Medication transitions and predictors of illicit substance use during opioid agonist treatment: a three-year follow-up study

Abstract

Abstract Background For opioid use disorder (OUD), pharmacological therapy using methadone or buprenorphine, plus psychosocial support, is the most effective opioid agonist treatment (OAT). Long-acting injectable buprenorphine (LAIB) is the newest buprenorphine formulation. This study evaluated LAIB within a naturalistic clinical setting, compared with standard OAT (sublingual buprenorphine and methadone). Methods This observational study included patients from an OAT outpatient clinic in Agder County, Norway. Data were extracted from hospital medical records in May 2022. The cohort was followed up in February 2025. Medication-group transitions and outcomes were assessed by examining switching, discontinuation, mortality, and illicit substance use over three years. Results The study included 424 patients. The LAIB group was significantly younger than the standard OAT groups. During the study period, 13.2% of patients switched medications, increasing the LAIB group from 17% to 22%. Comparable proportions of patients experienced negative outcomes: 10% discontinued treatment, and 4% died. At follow‑up, illicit substance-use problems were less frequent in the sublingual buprenorphine group than the other groups, a finding that appears to have been influenced by differential attrition. Baseline substance use was the strongest predictor of illicit substance use at follow‑up. Conclusions The LAIB group slightly increased during the study period. Transitions between medication groups appeared to yield better substance-use outcomes at follow-up in the sublingual buprenorphine group, compared to in other groups. Baseline substance use was the strongest predictor of illicit use at follow‑up, suggesting that individual clinical characteristics may contribute more to outcomes than the specific medication pathway. Trial registration Clinical trial: number not applicable.