Teen Cannabis Use Linked to Slower Brain Development in Major U.S. Study
A study of over 11,000 teenagers found that those who start using cannabis experience slower growth in memory, attention, and thinking speed during critical brain development years. Users initially performed as well as peers, but their cognitive progress plateaued while non-users continued improving.
Major Long-Term Research Finding
Researchers at the University of California San Diego have found that teenagers who start using cannabis may develop memory and thinking abilities more slowly than teens who do not use it. The findings were published in Neuropsychopharmacology and were based on data from more than 11,000 participants in the Adolescent Brain Cognitive Development (ABCD) Study, the largest long-term investigation of brain development.
Study Design and Scope
The researchers followed 11,036 children starting at ages 9 to 10 through ages 16 and 17, tracking both their cognitive performance and substance use. This longitudinal approach allowed scientists to observe how cognitive abilities changed over time between cannabis users and non-users.
The Key Findings
Teens who start using cannabis may experience slower growth in memory, attention, language, and processing speed. Their abilities often developed normally at first, then began leveling off while nonusers continued improving. THC appeared to be the most likely driver, especially for worsening memory.
"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 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."
Why This Matters
During adolescence, the brain is rapidly developing, and even small changes in memory, attention or thinking speed can affect school performance and daily life. The researchers note that the study does not prove cannabis use directly causes these changes. Other factors—such as environment or personality—may play a role. However, the team accounted for many of these influences, including family background, mental health and use of other substances, as well as for each participant's prior cognitive performance.