Psychological trauma and overdose risk : investigating the links between childhood trauma and drug-related harms in adulthood

Background: Childhood trauma is common among people who use drugs (PWUD), and is associated with increased overdose risk. Studies examining this relationship in the era of the unregulated drug supply dominated by synthetic opioids like fentanyl are lacking. In addition, emerging evidence suggests trauma experiences and impacts vary by sex. Thus, I reviewed the literature and examined the longitudinal relationships between childhood trauma and non-fatal overdose by sex before and after the 2016 fentanyl-driven overdose crisis. Methods: I conducted a systematic review with narrative synthesis (Study 1) to identify factors linking psychological trauma, and more specifically childhood trauma, to drug overdose. In Study 2, I used pooled data from three community-recruited cohorts of PWUD in Vancouver and applied adjusted generalized estimating equations (GEE) to estimate the longitudinal relationship between childhood trauma and non-fatal overdose. Results: In Study 1, I reviewed 35 eligible articles that included 5,469,238 participants. In these studies, individuals with additional vulnerabilities had higher overdose risk, with mental health conditions, substance use behaviours, and access to health and social services identified as relevant factors. Study 2 included 3,221 participants. The fentanyl-dominant period was associated with increased risk of overdose (Adjusted Odds Ratio [AOR]=1.42, 95% confidence interval [CI]: 1.01–2.00). Emotional abuse (AOR=1.28, 95% CI: 1.12–1.45), emotional neglect (AOR=1.14, 95% CI: 1.00–1.30), physical abuse (AOR=1.30, 95% CI: 1.14–1.48), and sexual abuse (AOR=1.27, 95% CI: 1.10–1.45) were each associated with a higher risk of non-fatal overdose, with significant associations for men and women at similar rates. This association did not change in the fentanyl era despite increased overdose risk. Conclusions: I found that childhood trauma is associated with increased overdose risk at comparable rates in sex-stratified analyses, and often co-occurs with mental health issues, higher-risk substance use behaviours, and social-structural vulnerabilities. Although the odds of non-fatal overdose have more than doubled in the era of fentanyl, I did not find evidence of a change in the relationship between experiencing childhood trauma and overdose risk. Public health strategies should prioritize trauma-informed services for PWUD. Effective overdose prevention strategies must address both individual trauma and systemic inequities.