84 of 99 Brain Imaging Studies Found Cannabis Changes Young Brains

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.

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.

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.

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.

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.