Associations Between Pain Severity and Opioid Agonist Treatment Among People With Drug Injection Experience in Australia

ABSTRACT Introduction Pain is highly prevalent among people with opioid use disorder (OUD), yet it is often undertreated. Whether opioid agonist treatment (OAT) improves pain outcomes is unknown among this target population. This research aimed to explore associations between pain severity and current OAT status in a longitudinal cohort of people who inject drugs. Methods Data were drawn from the Melbourne Injecting Drug User Cohort Study (SuperMIX), comprising individuals with a drug injection history recruited from areas across Greater Melbourne and Geelong, Australia, between 2008 and 2024. Eligible participants were adults who reported ever being in OAT for at least one time point. Participants were classified into four groups based on their self‐reported pain level (from none to severe). Multilevel ordinal logistic regression with a participant‐level random intercept examined the association between pain severity and current OAT status, comparing current OAT (methadone or buprenorphine) with no current OAT as the reference category. Current OAT status was treated as a time‐varying exposure, with methadone and buprenorphine examined separately in sensitivity analyses. Models were adjusted for demographic and clinical characteristics and substance use history. Results A total of 1328 participants were eligible for inclusion. At baseline, most were male (67.7%), on government income support (81.9%), and had pain at any level in the past 4 weeks (66.0%), with a mean age of 36.7 (SD 10.6) years. No association between pain severity and current OAT status was observed, while several other factors associated with higher pain severity were identified, such as older age, poorer overall health and the use of other opioids. Discussion and Conclusions While OAT status was not associated with pain severity in this study, several other factors associated with higher pain severity were identified. These findings highlight the multifactorial nature of pain in this population and the importance of considering broader physical and emotional health when managing pain.