This paper reviews the use of methadone maintenance programmes and examines the rationale for their continuance. The paper outlines the account of methadone use from the 1964 trials of Dole and Nyswander. Methadone actually effectively transfers dependency form one drug to another and this difficulty is discussed. The paper looks at the benefits that methadone maintenance can bring about for users and society as a whole. Research has shown that the provision of methadone reduces heroin use and crime, significantly reduces mortality among opiate users, and reduces the rates of HIV infection and risky behaviour. methadone maintenance is unlikely to protect the substantial number of patients who continue to use heroin sporadically from hepatitis C. Research reviewed shows that maintenance does not prolong dependence any longer than would occur in the absence of treatment or in cases where the person enters some other form of treatment. Evidence points to high doses of methadone over longer rather than short periods of treatment. The review also highlights that the risks are greatest in the first two weeks of treatment, with an increased rate of overdose. After four decades of research, the review concludes that methadone maintenance is an effective treatment for opioid dependence, and that its widespread application throughout the world is a good example of an evidence-based intervention for the treatment of drug dependence.