Replication data for: Do Medical Marijuana Laws Increase Marijuana Use? Replication Study and Extension

PURPOSE: To replicate a prior study that found greater adolescent marijuana use in states that have passed medical marijuana laws, and extend this analysis by accounting for confounding by unmeasured state characteristics and measurement error. METHODS: We obtained state-level estimates of marijuana use from the 2002-2009 National Survey on Drug Use and Health. We used two-sample t-tests and random-effects regression to replicate previous results. We used difference-in-differences regression models to estimate the causal effect of medical marijuana laws on marijuana use, and simulations to account for measurement error. RESULTS: We replicated previously published results showing higher marijuana use in states with medical marijuana laws. Difference-in-differences estimates suggested that passing medical marijuana laws decreased past-month use among adolescents by 0.53 percentage points (95% CI: 0.03-1.02) and had no discernible effect on the perceived riskiness of monthly use. Models incorporating measurement error in the state estimates of marijuana use yielded little evidence that passing medical marijuana laws affects marijuana use. CONCLUSIONS: Accounting for confounding by unmeasured state characteristics and measurement error had an important effect on estimates of the impact of medical marijuana laws on marijuana use. We find limited evide nce of causal effects of medical marijuana laws on measures of reported marijuana use.