterogeneity in the responsiveness of different populations to particular laws is important for interpreting the mixed findings from the literature, and we highlight the limitations of the existing literature in providing clear insights into the probable effects of marijuana legalization.

Medical marijuana laws and adolescent use of marijuana and other substances: Alcohol, cigarettes, prescription drugs, and other illicit drugs

BACKGROUND

Historical shifts have taken place in the last twenty years in marijuana policy. The impact of medical marijuana laws (MML) on use of substances other than marijuana is not well understood. We examined the relationship between state MML and use of marijuana, cigarettes, illicit drugs, nonmedical use of prescription opioids, amphetamines, and tranquilizers, as well as binge drinking.

METHODS

Pre-post MML difference-in-difference analyses were performed on a nationally representative sample of adolescents in 48 contiguous U.S. states. Participants were 1,179,372U.S. 8th, 10th, and 12th graders in the national Monitoring the Future annual surveys conducted in 1991-2015. Measurements were any self-reported past-30-day use of marijuana, cigarettes, non-medical use of opioids, amphetamines and tranquilizers, other illicit substances, and any past-two-week binge drinking (5+ drinks per occasion).

RESULTS

Among 8th graders, the prevalence of marijuana, binge drinking, cigarette use, non-medical use of opioids, amphetamines and tranquilizers, and any non-marijuana illicit drug use decreased after MML enactment (0.2-2.4% decrease; p-values:<0.0001-0.0293). Among 10th graders, the prevalence of substance use did not change after MML enactment (p-values: 0.177-0.938). Among 12th graders, non-medical prescription opioid and cigarette use increased after MML enactment (0.9-2.7% increase; p-values: <0.0001-0.0026).

CONCLUSIONS

MML enactment is associated with decreases in marijuana and other drugs in early adolescence in those states. Mechanisms that explain the increase in non-medical prescription opioid and cigarette use among 12th graders following MML enactment deserve further study.

US Epidemiology of Cannabis Use and Associated Problems

This review provides an overview of the changing US epidemiology of cannabis use and associated problems. Adults and adolescents increasingly view cannabis as harmless, and some can use cannabis without harm. However, potential problems include harms from prenatal exposure and unintentional childhood exposure; decline in educational or occupational functioning after early adolescent use, and in adulthood, impaired driving and vehicle crashes; cannabis use disorders (CUD), cannabis withdrawal, and psychiatric comorbidity. Evidence suggests national increases in cannabis potency, prenatal and unintentional childhood exposure; and in adults, increased use, CUD, cannabis-related emergency room visits, and fatal vehicle crashes. Twenty-nine states have medical marijuana laws (MMLs) and of these, 8 have recreational marijuana laws (RMLs). Many studies indicate that MMLs or their specific provisions did not increase adolescent cannabis use. However, the more limited literature suggests that MMLs have led to increased cannabis potency, unintentional childhood exposures, adult cannabis use, and adult CUD. Ecological-level studies suggest that MMLs have led to substitution of cannabis for opioids, and also possibly for psychiatric medications. Much remains to be determined about cannabis trends and the role of MMLs and RMLs in these trends. The public, health professionals, and policy makers would benefit from education about the risks of cannabis use, the increases in such risks, and the role of marijuana laws in these increases.

Legal cannabis laws, home cultivation, and use of edible cannabis products: A growing relationship?

BACKGROUND

Over half of U.S. states have enacted legal cannabis laws (LCL). In parallel, edible cannabis products (i.e., edibles) have presented new regulatory challenges. LCL provisions that dictate access to cannabis (e.g., home cultivation (HC) or dispensaries (DSP)) may impact edible production and use. This study examined relationships among HC and DSP provisions, cannabis cultivation, and edible use.

METHODS

An online cannabis use survey was distributed using Facebook. Data were collected from 1813 cannabis-using adults. U.S. states were classified as states without LCL (Non-LCL) or LCL states that: (1) only permit DSP (LCL DSP-only), (2) only permit HC (LCL HC-only), or (3) permit HC and DSP (LCL HC+DSP). Analyses tested associations among these classifications, cannabis growing, and edible use and procurement.

RESULTS

Individuals in LCL HC-only and LCL HC+DSP states were more likely to report currently growing cannabis at home (OR: 3.3, 95% CI: 1.7, 6.2; OR: 3.9, 95% CI: 2.4, 6.3, respectively) and past-month edible use (OR: 2.1, 95% CI: 1.4, 3.4; OR: 2.9, 95% CI: 2.2, 3.9, respectively) than individuals in LCL DSP-only states. Regardless of state, those who had grown cannabis were more likely to have made edibles than those who had never grown cannabis (OR: 2.2, 95% CI: 1.8, 2.6). Individuals in LCL HC-only states were more likely to have made edibles in the past month than individuals from Non-LCL (OR: 2.75, 95% CI: 1.5, 5.3) and DSP-only states (OR: 2.1, 95% CI: 1.0, 4.4). Individuals in LCL HC+DSP states were more likely to have purchased edibles in the past month than individuals from Non-LCL (OR: 3.7, 95% CI: 2.4, 5.6) and DSP-only states (OR: 3.2, 95% CI: 1.8, 5.5).

