The enactment of state laws allowing for the limited legal use of cannabis by qualified patients has little to no causal effect on broader marijuana use, according to data published online in the journal Annals of Epidemiology.
Investigators at McGill University in Montreal obtained state-level estimates of marijuana use from the 2002 through 2009 US National Survey on Drug Use and Health. Researchers used difference-in-differences regression models to estimate the causal effect of medical cannabis laws on marijuana use, and simulations to account for measurement error.
Authors reported: “Difference-in-differences estimates suggested that passing MMLs (medical marijuana laws) decreased past-month use among adolescents … and had no discernible effect on the perceived riskiness of monthly use. … [These] estimates suggest that reported adolescent marijuana use may actually decrease following the passing of medical marijuana laws.”
They concluded, “We find limited evidence of causal effects of medical marijuana laws on measures of reported marijuana use.”
Previous investigations by researcher teams at Brown University in 2011 and Texas A&M in 2007 made similar determinations, concluding, “[C]onsistent with other studies of the liberalization of cannabis laws, medical cannabis laws do not appear to increase use of the drug.”
The findings are in direct conflict with public statements made by Drug Czar Gil Kerlikowske, who in recent years has frequently alleged that the passage of medical cannabis laws is directly responsible for higher levels of self-reported marijuana consumption among US teenagers.
Full text of the study, “Do Medical Marijuana Laws Increase Marijuana Use? Replication Study and Extension,” can be read online here.