A systematic review of 43 longitudinal studies found that heavy adolescent alcohol and cannabis use were each associated with distinct patterns of brain structure and function disruption.
Parents, educators, adolescent health professionals, and anyone interested in how substances affect the developing brain.
43 longitudinal studies reviewed across five databases
What the researchers found
Heavy alcohol use was associated with widespread decreases in gray matter volume and slowed white matter growth, while heavy cannabis use was linked to decreased subcortical volume and increased cortical thickness. Co-use studies generally found more pronounced effects from alcohol than cannabis.
Why it matters
Adolescence is a critical period for brain development, and alcohol and cannabis are the two most commonly used substances during this window. Understanding their distinct and combined effects helps inform prevention messaging and policy.
The numbers in context
43 longitudinal studies included; 18 focused on alcohol, 13 on cannabis, 12 on co-use; over 700 articles initially screened
How the study worked
Researchers searched five databases using 30 search terms and identified 43 longitudinal studies with at least 50 participants that examined structural or functional brain outcomes related to adolescent alcohol and/or cannabis use. Studies included 18 on alcohol, 13 on cannabis, and 12 on co-use.
What this study cannot tell us
Relatively small sample sizes and demographic homogeneity across included studies. Significant methodological heterogeneity. Difficult to disentangle effects of co-use. Cannot fully account for pre-existing differences.
How to read the evidence
Comprehensive systematic review of longitudinal studies with rigorous inclusion criteria and multi-database search strategy.
When this study was published
Published in 2021.
The bigger picture
This review suggests alcohol may pose a greater neurodevelopmental risk than cannabis during adolescence, though both substances are associated with measurable brain changes. The findings highlight the need for nuanced messaging rather than treating all substance effects as equivalent.
Questions still open
- Are the observed brain changes reversible with sustained abstinence? How does cannabis potency affect the magnitude of effects? Do these structural changes translate to meaningful real-world cognitive differences?
Common questions
Which substance appeared more harmful to the developing brain?
Were the effects dose-dependent?
Read the original research
Alcohol and Cannabis Use and the Developing Brain.
Alcohol research : current reviews, 41(1), 11
Citation
Lees, Briana; Debenham, Jennifer; Squeglia, Lindsay M. (2021). Alcohol and Cannabis Use and the Developing Brain.. Alcohol research : current reviews, 41(1), 11. https://doi.org/10.35946/arcr.v41.1.11
Explore the wider topic
- How to Talk to Your Teenager About Weed (Without Losing Them)
- My Kid's Friends Smoke Weed: A Parent's Guide
- I Smoke Weed But Don't Want My Kids To: Navigating the Hypocrisy
- Quitting Weed as a Parent: Why It Is the Hardest and Most Important Quit
- Quitting Weed as a Teen or Young Adult
- My Kid Is Smoking Weed: A Parent's Guide