Study identifies overdose risks in people facing severe co-occurring disorders

People with concurrent substance use and mental disorders (CD) experience a disproportionately higher risk of overdose compared to people with substance use disorder alone. However, predictors among individuals with severe concurrent disorders (SCD) in tertiary care settings remain poorly characterized. We aimed to identify factors associated with frequent non-fatal overdose using statistical learning methods. Data were obtained from the Reducing Overdose and Relapse: Concurrent Attention to Neuropsychiatric Ailments and Drug Addiction (ROAR CANADA) longitudinal cohort of individuals with SCD treated at three tertiary centres in British Columbia (N = 326). Frequent overdose (FO) was defined as more than the median number of lifetime self-reported overdoses (>2). Candidate variables included sociodemographic characteristics, substance use patterns, impulsivity, and trauma history. Elastic Net regularized regression with bootstrap stability selection identified key predictors. Stability-selected variables were entered into a principal component logistic regression model to assess predictive performance. Recent heroin or fentanyl use was the most stable predictor of FO (100% selection), followed by Hepatitis C diagnosis (98%), being single (98%), recent crack cocaine use (95%), history of sexual abuse (88%), and history of physical abuse (87%). Being unhoused, prior hospitalization, and life-threatening illness were also associated with increased risk. Variables inversely associated with FO included recent cannabis use (94%), white ethnicity (87%), and perceived access to instrumental support (84%). Chi-square analyses showed significant associations between FO and recent heroin or fentanyl use (OR 6.99; 95% CI 4.29-11.38), Hepatitis C diagnosis (OR 4.02; 95% CI 2.12-7.64), recent crack cocaine use (OR 2.36; 95% CI 1.49-3.75), and history of physical trauma (OR 2.06; 95% CI 1.28-3.31). The model demonstrated moderate discrimination (area under the curve (AUC) = 0.78; sensitivity 66.2%; specificity 77.5%). To address the prolonged overdose crisis, findings suggest that integrated treatment of patients' polysubstance use, comorbidities, and social support is important for risk prevention. Future studies should involve validation in a larger, demographically diverse, sample.