Injecting drug users (IDUs) represent a patient group where there are formidable challenges in HIV treatment. Difficulties in management arise not only from substance abuse but also because of high rates of social instability and psychiatric co-morbidities. Furthermore, many in this patient group have hepatitis C co-infection. These confounding factors negatively impact adherence to, and ultimately the efficacy of treatment and can affect physician perception when prescribing antiretrovirals. Concurrent methadone therapy further complicates HIV treatment because of its potential side effects and interactions with antiretrovirals. However, methadone maintenance therapy also represents an important opportunity to engage patients in consistent medical care and has been shown to improve adherence to antiretroviral treatment and thus viral suppression.