Cannabis-induced psychosis-like experiences are associated with high schizotypy.
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.


METHODS
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.


CONCLUSIONS
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.
Barkus
E J
EJ
Neuroscience and Psychiatry Unit, University of Manchester, Manchester, UK. emma.j.barkus@manchester.ac.uk
Stirling
J
J
Hopkins
R S
RS
Lewis
S
S
D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000009:adverse effects / Q000523:psychology*; D010552:Personality Assessment; D011605:Psychoses, Substance-Induced / Q000209:etiology / Q000523:psychology*; D012307:Risk Factors; D012569:Schizotypal Personality Disorder / Q000209:etiology / Q000523:psychology*; D011795:Surveys and Questionnaires