Teen cannabis initiation linked to slower growth in memory and thinking skills

A large longitudinal study found that adolescents who begin using cannabis show slower improvement in memory, attention, language and processing speed, with THC identified as the likely driver of memory decline.

A longitudinal analysis of more than 11,000 participants in the Adolescent Brain Cognitive Development study revealed that teenagers who initiate cannabis consumption exhibit slower development in memory, attention, language and processing speed than their non-using counterparts. Early in the study, some users performed on par with peers, but as cannabis use began, their cognitive gains stalled while controls kept improving.

Combined self-reports and toxicology (hair, urine, saliva) linked the effect primarily to tetrahydrocannabinol, with no similar pattern for cannabidiol. Although the gaps are modest, researchers warn they may accumulate to affect academic performance and everyday tasks. The investigators controlled for family background, mental health, other substance use and baseline cognition, and plan to monitor the cohort into young adulthood to assess long-term outcomes. Lead author Natasha Wade emphasized delaying cannabis use to support healthy brain development as the drug becomes more accessible.