Researchers at the University of California, San Diego have found that teens who start using cannabis show slower growth in thinking and memory skills as they grow up. The study, published on April 20, 2026 NeuropsychopharmacologyThe largest long-term study of brain development in American youth, the Adolescent Brain Cognitive Development (ABCD) study analyzed data from more than 11,000 participants.
“Adolescence is a critical time for brain development, and what we’re seeing is that teens who start using cannabis are not 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 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.”
Researchers followed 11,036 children from ages 9 to 10 until ages 16 and 17, tracking both their cognitive performance and substance use. To get a clearer picture of cannabis use, the team combined self-reports with biological testing – such as hair, urine and saliva samples – that can detect drug exposure up to several months as recently as possible.
Across a range of skills – including memory, attention, language and processing speed – teens who used cannabis showed limited growth over time compared to those who did not use. In some cases, these teens performed just as well – or even slightly better – than when they were younger. But as they grew older and started using cannabis, their progress slowed, while their peers continued to improve.
The study also looked more closely at various components of cannabis. In a small group of participants, teens exposed to tetrahydrocannabinol (THC) – the main intoxicating component in cannabis – showed worse memory over time than those who did not use cannabis. Adolescents with evidence of cannabidiol (CBD) did not show the same pattern, although that group was smaller.
These results point to THC as a potential driver of the changes we are seeing. It also highlights how complex cannabis products can be, especially since some products labeled as CBD may still contain THC.”
Natasha Wade, UC San Diego Health Sciences
Although the differences observed in the study were relatively minor, researchers say they could still matter. During adolescence, the brain is developing rapidly, and even small changes in memory, attention, or thinking speed can affect school performance and daily life.
The researchers say the study does not prove that cannabis use directly causes these changes. Other factors – such as environment or personality – may play a role. However, the team took into account many of these influences, including family background, mental health and other substance use, as well as each participant’s prior cognitive performance.
The team will continue to track participants into young adulthood to better understand the long-term effects of cannabis use, including how timing and frequency of use may shape brain development.
“Delaying cannabis use helps with healthy brain development,” Wade said. “As cannabis becomes more widely available, it is important for families and teens to understand how it may affect the developing brain.”
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Journal Reference:
Wade, NE, and others. (2026). Longitudinal neurocognitive trajectories in a large cohort of youth who use cannabis: combining self-report and toxicology. Neuropsychopharmacology. doi:10.1038/s41386-026-02395-1. https://www.nature.com/articles/s41386-026-02395-1.
