Teen cannabis use slows memory, attention growth
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- UC San Diego researchers tracked 11,036 children from ages 9–10 through 16–17 via the Adolescent Brain Cognitive Development (ABCD) Study, finding cannabis users showed slower cognitive gains across memory, attention, language, and processing speed.
- The study, published in Neuropsychopharmacology, combined participant self-reports with hair, urine, and saliva toxicology tests to measure cannabis exposure ranging from recent use to use several months prior.
- THC exposure specifically linked to greater memory declines over time; the same pattern was not observed among teens with evidence of only CBD exposure, though that subgroup was smaller.
- Some cannabis-using teens initially performed as well as or slightly better than peers before their cognitive gains leveled off while non-users continued improving.
- Lead author Natasha Wade, PhD, said the differences "may seem small at first, but they can add up" in ways that affect learning, memory, and everyday functioning.
- The researchers adjusted for family background, mental health, other substance use, and each participant's prior cognitive abilities, and explicitly noted the findings do not establish direct causation.
- The study was funded in part by the National Institute on Drug Abuse, with the team planning to continue monitoring participants into young adulthood to examine age of onset and frequency of use.
Why it matters: With 11,036 participants and biological toxicology confirmation rather than self-report alone, this is among the most rigorously sampled longitudinal evidence linking adolescent cannabis use — specifically THC — to slowed cognitive development. As legalization expands access, families and policymakers gain a data-backed reason to weigh delay-use messaging against widening availability.
