In MCPPs, the prescriber writes a prescription of Schedule II drugs on a preprinted, serially numbered prescription form in duplicate or triplicate format. The prescriber and dispenser each maintain a copy of the prescription, and the dispenser forwards a copy of the prescription to a State regulatory agency. The copies sent to the State agency are entered into a database from which aberrant prescribing, dispensing, and patient procuring patterns are identified. EDT, the electronic equivalent of MCPPs, is a computerized diversion control system that requires pharmacists and dispensing physicians to submit on tape or diskette Schedule II prescription and dispensing information to a centralized databank. In order for EDT to be implemented, the majority of pharmacies in the State must have adequate computer capabilities. Optimally designed drug diversion control systems have two primary goals. The first is to limit access to controlled substances to those with a legitimate medical need, thereby reducing illicit drug use. The second goal is to establish a system with the ability to track and identify instances when access controls are compromised. Also desirable, however, is a third goal: to minimize the intrusiveness of the drug control system into the legitimate practice of medicine. In the face of increasing government scrutiny there is growing concern in the medical community that controlled substances are under-prescribed. 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. 4 tables and 45 references