November 2023

One of the key issues talked about when it comes to cannabis is its effects on mental health. An estimated 26.2% of people with schizophrenia will have cannabis use disorder at some point in their lives, which is much higher than in the general public.(1) While some people with psychotic disorders say cannabis helps them to deal with their symptoms, unfortunately, studies show that using cannabis can make aspects of the disorder worse. For example, cannabis use has been linked to higher risks of treatment failure, hospitalisation, and reoccurrence of symptoms.(2)

A recent article by Argote et al. has looked at how the actual symptoms of schizophrenia spectrum disorders differ between those who use cannabis and those who don’t.(3) Their meta-analysis put together data from 21 different studies on the subject, producing interesting results. They found that, on average, people with schizophrenia spectrum disorders who used cannabis had more ‘positive’ symptoms, such as delusions and hallucinations, but also less ‘negative’ symptoms, such as such as lack of emotional expression, lack of speech and lack of motivation.

Meta-analyses like this aren’t able to conclude what might cause the findings, and so we can interpret these results in different ways. Is it possible that cannabis is affecting people’s brains, making some symptoms worse and others better? Are people with psychosis using cannabis as self-medication, to help with their negative symptoms? Or are people with psychosis who use cannabis fundamentally different in some way from those who don’t use cannabis – could some, perhaps, have not developed a psychotic disorder if they hadn’t used cannabis in the first place?

The authors of this paper consider all of these possibilities, but it will be up to future research to find the answers. In our lab, we have a number of different studies right now looking at how cannabis affects our minds, our behaviour and our health. One objective of our work is to find ways to reduce the risk of harm from cannabis use, especially in vulnerable populations such as people with psychotic disorders, using harm reduction and technology-based interventions.(4, 5) The more we learn about how cannabis links to psychosis, the better we can design ways to prevent the risk of harm, and the more we can empower people who chose to use cannabis to take control of their use and their health.