Oregon recreational marijuana legalization: Changes in undergraduates' marijuana use rates from 2008 to 2016.

There have been few studies of marijuana use before and after recreational marijuana legalization (RML) in affected states. We tested whether marijuana use rates increased more among college students in Oregon than in non-RML states following Oregon RML in July 2015. Repeated cross-sectional National College Health Assessment-II surveys were completed by random samples of students within participating colleges from 2008 to 2016. Data were from 4-year institutions that participated both before and after Oregon RML. Undergraduates (ages 18-26 years) from 2 institutions in Oregon (n = 7,412) and 123 institutions (n = 274,340) in non-RML U.S. states self-reported use of marijuana, tobacco, alcohol, and other drugs in the past 30 days. Mixed-effects regressions accounted for clustering of participants within institutions and controlled for individual-, context-, and institution-level factors as well as secular changes in substance use rates from 2008 to 2016. Following RML, Oregon students (compared to non-RML-state students) showed relative increases in rates of marijuana use (odds ratio [OR] = 1.29, 95% confidence interval [CI: 1.13, 1.48], p = .0002, and decreases in tobacco use rates (OR = .71, 95% CI [.60, .85], p < .0001). Changes in marijuana use after RML did not differ significantly for participants under and over age 21 years. Some study limitations would be addressed with higher survey response rates, inclusion of other Oregon institutions, and controls for marijuana and other substance policies. Still, findings are consistent with an effect of RML on rates of marijuana use among young adult college students, which may have important public health implications. (PsycINFO Database Record (c) 2018 APA, all rights reserved).