The hepatitis C virus (HCV) epidemic is a significant public health challenge in Australia. Current initiatives to expand access to HCV treatment focus on opiate substitution therapy (OST) settings where the prevalence of hepatitis C among clients is high. In Australia, the provision of OST for many clients is via large clinics, with an estimated median of 150 clients per service. Conceptually informed by the work of Michel Foucault, our analysis of the proposed integrated treatment model focuses on the critical but overlooked question of organisational culture and power operating within OST. We argue that the specific context of OST not merely reflects but actively participates in the political economy of social exclusion via which the socio-spatial segregation and stigmatisation of the service user as 'drug user' is enacted. This paper analyses data collected from two samples during 2008/9: OST clients living in New South Wales, Australia and a range of OST health professionals working in Australian settings. In total, 27 interviews were conducted with current OST clients; 19 by phone and 8 face-to-face. One focus group and 16 telephone interviews were conducted with OST health professionals. Our analysis of key themes emerging from the interview data suggests that the successful introduction of HCV treatment within the OST clinic is not a given. We are concerned that particular areas of tension, if not explicit contradiction, have been overlooked in current research and debates informing the proposed combination treatment model. We question the appropriateness of co-locating a notoriously arduous, exacting treatment (HCV) within the highly surveillant and regulatory environment of OST. While applauding the intention to improve access to HCV care and treatment for people who inject drugs we caution against a treatment model that risks further entrenching (socio-spatial) stigmatisation amongst those already experiencing significant marginalisation.