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 (1978-2008) 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 1.32-3.97). Schizophrenia nuclear symptoms were mainly related to alcohol (OR = 1.84, 95% CI 1.00-3.38) and multiple-drug use (OR = 2.35, 95% CI 1.38-4.02) 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; 1.59-4.23), whereas multiple-drug use in adolescence was associated predominantly with schizophrenia nuclear symptoms (OR = 1.75, 95% CI 1.01-3.03). 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.