The Dopamine Link: What Neuromelanin Tells Us About Cannabis and Psychosis
We are excited to share that our research was published this month in JAMA Psychiatry, and we wish to disseminate our findings so they can help others. Our study may offer new insight into how problematic cannabis use increases the risk of psychosis by affecting the brain’s dopamine system—a key pathway involved in movement, motivation, and mood.
Using a specialized brain scan called neuromelanin-sensitive MRI, we found that people with cannabis use disorder had higher levels of neuromelanin in a region of the brain called the substantia nigra; more specifically, within an area of it that has been previously linked to the severity of psychosis symptoms. Neuromelanin is a dark pigment that forms as a byproduct when dopamine, a chemical messenger in the brain, is broken down. Because neuromelanin accumulates in dopamine-producing brain cells, measuring it with this MRI technique gives us a non-invasive window into dopamine activity over time. Higher neuromelanin in the substantia nigra suggests that these brain cells have been producing and processing more dopamine, which is significant because excess dopamine in certain brain regions is a well-established factor in psychosis, including symptoms like hallucinations and delusions.
Dopamine plays a crucial role in how we move, feel pleasure, and respond to rewards, but too much dopamine—especially in areas like the striatum—has been linked to psychotic disorders such as schizophrenia. The substantia nigra, where we observed the increased neuromelanin, is the main source of dopamine-producing cells in the brain, and it sends signals to the striatum to help regulate these functions. By showing that heavy cannabis use is associated with higher neuromelanin in this area, our study provides a clearer biological explanation for why cannabis can sometimes trigger or worsen psychotic symptoms.
One of the most important findings from our research is that this effect was dose-dependent: the more severe a person’s cannabis use disorder, the stronger this neuromelanin increase. Even among people with schizophrenia, it was cannabis use—not the diagnosis itself—that was most closely tied to these neuromelanin increases. This suggests that excessive cannabis use could independently trigger brain changes that mimic or worsen psychotic symptoms, even in people without a prior mental health condition.
These findings are especially important for youth, and we hope young people will keep this information in mind when making decisions about cannabis use. The teenage and young adult years are a critical period for brain development, and the dopamine system is still maturing during this time. Because young brains are more adaptable and sensitive to outside influences, heavy cannabis use during adolescence may have a stronger and more lasting impact on dopamine pathways, potentially increasing the risk of developing psychosis later on. Since cannabis was legalized in Canada, there has been a noticeable increase in psychosis cases linked to its use. In fact, recent research suggests that living near cannabis retailers may increase the risk of needing mental health services for psychosis, especially in high-risk communities.
While many people think of cannabis as low risk, we hope our study adds to growing evidence that heavy, long-term use may change brain chemistry and allow people to make informed decisions about their substance use. This is particularly important for youth with a family history of psychosis or schizophrenia, those who are at high risk. The key takeaway is the importance of moderation and awareness. If you or someone you know experiences hallucinations or paranoia after using cannabis and are concerned, it’s important to seek medical advice. By sharing these findings, we hope to inform clinicians, patients, families, and the wider public about the potential mental health risks associated with frequent cannabis use, especially as cannabis becomes more widely available and accepted in society. For more information, you can read the full paper, “Convergence of Cannabis and Psychosis on the Dopamine System,” here.
By Jessica Ahrens, PhD Candidate