An investigation by the U.S. Government Accountability Office (GAO) identified several factors that have contributed to the increase in methadone-associated overdose deaths: 1) the drug's growing use for pain management has increased its availability to patients; 2) the lack of knowledge about the drug by practitioners and patients; and 3) abuse of diverted methadone by substance abusers. This report by the U.S. GAO to Congressional Requesters examines the regulation of methadone for pain management and opioid addiction, the factors contributing to an increase in methadone-associated overdose deaths, and the steps taken by government to prevent such deaths. Information for this review were obtained from interviews with Federal, State, and local officials, and reports from five States that had shown the largest increase in methadone-associated overdose deaths between 1999 and 2004. The investigation found that while lack of knowledge and abuse of diverted methadone have both contributed to an increase in overdose deaths, the circumstances under which the deaths have occurred have varied from State to State. Efforts by local, State, and Federal officials to combat this problem include implementing education, safety, and monitoring programs. Appendixes