A recent study published in JAMA Psychiatry, titled, Convergence of Cannabis and Psychosis on the Dopamine System, has identified a direct biological link between cannabis use disorder and an increased risk of psychosis. The research shows that those who heavily use marijuana may have elevated levels of the hormone dopamine in regions of the brain associated with psychosis. This happens especially in the substantia nigra (SN) and ventral tegmental areas (VTA). These are both midbrain structures, crucial for dopamine-related functions, which include motor control, reward processing, and motivation. While they both release dopamine, they have distinct roles and connect to different brain regions. The SN primarily contributes to motor control, while the VTA plays a significant role in reward and motivation. What Is The Role Of Dopamine In Your Brain?Dopamine is a key neurotransmitter responsible for regulating mood, motivation, learning, and motor control. An imbalance—particularly excessive dopamine—can disrupt normal brain functions and increase susceptibility to psychiatric conditions, including psychosis.“Excess levels of dopamine can disrupt normal brain processes and may increase the risk of psychosis, particularly in individuals who are already vulnerable,” explained study co-author Betsy Schaefer, a senior manager of clinical research operations at the London Health Sciences Center Research Institute in Ontario.How Was The Study Conducted?In order to look into the connection between cannabis use and dopamine, the researcher used an advanced MRI technique to monitor neuromelanin deposits in the brain. What exactly is neuromelanin? It is a substance that builds up over time as dopamine is broken down. As per a 2016 study published in Trends in Cognitive Sciences, titled The Locus Coeruleus: Essential for Maintaining Cognitive Function and the Aging Brain, neuromelanin plays both roles, as a neuroprotective and neurotoxic roles. It is a pigment which is produced in dopamine-producing neurons and while it can help protect against oxidative stress and excess metals, it can also accumulate and contribute to neuronal damage and disease progressions. These deposits appear as black spots in MRI scans and serve as indicators of dopamine activity. The study also included 25 individuals who were diagnosed with cannabis use disorder and 36 control participants without the disorder. The researchers were able to find that participants who heavily used cannabis had noticeable neuromelanin deposits in specific regions of the midbrain than their counterparts. “In people partaking in excess cannabis use, those spots are blacker than what they should be for their age compared to healthy individuals,” said senior researcher Dr. Lena Palaniyappan, adjunct professor at Western University’s Schulich School of Medicine & Dentistry. “This indicates they have high levels of dopamine, and in some cases are showing pigments someone 10 years older would have.”he key brain regions showing increased dopamine activity—the substantia nigra and ventral tegmental area—have long been linked to the onset of psychosis. According to researcher Ali Khan, assistant professor at Western University, these darker areas were observed in cannabis users regardless of whether they had experienced a first episode of schizophrenia.“This increase was seen in those with cannabis use disorder regardless of whether they have first-episode schizophrenia,” Khan noted.With Canada having legalized recreational cannabis use six years ago, the study underscores growing concerns about its long-term mental health impact, particularly on young users.