A landmark study published in late April 2026 found that teens who start using cannabis fall behind their peers in memory, attention, and thinking skills, and the gap widens over time.
What the Research Found
Researchers at the UC San Diego School of Medicine examined data from over 11,000 participants in the Adolescent Brain Cognitive Development (ABCD) Study, the largest long-term investigation of brain development in U.S. youth.
The team tracked children from ages 9–10 through 16–17, monitoring both cognitive performance and substance use over time.
To improve accuracy, researchers combined self-reported data with biological testing, including hair, urine and saliva samples, capable of detecting drug exposure spanning recent days to several months.
Across multiple abilities, such as memory, attention, language, and processing speed, teens who used cannabis exhibited slower development over time than their non-using peers.
In some cases, these teens performed comparably to peers at younger ages, but as cannabis use began, their progress leveled off while their peers continued to improve.
THC Is the Likely Driver
Not all components of cannabis appear equally harmful to developing brains. In a smaller group of participants, teens with signs of exposure to THC, the primary psychoactive compound in cannabis, experienced poorer memory outcomes over time.
Teens with evidence of cannabidiol (CBD) exposure did not exhibit the same pattern, although the sample size for the CBD group was small.
Lead author Dr. Natasha Wade, an assistant professor of psychiatry at UC San Diego, said the findings underscore the complexity of cannabis products, particularly since items labeled as CBD may still contain THC.
This distinction matters for addiction treatment: many teens and parents assume CBD-dominant products are risk-free, but product labeling is not always reliable.
Why Adolescent Brain Development Makes This Critical
The researchers note that the study does not prove cannabis use directly causes these changes, as 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, use of other substances, and each participant’s prior cognitive performance.
While the observed differences were relatively modest, researchers say they could still matter. During adolescence, the brain is rapidly developing, and even small changes in memory, attention or processing speed can affect school performance and daily life.
For young people already facing co-occurring mental health challenges, a common profile among teens entering addiction treatment, these cognitive setbacks can compound existing difficulties.
What This Means for Treatment Seekers
Parents and teens researching addiction treatment options should understand that cannabis is not a low-risk substance during the developmental years, even in states where it is legal.
Dr. Wade emphasized that delaying cannabis use supports healthy brain development, and that as cannabis becomes more widely available, it is important for families and teens to understand how it may affect the developing brain.
Effective adolescent addiction treatment programs address cannabis use disorder specifically, and many incorporate cognitive-behavioral therapy (CBT) to help teens build the executive function and coping skills that cannabis use may be disrupting.
Early intervention is key, the sooner a teen enters treatment, the more of that critical developmental window can be preserved.
Exploring Treatment Options
If you’re concerned about a teen’s cannabis use, comparing adolescent rehab centers is a practical first step. Look for programs that offer evidence-based therapies, and integrated mental health support for co-occurring conditions.
You can search Rehab.com’s directory to find thousands of rehab treatment centers across the country, including programs specifically designed for adolescents.
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