Cannabis use and age of admission to a psychiatric unit for first episode of psychosis

Abstract

Background: Research has implicated that cannabis has an aetiological role in psychosis, and thus one can hypothesize that the onset of psychosis in patients who use cannabis occurs earlier in life than those who do not use cannabis Aim: The aim of this study is to assess the possible influence of cannabis on the age of onset of patients with first episode of psychotic illness admitted to a psychiatric unit in the Maltese Islands. Methods and sample: This study is a one year prospective study that includes all ICD-10 first episode psychosis patients admitted to a psychiatric hospital in the Maltese Islands. Age of admission to hospital was used as proxy for age of onset of psychosis. Use of cannabis prior to admission was ascertained by urine testing. Results: The mean age of admission to hospital for first onset psychosis for patients whose urine was positive to cannabis was 24.63 years old, and for patients whose urine was negative to cannabis was 44.63 years old. This difference was statistically significant, using the Mann Whitney-U test p=0.001. Conclusion: The results indicate that cannabis use can precipitate an earlier onset of psychotic illness. Considering the widespread use of cannabis, and that earlier age of onset of psychosis is associated with worse prognosis, this issue is of public health concern.