Between roughly age 9 and 17, the human brain is supposed to get sharply better at remembering things. A new study tracking more than 11,000 American adolescents found that teenagers who started using cannabis during those years did not keep pace: their memory scores still improved, but at a noticeably slower rate than peers who never used the drug.
The findings, published in the journal Neuropsychopharmacology by Springer Nature, draw on one of the most ambitious research projects ever aimed at the teenage brain. They land at a moment when cannabis is legal for adult use in nearly half of U.S. states and when federal health officials are pressing for clearer data on what the drug does to developing minds.
What the ABCD cohort shows
The data come from the Adolescent Brain Cognitive Development (ABCD) Study, a National Institutes of Health-backed project that enrolled children at 21 sites across the country starting around age 9 and follows them with repeated brain scans, cognitive tests, and substance-use check-ins. It is the largest long-term study of adolescent brain development in the United States.
Rather than simply comparing cannabis users to non-users at a single point in time, the research team treated the moment a teenager first used cannabis as a turning point and then tracked what happened to cognitive growth afterward. They confirmed self-reported use with urine toxicology, a step that strengthens confidence in the data. The published analysis does not specify the exact number or proportion of participants who initiated cannabis use or the precise ages at which they began, though the cohort spans roughly age 9 through 17 and captures initiation events across that window.
The pattern was clearest for immediate recall, a measure of how well someone can hold and retrieve new information. Teens who never used cannabis showed steadily rising scores through their mid-teens. Those who began using the drug saw that upward curve flatten. The gap was not about a sudden drop in ability; it was about lost momentum during a window when the brain is normally building capacity fast.
The ABCD Study’s curated data releases, managed through the National Institute on Drug Abuse, give researchers the statistical power to detect differences that smaller studies have long struggled to pin down. Separate NIH-funded work using the same cohort has already shown that brain structure differences are tied to early substance use among adolescents, providing a biological backdrop: if cannabis exposure coincides with measurable anatomical changes, it is plausible those changes would surface in performance on memory and attention tasks.
What the study cannot tell us
This is observational research, not an experiment. No one randomly assigned teenagers to use cannabis, which means the study identifies an association, not proof of direct cause and effect.
That distinction matters because teens who start using cannabis often differ from non-users in ways that are difficult to fully account for, including family income, mental health history, sleep habits, and concurrent use of alcohol or nicotine. The ABCD dataset captures many of these variables, and the researchers adjusted for them, but ruling out every confounding factor in a study of real-world adolescents is essentially impossible.
Several other questions remain open. The analysis models cannabis initiation as a binary event, so it does not yet clarify whether occasional use carries the same cognitive cost as daily consumption. It also tracks participants only through about age 17, leaving unanswered whether the slower memory gains persist into early adulthood or eventually narrow as the brain matures. And the published findings do not break out results by product type or THC potency, a gap that matters given the sharp rise in high-potency concentrates and edibles marketed in legal states.
The full dataset is restricted to approved researchers through the NIH’s National Data Archive, so independent replication of the statistical models requires formal access. Future ABCD data releases, as participants move into their twenties, should help fill in these blanks.
Why this study carries weight
Plenty of earlier research has linked adolescent cannabis use to cognitive problems, but much of it relied on small samples, single-time-point comparisons, or self-reported drug use alone. The new findings stand out for three reasons: the sheer size of the cohort (more than 11,000 participants), the longitudinal design that captures change over years rather than a snapshot, and the use of biological verification alongside questionnaires.
The CDC’s public health guidance on cannabis and teens already warns about risks to memory and learning, but that guidance draws on an older and more varied evidence base. The ABCD results add something the field has needed: developmental trajectory data showing that the rate of cognitive improvement, not just a test score at one moment, is measurably different for teens who use cannabis.
What this means for families and clinicians
For parents and pediatricians, the practical message is fairly direct. The teenage brain is still building core capacities in memory and attention, and cannabis use appears to slow that construction. The study does not identify a safe age of initiation or a threshold dose below which no effect occurs. Given that gap, the most defensible guidance remains what major pediatric organizations have long recommended: delay cannabis exposure as long as possible during adolescence, when the brain’s growth curve is steepest.
Sharon Levy, a pediatrician and director of the Adolescent Substance Use and Addiction Program at Boston Children’s Hospital, has noted in prior commentary on ABCD findings that “the adolescent brain is uniquely vulnerable to substances, and the longer we can delay exposure, the better the outcomes tend to be.” While that remark predates this specific paper, it captures the clinical consensus that the new memory data reinforces.
The ABCD Study was designed specifically to answer questions like these, and its cohort will keep generating data for years. The memory findings reported here are one piece of a larger puzzle that includes brain structure, mental health, and academic outcomes. As participants age and new data releases arrive, the picture will sharpen. For now, the evidence points in a consistent direction: starting cannabis during the teenage years is associated with a measurable cognitive cost, even as researchers continue working to map the precise mechanism and long-term consequences.
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*This article was researched with the help of AI, with human editors creating the final content.
