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CAMH research reveals a link between cannabis use and psychosis

It has been long been known that cannabis users develop psychosis more often than non-users, but what is not fully clear is whether cannabis actually causes psychosis and, if so, who is most at risk. Researchers at CAMH have recently shown that while cannabis users had higher rates of psychotic experiences than non-users across the board, the difference was especially pronounced among those with high genetic predisposition to schizophrenia. 

Using data from a large-scale biomedical database containing participants’ in-depth genetic and health information, the researchers, led by Dr. Michael Wainberg, Scientist at the Krembil Centre for Neuroinformatics at CAMH, analyzed the relationship between genetics, cannabis use and psychotic experiences across more than 100,000 people.

Each person reported their frequency of past cannabis use, and whether they had ever had various types of psychotic experiences, such as auditory or visual hallucinations. The researchers also scored each person’s genetic risk for schizophrenia, by looking at which of their DNA mutations were more common among schizophrenia patients than among the general population.

These results are significant because they’re the first evidence we’ve seen that people genetically prone to psychosis might be disproportionately affected by cannabis. And because genetic risk scoring is still in its early days, the true influence of genetics on the cannabis-psychosis relationship may be even greater than what we found here.

Researchers found that people who used cannabis were more likely to have psychotic experiences, however, this increase was not uniform across the study group. Among the fifth of participants with the highest genetic risk scores for schizophrenia, it was 60 per cent, and among the fifth with the lowest scores, it was only 40 per cent. In other words, people genetically predisposed to schizophrenia were at disproportionately higher risk for psychotic experiences if they also had a history of cannabis use.

Notably, because much less is known about the genetics of schizophrenia in non-white populations, the study’s analysis was limited to self-reported white participants. This study, while limited in scope, is an important step forward in understanding how cannabis use and genetics may interact to influence psychosis risk. Researchers hope this research can lead to greater awareness of the connection between cannabis and psychosis and the potential risks of using this substance. This research offers a window into a future where genetics can help empower individuals to make more informed decisions about drug use.

This study is just one of many projects led by CAMH researchers who are exploring the unique risk factors for mental illness in young people. Since psychosis most often appears in people between the ages of 15 and 25, CAMH prioritizes the study of this age group to develop targeted ways to diagnose symptoms at the earliest stages. When psychosis is detected and treated early, young patients can potentially avoid a lifetime of disability and serious mental illness.

CAMH is home to the Slaight Family Centre for Youth in Transition, the first centre in Canada dedicated to understanding and treating severe mental illness, including addictions, in teens and young adults.