• Cannabis;
  • psychotic disorders;
  • Catechol-o-methyltransferase gene

Objective:  A functional polymorphism in the catechol-o-methyltransferase gene (COMT Val158Met) 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 Val158Met 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 Val158Met genotype moderates the association between cannabis and psychotic phenomena in the flow of daily life.