Heavy alcohol and cannabis use during adolescence linked to brain changes and cognitive effects
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.
Quick Facts
What This Study 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.
Key Numbers
43 longitudinal studies included; 18 focused on alcohol, 13 on cannabis, 12 on co-use; over 700 articles initially screened
How They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- 43 longitudinal studies reviewed across five databases
- Evidence Grade:
- Comprehensive systematic review of longitudinal studies with rigorous inclusion criteria and multi-database search strategy.
- Study Age:
- Published in 2021.
- Original Title:
- Alcohol and Cannabis Use and the Developing Brain.
- Published In:
- Alcohol research : current reviews, 41(1), 11 (2021)
- Authors:
- Lees, Briana(2), Debenham, Jennifer(5), Squeglia, Lindsay M(14)
- Database ID:
- RTHC-03285
Evidence Hierarchy
Analyzes all available research on a topic using a structured method.
What do these levels mean? →Frequently Asked Questions
Which substance appeared more harmful to the developing brain?
Based on the reviewed studies, heavy alcohol use was associated with more widespread brain changes than heavy cannabis use, though both showed measurable effects.
Were the effects dose-dependent?
For alcohol, yes. Several studies found that the severity of brain changes depended on the amount consumed. Cannabis findings were less consistent on dosing effects.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-03285APA
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
MLA
Lees, Briana, et al. "Alcohol and Cannabis Use and the Developing Brain.." Alcohol research : current reviews, 2021. https://doi.org/10.35946/arcr.v41.1.11
RethinkTHC
RethinkTHC Research Database. "Alcohol and Cannabis Use and the Developing Brain." RTHC-03285. Retrieved from https://rethinkthc.com/research/lees-2021-alcohol-and-cannabis-use
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.