Summary: Researchers uncovered critical evidence showing how adolescent cannabis use alters the neurophysiology of the teenage brain. The investigation demonstrates that repeated cannabis exposure during adolescence is directly associated with differences in deep-brain regions responsible for motivation and reward.
By utilizing specialized MRI techniques to measure tissue iron, a vital biomarker necessary for healthy dopamine system maturation, researchers revealed that frequent cannabis use, particularly with high-potency products, correlates with reduced dopamine-related development.
Key Facts
- The Dopamine Maturation Threat: Adolescence serves as a critical developmental window where the brain’s dopamine system—the primary network regulating motivation, learning, and reward processing—undergoes vital maturation.
- Tissue Iron as a Neural Marker: Brain tissue iron is a required biological cofactor for dopamine production that naturally increases during healthy teenage development, serving as a reliable, noninvasive indicator of dopamine system health.
- The High-Potency Gradient: Teaming up with the National Institute on Drug Abuse, researchers found that adolescents who repeatedly use cannabis exhibit signs of lower brain iron levels. This neurophysiological deficit is significantly more pronounced in teens using high-potency cannabis products.
- A Diagnostic Brain Imaging First: This research represents the first study in neuroscientific literature to explicitly evaluate how adolescent cannabis use relates to tissue iron levels in brain regions dense with dopamine activity.
- The Long-Term Adult Inversion: While THC temporarily spikes dopamine production in adults, long-term adult use can conversely blunt the brain’s capacity to release dopamine; the Bradley Hospital study fills a massive gap by tracking how these processes unfold in developing brains.
- Elevated Addiction Vulnerabilities: The study notes that approximately 10% to 20% of U.S. adolescents report using cannabis annually. Because the teenage brain is uniquely sensitive, early use increases the likelihood of developing cannabis use disorder or transitioning to other substances later in life.
- Next-Phase Longitudinal Mapping: Lead author Dr. Sarah A. Thomas, an Assistant Professor at the Warren Alpert Medical School of Brown University, emphasizes that the next step is tracking this cohort over time to determine how these reward-system alterations shape long-term cognitive and psychiatric outcomes.
Source: Brown University
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.
Key Questions Answered:
A: Because tissue iron is a necessary ingredient for the brain to build and release dopamine. In a healthy teenage brain, iron levels naturally go up as the reward system matures, making it an excellent, noninvasive MRI marker to test whether cannabis is disrupting normal development.
A: It makes the damage significantly worse. The Bradley Hospital study showed that while repeated cannabis use lowers dopamine-related markers across the board, teens using higher-potency products showed the most pronounced drops in brain iron levels.
A: Because the teenage brain is still actively building its motivation and reward infrastructure. Cannabis disrupts this critical construction phase, altering the dopamine system in ways that can blunt natural motivation and leave adolescents highly vulnerable to future addiction.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neuroscience and CUD research news
Author: Kelly Brennan
Source: Brown University
Contact: Kelly Brennan – Brown University
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“The role of subcortical brain tissue iron as an indicator of dopamine neurophysiology in adolescent cannabis use” by Sarah A. Thomas, Meghan A. Gonsalves, Gillian LeBlanc, Elizabeth Lorenc, Jane Metrik, Michael Frank, Sarah Ryan, Emily Olenik, Leslie Brick, Anthony Spirito & Jodi Gilman. Neuropsychopharmacology
DOI:10.1038/s41386-026-02444-9
Abstract
The role of subcortical brain tissue iron as an indicator of dopamine neurophysiology in adolescent cannabis use
Approximately 10–20% of U.S. adolescents report past-year cannabis use (CU). Although regular CU beginning in adolescence is expected to blunt dopamine-related neurophysiology, this hypothesis has not been tested in adolescents due to methodological limitations.
However, neurophysiology contributing to dopamine can be noninvasively indexed via subcortical tissue iron measured with magnetic resonance imaging (MRI). We examined adolescent CU quantity, frequency, and problems in relation to tissue iron in regions with high dopamine activity, hypothesizing that greater CU would be linked to less tissue iron.
Adolescents (n = 81; 64.2% female) aged 14–17 reporting either fewer than 5 lifetime cannabis episodes (n = 47) or more than 11 episodes (n = 34), with limited alcohol and nicotine use and no other illicit substance use, completed substance use assessments and an MRI. We calculated the inverse of the normalized T2* measurement (1/nT2*; lower values indicate less tissue iron) from resting-state functional scans by assessing relative T2* decay. 1/nT2* was estimated using subcortical masks for hypothesized regions.
Lower 1/nT2* signal was 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 cannabis use disorder (CUD) severity (b = –0.01, p = 0.003). Post-hoc analyses highlighted the VTA as a key region.
Results align with reduced dopamine-related neurophysiology associated with CU in adult and animal samples, and have implications for understanding adolescent CUD development. Measuring 1/nT2* offers an innovative, non-invasive method to index neurobiological alterations in adolescent CU.
