Cannabis may interfere with a teen brain’s reward system at a time of crucial development, and higher-potency cannabis products have more pronounced effects, Brown researchers found.

“Adolescence is a critical window for brain development,” says lead study author Sarah A. Thomas, PhD, an assistant professor of psychiatry and human behavior (research) and a clinical psychologist at Bradley Hasbro Children’s Research Center. “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.”

Approximately 10 to 20 percent of US adolescents report using cannabis. Use during the teenage years, compared to adulthood, is linked to a higher risk of developing cannabis use disorder and experimenting with other drugs. One possible reason is that cannabis disrupts the brain’s dopamine system, which helps regulate motivation, learning, and reward.

The federally funded study, which was published in Neuropsychopharmacology, assessed cannabis use quantity, frequency, and disorder severity among 81 participants aged 14 to 17. The researchers then 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.

The study found that in many brain regions, adolescents who use cannabis had significantly lower tissue iron levels than those who used little or none. “There seems to be something unique about using cannabis, compared to nicotine or alcohol, during adolescence, because the body’s own endocannabinoid system is what is helping to facilitate developing these brain regions, especially in these regions that are high in dopamine,” Thomas says. “And the regions that are high in dopamine tend to develop earlier than other parts of the brain.”

The results are particularly concerning, Thomas says, given the significant increase in potency of cannabis products compared to just a decade ago. “Higher potency is linked to more adverse outcomes,” she adds.

To better understand how early cannabis use shapes long-term outcomes, the research team is studying how it affects the dopamine system over time.