Associations between opioid agonist therapy exposure and chronic pain characteristics among people who inject drugs

Background: Up to 50% of people who inject drugs (PWID) live with chronic pain (intermittent or continuous pain lasting >3 months). Opioid agonist therapy (OAT), commonly prescribed for opioid use disorders, may contribute to pain management among PWID. However, little is known about the relation between OAT exposure and certain chronic pain characteristics: pain intensity, interference, and management, among PWID. This study aimed to examine the association between OAT exposure and chronic pain characteristics (pain intensity, interference, and management), among PWID living with chronic pain.

Methods: A cross-sectional study was conducted among participants of the HEPCO cohort, a cohort study involving three-monthly interviews with active PWID in Montreal, Canada (first visit data, 02.2017-11.2022). Data was collected on sociodemographic factors, drug use, and drug-related harms, using the HEPCO questionnaire. A chronic pain questionnaire was also administered and included a modified version of the Brief Pain Inventory to characterize chronic pain intensity and interference, and questions related to pain management strategies (e.g. physician visit for pain, requesting pain medication, and use of pain medication and other drugs to manage pain). Among participants reporting chronic pain, we conducted univariable and multivariable regression analyses to examine the association between OAT exposure and chronic pain characteristics, adjusting for sociodemographic factors, substance use, and drug-related harms. 

Results: Data from 612 participants were included, 292 participants (48%) reported chronic pain (mean age= 45.7 years, 84% male), of which 115 (39%) were on OAT. In univariable analysis, using medication prescribed for other concerns to manage pain (OR=2.67, 95% CI:1.6-4.5), using alcohol or other drugs to manage pain (OR=0.43, 95% CI:0.3-0.6), and mild pain interference (OR=0.67, 95% CI:0.5-0.9) were associated with OAT exposure. Moderate and severe pain intensity and interference, and other pain management strategies (access to pain medication, extra medical use of pain medication, etc.) were not associated with OAT exposure.  After adjusting for covariates in the multivariable analysis, using medication prescribed for other concerns to manage pain (OR=2.18, 95% CI:1.3-4.3) was associated with OAT exposure. Pain intensity, interference, and other pain management strategies were not associated with OAT exposure.

Conclusions: Consistent with previous results, many PWID living with chronic pain report being on OAT. Results indicate that PWID on OAT are using medications for other concerns to manage their pain, and they are without increased access to and use of pain medications. This suggests that OAT services do not adequately discuss and meet the chronic pain needs of PWID, and do not help optimize pain management among PWID, calling for reassessing the integration of care in OAT.