Summary: New research reveals how repeated cannabis use during adolescence can alter the developing brain. Using specialized MRI measures of tissue iron — a biological marker tied to dopamine system maturation — investigators found that frequent cannabis use, especially of high‑potency products, is associated with lower iron levels in deep brain regions involved in motivation and reward.
The study links adolescent cannabis exposure to neurophysiological differences in dopamine‑rich subcortical areas. Tissue iron rises naturally during healthy adolescent development and is essential for dopamine production; reduced tissue iron therefore signals disrupted maturation of reward circuitry.
Key Facts
- Critical window for dopamine maturation: Adolescence is a key period when the brain’s dopamine networks — which govern motivation, learning and reward processing — undergo important growth and refinement.
- Tissue iron as a neural marker: Iron in brain tissue is a necessary cofactor for dopamine synthesis and normally increases through the teenage years. Measuring tissue iron by MRI provides a noninvasive index of dopamine‑related neurodevelopment.
- Potency matters: In collaboration with the National Institute on Drug Abuse, researchers observed that repeated adolescent cannabis use is associated with signs of reduced tissue iron, with the strongest effects in teens using higher‑potency cannabis products.
- Imaging first: This is the first study to directly examine the relationship between adolescent cannabis use and subcortical tissue iron in regions dense with dopamine activity.
- Adult versus adolescent effects: While THC can temporarily increase dopamine signaling in adults, long‑term use in adults has been linked to a blunted ability to release dopamine. This study addresses the important and understudied question of how cannabis exposure influences dopamine‑related development in adolescents.
- Public health implications: An estimated 10–20% of U.S. adolescents report past‑year cannabis use. Because the teenage brain is especially sensitive, early and frequent use may raise the risk of later cannabis use disorder and increase vulnerability to other substance use.
- Next steps: Lead author Dr. Sarah A. Thomas and colleagues emphasize the need for longitudinal follow‑up to determine how these reward‑system alterations evolve over time and whether they predict long‑term cognitive or psychiatric outcomes.
Source: Brown University
New research from Bradley Hospital finds that adolescent cannabis use is linked to differences in brain regions that support motivation and reward.
Researchers report that teenagers who repeatedly used cannabis showed reductions in dopamine‑related neurophysiology, measured as lower tissue iron in subcortical regions. The association was stronger for use of higher‑potency cannabis products, suggesting that cannabis exposure during this developmental window may interfere with the brain’s reward system.
The findings were published in the journal Neuropsychopharmacology.
“Adolescence is a critical window for brain development,” said lead author Sarah A. Thomas, PhD, a clinical psychologist and research scientist at the Bradley Hasbro Children’s Research Center and 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 can change dopamine system development in ways that affect motivation, reward processing and vulnerability to addiction. The next step is to follow these participants over time to see how these changes evolve.”
About 10–20% of U.S. adolescents report using cannabis in the past year. Prior studies indicate the teenage brain is more sensitive than the adult brain to cannabis effects and that early use is associated with higher rates of cannabis use disorder and experimentation with other substances later in life. One plausible mechanism is disruption of the dopamine system — the neural network that regulates motivation, learning and reward.
In adults, THC — the principal psychoactive compound in cannabis — can temporarily raise dopamine signaling, while prolonged adult use has sometimes been associated with reduced dopamine release. However, much less is known about how cannabis affects dopamine‑related development during adolescence.
This National Institute on Drug Abuse‑funded study enrolled 81 adolescents aged 14–17 and assessed cannabis use quantity, frequency and related problems alongside MRI measurements of subcortical tissue iron. Tissue iron was estimated from resting‑state functional MRI metrics (the inverse of normalized T2*), with lower values indicating less tissue iron. Participants had limited alcohol and nicotine use and no other illicit substance use, allowing a clearer focus on cannabis effects.
Analyses showed that lower tissue iron signal was associated with greater cannabis exposure measures, including more daily concentrate hits, longer cumulative hours high, higher frequency of use, and greater cannabis use disorder severity. Post‑hoc regional analyses highlighted the ventral tegmental area (VTA) as an important locus of these associations.
These results are consistent with evidence from adult and animal studies that link cannabis use to reduced dopamine‑related neurophysiology. Measuring subcortical tissue iron with MRI offers a noninvasive, biologically grounded approach to index neurodevelopmental alterations related to adolescent cannabis use and has implications for understanding pathways to cannabis use disorder.
Key Questions Answered:
A: Tissue iron is required for dopamine synthesis, and iron levels normally rise during adolescence as the dopamine system matures. Because it can be measured noninvasively by MRI, tissue iron provides a useful marker to detect whether cannabis use is disrupting normal reward‑system development.
A: The study found a potency gradient: repeated use of higher‑potency products was linked to larger reductions in tissue iron. In other words, higher‑potency cannabis appeared to produce stronger associations with altered dopamine‑related markers.
A: The adolescent brain is still constructing its motivation and reward systems. Cannabis exposure during this formative period can disrupt that development, potentially reducing natural motivation and increasing susceptibility to future addiction.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional context was provided by staff reviewers.
About this neuroscience and CUD research news
Author: Kelly Brennan
Source: Brown University
Contact: Kelly Brennan, Brown University
Image credit: Neuroscience News
Original Research: “The role of subcortical brain tissue iron as an indicator of dopamine neurophysiology in adolescent cannabis use” by Sarah A. Thomas et al., published in Neuropsychopharmacology. DOI: 10.1038/s41386-026-02444-9. (Closed access)
Abstract
The role of subcortical brain tissue iron as an indicator of dopamine neurophysiology in adolescent cannabis use
Roughly 10–20% of U.S. adolescents report past‑year cannabis use. Although regular cannabis use beginning in adolescence is expected to blunt dopamine‑related neurophysiology, this hypothesis has not been thoroughly tested in adolescents. Subcortical tissue iron, measurable with MRI, provides a noninvasive index of neurophysiology that contributes to dopamine production. The study examined adolescent cannabis quantity, frequency and problem use in relation to tissue iron in dopamine‑rich regions, hypothesizing that greater cannabis exposure would relate to lower tissue iron.
Eighty‑one adolescents (ages 14–17; 64.2% female) reporting either fewer than five 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 MRI. The investigators calculated the inverse of normalized T2* (1/nT2*), where lower values indicate less tissue iron, from resting‑state functional scans within preselected subcortical masks.
Lower 1/nT2* signal was associated with increased daily concentrate hits, greater cumulative hours high, higher cannabis use frequency, and greater cannabis use disorder severity. Post‑hoc analyses pointed to the ventral tegmental area as a key region. These results align with evidence of reduced dopamine‑related neurophysiology associated with cannabis use in adult and animal studies and have implications for understanding adolescent cannabis use disorder development. Measuring 1/nT2* offers an innovative, noninvasive approach to index neurobiological alterations in adolescent cannabis use.