• Posted April 20, 2026

Weed Blunts Brain Development In Teens

Weed can blunt teenagers’ brain development across a range of skills, including memory, attention, language and processing speed, a new study says.

Teenagers who started using weed had slower gains in thinking and memory skills as they grew, researchers report today in the journal Neuropsychopharmacology.

“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 lead researcher Natasha Wade, an assistant professor of psychiatry at the University of California-San Diego.

“These differences may seem small at first, but they can add up in ways that affect learning, memory and everyday functioning,” she said in a news release.

For the new study, researchers tracked more than 11,000 children from 9 to 10 years of age until they were 16 and 17, following both their brain development and their substance use.

The team tracked weed use not only through kids’ self-reports, but by testing samples of hair, urine and saliva.

Results showed that teens who used weed had restricted development over time.

In some cases, weed users performed just as well as — or even better than — others when they were younger, but fell behind as they grew older. Their progress leveled off, while their peers continued to improve.

Researchers also found that THC levels in teenagers was related to worse memory over time, but not CBD levels. THC is the compound in weed that causes intoxication, while CBD is a non-intoxicating substance also found in the drug.

“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.”

Because of its design, the study cannot prove a direct cause-and-effect link between weed and blunted brain development, only an association, researchers said.

The team will continue tracking participants into young adulthood to better understand the long-term effects of cannabis use.

“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.”

More information

The U.S. Centers for Disease Control and Prevention has more on cannabis and teens.

SOURCE: University of California-San Diego, news release, April 15, 2026