A scoping review of 99 neuroimaging studies found that 85% reported differences in brain structure, function, or chemistry in adolescent and young adult cannabis users compared to non-users, though research quality was generally low.
Neuroscientists studying cannabis effects on developing brains, public health communicators, policymakers setting age restrictions.
85% of 99 brain imaging studies found differences in young cannabis users vs non-users
What the researchers found
Of 99 studies meeting inclusion criteria (from 3,901 initially screened), 84 (85%) found differences in brain structure, function, and/or metabolite concentrations in cannabis users aged 14-25 compared to non-using controls. Only 5 studies explicitly assessed sex/gender differences, with all 5 finding that sex influenced the effect of cannabis on the brain.
Why it matters
The sheer volume of studies finding brain differences (85%) makes a strong case that cannabis use during adolescence and young adulthood is associated with detectable brain changes. However, the review also highlights that the existing research is of generally low quality and lacks long-term follow-up.
The numbers in context
3,901 sources screened; 99 included; 84/99 (85%) found brain differences; 5 studies examined sex differences, all 5 found effects; ages 14-25.
How the study worked
Scoping review following standard methodology, searching databases for neuroimaging studies assessing effects of cannabis use between ages 14-25 on brain structure, function, and metabolite concentrations. Yielded 3,901 sources, of which 99 met inclusion criteria.
What this study cannot tell us
Scoping review does not assess study quality or synthesize effect sizes. The 85% figure includes studies of varying quality and rigor. Publication bias may inflate the proportion of positive findings. Most studies are cross-sectional, limiting causal inference. Heterogeneous methodology makes direct comparisons difficult.
How to read the evidence
Moderate: Comprehensive scoping review covering 99 studies with consistent findings, but low quality of underlying studies and publication bias concerns temper the strength of conclusions.
When this study was published
Published in 2025.
The bigger picture
This review provides a comprehensive map of the neuroimaging evidence on youth cannabis use, covering structural MRI, fMRI, and MRS studies. While the weight of evidence points to cannabis-associated brain changes in young people, the low quality of individual studies and lack of longitudinal data mean definitive causal conclusions remain elusive.
Questions still open
- Are the observed brain differences clinically meaningful? Do they resolve with cessation? Why have so few studies examined sex differences? What would high-quality longitudinal studies show?
Common questions
Does this prove cannabis damages young brains?
Why does age matter for cannabis brain effects?
Read the original research
Cannabis use in adolescence and young adulthood and its effects on brain structure and function: a scoping review.
Frontiers in psychiatry, 16, 1644105
Citation
Nosko, Lilith; Crocker, Candice E; Tibbo, Phil G. (2025). Cannabis use in adolescence and young adulthood and its effects on brain structure and function: a scoping review.. Frontiers in psychiatry, 16, 1644105. https://doi.org/10.3389/fpsyt.2025.1644105
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