A systematic review of 41 neuroimaging studies found cannabis modulated brain function (especially prefrontal blood flow) but found minimal evidence of major structural brain changes.
Read this if you want to know what brain scans actually show about the effects of cannabis use.
Only 3 of 8 structural studies found brain differences in cannabis users
What the researchers found
Researchers systematically reviewed 66 brain imaging studies, of which 41 met inclusion criteria. Among the 33 functional imaging studies, resting brain blood flow in the prefrontal cortex was consistently lower in cannabis users compared to non-users.
When THC or marijuana was administered acutely, the pattern reversed: resting brain activity increased, and frontal and anterior cingulate cortex activation rose during cognitive tasks.
Among the 8 structural imaging studies, only 3 found any differences between cannabis users and controls. The overall conclusion was that cannabis primarily affected brain function rather than brain structure.
Why it matters
This comprehensive review provided an evidence snapshot showing that while cannabis use was associated with measurable changes in brain function, structural brain changes were minimal based on available imaging technology at the time.
The numbers in context
66 studies identified, 41 met inclusion criteria. 33 functional imaging studies and 8 structural studies reviewed. Only 3 of 8 structural studies found differences between users and controls.
How the study worked
Systematic review searching Medline, EMBASE, LILACS, and PsycLIT through January 2009. Identified 66 studies, of which 41 met inclusion criteria (33 functional studies using SPECT/PET/fMRI and 8 structural studies using volumetric MRI/DTI). Heterogeneity across studies precluded meta-analysis.
What this study cannot tell us
High heterogeneity across studies prevented meta-analysis. Imaging technology available through 2009 may have been insufficient to detect subtle structural changes. Many studies had small sample sizes and varied methodologies.
How to read the evidence
Systematic review with comprehensive search strategy across multiple databases, though heterogeneity prevented meta-analysis.
When this study was published
Published in 2010, covering studies through January 2009. Brain imaging technology and cannabis neuroimaging research have advanced substantially since.
The bigger picture
The finding that cannabis affected brain function more than structure suggested effects might be more reversible than previously feared, though the functional changes in prefrontal regions raised concerns about executive function and decision-making.
Questions still open
- Are the functional brain changes reversible with abstinence? Would more advanced imaging techniques reveal structural changes missed by earlier technology?
Common questions
Does cannabis cause visible brain damage on scans?
What brain region was most affected by cannabis use?
Read the original research
Neuroimaging in cannabis use: a systematic review of the literature.
Psychological medicine, 40(3), 383-98
Citation
Martín-Santos, R; Fagundo, A B; Crippa, J A; Atakan, Z; Bhattacharyya, S; Allen, P; Fusar-Poli, P; Borgwardt, S; Seal, M; Busatto, G F; McGuire, P. (2010). Neuroimaging in cannabis use: a systematic review of the literature.. Psychological medicine, 40(3), 383-98. https://doi.org/10.1017/S0033291709990729
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