Purpose: To test the hypothesis that recent onset psychotic patients who use cannabis will have psychotic symptoms that are more severe and more persistent than those who do not use cannabis.
Subjects and methods: We carried out a 4-year follow-up study of a cohort of 119 patients with recent onset of psychosis. The patients were divided into four groups according to duration of cannabis use, taking index admission and follow-up as reference points.
Results: Those subjects who persisted in the use of cannabis had more positive (but not negative) symptoms and a more continuous illness at follow-up.
Limitations: The main limitations of the study were: the relatively small sample size, and that the excess of male subjects and the presence of cannabis induced psychosis could have a confusing impact on the interpretation of the results.
Conclusion: It is possible that psychotic patients who use cannabis are at a greater risk of a more continuous illness with more positive symptoms than those who do not.