Adolescent cannabis use was linked to cortical thinning, especially in males, and some brain differences existed before use began
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Each weekly increase in cannabis use equivalent to 17.9% of annual cortical thinning in males
- Evidence Grade:
- Strong: longitudinal design with repeated neuroimaging, high follow-up rate, and sophisticated statistical methods separating risk factors from consequences.
- Study Age:
- 2026 publication following adolescents ages 12-17 with three neuroimaging sessions.
- Original Title:
- Independent brain cortical signatures of risk for adolescent cannabis use and consequences of such use are moderated by sex.
- Published In:
- Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 51(2), 497-505 (2026)
- Authors:
- Watts, Jeremy J(3), Navarri, Xavier(2), Conrod, Patricia J(7)
- Database ID:
- RTHC-08706
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Does cannabis thin the brain in teens?
This study found that in years when teens used more cannabis, their cortex was thinner. In males, each once-per-week increase was associated with a reduction equivalent to about 18% of the normal annual thinning rate.
Were the brain differences caused by cannabis or did they exist before?
Both. Males showed pre-existing cortical thickness patterns that predicted cannabis use before it started, AND showed additional thinning in years of heavier use. This suggests brain vulnerability and cannabis effects work together.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-08706APA
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
MLA
Watts, Jeremy J, et al. "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, 2026. https://doi.org/10.1038/s41386-025-02249-2
RethinkTHC
RethinkTHC Research Database. "Independent brain cortical signatures of risk for adolescent..." RTHC-08706. Retrieved from https://rethinkthc.com/research/watts-2026-independent-brain-cortical-signatures
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.