Aims To explore identity transformation among service users attending opiate substitution therapy (OST) clinics following the introduction of hepatitis C (HCV) care and treatment. Design An interview-based substudy of the Australian ETHOS (Enhancing Treatment for Hepatitis C in Opiate Substitution Settings) project. Setting Three OST clinics and one community health centre (operating a public OST) in New South Wales, Australia. Participants were interviewed at the recruitment sites. Participants The sample consisted of 57 OST service users concurrently living with HCV, 16 staff, including specialist HCV clinicians, and three peer-support workers, employed on the ETHOS project. Measurements Semi-structured interviews. Findings Service-user participants largely welcomed the introduction of HCV treatment as a practical, clinical intervention that also intimated a more comprehensive, holistic form of care. Negative stereotypes characteristic of OST settings-of limited, routinized clinical exchanges and minimal social-care interaction-were unsettled, opening up the possibility of new relations between staff and service users. The shift in the dynamic of the clinical encounter to address health in addition to dependence appeared to catalyse transformative possibilities not only for the therapeutic alliance but also for service-user understandings of self and identity. Conclusion Trial introduction of HCV care and treatment in selected Australian opiate substitution therapy (OST) clinics may have facilitated alternative, 'non-addict' identities to emerge from a clinical setting where the stigmatizing figure of 'the drug user' has traditionally prevailed.