Review of 63 neuroimaging studies finds adolescent cannabis users show brain changes, but causation remains unclear | Research

The takeaway

A review of 43 studies on adolescent cannabis users and 20 on age-of-onset effects found compromised frontoparietal structure and function, but whether these changes are caused by adolescent-specific use or general cannabis factors remains uncertain.

Neuroscience researchers, youth health policymakers, parents interested in adolescent brain effects

43 adolescent user studies vs. 20 onset-age studies gave divergent results

What the researchers found

Adolescent cannabis users showed alterations mainly in frontal and parietal regions and associated brain activation related to inhibitory control, reward, and memory. However, adult studies examining onset age were more mixed, with many not finding age-of-onset effects on brain imaging metrics.

Why it matters

Determining whether adolescence is a uniquely vulnerable period for cannabis effects on the brain, or whether observed differences reflect general use factors, has major implications for policy and prevention.

The numbers in context

43 studies on adolescent cannabis users; 20 studies on onset age effects in adults. Most consistent findings in frontal and parietal regions related to inhibitory control, reward, and memory.

How the study worked

PubMed and Scopus searches for empirical neuroimaging studies examining brain effects in adolescent cannabis users and adult studies exploring age-of-onset effects. 43 adolescent user studies and 20 onset-age studies identified.

What this study cannot tell us

Most underlying studies are cross-sectional; difficulty separating adolescent-specific effects from general cannabis use factors; varied definitions of "adolescent" across studies; limited control for confounders.

How to read the evidence

Comprehensive review of neuroimaging literature, but most underlying studies are cross-sectional with limited control for confounders.

When this study was published

Published in 2020.

The bigger picture

The disconnect between adolescent user studies (showing consistent effects) and adult onset-age studies (showing mixed results) suggests confounders like depressive symptoms or use chronicity may be driving some findings.

Questions still open

Are the brain changes observed in adolescent cannabis users driven by the developmental timing of use or by correlated factors like mental health symptoms?

Common questions

Is the adolescent brain more vulnerable to cannabis?

Studies directly comparing adolescent users to non-users consistently show brain differences. However, studies in adults that examined whether earlier onset of use matters gave mixed results, suggesting it is still unclear whether adolescence is uniquely vulnerable or whether other factors explain the findings.

What brain areas are most affected?

Frontal and parietal regions were most consistently implicated, particularly in relation to inhibitory control, reward processing, and memory. Adolescent cannabis users often showed hyperactive brain responses to task-based stimuli compared to non-users.

Read the original research

Cannabis Use in Adolescence: A Review of Neuroimaging Findings.

Journal of dual diagnosis, 16(1), 83-105

View on PubMed ↗Publisher’s paper ↗

Citation

Chye, Yann; Christensen, Erynn; Yücel, Murat. (2020). Cannabis Use in Adolescence: A Review of Neuroimaging Findings.. Journal of dual diagnosis, 16(1), 83-105. https://doi.org/10.1080/15504263.2019.1636171