A longitudinal neuroimaging study of 136 adolescents found that cannabis use was associated with reduced cortical thickness, with males showing a 0.005 mm reduction per weekly use increase, and pre-existing brain signatures predicted which males were more likely to use cannabis.
Neuroscientists, adolescent health researchers, parents of teens
Each weekly increase in cannabis use equivalent to 17.9% of annual cortical thinning in males
What the researchers found
In years when adolescents used more cannabis than their personal average, cortical thickness was lower (p = 0.047). This effect was stronger in males, where each once-per-week increase in use was associated with a 0.005 mm reduction in cortical thickness, equivalent to about 17.9% of the annual rate of cortical thinning. The thinning was greatest in brain regions with highest CB1 receptor gene expression. Males also showed a pre-existing cortical thickness signature associated with cannabis use propensity, present before any cannabis exposure.
Why it matters
This study helps answer a long-standing question: do brain differences cause cannabis use or does cannabis cause brain differences? The answer appears to be both, at least in males, which has major implications for understanding adolescent vulnerability.
The numbers in context
136 adolescents; 74 female; 3 neuroimaging sessions ages 12-17; 90% follow-up; within-person effect: -0.0023 mm per weekly use increase (p = 0.047); males: -0.005 mm (p = 0.0017); 17.9% of annual cortical thinning rate; CB1 receptor gene correlation: rho = -0.33 (sample), rho = -0.5 (males)
How the study worked
Longitudinal study with 136 adolescents (74 female) completing three neuroimaging sessions and annual assessments from ages 12 to 17, with 90% follow-up. Cannabis use was disaggregated into between-person (vulnerability) and within-person (time-varying) components using multilevel modeling, controlling for age, sex, and alcohol use.
What this study cannot tell us
Relatively small sample (136 adolescents). Cannabis use was relatively low in this age group. Cannot fully rule out other substance use effects. Cortical thinning is a normal developmental process, making it challenging to determine clinical significance.
How to read the evidence
Strong: longitudinal design with repeated neuroimaging, high follow-up rate, and sophisticated statistical methods separating risk factors from consequences.
When this study was published
2026 publication following adolescents ages 12-17 with three neuroimaging sessions.
The bigger picture
This is one of the first studies to separate pre-existing brain risk factors from consequences of cannabis use using longitudinal data. The finding that both exist simultaneously, particularly in males, adds nuance to the debate about cannabis and the developing brain.
Questions still open
- Why are males more affected than females? Do the pre-existing brain signatures in males reflect genetic or environmental factors? Does the cannabis-associated cortical thinning translate to cognitive or functional impairments?
Common questions
Does cannabis thin the brain in teens?
Were the brain differences caused by cannabis or did they exist before?
Read the original research
Independent brain cortical signatures of risk for adolescent cannabis use and consequences of such use are moderated by sex.
Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 51(2), 497-505
Citation
Watts, Jeremy J; Navarri, Xavier; Conrod, Patricia J. (2026). Independent brain cortical signatures of risk for adolescent cannabis use and consequences of such use are moderated by sex.. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 51(2), 497-505. https://doi.org/10.1038/s41386-025-02249-2
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