Linking substance use with symptoms of subclinical psychosis in a community cohort over 30 years

Aims The aim of the study was to examine the temporal associations between substance use and subclinical psychosis symptoms. Design Data from a prospective community study sampled within a single cohort over 30 years (19782008) were analysed with discrete-time hazard models. Setting General population-based sample. Participants At initial sampling in 1978 males (n = 292) were 19 and females (n = 299) were 20 years old. Measurements Two psychosis syndromes representing schizotypal signs and schizophrenia nuclear symptoms and various substance use variables including cannabis, alcohol, tobacco and multiple-drug use (i.e. cannabis combined with other drugs). Findings In bivariate analyses, schizotypal signs were predominantly associated with regular cannabis use in adolescence (OR = 2.29, 95% CI 1.323.97). Schizophrenia nuclear symptoms were mainly related to alcohol (OR = 1.84, 95% CI 1.003.38) and multiple-drug use (OR = 2.35, 95% CI 1.384.02) during adolescence. Multivariate analyses showed that, in particular, regular cannabis use during adolescence was associated with the occurrence of subsequent schizotypal symptoms over a 30-year period (OR = 2.60, 95% CI; 1.594.23), whereas multiple-drug use in adolescence was associated predominantly with schizophrenia nuclear symptoms (OR = 1.75, 95% CI 1.013.03). Alcohol misuse was only slightly associated with the onset of such symptoms. Conclusions A significant portion of the occurrence of subclinical psychosis symptoms in adulthood can be attributed to excessive cannabis and multiple-drug use during adolescence. This is in line with the hypothesis that long-term sensitization of dopaminergic brain receptors plays a role in developing psychotic symptoms.