Substance use and sociodemographic background as risk factors for lifetime psychotic experiences in a non-clinical sample.

INTRODUCTION: Psychotic experiences (PE) are relatively common in the general population. PE is associated with mental health impairment and may be predictive of clinical psychosis. Substance use predicts PE, but the association is insufficiently understood, particularly the role of illicit substances. The purpose of this study was to describe PE (visual and auditory hallucinations and delusions of reference and persecution) in a population characterized by high levels of substance use and to investigate substance use and sociodemographic background characteristics as risk factors for PE.

METHODS: We used data from the Norwegian Offender Mental Health and Addiction Study (NorMA), a cross-sectional survey of 1499 individuals from Norwegian prisons. The outcome was one, two, three or four types of PE during the lifetime. The association between different variables and PE was investigated using multinomial logistic regression with three outcome categories: 0 PE, 1-2 PE and 3-4 PE.

RESULTS: The prevalence of lifetime PE was 53.7%. Several substances were strongly associated with PE: For cannabis, the adjusted relative risk ratio (RRR) of 1-2 PE was 2.78 (95% CI 1.89-4.10) and of 3-4 PE it was 4.36 (2.58-7.36). For amphetamine, the RRR of 1-2 PE was 3.26 (2.11-5.05) and of 3-4 PE it was 5.93 (3.72-9.46). For all variables, the association to PE was stronger with more types of PE.

CONCLUSIONS: High levels of alcohol use, and lifetime use of cannabis, amphetamine and heroin were associated with PE. These effects were robust even when the substance use variables were adjusted against each other. This research received no specific grant from any funding agency, commercial or not-for-profit sectors.