Narcotics and other prescription drugs play a significant and legitimate role in medical practice. The illicit use of prescribed medicines, however, remains a major problem. This paper examines the effectiveness of two drug diversion control programs, multiple copy prescriptions programs (MCPP) and electronic data transfer (EDT) systems, and their impact on medical practice. Current evidence demonstrates that these programs decrease prescription drug use, with much of the decrease due to declines in inappropriate use. MCPPs appear more effective than EDT in preventing diversion. More research is needed. however, to assess their effects on medical practice, particularly patient quality of care.