OBJECTIVES: Many chronic users of immediate-release opioids (IROs) initiating treatment with extended-release opioids (EROs) are steered towards generic options, even if switching molecules is required. Switching may introduce uncertainty for patients regarding dosing, titration and efficacy. This study assessed treatment patterns among patients chronically-treated with IR oxycodone who initiate ERO treatment, and describes differences between patients initiating treatment on the same molecule and those who switch molecules. METHODS: Commercially-insured patients aged <65 were selected from de-identified OptumHealth Reporting and Insights claims data, 2011-2014. Chronic IR oxycodone users were defined as patients with ≥2 continuous prescriptions and ≥60 days supply leading up to initiation of ERO treatment (index). Patients were excluded if they had claims for EROs during a 6-month baseline period or possible opioid replacement therapy (methadone/buprenorphine) during the 6-month follow-up period, and were required to be continuous users of opioids throughout follow-up. The sample was stratified based on whether ER therapy was initiated on the same molecule (ER oxycodone) or different molecules. Treatment patterns and pill count were assessed for both cohorts. RESULTS: During baseline,