MONTREAL, QB — 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.”