The efficiency of an antiretroviral drug Efavirenz (EFV) was assessed for HIV suffers on a methadone programme. Efavirenz is preferred to other antiretroviral therapies in that is a once-daily preparation taken wither in the morning at night to reduce neurological side effects. A cohort group of 46 received EFV as part of a combination antiretroviral therapy. Two thirds of the group were antiretroviral-experienced, the remainder were new to the treatment. Fifteen patients experienced neurological symptoms such as dizziness and altered sleeping patterns in the first five days of treatment, with these symptoms resolved within 5-7 days. These symptoms are consistent with methadone withdrawal and may result in problems if the patient returns to illicit drugs to counteract these symptoms or may discontinue their medication once a relationship between the new medication and symptoms are made. Overall EFV proved its efficiency and ability to translate into good patient outcome in clinical practice. The paper concludes that when EFV is used for IDUs the early neurological symptoms must not be confused for withdrawal for reasons stated earlier.