Relapse in substance‐induced psychosis and associated risk factors. A Nationwide register‐linkage study from Sweden

Abstract

<p><strong>Background and aims: </strong>Substance-induced psychoses (SIP) have the potential to relapse and convert into schizophrenia-spectrum disorders. However, risk factors associated with SIP relapse remain unknown. The aim of this study was to measure the incidence and risk of SIP relapse and associating risk factors.</p><p><strong>Design, setting and participants: </strong>Population based register study that identified people with first-time SIP between 2006 and 2016 (n = 7320) from Swedish nation-wide registers to examine incidence of relapse and associated risk factors during 2-year follow-up. Participants were censored to death, emigration and the diagnosis of other psychotic illness. Risk factors associated with relapse were studied using multivariable Cox models.</p><p><strong>Measurements: </strong>SIP was measured via related diagnostic codes (ICD-10: F1x.5) collected from the National Patient Register (NPR). SIP relapse was measured as hospitalization due to SIP during 2-year follow-up also collected from the NPR. Potential risk factors included demographic characteristics, psychiatric comorbidities, sickness absence and disability pension collected from nationwide registers.</p><p><strong>Findings: </strong>Of the study population (n = 7320), 20.0% (n = 1463) had a SIP relapse during the follow-up (median time 126 days, interquartile range 56-321) and 83.3% had the same type of SIP as 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 (meth)amphetamine (19.7%). Factors associated with SIP relapse were previous substance use disorder [hazard ratio (HR) = 1.37, 95% confidence interval (CI) = 1.20-1.56], younger age (16-29 years, HR = 1.29, 95% CI = 1.05-1.58, versus 50-65), being born abroad (HR = 1.23, 95% CI = 1.07-1.41), attention deficit hyperactivity disorder (HR = 1.21, 95% CI = 1.05-1.39), having had 1-90 days sick leave during the previous year (HR = 1.19, 95% CI = 1.01-1.44), and cannabis- (HR = 2.42, 95% CI = 1.98-2.96), (meth)amphetamine- (HR = 1.49, 95% CI = 1.23-1.81) or multi-substance- (HR = 1.81, 95% CI = 1.52-2.15) induced psychosis compared with alcohol-induced psychosis.</p><p><strong>Conclusions: </strong>In Sweden, 20% of people with substance-induced psychosis between 2006 and 2016 had a relapse within 2 years follow-up. Cannabis-induced psychosis had the shortest time lapse between episodes. Risk factors for relapse included attention deficit hyperactivity disorder, substance-use disorder, younger age, previous sickness absence and being born outside Sweden.</p>