The importance of PMPs is clear from evidence that addiction, overdoses, and deaths that involve non-medical prescription drug use have increased significantly over the last decade, surpassing those due to illicit drugs such as heroin and cocaine. Narcotic pain relievers are the most abused of the non-medical prescription drugs. PMPs collect data from pharmacies on dispensed controlled substance prescriptions. PMPs are important tools in curbing major sources of prescription drug diversion, which include prescription fraud, forgeries, doctor shopping, and medically unwarranted prescribing by some practitioners and pharmacists. Currently, 48 States and 1 U.S. Territory have enacted legislation that establishes a PMP; 38 States have operational PMPs. This report presents a sampling of studies that show PMPs can help in improving prescribing procedures and reducing the diversion of controlled substances. The studies indicate that States with PMPs and States with pro-active PMPs have lower rates of treatment admissions for the abuse of prescription drugs, reduced doctor shopping, and less diversion of non-medical prescription drugs. Also, States with PMPs have smaller increases in opiate exposures related to abuse and misuse, as well as lower outpatient drug claims. In addition, States without PMPs are more likely to experience higher rates of controlled substance distribution. Studies also indicate that PMP data have assisted in the investigation of drug diversion and reduced the number of investigations needed. Other benefits of PMPs include assisting in drug abuse prevention and surveillance, as well as the validation of patient self-reports on the use of medications. 35 notes