Using Claims Data to Examine Hospital Readmission Risk in Patients With Schizophrenia and Comorbid Marijuana Use Disorders

Objective: Few epidemiologic studies have examined marijuana use disorder and repeated hospitalizations related to schizophrenia. To address this gap, this study examines time to readmission by indicators for recent marijuana use disorder in the presence of alcohol use disorder (AUD) and other drug use disorder. Method: Our sample consisted of 4,349 patients with a primary diagnosis of schizophrenia spectrum disorder (SSD) in 2005 in individually linked California Health Care Cost and Utilization Project (CA HCUP) data. Readmissions were assessed from 2005 to 2011. Predictors for readmission were examined using a stratified, recurrent-event, Cox proportional hazards model. Sensitivity analyses were conducted on patients readmitted in 2010 or 2011. Results: We found that having marijuana use disorder or AUD alone within 90 days of initial hospitalization was associated with longer times until first readmission. A lower risk of readmission for those with recent marijuana use disorder persisted through the fifth readmission (hazard ratio [BR] = 0.92, 95% CI [0.85, 0.99]) but was not significant in the sixth or greater readmission nor in sensitivity analyses. SSD patients with recent other drug use disorder had an increased risk for a second to fifth readmission (HR = 1.13, 95% CI [1.06, 1.20]). Those with recent AUD had an increased risk for a sixth or greater readmission (HR = 1.15, 95% CI [1.07, 1.23]). Both of these results remained significant in the sensitivity analysis. Conclusions: We found that AUD and other drug use disorder increase readmission risk in patients with SSD after a first hospitalization, whereas marijuana use disorder does not appear to be associated with an increased risk for readmission.