California Marijuana Legalization Linked to Increased Adolescent Alcohol-Cannabis Co-Use | Research

The takeaway

Analysis of 3.3 million California students found recreational marijuana legalization was associated with a 6% increase in alcohol-cannabis co-use overall, and a 58% increase among past-month drinkers.

Cannabis policy researchers; school prevention program designers; state legislators considering legalization impacts on youth.

58% increase in co-use among past-month drinkers post-legalization

What the researchers found

Recreational legalization was associated with greater odds of co-use overall (OR=1.06) and much greater odds among past-month drinkers (OR=1.58) and heavy drinkers (OR=1.25). Paradoxically, among past-month marijuana users, co-use odds decreased (OR=0.76). Among co-users, marijuana use frequency increased.

Why it matters

This is one of the largest studies examining whether marijuana legalization affects youth substance use patterns. The finding that alcohol-using youth are the most likely to add marijuana co-use has important implications for substance prevention programs.

The numbers in context

3,319,329 students. Overall co-use: OR=1.06 (95% CI 1.05-1.07). Among past-month drinkers: OR=1.58 (95% CI 1.52-1.62). Among heavy drinkers: OR=1.25 (95% CI 1.21-1.29). Among past-month marijuana users: OR=0.76 (95% CI 0.74-0.78). Among co-users, marijuana frequency increased (β=0.36).

How the study worked

Repeated cross-sectional data from 3,319,329 California 7th, 9th, and 11th graders participating in the California Healthy Kids Survey from 2010-2011 to 2018-2019. Multilevel regression analyzed changes before and after 2016 recreational legalization, controlling for demographics, survey year, and urbanicity.

What this study cannot tell us

Cross-sectional design means individual students were not tracked over time. The study cannot definitively attribute changes to legalization versus other trends. Self-reported substance use may be affected by changing social desirability around marijuana. The overall 6% increase is small in absolute terms.

How to read the evidence

Strong: massive sample (3.3 million students) across 9 academic years with appropriate multilevel modeling.

When this study was published

Published in 2022, covering 2010-2019.

The bigger picture

The differential effect is striking: legalization appears to pull alcohol-using teens toward adding marijuana, while marijuana-using teens actually became less likely to add alcohol. This asymmetry suggests legalization changes the social dynamics of substance use in complex ways.

Questions still open

Why does legalization increase co-use among drinkers but decrease it among marijuana users? Are the increased co-use patterns sustained years after legalization? Would higher marijuana taxes or fewer retail outlets reduce co-use among adolescents?

Common questions

Did marijuana legalization increase youth drug use?

The overall co-use increase was modest (6%). The more important finding was that legalization had different effects depending on existing substance use: it pulled alcohol-using teens toward co-use with marijuana, while marijuana-using teens actually became less likely to also drink.

What can be done to reduce co-use among adolescents?

The authors suggest limiting retail outlet numbers and hours, restricting advertising, and raising taxes on both alcohol and marijuana. Prevention programs may also need to address co-use specifically rather than treating each substance separately.

Read the original research

Recreational Marijuana Legalization and Co-use With Alcohol Among Adolescents.

American journal of preventive medicine, 62(1), 57-64

View on PubMed ↗Publisher’s paper ↗

Citation

Paschall, Mallie J; García-Ramírez, Grisel; Grube, Joel W. (2022). Recreational Marijuana Legalization and Co-use With Alcohol Among Adolescents.. American journal of preventive medicine, 62(1), 57-64. https://doi.org/10.1016/j.amepre.2021.06.003