Researchers at UC San Diego tracked over 11,000 teens from ages 9-17 and found that those using cannabis showed slower gains in memory, attention, and thinking speed compared to non-users, with THC exposure specifically linked to worse memory development. The difference may seem modest but compounds during critical brain development years and can affect school performance and daily functioning. The study doesn't prove causation—other factors like environment and personality may play a role—but researchers controlled for many confounding variables including family background, mental health, and prior cognitive performance. The research was published today in the peer-reviewed journal Neuropsychopharmacology and funded by the National Institute on Drug Abuse.