CONCLUSION

Specific LCL provisions may differentially affect individuals' propensity to grow cannabis and make, buy, and use edible cannabis products. Permitting home cultivation contributes to a greater likelihood of growing cannabis. Those who grow cannabis economize the plant by creating homemade edible cannabis products. Conversely, permitting dispensaries increases the likelihood of purchasing edibles. The psychoactive effects of edibles with unknown and variable cannabinoid content will be unpredictable. Policymakers should carefully consider how specific LCL provisions can affect patterns of cannabis edible product access and quality.

Cannabis use, attitudes, and legal status in the U.S.: A review

Cannabis is widely used among adolescents and adults. In the U.S., marijuana laws have been changing, and Americans increasingly favor legalizing cannabis for medical and recreational uses. While some can use cannabis without harm, others experience adverse consequences. The objective of this review is to summarize information on the legal status of cannabis, perceptions regarding cannabis, prevalence and time trends in use and related adverse consequences, and evidence on the relationship of state medical (MML) and recreational (RML) marijuana laws to use and attitudes. Twenty-nine states now have MMLs, and eight of these have RMLs. Since the early 2000s, adult and adolescent perception of cannabis use as risky has decreased. Over the same time, the prevalence of adolescent cannabis use has changed little. However, adult cannabis use, disorders, and related consequences have increased. Multiple nationally representative studies indicate that MMLs have had little effect on cannabis use among adolescents. However, while MML effects have been less studied in adults, available evidence suggests that MMLs increase use and cannabis use disorders in adults. While data are not yet available to evaluate the effect of RMLs, they are likely to lower price, increase availability, and thereby increase cannabis use. More permissive marijuana laws may accomplish social justice aims (e.g., reduce racial disparities in law enforcement) and generate tax revenues. However, such laws may increase cannabis-related adverse health and psychosocial consequences by increasing the population of users. Dissemination of balanced information about the potential health harms of cannabis use is needed.

Changes in undergraduates' marijuana, heavy alcohol and cigarette use following legalization of recreational marijuana use in Oregon

BACKGROUND AND AIMS

Recreational marijuana legalization (RML) went into effect in Oregon in July 2015. RML is expected to influence marijuana use by adolescents and young adults in particular, and by those with a propensity for substance use. We sought to quantify changes in rates of marijuana use among college students in Oregon from pre- to post-RML relative to college students in other states across the same time period.

DESIGN

Repeated cross-sectional survey data from the 2012-16 administrations of the Healthy Minds Study.

SETTING

Seven 4-year universities in the United States.

PARTICIPANTS

There were 10 924 undergraduate participants. One large public Oregon university participated in 2014 and 2016 (n = 588 and 1115, respectively); six universities in US states where recreational marijuana use was illegal participated both in 2016 and at least once between 2012 and 2015.

MEASUREMENTS

Self-reported marijuana use in the past 30 days (yes/no) was regressed on time (pre/post 2015), exposure to RML (i.e. Oregon students in 2016) and covariates using mixed-effects logistic regression. Moderation of RML effects by recent heavy alcohol use was examined.

FINDINGS

Rates of marijuana use increased from pre- to post-2015 at six of the seven universities, a trend that was significant overall. Increases in rates of marijuana use were significantly greater in Oregon than in comparison institutions, but only among students reporting recent heavy alcohol use.

CONCLUSIONS

Rates of Oregon college students' marijuana use increased (relative to that of students in other states) following recreational marijuana legislation in 2015, but only for those who reported recent heavy use of alcohol. Such alcohol misuse may be a proxy for vulnerabilities to substance use or lack of prohibitions (e.g. cultural) against it.

U.S. cannabis legalization and use of vaping and edible products among youth

BACKGROUND

Alternative methods for consuming cannabis (e.g., vaping and edibles) have become more popular in the wake of U.S. cannabis legalization. Specific provisions of legal cannabis laws (LCL) (e.g., dispensary regulations) may impact the likelihood that youth will use alternative methods and the age at which they first try the method - potentially magnifying or mitigating the developmental harms of cannabis use.

METHODS

This study examined associations between LCL provisions and how youth consume cannabis. An online cannabis use survey was distributed using Facebook advertising, and data were collected from 2630 cannabis-using youth (ages 14-18). U.S. states were coded for LCL status and various LCL provisions. Regression analyses tested associations among lifetime use and age of onset of cannabis vaping and edibles and LCL provisions.

RESULTS

Longer LCL duration (OR_vaping: 2.82, 95% CI: 2.24, 3.55; OR_edibles: 3.82, 95% CI: 2.96, 4.94), and higher dispensary density (OR_vaping: 2.68, 95% CI: 2.12, 3.38; OR_edibles: 3.31, 95% CI: 2.56, 4.26), were related to higher likelihood of trying vaping and edibles. Permitting home cultivation was related to higher likelihood (OR: 1.93, 95% CI: 1.50, 2.48) and younger age of onset (β: -0.30, 95% CI: -0.45, -0.15) of edibles.

