OBJECTIVES

: Substance use disorders (SUDs) can co-occur with schizophrenia, but little is known about their associations with illness severity. We analyzed electronic health record (EHR) data to determine the prevalence of comorbid SUDs in people with schizophrenia and their associations with illness severity.

METHODS

: Data from the MindLinc EHR dataset were analyzed using NeuroBlu. A cohort of adults with a diagnosis of schizophrenia (ICD-10 F20*) was assembled. The exposure was defined as the presence of a comorbid SUD. The outcome measure was severe illness defined as a Clinical Global Impression Severity (CGI-S) score of 5 or greater documented within 30 days of schizophrenia diagnosis. Age, gender, race, marital status, employment status and year of schizophrenia diagnosis were included as covariates in a multivariable logistic regression analysis.

RESULTS

: A total of 13,634 adults with schizophrenia were included (F10* alcohol: 8.8%; F11* opioid: 2.1%; F12* cannabis: 7.2%; F14* cocaine: 3.7%; F15* stimulant: 1.2%; F17* nicotine: 1.8%) of which 12,676 (93.0%) had a documented CGI-S score. Comorbid cannabis use disorder (F12*) was associated with greater illness severity (mean CGI-S: 4.89; odds ratio: 1.68, 95% CI 1.32 to 2.14, p<0.001) and comorbid opioid use disorder (F11*) was associated with lower illness severity (mean CGI-S: 4.23; OR: 0.56, 0.37 to 0.83, p=0.004) compared to patients without comorbid SUD (mean CGI-S: 4.25).

CONCLUSIONS

: Comorbid SUDs vary in their associations with illness severity. Comorbid cannabis use disorder is associated with greatest illness severity consistent with its potential etiological role in schizophrenia. Conversely, opioid use disorder is associated with least illness severity. This could reflect differences in the clinical characteristics and functioning of individuals who use opioids compared to those who use other substances. Further analyses of healthcare service utilization could address the degree to which different comorbid SUDs are associated with worse clinical outcomes.