UC San Diego ABCD analysis links teen cannabis start to slower cognitive gains

University of California San Diego researchers report that teenagers who start using cannabis may develop memory and thinking abilities more slowly than peers who do not, according to ScienceDaily. The findings appear in Neuropsychopharmacology and draw on more than 11,000 participants in the Adolescent Brain Cognitive Development study. Lead author Natasha Wade said adolescence is a critical window for brain development and that teens who begin cannabis use are not improving at the same rate as peers. The team followed 11,036 children from ages 9 to 10 through ages 16 and 17, combining self-reports with hair, urine, and saliva tests that can flag recent use and exposure from months earlier. Cannabis users showed slower improvement in memory, attention, language, and processing speed. Some had performed as well as or slightly better than peers at younger ages, then leveled off after use began while non-users continued to improve. In a smaller subgroup, evidence of tetrahydrocannabinol exposure tracked greater declines in memory over time than non-use; the same pattern was not seen for cannabidiol exposure, though that group was limited. The study does not prove cannabis caused the slower growth. Researchers adjusted for family background, mental health, other substances, and pre-use cognitive scores. Differences were relatively modest but may still matter for learning and daily function during rapid adolescent brain development.