Evidence is mixed on how young adults’ cannabis and alcohol use and co-use patterns have changed following recreational cannabis legalization (RCL). Incorporating measures of frequency and intensity of use we examined changes in college students' use and co-use patterns following RCL.

Four-year college students (n = 845,589) ages 18–24 years participated in the National College Health Assessment between 2008 and 2018, including students from 7 states that enacted RCL and 42 that did not. Latent profile analyses identified six patterns of use from four indicator variables tapping frequency of cannabis use and frequency and intensity of alcohol use: Abstainers, Light Alcohol Only, Heavy Alcohol Only, Predominantly Heavy Cannabis Use, Moderate Co-use, and Heavy Co-use.

Regression models that adjusted for time and person- and institution-level covariates indicated that students’ exposure to RCL was associated with lower odds of being in the two alcohol-only use classes, higher odds of being in the Predominantly Heavy Cannabis Use, Heavy Co-Use and Abstainers classes, and was not significantly related to Moderate Co-Use class membership.

RCL was positively associated with patterns of frequent cannabis use and frequent and intense co-use but also with abstinence. Use of alcohol-only became less prevalent after RCL. Research on how RCL influences the prevalence of problematic patterns of substance use will inform and improve prevention efforts.