In a study of 1,003 young adults using brain imaging, those with over 1,000 lifetime cannabis uses showed reduced brain activation during working memory tasks, even after accounting for recent use.
Neuroscientists, clinicians counseling cannabis users, public health professionals, regular cannabis users
What the researchers found
Using Human Connectome Project data, heavy lifetime cannabis users (>1,000 uses, n=88) showed significantly lower brain activation during a working memory task compared to nonusers, with a moderate effect size (Cohen d = -0.28). Affected regions included the anterior insula, medial prefrontal cortex, and dorsolateral prefrontal cortex. Recent cannabis use (detected by urine testing) was associated with lower performance on working memory and motor tasks, but these associations did not survive statistical correction. No other cognitive tasks (reward, emotion, language, motor, relational, theory of mind) showed associations with lifetime heavy use.
Why it matters
This is one of the largest neuroimaging studies to separate lifetime cannabis use history from recent use effects. The finding that working memory deficits persist even when controlling for recent use suggests heavy long-term cannabis use may leave lasting traces on brain function.
The numbers in context
1,003 young adults; 88 heavy users (>1,000 uses), 179 moderate (10-999), 736 nonusers; heavy use effect on working memory: Cohen d = -0.28 (95% CI: -0.50 to -0.06); affected regions: anterior insula, medial prefrontal cortex, dorsolateral prefrontal cortex
How the study worked
Cross-sectional study of 1,003 young adults (ages 22-36) from the Human Connectome Project. Functional MRI during seven cognitive tasks. Cannabis use history from structured clinical interviews. Recent use detected via urine toxicology on scan day. Linear mixed-effects regression with false discovery rate correction.
What this study cannot tell us
Cross-sectional design cannot determine whether reduced activation preceded or followed cannabis use. Self-reported lifetime use may be inaccurate. The heavy user group (n=88) was relatively small. Data collected 2012-2015 may not reflect current cannabis potency.
How to read the evidence
Strong: large sample, validated neuroimaging protocol, structured clinical assessments, and rigorous statistical correction.
When this study was published
2025 publication using 2012-2015 Human Connectome Project data
The bigger picture
Working memory is foundational to daily cognitive functioning. If heavy cannabis use is associated with lasting reductions in working memory brain activation, this has implications for millions of regular users, particularly those who started young.
Questions still open
- Are these working memory activation differences reversible with sustained abstinence?
- Would these patterns be more pronounced with higher-potency modern cannabis products?
Read the original research
Brain Function Outcomes of Recent and Lifetime Cannabis Use.
JAMA network open, 8(1), e2457069
Citation
Gowin, Joshua L; Ellingson, Jarrod M; Karoly, Hollis C; Manza, Peter; Ross, J Megan; Sloan, Matthew E; Tanabe, Jody L; Volkow, Nora D. (2025). Brain Function Outcomes of Recent and Lifetime Cannabis Use.. JAMA network open, 8(1), e2457069. https://doi.org/10.1001/jamanetworkopen.2024.57069
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