Researchers at the University of California, San Diego, found that teens who started using marijuana showed slower improvement in their thinking and memory skills as they grew up. This study was published on April 20, 2026. neuropsychopharmacologyanalyzed data from more than 11,000 participants in the Adolescent Brain Cognitive Development (ABCD) study, the largest longitudinal study of brain development in American youth.
“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 other young people,” said Dr. Natasha Wade, assistant professor of psychiatry at the University of California, San Diego School of Medicine, and lead author of the study. “These differences may seem small at first, but cumulatively they can impact learning, memory, and daily life.”
Researchers followed 11,036 children from ages 9 to 10 to 16 and 17, tracking both their cognitive abilities and drug use. To get a clearer picture of cannabis use, the researchers combined self-reporting with biological tests such as hair, urine, and saliva samples that can detect recent months of drug exposure.
Across a variety of skills, including memory, attention, language, and processing speed, teens who used cannabis had more limited growth over time than those who did not use. In some cases, these teens performed as well or even slightly better than their peers when they were younger. But as they got older and started using cannabis, their progress leveled off, while their peers continued to make progress.
The study also took a closer look at various components of cannabis. In a smaller group of participants, they found that teens with evidence of exposure to tetrahydrocannabinol (THC), the main intoxicating ingredient in marijuana, had worse memory performance over time than those who did not use marijuana. Teens with evidence of cannabidiol (CBD) did not show the same pattern, although the group was smaller.
These results indicate that THC may be the driving force behind 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
Researchers say the differences seen in this study were relatively modest, but still potentially important. The brain develops rapidly during adolescence, and even small changes in memory, attention, and thinking speed can affect school performance and daily life.
The researchers note that this study does not prove that cannabis use directly causes these changes. Other factors such as environment and personality may play a role. However, the team took into account many of these influences, including each participant’s prior cognitive ability, as well as family background, mental health, and other substance use.
The research team plans to continue following the participants into adulthood to better understand the long-term effects of cannabis use, including how the timing and frequency of cannabis use affects brain development.
“Delaying cannabis use supports healthy brain development,” Wade said. “As cannabis becomes more widely available, it’s important that families and teens understand how it can affect the developing brain.”
sauce:
University of California, San Diego Health Sciences
Reference magazines:
Wade, Nebraska; 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.
