Cannabis use has been associated with psychosis from the very early years of prohibition. This study found little evidence to support that association and developed this study to help provide better evidence. It was published in the journal Psychiatry and Clinical Neurosciences in April 2023.
The study focused on examining people at clinical high risk of psychosis. They also wanted to determine if cannabis use was associated with the persistence of psychotic symptoms.
Included were 334 patients from Europe, Australia, and South America who were clinically determined to be at high risk for psychosis and 67 healthy control participants. 95% of the participants were between the ages of 16 and 35. For two years, the participants were assessed on the following metrics:
- Cannabis Use (using a modified version of the Cannabis Experience Questionnaire)
- Transition to psychosis and persistence of psychotic symptoms (using the Comprehensive Assessment of At-Risk Mental States criteria)
- Level of functioning at follow up (using the Global Assessment of Functioning disability scale)
"Clinical High-Risk (CHR) state is a clinical syndrome that typically occurs in adolescents and young adults". It means that there is a high likelihood of that person eventually developing a psychotic disorder. The average rate that CHR individuals become psychotic within two years is about 19%.
The bottom line is that they did not find an association between cannabis use and psychosis, even among those considered to be prone to developing psychosis.
16.2% of the clinical high-risk sample developed psychosis [vs. 19% in the general population]
Of those who did not become psychotic, 51.4% had persistent symptoms and 48.6% were in remission.
There was no significant association between any measure of cannabis use at baseline and either transition to psychosis, the persistence of symptoms, or functional outcome.
These findings contrast with epidemiological data that suggest that cannabis use increases the risk of psychotic disorder.
The abstract and full text article (in PDF form) is here at Wiley Online Library.