A landmark U.S. study of more than 11,000 adolescents revealed that cannabis use during the teen years is associated with slower gains in key cognitive skills essential for brain development.

Researchers from the University of California, San Diego School of Medicine analyzed data from the Adolescent Brain Cognitive Development (ABCD) Study, the largest long-term investigation of youth brain development funded by the National Institutes of Health. The findings, published on April 20, 2026, in the journal Neuropsychopharmacology, tracked 11,036 participants from ages 9 to 17 across 21 U.S. sites.

The study combined self-reported cannabis use with objective biological tests, including hair, urine, saliva, and breath samples, to accurately detect exposure. Cannabis users demonstrated flattened neurocognitive trajectories compared to non-users. While some users performed as well as or better than peers before starting use, their improvement stalled in areas such as immediate and delayed memory, processing speed, inhibitory control, visuospatial processing, language, and working memory.

In a subsample with hair toxicology data, those exposed to THC, the primary psychoactive component in cannabis, exhibited worse episodic memory development over time. Teens with CBD exposure did not show the same deficits, though this group was smaller. Lead author Natasha E. Wade, an assistant professor of psychiatry at UC San Diego, stated, "Adolescence is a critical time for brain development, and what we’re seeing is that teens who start using cannabis aren’t improving at the same rate as their peers."

The analysis controlled for numerous factors, including sociodemographics, family history of substance use disorders, prenatal exposures, mental health, other substance use, and prior cognitive performance. Statistical models used linear mixed-effects approaches with false discovery rate corrections, confirming significant interactions between cannabis use and age across domains (βs = -0.11 to -0.52).

Though the differences were modest, Wade noted they "may seem small at first, but they can add up in ways that affect learning, memory, and everyday functioning." The study does not establish causation, as unmeasured factors like personality or environment could contribute, and long-term effects into adulthood remain under observation.

These results come amid increasing cannabis legalization and availability, with higher-potency products raising concerns. Wade emphasized, "Delaying cannabis use supports healthy brain development. As cannabis becomes more widely available, families and teens need to understand how it may affect the developing brain." A New York Post report highlighted the study's relevance, noting rising teen exposure risks from edibles and mislabeled products.

The ABCD Study continues to follow participants, promising further insights into substance use impacts during this vulnerable period.