This paper sheds light on previous inconsistencies identified in the literature regarding the relationship between medical marijuana laws (MMLs) and recreational marijuana use by closely examining the importance of policy dimensions (registration requirements, home cultivation, dispensaries) and the timing of when particular policy dimensions are enacted. Using data from our own legal analysis of state MMLs, we evaluate which features are associated with adult and youth recreational and heavy use by linking these policy variables to data from the Treatment Episodes Data System (TEDS) and the National Longitudinal Survey of Youth (NLSY97). We employ differences-in-differences techniques, controlling for state and year fixed effects, allowing us to exploit within-state policy changes. We find that while simple dichotomous indicators of MML laws are not positively associated with marijuana use or abuse, such measures hide the positive influence legal dispensaries have on adult and youth use, particularly heavy use. Sensitivity analyses that help address issues of policy endogeneity and actual implementation of dispensaries support our main conclusion that not all MML laws are the same. Dimensions of these policies, in particular legal protection of dispensaries, can lead to greater recreational marijuana use and abuse among adults and those under the legal age of 21 relative to medical marijuana laws without this supply source.

Recent work finds that medical marijuana laws reduce the daily doses filled for opioid analgesics among Medicare Part-D and Medicaid enrollees, as well as population-wide opioid overdose deaths. We replicate the result for opioid overdose deaths and explore the potential mechanism. The key feature of a medical marijuana law that facilitates a reduction in overdose death rates is a relatively liberal allowance for dispensaries. As states have become more stringent in their regulation of dispensaries, the protective value generally has fallen. These findings suggest that broader access to medical marijuana facilitates substitution of marijuana for powerful and addictive opioids.

IMPORTANCE Historical shifts are occurring in marijuana policy. The effect of legalizing marijuana for recreational use on rates of adolescent marijuana use is a topic of considerable debate.OBJECTIVE To examine the association between the legalization of recreational marijuana use in Washington and Colorado in 2012 and the subsequent perceived harmfulness and use of marijuana by adolescents. DESIGN, SETTING, AND PARTICIPANTSWe used data of 253 902 students in eighth, 10th, and 12th grades from 2010 to 2015 from Monitoring the Future, a national, annual, cross-sectional survey of students in secondary schools in the contiguous United States. Difference-indifference estimates compared changes in perceived harmfulness of marijuana use and in past-month marijuana use in Washington and Colorado prior to recreational marijuana legalization (2010-2012) with postlegalization (2013-2015) vs the contemporaneous trends in other states that did not legalize recreational marijuana use in this period. MAIN OUTCOMES AND MEASURESPerceived harmfulness of marijuana use (great or moderate risk to health from smoking marijuana occasionally) and marijuana use (past 30 days). RESULTSOf the 253 902 participants, 120 590 of 245 065(49.2%) were male, and the mean (SD) age was 15.6 (1.7) years. In Washington, perceived harmfulness declined 14.2% and 16.1% among eighth and 10th graders, respectively, while marijuana use increased 2.0% and 4.1% from 2010-2012 to 2013-2015. In contrast, among states that did not legalize recreational marijuana use, perceived harmfulness decreased by 4.9% and 7.2% among eighth and 10th graders, respectively, and marijuana use decreased by 1.3% and 0.9% over the same period. Difference-in-difference estimates comparing Washington vs states that did not legalize recreational drug use indicated that these differences were significant for perceived harmfulness (eighth

Background Adolescent marijuana use is associated with adverse later-life consequences, so identifying factors underlying adolescent use is of substantial public health importance. The relationship of U.S. state medical marijuana laws (MML) to adolescent marijuana use has been controversial. Such laws could convey a message about marijuana acceptability that increases marijuana use soon after passage, even if implementation is delayed or the law narrowly limits use. We used 24 years of U.S. national data to examine the relationship between state MML and adolescent marijuana use. Methods Data came from 1,098,270 U.S. adolescents in 8th, 10th, and 12th grade in the national Monitoring the Future annual surveys conducted between 1991–2014. The main outcome was any marijuana use in the prior 30 days. Using multilevel regression modeling, we examined marijuana use in adolescents nested within states, including whether marijuana use was higher overall in states that ever passed a MML up to 2014, and whether the risk of use changed after state MML were passed. Individual-, school- and state-level covariates were controlled. Findings Overall, marijuana use was more prevalent in states that enacted MML up to 2014 than in other states (AOR=1.27, 95%CI=1.07–1.51). Pre- and post-MML risk did not differ in the full sample (AOR=0.92, 95%CI=0.82–1.04). A significant interaction (p<0.001) indicated differential post-MML risk by grade. In 8th graders, post-MML use decreased (AOR=0.73, 95%CI=0.63–0.84), while no significant change occurred in 10th or 12th graders. Results were generally robust across sensitivity analyses. Interpretation Previous evidence and this study show that MML passage does not result in increased adolescent marijuana use. However, overall, adolescent use is higher in states that ever enacted MML than in other states. State-level risk factors other than MML may contribute to both marijuana use and MML, warranting investigation. An observed 8th-grade post-MML decrease also merits further study. Funding U.S. National Institute on Drug Abuse, Columbia University Mailman School of Public Health, New York State Psychiatric Institute.

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