Key Takeaways
- Heavy cannabis use is linked to changes in dopamine-related brain regions associated with psychosis, based on new imaging research.
- The more severe the cannabis use, the stronger the brain changes observed, suggesting a dose-dependent relationship.
- While the study doesn’t prove causation, it raises important questions about long-term brain effects and the need for early intervention in young users.
Researchers have found a link between heavy cannabis use and changes in dopamine-related brain activity—a phenomenon associated with a higher risk of psychosis.
Cannabis and The Brain
A new Canadian study, published in the journal JAMA Psychiatry, highlights a significant association between heavy cannabis use and brain changes that may be tied to psychosis. Using brain imaging, the researchers observed elevated neuromelanin-MRI signals, which are a proxy for increased dopamine activity, in a key brain region among individuals with cannabis use disorder.
Excess Dopamine in the Brain
Conducted in London, Ontario, by teams from the London Health Sciences Centre Research Institute (LHSCRI) and the Western University School of Medicine, the study used a non-invasive imaging technique called neuromelanin-sensitive MRI. Neuromelanin, a dark pigment, naturally builds up in the brain with age, but when dopamine activity is elevated, it accumulates more rapidly and appears as dark spots on scans.
“In people who consume cannabis excessively, these spots are darker than they should be for their age—sometimes comparable to those of people ten years older,” said Lena Palaniyappan, a professor at McGill and lead author of the study, in a press release. She added, “We have evidence of a significant association between cannabis use disorder and elevated neuromelanin-MRI signals, which reflect dopamine function, in brain regions previously linked to psychosis.”
A Warning Sign for Young Users
The research included 61 young adults, some of whom were in the early stages of schizophrenia. “The increase in dark spots was seen in a specific brain area—the substantia nigra and the ventral tegmental area—and it was present in individuals with cannabis use disorder, including those without schizophrenia,” said co-author Ali Khan.
Since cannabis legalization in Canada, emergency rooms are seeing more young people experiencing cannabis-induced psychotic episodes. “We try to intervene at the very first episode because it can push their brain toward a more severe form of psychosis,” said a clinician from the Prevention and Early Intervention Program for Psychoses (PEPP) at LHSC.
The study also found a dose-dependent relationship between the severity of cannabis use disorder and the neuromelanin-MRI signal—individuals with more severe symptoms showed stronger signals. However, the authors note that while these findings are consistent with dopamine-related pathways implicated in psychosis, they do not establish a causal relationship between cannabis use and schizophrenia.
According to researcher Betsy Schaefer, the study sheds light on cannabis’s potential neurological effects and the biological mechanisms that may connect the drug to mental health risks. Jessica Ahrens, a PhD student who contributed to the study, emphasized the importance of preventative action and hopes the findings “will encourage healthcare providers to offer alternatives to cannabis for coping with stress and challenges.”
Related Reading:
High-Potency Cannabis Linked to Greater Addiction, Psychosis Risk: What to Know
Brain Stimulation Shows Promise for Cannabis Use Disorder in People with Schizophrenia
FAQs: Cannabis, the Brain, and Psychosis Risk
What is the study about?
It examined whether people with cannabis use disorder show signs of altered dopamine activity in brain regions linked to psychosis.
What did the researchers find?
They found that people with cannabis use disorder had elevated neuromelanin-MRI signals in dopamine-related brain areas especially the substantia nigra and ventral tegmental area (SN/VTA) which suggests long-term changes in dopamine function.
What is dopamine, and why does it matter here?
Dopamine is a chemical messenger in the brain involved in reward, motivation, learning, and movement. When it’s overactive in certain regions, it’s been linked to hallucinations, delusions, and other symptoms of psychosis.
How does cannabis affect dopamine?
Cannabis can increase dopamine release in the short term, especially with THC. Over time, heavy use may dysregulate the dopamine system, possibly increasing the risk of psychiatric symptoms.
What is neuromelanin-sensitive MRI?
It’s a brain scan that detects neuromelanin, a pigment that builds up as dopamine is processed. It acts as a long-term marker of dopamine activity.
What’s the substantia nigra and ventral tegmental area (SN/VTA)?
They’re deep brain regions where dopamine-producing neurons live. They play a key role in how we process rewards, control movement, and respond to stimuli—functions that are disrupted in psychosis.
Does this mean cannabis causes schizophrenia?
No. The study found a strong association, not proof of causation. Many people who use cannabis don’t develop psychosis, but heavy use may raise the risk.
What’s a dose-dependent effect?
It means the more severe the cannabis use disorder, the greater the brain changes observed, suggesting a link between usage level and risk.
Is this the same as feeling high?
No. The study measured longer-term brain changes related to dopamine buildup, not just the immediate effects of THC.
Did the study look at treatment or recovery?
Yes. Some participants with schizophrenia were on treatment, which may have lowered their dopamine signals. But the brain changes tied to cannabis were seen regardless of treatment.
Can the brain changes be reversed?
That’s still unclear. The signals stayed elevated after a year, so they might last, but the study didn’t track what happens if someone stops using. More research is needed.
What does “heavy use” mean in the study?
It refers to people with cannabis use disorder—regular, long-term use starting in teens, with symptoms like trouble cutting back and using despite problems.
Should young people be concerned?
Yes. The brain is still developing into your mid-20s, and heavy cannabis use during that time might affect how the dopamine system works. It’s worth taking seriously.
What should someone do if they’re using cannabis a lot?
Check in with your doctor or a counselor. If you’re using to deal with stress or sleep, there may be safer ways. Getting support early can help protect your mental health down the road.
Bottom Line
This study doesn’t prove cannabis causes psychosis, but it does add to growing concerns about how the drug might affect the brain, especially with frequent, long-term use. The results suggest cannabis could impact the same dopamine pathways involved in serious mental health conditions like schizophrenia. As legalization continues across the U.S., these findings raise questions about whether current treatment advice and public awareness are keeping up. For people who use cannabis regularly, it’s a good time to pay attention to mental health changes, talk to a doctor if anything feels off, and take a cautious, informed approach.
References
Ahrens, J., Ford, S. D., Schaefer, B., Reese, D., Khan, A. R., Tibbo, P., Rabin, R., Cassidy, C. M., & Palaniyappan, L. (2025). Convergence of cannabis and psychosis on the dopamine system. JAMA Psychiatry. Advance online publication. https://doi.org/10.1001/jamapsychiatry.2025.0432
