A drug which diminishes the awareness of sensory impulses, especially pain, by the brain. This action makes narcotics useful therapeutically as analgesics. While they are the most powerful pain-relieving agents available, their use is complicated by a number of undesirable side actions. Indeed, much research in this area has been directed toward a search for an agent having the same degree of analgesic properties as morphine, the most widely used of the narcotics, but without its undesirable side actions.