Scientists at the University of California San Diego have documented that cannabis use among adolescents is associated with slower development of cognitive abilities compared to teenagers who do not use the substance. The research, published in Neuropsychopharmacology, analyzed data from the Adolescent Brain Cognitive Development (ABCD) Study, a comprehensive long-term examination of brain development in American youth.
The investigation tracked more than 11,000 children from ages 9 and 10 through ages 16 and 17, monitoring their cognitive performance alongside substance use patterns. Researchers employed both self-reported data and biological testing—including hair, urine, and saliva samples—to accurately assess cannabis exposure across various timeframes. Teenagers who used cannabis demonstrated slower improvement in multiple cognitive domains, including memory, attention, language, and processing speed. Some users initially performed comparably to or marginally above their peers during childhood, but their cognitive gains plateaued after cannabis use began while non-users continued advancing.
Investigators examined whether specific cannabis compounds produced different effects. Adolescents with detected exposure to tetrahydrocannabinol (THC), cannabis’s primary psychoactive component, showed greater memory performance declines than non-users. This pattern did not appear in the limited sample of teenagers with cannabidiol (CBD) exposure. Researchers noted that THC likely accounts for the observed cognitive changes and cautioned that some products marketed as CBD may still contain THC.
While the identified cognitive differences were modest, researchers emphasized that during adolescence’s rapid brain development period, even minor changes in memory and processing could meaningfully affect academic performance and daily functioning. The research does not definitively establish causation between cannabis and slower cognitive growth, as environmental factors and personal characteristics may also contribute. Nevertheless, the analysis controlled for numerous variables including family background, mental health, other substance use, and baseline cognitive abilities.
The research team intends to continue monitoring participants into adulthood to better understand long-term cannabis effects and whether factors such as age of first use and frequency of consumption influence brain development outcomes.
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