"We replicated the findings of Wall et al. (2) that marijuana use was higher in states that have passed MMLs, and our analysis suggests this is unlikely to be a causal association. Our difference-in-differences estimates suggest little detectable effects of passing MMLs on marijuana use or perceived riskiness of use among adolescents or adults, which is consistent with some limited prior evidence on arrestees and emergency department patients (17). Future analyses that take advantage of additional policy changes may provide further evidence on this question, but our results suggest that such analyses should adequately control for potential confounding by unmeasured state characteristics."


Sam Harper, Erin C. Strumpf, and Jay S. Kaufman, "Do Medical Marijuana Laws Increase Marijuana Use? Replication Study and Extension," Annals of Epidemiology, March 2012 (Vol. 22, Issue 3, Pages 207-212, DOI: 10.1016/j.annepidem.2011.12.002).