Marijuana use trends among college students in states with and without legalization of recreational use: initial and longer‐term changes from 2008 to 2018

Background and aims Young adult college students in the United States are likely to be affected by marijuana liberalization trends. However, changes in students’ marijuana use following recreational marijuana legalization (RML) have not been examined in more than one RML state at a time, or beyond 1–2 years post‐legalization. Design Cross‐sectional National College Health Assessment survey administered twice yearly from 2008 to 2018. Setting A total of 587 4‐year colleges and universities in 48 US states. Participants Undergraduates aged 18–26 years attending college in US states that did (n = 234 669 in seven states) or did not (n = 599 605 in 41 states) enact RML between 2008 and 2018. Measurements Self‐reported marijuana use (past 30 days) and individual and contextual covariates, institution‐provided institutional and community covariates and publicly available dates when states enacted RML. Findings Adjusting for covariates, state differences and state‐specific linear time trends (accounting for pre‐RML trends), prevalence of 30‐day marijuana use increased more among students exposed to RML [odds ratio (OR) = 1.23, 95% confidence interval (CI) = 1.19–1.28, P