Relations between depression and cannabis use among college students in evolving state cannabis policy environments

Depression is a risk factor for cannabis use, an association that may change as state cannabis policies evolve. The present study uses individual-level data on college students and a continuous measure of state cannabis policy restrictiveness to examine this question.

Undergraduates (n = 902,486) ages 18-24 years from 591 four-year institutions in 47 states completed a cross-sectional survey between 2008 and 2019, including items assessing significant 30-day depressive symptoms, 12-month depression diagnosis or treatment, and 30-day cannabis use and frequent (20 + days) use. Time-varying, state-level cannabis policy restrictiveness was measured with the Cannabis Policy Scale (CPS).

From 2008-2019 prevalence increased for 30-day depressive symptoms (15.3-26.7%) and frequent cannabis use (3.3-5.2%). Depression measures were associated with cannabis use outcomes [odds ratios (OR) ranged from 1.54 to 2.13, p < 0.0001]. Effects were modestly but significantly weaker in less restrictive than in more restrictive state cannabis policy environments. For example, depressive symptoms were less associated with increased odds of 30-day cannabis use in the least restrictive states [OR (95% CI) = 1.47 (1.42-1.52), p < 0.0001] than in the most restrictive states [OR (95% CI) = 1.57 (1.54-1.59), p < 0.0001; interaction p = 0.0017]. There was no evidence that depression prevalence was higher among students exposed to less restrictive cannabis policies.

Depression and frequent cannabis use co-occurred across restrictive and liberal state cannabis policy environments, and both conditions increased in prevalence across the study period. Depression was a somewhat weaker risk factor for cannabis use when and where cannabis was more legal and accessible.