A recent study out of the UC San Diego School of Medicine has found that teenagers who start using cannabis experience slower development in their thinking and memory abilities over time.
The study, published on April 20, 2026, in Neuropsychopharmacology, examined data from 11,036 participants in the Adolescent Brain Cognitive Development (ABCD) Study—the largest long-term research project on brain development in U.S. youth. Researchers followed children from ages 9–10 into ages 16–17, tracking both substance use and cognitive performance. They used a combination of self-reports and objective toxicological measures (urine, saliva, and hair samples) to better detect cannabis exposure.
Findings showed that, across a range of skills (including memory, language, and processing speed) teens who used cannabis exhibited slower gains (restricted developmental trajectories) over time compared to non-users. Interestingly, at younger ages, some future cannabis users performed as well as or slightly better than non-users. However, as they aged and began using cannabis, their cognitive development stalled relative to peers who continued to progress.
The study also examined cannabis components in a smaller subset with hair testing. Teens with evidence of tetrahydrocannabinol (THC) exposure (the main psychoactive component) showed more significant memory declines over time than non-users. In contrast, teens with evidence of cannabidiol (CBD) did not exhibit this pattern (though the CBD group was small).
“These results point to THC as a likely driver of the changes we’re seeing,” said lead researcher Natasha Wade. “It also highlights how complex cannabis products can be, especially since some products labelled as CBD may still contain THC.”
Despite the modest size of the differences, the findings are noteworthy during a period of rapid brain development: even small changes in memory, attention, or processing speed can influence school performance and daily life.
Despite the differences being modest in statistical terms, the real-world stakes are high. During a period of rapid and foundational brain development, even small deficits in memory, attention, or thinking speed can impair school performance, learning, decision-making, and long-term life outcomes.
The researchers rightly note that the study does not prove direct causation on its own, and other factors (environment, personality, genetics) may play a role. Yet the associations held strong even after adjusting for family background, mental health, other substance use, and prior cognitive performance. This is not isolated data—it adds to a large and growing body of evidence showing adolescence is a uniquely vulnerable window for cannabis harms.
These findings should serve as a loud wake-up call. Public health experts, parents, educators, and policymakers must be unequivocal: adolescents should not use cannabis. The developing brain is simply too precious and too sensitive to risk interference from THC. With today’s high-potency products widely available, the potential for harm is greater than ever.
As evidence from major studies such as ABCD emerges, it’s clear that the effects of cannabis, particularly during adolescence, are more significant than many acknowledge. The data is undeniable. Safeguarding the next generation requires taking this science seriously and acting on it.
*Written by FF staff writers*
