Although phencyclidine (PCP) and drugs of similar chemical structure are often called hallucinogens, they rarely produce hallucinations. The sensory distortions or apparent hallucinations that PCP does produce are not the same type as the hallucinations produced by use of LSD. Instead, PCP belongs to a unique class of drugs often called the dissociative anesthetics. (These drugs produce a brief period of anesthesia during which individuals feel as if they are dissociated, or separated, from their bodies.) This category includes ketamine, which has recently emerged as a widely abused drug in this class. Other drugs in this class have been manufactured with effects similar to those of PCP and ketamine, and are considered early examples of "designer drugs."

PCP was developed in the 1950s as an anesthetic for veterinary surgery and the capture of wild animals and later was tested in human surgical patients. The negative side...