Neuromelanin MRI imaging found that cannabis use disorder was associated with elevated dopamine function in the same midbrain region previously linked to psychosis severity.
Psychiatrists, neuroscience researchers, psychosis risk specialists, addiction medicine professionals
Dose-dependent: more CUD symptoms = higher dopamine signal
What the researchers found
Cannabis use disorder (CUD) was associated with elevated neuromelanin-MRI signal in a set of ventral substantia nigra/ventral tegmental area voxels (387 of 2,060 voxels, corrected P=0.03). CUD was also associated with elevated signal in a region previously linked to psychosis severity (P=0.04), with a dose-dependent relationship (more severe CUD symptoms correlated with higher signal, P=0.03). In contrast, first-episode schizophrenia alone did not reach significance in this analysis.
Why it matters
This study provides neuroimaging evidence for a specific biological mechanism linking cannabis use to psychosis risk. The finding that cannabis use disorder affects the same dopamine pathway implicated in psychosis suggests a shared neural substrate, not just a statistical association.
The numbers in context
n=61 (25 with CUD, 36 without); 387 of 2,060 SN/VTA voxels showed elevated signal with CUD (corrected P=0.03); dose-dependent CUD severity association (P=0.03); 1-year follow-up for 37 participants
How the study worked
Longitudinal observational cohort study recruiting from an early psychosis service and surrounding communities in London, Ontario (2019-2023). 61 participants (36 without CUD, 25 with CUD; some with first-episode schizophrenia in each group). Neuromelanin-sensitive MRI used as a proxy measure of dopamine function. One-year follow-up for 37 participants.
What this study cannot tell us
Small sample size (61 total, 25 with CUD). Neuromelanin MRI is a proxy measure of dopamine function, not a direct measurement. Cannot determine whether CUD causes dopamine changes or whether pre-existing dopamine differences predispose to both CUD and psychosis. Cross-sectional associations with limited longitudinal change data.
How to read the evidence
Published in JAMA Psychiatry with novel neuroimaging methodology and dose-response relationship, but small sample size and inability to establish causal direction limit confidence.
When this study was published
2025 publication; participants recruited 2019-2023
The bigger picture
The dopamine hypothesis of psychosis is one of the most established frameworks in psychiatry. Finding that cannabis use disorder converges on this same dopamine pathway provides a biological explanation for the epidemiological link between heavy cannabis use and psychosis, published in JAMA Psychiatry.
Questions still open
- Do dopamine function changes normalize after sustained cannabis abstinence? Could neuromelanin MRI serve as a biomarker to identify cannabis users at highest psychosis risk?
Common questions
What does neuromelanin MRI measure?
Does this prove cannabis causes psychosis?
Read the original research
Convergence of Cannabis and Psychosis on the Dopamine System.
JAMA psychiatry, 82(6), 609-617
Citation
Ahrens, Jessica; Ford, Sabrina D; Schaefer, Betsy; Reese, David; Khan, Ali R; Tibbo, Philip; Rabin, Rachel; Cassidy, Clifford M; Palaniyappan, Lena. (2025). Convergence of Cannabis and Psychosis on the Dopamine System.. JAMA psychiatry, 82(6), 609-617. https://doi.org/10.1001/jamapsychiatry.2025.0432
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