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Cannabis impairs brain function in young people prone to psychosis
Last reviewed: 02.07.2025
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Young people at risk of psychosis show reduced connectivity between brain cells, and cannabis use may exacerbate this deficit, a new study has found. The discovery opens the door to new psychosis treatments that target symptoms that current medications do not address.
A unique study conducted by scientists from McGill University has found a significant reduction in the density of synapses – the connections between neurons that enable communication in the brain – in people at risk of developing psychosis compared to a control group of healthy participants.
Main results of the study
The study was published in the journal JAMA Psychiatry.
"Not everyone who uses cannabis will develop psychosis, but for some people the risk is significantly higher. Our study helps clarify why this happens," said Dr. Romina Mizrahi, the study's senior author and a professor in the department of psychiatry at McGill University.
"Cannabis appears to disrupt the brain's natural process of cleaning and pruning synapses, which is important for healthy brain development."
Hope for new treatments
Using state-of-the-art brain scanning technology, the team studied 49 participants aged 16 to 30, including people with recent symptoms of psychosis and those considered at high risk. The results show that reduced synaptic density is associated with social withdrawal and lack of motivation – symptoms that are difficult to treat.
"Current medications primarily target hallucinations, but they do not address the problems that interfere with social relationships, work, or school," explained first author Belen Blasco, a doctoral student in McGill University's integrated neuroscience program.
"By focusing on synaptic density, we may be able to develop future therapies that improve social function and quality of life in people with psychosis."
Cannabis and psychosis
While cannabis is a known risk factor for psychosis that can progress to schizophrenia, this study is the first to document structural changes in the brain of a high-risk group in real time.
The team's next phase of research will examine whether these brain changes can predict the development of psychosis, allowing for earlier interventions.