Teen Cannabis Use Linked to Slower Cognitive Growth, THC Identified as Key Driver

A new study from UC San Diego School of Medicine (搜索)搜索该词条 has found that adolescents who use cannabis experience slower cognitive growth across multiple domains, including memory, attention, language, and processing speed, compared to their peers who abstain. The research, which tracked more than 11,000 children from ages 9–10 through ages 16–17, provides some of the most detailed evidence to date on how cannabis use intersects with the trajectory of brain development during adolescence.

"Adolescence is a critical time for brain development, and what we're seeing is that teens who start using cannabis aren't improving at the same rate as their peers," said Natasha Wade, PhD, assistant professor in the Department of Psychiatry at UC San Diego School of Medicine (搜索)搜索该词条 and lead author of the study. "These differences may seem small at first, but they can add up in ways that affect learning, memory and everyday functioning."

Study Design and Measurement Approach

The research team followed 11,036 children participating in the Adolescent Brain Cognitive Development (ABCD) Study, one of the largest longitudinal studies of youth in the United States. To measure cannabis exposure with greater precision, the researchers employed both self-reported data and biological testing. Hair, urine, and saliva samples were used to identify drug exposure, capturing everything from recent use to use that had occurred several months earlier.

The study design allowed researchers to track changes in cognitive performance over time while monitoring participants' use of cannabis and other substances. Some participants who later used cannabis initially performed as well as, or slightly better than, other children at younger ages. After they began using cannabis, however, their cognitive gains tended to level off, while teens who did not use cannabis continued to improve.

THC Implicated as the Likely Driver

Within a smaller subgroup of participants, the researchers examined whether specific cannabis compounds were associated with different cognitive outcomes. Teenagers with evidence of tetrahydrocannabinol查看药品详情 (THC) exposure—the primary intoxicating compound in cannabis—experienced greater declines in memory performance over time than teens who did not use cannabis.

The same pattern was not observed among teenagers with evidence of cannabidiol查看药品详情 (CBD) exposure, although the researchers cautioned that the number of participants in that group was limited.

"These results point to THC as a likely driver of the changes we're seeing," Wade said. "It also highlights how complicated cannabis products can be, especially since some products labeled as CBD may still contain THC."

Modest Differences, Meaningful Consequences

The cognitive differences identified in the study were relatively modest in magnitude. However, the researchers emphasized that even small changes may carry real-world consequences given that the brain develops rapidly during adolescence. Minor differences in memory, attention, or thinking speed could influence classroom performance, learning, and everyday activities.

The findings do not establish that cannabis directly caused the slower cognitive growth. Environmental conditions, personality traits, and other factors could also contribute to the observed differences. The researchers adjusted their analysis for many possible influences, including family background, mental health, the use of other substances, and each participant's cognitive abilities before cannabis use began.

Broader Context of Adolescent Substance Use

The study adds to a growing body of research on adolescent substance use patterns. Related findings from the ABCD Study, published in Drug and Alcohol Dependence Reports, indicate that by age 16, 38% of participants reported having used at least one substance during their lifetime, with alcohol, cannabis, and nicotine being the most commonly reported. Polysubstance use—using two or more substances—was reported by nearly 15% of participants, with the most common combination being nicotine and cannabis.

Notably, the broader ABCD data also revealed sex-based differences in substance use trajectories. Boys reported higher rates of substance use before age 12, but beginning around age 13, girls reported higher rates of alcohol, cannabis, and nicotine use, with the largest differences seen for nicotine.

Future Directions

The research team plans to continue monitoring participants as they enter young adulthood. Future analyses may offer a clearer picture of the long-term effects of cannabis and reveal whether the age at which use begins, as well as the frequency of use, influences brain development outcomes.

"Delaying cannabis use supports healthy brain development," Wade said. "As cannabis becomes more widely available, it's important for families and teens to understand how it may affect the developing brain."

The study was funded in part by the National Institute on Drug Abuse查看公司主页 through multiple awards, including DA050779 (PI: Wade), DA064409 (PI: Sullivan), DA062011 (PI: Wallace), and additional grants supporting co-authors from UC San Diego, the University of Sydney, University of Wisconsin-Milwaukee, and Columbia University.