4. Substance-induced psychosis and later schizophrenia or bipolar disorder: transition rates and the role of infections

The aim was to investigate transition to schizophrenia spectrum or bipolar disorders following different types of substance induced psychosis (SIP), and the impact of the number of SIP episodes and infections on such transitions.

Based on the Norwegian Patient Registry, we included all subjects with a SIP diagnosis from 2010 to 2015 (n=3,187). The Kaplan-Meier method was used to estimate cumulative transition rates from SIP to schizophrenia spectrum disorder or bipolar disorder. Cox proportional hazard regression was used to estimate hazard ratios (HRs) for transition to schizophrenia spectrum or bipolar disorders associated with gender, different age groups, types of SIP and number of SIP emergency admissions, and timing, type, and number of infections. Conflict of interest: none.

The six-year cumulative transition rate from SIP to schizophrenia spectrum disorder was 27.6% (95% CI 25.6-29.7), and the risk of transition was higher in younger men, in those with repeated SIP emergency admissions, and in those with cannabis-induced psychosis and SIP induced by multiple substances. The cumulative transition rate from SIP to bipolar disorder was 4.5% (95% CI 3.6-5.5), and women had higher risk of transition. Infections were not associated with increased risk of transition to the two disorders.

Transition rates from SIP were six times as high to schizophrenia spectrum disorder as to bipolar disorder. Type of SIP, number of SIP admissions, but not infections affected the risk of the transition.