Teenagers who smoke marijuana are less intelligent – New Research

• Posted on May 6, 2026May 6, 2026
• by Nana Kwesi Coomson
• Comment

A study led by Natasha Wade, PhD, using data from more than 11,000 adolescents in the Adolescent Brain Cognitive Development (ABCD) Study, found that teens who use cannabis tend to show slower cognitive development compared to those who do not, particularly in areas linked to memory, focus, and thinking speed.

A major new study from the University of California San Diego School of Medicine have found that the use of marijuana in teenagers could be quietly slowing how their brains develop.

The lead author of the study, Natasha Wade, PhD, analysed data from more than 11,000 adolescents in the Adolescent Brain Cognitive Development (ABCD) Study and found a clear pattern: teens who used cannabis showed slower cognitive development than those who didn’t.

Researchers observed that while most teens naturally improve in thinking, learning, and memory as they grow, cannabis users didn’t keep up.

Instead, they appeared to lag behind in key mental skills like:

• memory
• focus thinking
• speedIn simple terms, their brains weren’t progressing at the same pace.

That gap might not seem obvious at first—but over time, it could mean: these cannabis users are struggling to keep up in class, forgetting things more often, and finding it harder to concentrate making slower or poorer decisions. These are the very skills teenagers rely on to succeed in school and everyday life.

Researchers stress that the findings show a strong link but not a final verdict—and brain development can be influenced by many factors. Still, the consistency of the results is enough to raise serious concerns.

As cannabis becomes more accepted globally, one question is becoming harder to ignore: Are teenagers being told the full story about what it could be doing to their brains?