The design of medical marijuana laws and adolescent use and heavy use of marijuana: Analysis of 45 states from 1991 to 2011

Objectives: To assess the association between U.S. state medical marijuana laws (MML), the most liberal category of marijuana policies before legalization, their specific provisions, and adolescent past-30-day use and heavy marijuana use. Methods: This quasi-experimental study used state Youth Risk Behavior Survey (YRBS) data collected during 1991-2011 from 45 states (N = 715,014) to examine MML effects, taking advantage of heterogeneity across states in MML status and design. Multiple logistic regression modeling was used to adjust for state and year effects, and youth demographics. Results: Unadjusted analyses found that MMLs were associated with higher rates of adolescent past-30 day marijuana use (odds ratio [OR] = 1.08, 95% confidence interval, [(CI) = 1.03, 1.131) and heavy marijuana use (OR = 1.12, [CI = 1.05, 1.21]). However, analyses adjusting for state/year effects found a 7% lower odds of use (OR = 0.99, [CI = 0.98, 0.999]) and no difference in heavy use. In the adjusted models, years since MML enactment (OR = 0.93, [CI = 0.86,0.99]) and MML inclusion of more liberalized provisions (OR = 0.98, [CI = 0.96,0.998]) were associated with slightly lowered odds of past-30-day marijuana use. Conversely, allowance for >= 2.5 usable marijuana ounces was associated with higher past-30-day marijuana use odds (OR = 1.21, [Cl = 1.09, 1.34]) and a voluntary vs. mandatory patient registration with higher odds of both past-30-day use (OR = 1.41, [CI = 1.28, 1.56]) and heavy use (OR = 1.23, [CI = 1.08, 1.40]). Conclusions: MML enactment, years since enactment, and inclusion of more liberalized provisions were not associated with increased adolescent marijuana use in this dataset after adjusting for state and year effects; however, higher possession limits and a voluntary registration were. It is possible that state norms are the impetus for MML enactment. (C) 2016 Elsevier Ireland Ltd. All rights reserved.