Chronic Teen Cannabis Use Linked to Reduced Brain Iron and Dopamine Dysfunction, Raising Addiction Risk
Key Insights
A Brown University study finds that repeated adolescent cannabis use is associated with significantly lower tissue iron levels in dopamine-rich brain regions, suggesting disrupted dopamine system maturation.
The study of 81 teens aged 14–17 is the first to use MRI-based tissue iron measurement as a noninvasive marker of dopamine neurophysiology in adolescent cannabis users.
Higher-potency cannabis products and greater frequency of use showed more pronounced reductions in tissue iron, with daily concentrate hits and CUD severity both negatively associated with iron levels.
A new study from Brown University researchers provides the first neuroimaging evidence that repeated cannabis use during adolescence is associated with reduced tissue iron levels in brain regions critical for dopamine function, raising concerns about long-term impacts on motivation, reward processing, and addiction vulnerability.
Published in Neuropsychopharmacology, the federally funded study examined 81 participants aged 14 to 17 and found that cannabis use quantity, frequency, hours spent under the influence, and cannabis use disorder (search) (CUD) severity were all negatively associated with markers for tissue iron — a necessary cofactor in dopamine production that naturally increases during healthy adolescent brain development.
“Adolescence is a critical window for brain development,” said lead study author Sarah A. Thomas, PhD, an assistant professor of psychiatry and human behavior (research) at Brown University’s Warren Alpert Medical School and a clinical psychologist at Brown University Health’s 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.”
A Novel Method for Measuring Dopamine Neurophysiology
Tissue iron serves as a reliable, noninvasive biomarker linked to dopamine activity. Using magnetic resonance imaging, the researchers calculated the inverse of normalized T2* measurement (1/nT2*), where lower values indicate less tissue iron, from resting-state functional scans across subcortical brain regions with high dopamine activity.
The study is the first in neuroscientific literature to explicitly evaluate how adolescent cannabis use relates to tissue iron levels in dopamine-dense brain regions. Previous research in adults has shown that while THC can temporarily boost dopamine production, long-term cannabis use may blunt the brain’s capacity to produce and release dopamine — though findings have been mixed. Until now, this hypothesis had not been tested in adolescents due to methodological limitations.
Dose-Dependent Effects and High-Potency Concerns
The results revealed a clear dose-response relationship. Lower 1/nT2* signal was significantly associated with increased daily concentrate hits (b = −0.01, p < 0.001), cannabis hours high (b = −0.01, p = 0.016), CU frequency (b = −0.01, p = 0.01), and CUD severity (b = −0.01, p = 0.003). Post-hoc analyses highlighted the ventral tegmental area (VTA) as a key region of interest.
The pronounced effects observed with high-potency cannabis products are particularly concerning given the increasing availability of concentrates in the legal and illicit markets. The researchers note that higher-potency products showed more pronounced reductions in dopamine-related neurophysiology.
Adolescent Vulnerability and Public Health Implications
Approximately 10% to 20% of U.S. adolescents report past-year cannabis use. Research has consistently shown that the developing teenage brain is more sensitive to the effects of cannabis than the adult brain, and teens who use cannabis are more likely than adults to develop cannabis use disorder (search) and to experiment with other substances in the future.
The study cohort included 81 adolescents (64.2% female) aged 14–17, with 47 reporting fewer than five lifetime cannabis episodes and 34 reporting more than 11 episodes. Participants had limited alcohol and nicotine use and no other illicit substance use, allowing the researchers to isolate cannabis-specific effects.
“The next step is understanding how this may change over time,” Thomas said, emphasizing the need for longitudinal tracking of this cohort to determine how reward-system alterations shape long-term cognitive and psychiatric outcomes.
The findings add to a growing body of evidence that cannabis use during adolescence may have negative effects on brain development and underscore the importance of understanding how early use shapes long-term outcomes, particularly as cannabis legalization expands and adolescent access potentially increases.