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Vol. 39, No. 4, 2006
Issue release date: June 2006
Psychopathology 2006;39:175–178

Cannabis-Induced Psychosis-Like Experiences Are Associated with High Schizotypy

Barkus E.J. · Stirling J. · Hopkins R.S. · Lewis S.
aNeuroscience and Psychiatry Unit, University of Manchester, and bDepartment of Psychology and Speech Pathology, Manchester Metropolitan University, Manchester, UK

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Objective: Recent studies have suggested that cannabis use is a risk factor for developing schizophrenia. We tested the hypothesis that cannabis use increases the likelihood of psychosis-like experiences in non-clinical participants who scored highly on a measure of schizotypy. Method: The psychological effects of cannabis were assessed in 137 healthy individuals (76% female, mean age 22 years) using a newly developed questionnaire concerned with subjective experiences of the drug: the Cannabis Experiences Questionnaire. The questionnaire has three subscales: Pleasurable Experiences, Psychosis-Like Experiences and After-Effects. Respondents also completed the brief Schizotypal Personality Questionnaire. Results: Cannabis use was reported by 72% of the sample. Use per se was not significantly related to schizotypy. However, high scoring schizotypes were more likely to report both psychosis-like experiences and unpleasant after-effects associated with cannabis use. The pleasurable effects of cannabis use were not related to schizotypy score. Conclusion: High scoring schizotypes who use cannabis are more likely to experience psychosis-like phenomena at the time of use, and unpleasant after-effects. Our results are consistent with the hypothesis that cannabis use is a risk factor for full psychosis in this group.

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