Objective: The legalization of recreational marijuana use and retail sales raises concerns about possible effects on marijuana use among adolescents. We evaluated the effects of recreational marijuana legalization (RML) in California in November 2016 on use among adolescents and investigated subgroup differences in these effects.

Method: We analyzed data from successive cross-sectional samples of 7th, 9th, and 11th grade students (N = 3,330,912) who participated in the California Healthy Kids Survey from 2010–2011 to 2018–2019. Participants reported grade, sex, ethnicity, race, and lifetime and past-30-day marijuana use.

Results: Multilevel analyses showed that RML was associated with increases in the likelihood of lifetime (odds ratio = 1.18, 95% CI [1.15, 1.21], p < .01) and past-30-day marijuana use (odds ratio = 1.23, 95% CI [1.20, 1.26], p < .01) relative to previous downward trends. RML was more strongly associated with increases in prevalence of marijuana use among 7th versus 9th and 11th graders, females versus males, non-Hispanic versus Hispanic youth, and White versus African American, American Indian/Native Alaskan, and multiracial youth. Overall, RML was not significantly associated with frequency of past-30-day use among users, although stronger positive associations between RML and frequency of use were found for 11th graders, Asian Americans, and African Americans. The association was weaker for females.

Conclusions: RML in California was associated with an increase in adolescent marijuana use in 2017–2018 and 2018–2019. Demographic subgroup differences in these associations were observed. Evidence-based prevention programs and greater local control on retail marijuana sales may help to reduce marijuana availability and use among adolescents.