Predictors of conversion to psychosis and mortality in first-episode substance-induced psychosis: a nationwide register-based study in South Korea

Objective Substance-induced psychosis (SIP) is associated with a substantial risk of progression to schizophrenia spectrum disorders (SSD), bipolar disorder (BD), and premature mortality. However, evidence from Asia, particularly South Korea (SK), remains limited. Methods We conducted a retrospective, nationwide, population-based cohort study using the Korean National Health Insurance Claims Database (2003–2012) with follow-up through 2017. Individuals aged 18–60 years with a first episode of SIP (FE-SIP) were identified after excluding those with ICD-10 codes for substance use disorders (SUD; F10-F19) and other neuropsychiatric disorders (F00–F09, F20–F29, F30.x, F31.x, F32.3, or F33.3) during a 1-year washout. Incidence was estimated using national census data. Conversion to first-episode psychosis (FEP-SSD or -BD) was examined using cumulative incidence function and Cox regression. Standardized mortality ratios (SMRs) were calculated against the general population and a SUD reference cohort. Results A total of 2244 individuals with FE-SIP were identified. The average annual incidence proportion was 0.7 per 100,000, peaking in 2005. Over a median follow-up of 9.3 years, 655 individuals (33.2%) converted to FEP, with cumulative conversion rates of 23.3% at 5 years, and 28.8% at 10 years. Younger age, female sex, disability, longer initial hospitalization, and use of other stimulants were significant predictors of conversion. All-cause mortality was markedly elevated (SMR 33.3 vs general population; SMR 1.49 vs SUD cohort), particularly among young men. Conclusions Despite a low incidence of FE-SIP in SK, the risks of conversion to FE-SSD/FE-BD and premature mortality are substantial. Findings underscore the need for early detection, psychoeducation, and integrated care tailored to high-risk individuals, especially within the first two years after diagnosis.