A meta-analysis of 6 brain imaging studies found no significant gray matter volume differences between cannabis-using and non-using youth overall, but age and sex influenced the pattern of subtle differences.
Neuroscientists studying adolescent brain development, pediatricians counseling families about cannabis, and researchers interpreting neuroimaging findings in context.
No significant overall brain volume difference between teen cannabis users and controls
What the researchers found
No regions showed significant gray matter volume differences between 357 cannabis-using and 404 typically developing youth. Meta-regressions revealed age effects in the superior temporal gyrus (older users showed decreased, younger users increased volume). A higher proportion of females was associated with increased volume in the middle occipital gyrus in users vs. controls.
Why it matters
This meta-analysis challenges the assumption of dramatic brain volume changes from adolescent cannabis use, while highlighting that developmental timing and sex may determine where and how subtle effects emerge.
The numbers in context
6 VBM studies, 357 cannabis users (mean age 16.68, 71% male), 404 controls (mean age 16.77, 63% male). No significant main effect. Age moderated STG differences. Sex moderated middle occipital gyrus differences.
How the study worked
Systematic review (1,326 citations, 24 included qualitatively) with seed-based d mapping (SDM) meta-analysis of 6 whole-brain VBM studies. Meta-regressions examined effects of age, sex, and cannabis use duration on gray matter volume differences.
What this study cannot tell us
Only 6 studies met strict inclusion criteria. Studies varied in cannabis use definitions and covariates. VBM methodology may miss subtle or regional-specific changes. Meta-regression with few studies has limited power.
How to read the evidence
Systematic meta-analysis following PRISMA guidelines, but limited by few eligible studies and heterogeneous cannabis exposure measures.
When this study was published
2021 meta-analysis. Provides a balanced perspective on adolescent cannabis neuroimaging findings.
The bigger picture
The null main finding is notable: structural brain volume changes from adolescent cannabis use, if they exist, appear subtle and context-dependent rather than dramatic and universal.
Questions still open
- Do other neuroimaging methods (cortical thickness, diffusion tensor imaging) show effects that VBM misses? Would larger studies with more detailed cannabis exposure data reveal consistent patterns? Are the age-dependent effects reflecting developmental timing?
Common questions
Does cannabis change teen brain structure?
Why do some studies find brain differences and this meta-analysis doesn't?
Read the original research
Age- and Sex-Related Cortical Gray Matter Volume Differences in Adolescent Cannabis Users: A Systematic Review and Meta-Analysis of Voxel-Based Morphometry Studies.
Frontiers in psychiatry, 12, 745193
Citation
Allick, Aliyah; Park, Grace; Kim, Kwon; Vintimilla, Michelle; Rathod, Krutika; Lebo, Rachael; Nanavati, Julie; Hammond, Christopher J. (2021). Age- and Sex-Related Cortical Gray Matter Volume Differences in Adolescent Cannabis Users: A Systematic Review and Meta-Analysis of Voxel-Based Morphometry Studies.. Frontiers in psychiatry, 12, 745193. https://doi.org/10.3389/fpsyt.2021.745193
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