East Providence, R.I. – A new study from Bradley Hospital researchers shows that cannabis use during adolescence is associated with differences in brain regions involved in motivation and reward, which support healthy development.
The researchers found that teens who repeatedly used cannabis showed signs of reduced dopamine‑related neurophysiology, with higher-potency products showing more pronounced effects, suggesting that cannabis may interfere with the brain’s reward system at a time of crucial development. Their findings were published in Neuropsychopharmacology.
“Adolescence is a critical window for brain development,” said lead study author Sarah A. Thomas, PhD, a clinical psychologist and research scientist at the Bradley Hasbro Children's Research Center and an Assistant Professor of Psychiatry and Human Behavior (research) at the Warren Alpert Medical School of Brown University. “Our findings suggest that repeated cannabis use during this period has the potential to alter the dopamine system in ways that could affect motivation, reward processing and vulnerability to addiction. The next step is understanding how this may change over time.”
Approximately 10 to 20% of U.S. adolescents report using cannabis in the past year. Scientists know that the developing teenage brain is more sensitive to the effects of cannabis than the adult brain. Research has also shown that teens who use cannabis are more likely than adults to develop cannabis use disorder and to experiment with other substances in the future. One possible reason is that cannabis disrupts the brain’s dopamine system — the network that helps regulate motivation, learning and reward.
In adults, THC, which is the main psychoactive ingredient in cannabis, can temporarily boost dopamine production. But long‑term cannabis use may have the opposite effect, reducing the brain’s ability to produce and release dopamine, although findings have been mixed. While this effect has been studied in adults, much less is known about how cannabis affects dopamine‑related development in teenagers.
In a National Institute on Drug Abuse-funded study with 81 participants aged 14 to 17, the researchers assessed cannabis use quantity, frequency, and problems and used MRI to measure tissue iron in brain regions with high dopamine activity. Tissue iron is a necessary factor in the production of dopamine and naturally increases during adolescence as the dopamine system matures, making it a useful indicator of healthy development.
According to the researchers, this is the first study to examine how cannabis use in teens relates to tissue iron levels in the brain — a reliable, noninvasive marker linked to dopamine activity.
These results, the researchers said, add to growing evidence that cannabis use during adolescence may have negative effects on the brain and highlight the importance of understanding how early use shapes long‑term outcomes.
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