The impact of state medical marijuana legislation on adolescent marijuana use.

PURPOSE The state-level legalization of medical marijuana has raised concerns about increased accessibility and appeal of the drug to youth. The objective of this study was to assess the impact of medical marijuana legalization across the United States by comparing trends in adolescent marijuana use between states with and without legalization of medical marijuana. METHODS The study utilized data from the Youth Risk Behavioral Surveillance Survey between 1991 and 2011. States with a medical marijuana law for which at least two cycles of Youth Risk Behavioral Surveillance data were available before and after the implementation of the law were selected for analysis. Each of these states was paired with a state in geographic proximity that had not implemented the law. Chi-squared analysis was used to compare characteristics between states with and without medical marijuana use policies. A difference-in-difference regression was performed to control for time-invariant factors relating to drug use in each state, isolating the policy effect, and then calculated the marginal probabilities of policy change on the binary dependent variable. RESULTS The estimation sample was 11,703,100 students. Across years and states, past-month marijuana use was common (20.9%, 95% confidence interval 20.3-21.4). There were no statistically significant differences in marijuana use before and after policy change for any state pairing. In the regression analysis, we did not find an overall increased probability of marijuana use related to the policy change (marginal probability .007, 95% confidence interval -.007, .02). CONCLUSIONS This study did not find increases in adolescent marijuana use related to legalization of medical marijuana.