Impact of Medical Marijuana Laws on State-Level Marijuana Use by Age and Gender, 2004-2013

In states that have passed medical marijuana laws (MMLs), marijuana use (MU) increased after MML enactment among people ages 26 and older, but not among ages 12-25. We examined whether the age-specific impact of MMLs on MU varied by gender. Data were obtained from the 2004-2013 restricted-use National Survey on Drug Use and Health, aggregated at the state level. The exposure was a time-varying indicator of state-level MML (0=No Law, 1=Before Law, 2=After Law). Outcomes included past-month MU prevalence, daily MU prevalence among past-year users (i.e., 300+days/year), and past-year marijuana use disorder (MUD) prevalence. Linear models tested the state-level MML effect on outcomes by age (12-17, 18-25, 26+) and gender. Models included a state-level random intercept and controlled for time- and state-level covariates. Past-month MU did not increase after enactment of MML in men or women ages 12-25. Among people 26+, past-month MU increased for men from 7.0% before to 8.7% after enactment (+1.7%, p<0.001) and for women from 3.1% before to 4.3% after enactment (+1.1%, p=0.013). Among users 26+, daily MU also increased after enactment in both genders (men 16.3 to 19.1%, +2.8%, p=0.014; women 9.2 to 12.7%, +3.4%, p=0.003). There were no statistically significant increases in past-year MUD prevalence for any age or gender group after MML enactment. Given the statistically significant increase in daily use among past-year users aged 26+ following enactment, education campaigns should focus on informing the public of the risks associated with regular marijuana use.