Largest Long-Term US Brain Development Study: Possible Link Between Marijuana Use in Teens and Slower Brain
Last Updated: Wednesday April 22, 2026
(Fox 5/KUSI) A new [University of California] San Diego study found that there could be a connection between marijuana use and slower development of memory, focus and thinking speed in teenagers.
Published in Neuropsychopharmacology, the study tracked 11,036 children starting at age nine to 10 until they were 16 to 17, making it the largest long-term study on brain development in the U.S.
The researchers tracked the children’s cognitive performance and marijuana use using self-reporting as well as hair, urine and saliva samples.
According to the study’s results, teens who used marijuana showed restricted growth over time in a range of skills, including memory, attention, language and processing speeds.