Treatment service provision for problem drug users in the Republic of Ireland until the mid-1980s was centralized, specialist and ideologically tending towards abstinence models of intervention. However, in the context of continuing heroin use and its accompanying public health risks, all these features of policy and service provision changed gradually over the next decade. This paper looks in detail at the evolution of the methadone protocol of 1998, which institutionalized and regulated methadone prescribing by general medical practitioners in Ireland. It discusses the main stakeholders, lists the sequence of events and looks analytically at the policy process. It is concluded that the introduction of the methadone protocol was a pragmatic success, albeit one which departed significantly from conventional beliefs about policy transparency in democratic societies.