Widely known as PCP, PHENCYCLIDINE is an important drug of abuse in the United States, even though its use has declined since the 1980s. PCP is difficult to classify pharmacologically and is considered separately from the hallucinogens. The drug has not been studied systematically in animals, although research done in 1973 and 1980 indicated that it produces dependence in monkeys. As of 1999, its effects on the human central nervous system are poorly understood. It produces a unique type of hallucinatory effect and is used both by smoking and ingestion. Persons under the influence of PCP experience mood changes, perceptual distortions, and feelings of dissociation from their surroundings. Since their judgment is impaired, they may take unnecessary risks. They may become unpredictable and violent. In certain individuals, PCP use, especially if repeated often, can result in the production of a mental disturbance referred to as...