COMT Val 158 Met moderation of cannabis‐induced psychosis: a momentary assessment study of ‘switching on’ hallucinations in the flow of daily life

Objective:  A functional polymorphism in the catechol‐ o ‐methyltransferase gene (COMT Val 158 Met) may moderate the psychosis‐inducing effects of cannabis. In order to extend this finding to dynamic effects in the flow of daily life, a momentary assessment study of psychotic symptoms in response to cannabis use was conducted. Method:  The experience sampling technique was used to collect data on cannabis use and occurrence of symptoms in daily life in patients with a psychotic disorder ( n  = 31) and healthy controls ( n  = 25). Results:  Carriers of the COMT Val 158 Met Val allele, but not subjects with the Met/Met genotype, showed an increase in hallucinations after cannabis exposure, conditional on prior evidence of psychometric psychosis liability. Conclusion:  The findings confirm that in people with psychometric evidence of psychosis liability, COMT Val 158 Met genotype moderates the association between cannabis and psychotic phenomena in the flow of daily life.