Study Tracks 11,000 Youths, Finds Cannabis Use Linked to Slower Brain Development
A federally funded U.S. study tracking 11,036 children found cannabis use linked to slower cognitive development in memory, attention, and processing speed during adolescence. Researchers at UC San Diego identified THC as a key factor driving these effects, while emphasizing the findings do not prove causation but align with public health warnings.
Researchers from the University of California San Diego School of Medicine published findings April 20 in *Neuropsychopharmacology* linking cannabis use to slower cognitive development in adolescents. The study, part of the federally funded Adolescent Brain Cognitive Development (ABCD) Study, followed 11,036 children from ages 9-10 to 16-17, combining self-reported data with biological testing to confirm cannabis exposure. Key cognitive skills—memory, attention, language, and processing speed—showed slower improvement in cannabis users compared to peers. While early performance was similar or slightly better among future users, cognitive growth plateaued once cannabis use began, with non-users continuing to advance. The study isolated THC as the primary compound associated with worsening memory performance, particularly in a subgroup with biological evidence of exposure. No similar pattern was observed for cannabidiol (CBD), though sample sizes were limited. Lead author Natasha Wade, an assistant professor of psychiatry, noted the differences may seem modest but could accumulate to impact learning and daily functioning. The findings persisted even after accounting for factors like family background, mental health, and other substance use, aligning with CDC warnings about adolescent cannabis use. Researchers emphasized the study does not prove causation but highlights risks during a critical brain development period. The ABCD Study will continue tracking participants into young adulthood to assess long-term cognitive outcomes as cannabis legalization expands in the U.S.
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