Association between comorbid chronic pain or prior hospitalization for mental illness and substance use treatment among a cohort at high risk of opioid overdose

Introduction: Chronic pain and serious mental illness increase risk of opioid use, and opioid use can exacerbate both conditions. Substance use disorder (SUD) treatment can be lifesaving, but chronic pain and serious mental illness may make recovery challenging. We evaluated the association between current chronic pain and prior hospitalization for mental illness and 90-day SUD treatment engagement, among emergency department (ED) patients at high risk of opioid overdose. Methods: We conducted a cohort analysis of 648 ED patients enrolled in a randomized controlled trial in Rhode Island. We linked baseline study data on chronic pain and prior hospitalization for mental illness to statewide administrative data on state-licensed treatment programs (including methadone) and buprenorphine treatment via prescription. We defined treatment engagement as initiation of a state-licensed treatment program, transfer between state-licensed programs/providers, or a buprenorphine prescription (re-)fill. We used modified Poisson models to estimate the association between each baseline comorbidity and treatment engagement within 90 days following the ED visit, adjusted for a priori potential confounders. In an exploratory analysis, models were stratified by baseline treatment status. Results: The mean age of participants was 37 years; 439 (68 %) were male, and 446 (69 %) had been recently unhoused. Overall, 278 participants (43 %) engaged in treatment within 90 days of the ED visit. Participants with prior hospitalization for mental illness were more likely to engage in treatment than those without (adjusted risk ratio [ARR] = 1.24, 95 % confidence interval [CI] = 1.01-1.53), although this association was only among those already accessing treatment at baseline (ARR = 1.58, 95 % CI = 1.10-2.27). Chronic pain was not associated with 90-day treatment engagement overall (ARR = 1.12, 95 % CI = 0.91-1.38) or within baseline treatment subgroups. Conclusions: Among ED patients at high risk of opioid overdose and accessing treatment at baseline, those with prior hospitalization for mental illness (but not chronic pain) were more likely to engage in treatment following the ED visit, which may reflect disproportionate initiation of additional treatment programs, transfer between programs/providers, or ongoing buprenorphine treatment. Touchpoints within the medical system should be leveraged to ensure that everyone, including those with serious mental illness, can access high-quality SUD treatment at the desired intensity level.