Mortality Rates and cause-specific mortality in Patients with Substance-Induced Psychosis

BACKGROUND: SIP is characterized as a brief psychotic syndrome that occurs during or following the use of psychoactive substances. Previous research into the prognosis of SIP has mostly centred on the potential conversion from SIP to schizophrenia (SCH). Furthermore, the mortality studies among individuals with psychosis and substance use have primarily concentrated on patients diagnosed with SCH, or they have compared patients with SIP to those with SCH. 
OBJECTIVE: This study aims to examine all-cause and cause-specific mortality rates among individuals diagnosed with substance-induced psychosis (SIP) regardless of whether they convert to SCH or not. METHODS: This cohort study included 10,361 working-aged (16-65) patients with a first episode of SIP between 2006-2020 identified from Swedish nationwide registers of inpatient and specialized outpatient care, sickness absence and disability pension. For the 5-year follow-up analysis, we included 6557 individuals with SIP diagnosed between 2006-2015. Kaplan-Meier survival curves were generated to examine various causes of death including all causes, natural causes, external causes, suicides, accidental deaths and deaths by poisoning. We also conducted separate analyses for subgroups, including those with alcohol-induced psychosis, cannabis-induced psychosis, (meth)amphetamine-induced psychosis, and mixed substance use -induced psychosis. To assess mortality outcomes, we computed Standardized Mortality Ratios (SMR) for all causes of death, and separately for natural and external causes against Swedish general population. 
RESULTS:  During the 5-year follow-up period, the overall mortality rate was 11%, showing variations among different subgroups of patients with SIP (ranging from 5% for those with cannabis-induced psychosis to 15% for those with alcohol-induced psychosis). 64% of deaths resulted from external causes. 
Kaplan-Meier survival analysis revealed distinct mortality patterns among different SIP groups. Patients with alcohol-induced psychosis were more likely to die from natural causes, while patients with amphetamine-induced and mixed substance -induced psychosis had higher incidence of deaths by poisoning or accidents. Patients with cannabis-induced psychosis had a lower overall mortality rate but were more susceptible to suicide (accounting for 40% of all deaths within this group). 
Overall, the SMR for any SIP was 9.67 (95%CI 9.15-10.19). Among specific SIP groups, cannabis-induced psychosis had the lowest SMR of 4.46 (3.60-5.31) while alcohol-induced SIP had the highest 14.27 (12.94-15.60). When considering external causes, the SMR was 27.12 (CI 25.26-29) and for natural causes it was 4.91 (CI 4.50-5.33). 
CONCLUSION: Patients with SIP face significantly elevated mortality rates. Further research is needed to identify interventions to improve their prognosis.