Abstract
Aims: The aim of the study was to examine the temporal associations between substance use and sub-clinical psychosis symptoms. Design: Data from a prospective community study sampled within a single cohort over 30 years (1978-2008) were analyzed 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, alcohol (OR = 1.48, 95%-CI = 1.05-2.09), tobacco (OR = 1.76, 95%-CI = 1.09-2.82), and cannabis (OR = 2.29, 95%-CI = 1.32-3.97) were associated with schizotypal signs. Schizophrenia nuclear symptoms were related to alcohol (OR = 1.84, 95%-CI = 1.00-3.38), cannabis (OR = 1.59, 95%-CI = 1.03-2.46), and multiple-drug use (OR = 2.35, 95%-CI = 1.38-4.02). 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 predominantly associated 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.