New opioid use and risk of opioid-related adverse events among adults with intellectual and developmental disabilities in Ontario, Canada

BACKGROUND: Individuals with intellectual and developmental disability (IDD) can have a high prevalence of pain, which can be managed with prescription opioids. However, the prevalence of substance use disorder is also high in this population, raising concern about opioid-related adverse events. AIMS: To assess the risk of opioid-related adverse events following opioid initiation among adults with versus without IDD. METHOD: We conducted a population-based, propensity score matched cohort study on all adults starting prescription opioid therapy in Ontario, Canada, between January 2013 and December 2018. The outcomes of interest were opioid toxicity, new opioid use disorder (OUD) diagnosis and dose escalation (≥90 mg morphine or equivalent) in the year after opioid initiation. We used Cox proportional hazards models to assess the association between IDD diagnosis and each outcome. RESULTS: The hazards of opioid toxicity and OUD were significantly higher in those with IDD compared with those without IDD in unmatched analyses (opioid toxicity hazard ratio 3.19, 95% CI 2.81–5.18; OUD hazard ratio 2.36, 95% CI 2.10–2.65), whereas the hazard of dose escalation was significantly lower (hazard ratio 0.76, 95% CI 0.66–0.88). Findings were no longer significant in propensity score matched models for opioid toxicity and dose escalation, whereas the hazard of OUD diagnosis was attenuated substantially in those with IDD (hazard ratio 0.79, 95% CI 0.68–0.91). CONCLUSIONS: IDD diagnosis is not a driver of opioid-related harm. The increased risk we observed is likely driven by various risk factors often present in this population.