As cannabis becomes legal in more places around the world, questions about its long-term health effects have become increasingly important.
Millions of people use cannabis for relaxation or medical treatment, yet scientists know that it can affect the brain in different ways. While many users experience only temporary effects, a small number develop serious mental health problems, including psychosis. Researchers have been trying to understand why this happens.
Psychosis affects the way a person experiences reality. It may cause hallucinations, false beliefs, confused thinking, and major changes in behaviour. Earlier studies have repeatedly linked heavy cannabis use with a higher chance of psychosis, but the reason for this connection has remained unclear.
Researchers from the University of Pennsylvania Perelman School of Medicine and Children’s Hospital of Philadelphia investigated whether a brain chemical called glutamate might provide the missing explanation. Their findings were published in the journal Molecular Psychiatry.
Glutamate helps billions of brain cells send signals to one another. Without the right amount of glutamate, the brain cannot process information normally. Earlier research had already suggested that abnormal glutamate activity might play a role in schizophrenia and other psychiatric illnesses.
The research included 79 participants representing a wide range of mental health conditions. Some had no psychiatric illness, some were at high risk of psychosis, and others had confirmed psychosis.
The scientists measured symptoms, recorded cannabis use, verified recent use with urine testing, and examined brain chemistry using powerful 7-Tesla magnetic resonance spectroscopy.
The brain scans focused on the anterior cingulate cortex, an area that helps regulate emotions, behaviour, decision-making, and attention. Measuring glutamate in this region allowed the researchers to compare brain chemistry with mental health symptoms.
The study found two separate patterns. Cannabis use was linked with stronger psychosis symptoms, and lower glutamate levels were also linked with stronger symptoms. When both factors occurred together, the association became even stronger.
Cannabis users with lower glutamate levels showed the highest levels of hallucinations and delusions. Additional analyses suggested that altered glutamate activity might also worsen depressive and manic symptoms.
Researchers also observed that people with psychosis generally had lower glutamate levels than healthy participants, particularly if they also used cannabis. This finding strengthens the idea that changes in glutamate may be involved in the illness.
Although these results are encouraging, they do not prove cause and effect. The study cannot determine whether cannabis changes glutamate or whether some people naturally have lower glutamate before using cannabis. Long-term studies that follow people before and after cannabis exposure will be needed to answer that question.
If future research confirms these findings, scientists may be able to develop medicines that target glutamate or identify high-risk individuals before serious symptoms develop. Such advances could improve prevention and treatment for people vulnerable to psychosis.
This research provides valuable biological evidence supporting earlier observations about cannabis and mental illness. Its strengths include modern brain imaging and careful confirmation of cannabis use.
However, the relatively small number of participants means the results should be interpreted carefully until larger studies repeat them. Even so, the work represents an important step toward understanding why cannabis appears to affect mental health differently from one person to another. The study was published in Molecular Psychiatry.
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Source: University of Pennsylvania Perelman School of Medicine.
