3. Relapse rate of substance-induced psychosis and associated risk factors. A nationwide registerlinkage study

Aim of this study was to investigate the risk of substance-induced psychosis (SIP) relapse and determine associating clinical and socioeconomic risk factors.

Persons with first-time SIP during 2006-2016 at age of 16-65 years in Sweden were identified from inpatient and specialized outpatient care registers. Register-based data on hospital care, specialized outpatient care, sickness absence and disability pensions were collected from the nationwide registers. Outcome was SIP relapse, defined as hospitalization due to the same or different type of SIP than the first SIP during two-year-follow-up. People were censored to death, emigration and diagnosis of psychotic illness. Comorbidities and socioeconomic factors associated with relapse were studied by adjusted Cox models. Conflict of interest: none.

Of the study population (n=7320), 20.0% (N=1463) had a SIP relapse during two years follow-up (median time 126 days, IQR 56-321) and 83.3% had the same type of SIP than their first SIP. Relapse was most common for those whose first SIP was induced by cannabis (25.7%), followed by multi-substance use (23.8%) and stimulant (19.7%). Factors associated with SIP relapse were previous substance use disorder (HR 1.37, 95%CI 1.20-1.56), younger age (16-29 years, 1.29, 1.05- 1.58, versus 50-65), being born abroad (1.23, 1.07-1.41), ADHD (1.21, 1.05-1.39), having had 1-90 days sick leave during previous year (1.19, 1.01-1.44), and cannabis (2.42, 1.98-2.96), stimulant (1.49, 1.23-1.81) or multi-substance (1.81, 1.52-2.15) induced psychosis compared with alcohol induced psychosis.