CONCLUSION

Specific provisions of LCL appear to impact the likelihood, and age at which, youth use alternative methods to consume cannabis. These methods may carry differential risks for initiation and escalation of cannabis use. Understanding associations between LCL provisions and methods of administration can inform the design of effective cannabis regulatory strategies.

US Adult Illicit Cannabis Use, Cannabis Use Disorder, and Medical Marijuana Laws: 1991-1992 to 2012-2013

Importance

Over the last 25 years, illicit cannabis use and cannabis use disorders have increased among US adults, and 28 states have passed medical marijuana laws (MML). Little is known about MML and adult illicit cannabis use or cannabis use disorders considered over time.

Objective

To present national data on state MML and degree of change in the prevalence of cannabis use and disorders.

Design, Participants, and Setting

Differences in the degree of change between those living in MML states and other states were examined using 3 cross-sectional US adult surveys: the National Longitudinal Alcohol Epidemiologic Survey (NLAES; 1991-1992), the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC; 2001-2002), and the National Epidemiologic Survey on Alcohol and Related Conditions-III (NESARC-III; 2012-2013). Early-MML states passed MML between NLAES and NESARC ("earlier period"). Late-MML states passed MML between NESARC and NESARC-III ("later period").

Main Outcomes and Measures

Past-year illicit cannabis use and DSM-IV cannabis use disorder.

Results

Overall, from 1991-1992 to 2012-2013, illicit cannabis use increased significantly more in states that passed MML than in other states (1.4-percentage point more; SE, 0.5; P = .004), as did cannabis use disorders (0.7-percentage point more; SE, 0.3; P = .03). In the earlier period, illicit cannabis use and disorders decreased similarly in non-MML states and in California (where prevalence was much higher to start with). In contrast, in remaining early-MML states, the prevalence of use and disorders increased. Remaining early-MML and non-MML states differed significantly for use (by 2.5 percentage points; SE, 0.9; P = .004) and disorder (1.1 percentage points; SE, 0.5; P = .02). In the later period, illicit use increased by the following percentage points: never-MML states, 3.5 (SE, 0.5); California, 5.3 (SE, 1.0); Colorado, 7.0 (SE, 1.6); other early-MML states, 2.6 (SE, 0.9); and late-MML states, 5.1 (SE, 0.8). Compared with never-MML states, increases in use were significantly greater in late-MML states (1.6-percentage point more; SE, 0.6; P = .01), California (1.8-percentage point more; SE, 0.9; P = .04), and Colorado (3.5-percentage point more; SE, 1.5; P = .03). Increases in cannabis use disorder, which was less prevalent, were smaller but followed similar patterns descriptively, with change greater than never-MML states in California (1.0-percentage point more; SE, 0.5; P = .06) and Colorado (1.6-percentage point more; SE, 0.8; P = .04).

Conclusions and Relevance

Medical marijuana laws appear to have contributed to increased prevalence of illicit cannabis use and cannabis use disorders. State-specific policy changes may also have played a role. While medical marijuana may help some, cannabis-related health consequences associated with changes in state marijuana laws should receive consideration by health care professionals and the public.

State and National Contexts in Evaluating Cannabis Laws: A Case Study of Washington State

As of January 2016, 23 U.S. states and the District of Columbia have legalized medical or nonmedical cannabis, with more likely to follow. This dynamic policy context represents a substantial challenge for policy evaluation. Part I of this article provides a summary of state-level cannabis policy components across states and federal action regarding state-level policies. Part II presents a detailed history of cannabis policies in Washington State from 1998 to 2015 and analyzes the potential impacts of the policy changes on cannabis supply and demand. As an early adopter of both medical and nonmedical cannabis policies, Washington State provides an excellent example of the key elements to be considered in evaluating the relationship between policy changes and cannabis use. We highlight the importance of the interplay of federal enforcement priorities and previously adopted state-level cannabis regimes in interpreting the potential impacts of new cannabis policies.

State Medical Marijuana Laws and the Prevalence of Opioids Detected Among Fatally Injured Drivers

OBJECTIVES

To assess the association between medical marijuana laws (MMLs) and the odds of a positive opioid test, an indicator for prior use.

METHODS

We analyzed 1999-2013 Fatality Analysis Reporting System (FARS) data from 18 states that tested for alcohol and other drugs in at least 80% of drivers who died within 1 hour of crashing (n = 68 394). Within-state and between-state comparisons assessed opioid positivity among drivers crashing in states with an operational MML (i.e., allowances for home cultivation or active dispensaries) versus drivers crashing in states before a future MML was operational.

RESULTS

State-specific estimates indicated a reduction in opioid positivity for most states after implementation of an operational MML, although none of these estimates were significant. When we combined states, we observed no significant overall association (odds ratio [OR] = 0.79; 95% confidence interval [CI] = 0.61, 1.03). However, age-stratified analyses indicated a significant reduction in opioid positivity for drivers aged 21 to 40 years (OR = 0.50; 95% CI = 0.37, 0.67; interaction P < .001).

CONCLUSIONS

Operational MMLs are associated with reductions in opioid positivity among 21- to 40-year-old fatally injured drivers and may reduce opioid use and overdose.