Post-legalization changes in marijuana use in a sample of young California adults

Increasing marijuana use among young adults is a concern due to substantial acute and chronic health risks. More widespread use of marijuana may also lead to increased use of nicotine and tobacco products. California legalized commercial sales of marijuana for recreational use as of January 2018. To our knowledge no studies to date have examined subsequent changes in marijuana use. The goal of this study was to test the hypothesis that marijuana use frequency increased following legalization of recreational sales. We also hypothesized that increased marijuana frequency would predict greater frequency of nicotine/tobacco consumption.

The study was a secondary analysis of a longitudinal study of tobacco use among non-daily cigarette smokers. Participants were 563 young adults (aged 18-24) enrolled in 2015-16 and followed quarterly for 3 years.

A piecewise multilevel regression model indicated that marijuana use frequency did not change over time, including following legalization. More frequent use was associated with younger age and identifying as white (ps < 0.001, which did not change after legalization. Marijuana frequency was moderated by sex (p < .001), with women reporting increasing and men decreasing use over time. It was also associated with tobacco use, and particularly with e-cigarette use following legalization (ps < 0.05).

Findings suggest legalization of recreational marijuana sales had a negligible overall impact on days of use among young adults, but may have prompted increased interest in marijuana among some, particularly women and e-cigarette users. The continuously evolving landscape around these products indicates that ongoing surveillance is critical.