IMS Report " Despite the drawbacks of currently available pain products, U.S. sales in 2000 of narcotic and non-narcotic analgesics exceeded $4.6 billion.		Pain Identifying the etiology of pain is essential to its management. Pain is defined as unpleasant sensory and emotional experience associated with actual or potential tissue damage discomfort. Drugs for the treatment of pain, or analgesics, have historically been placed into one of three general categories: narcotics like morphine, codeine, Demerol, and Percodan; non-narcotic prostaglandin inhibitors like aspirin, acetaminophen, ibuprofen and COX-2 inhibitors; and other analgesics. While drugs in all three of these categories are regularly used in the treatment of pain, their use has been limited because of various side effect profiles. In addition, administering these drugs for extended durations has been problematic. Although prostaglandin inhibitors have been used for the treatment of pain, particularly pain associated with inflammation, their efficacy is limited to milder types of pain and they often display undesirable side effects relating to the gastrointestinal tract and the liver. Narcotics are also used to treat pain, but tolerance develops rapidly and higher doses eventually lead to physical dependence and additional side effects, including respiratory depression. Alternative strategies for identifying potentially novel analgesics include altering certain neurotransmitter systems involved in mediating the sensation of pain. Preclinical studies have implicated the neurotransmitters glutamate, norepinephrine and serotonin in pain reduction. Treatments that interfere with certain glutamate receptors or that increase the actions of norepinephrine and serotonin have been reported to produce analgesic effects in animals.