A psychoactive drug with central nervous system depressant, stimulant, analgesic, and hallucinogenic effects. It was introduced into clinical medicine as a dissociative anaesthetic but its use was abandoned because of the frequent occurrence of an acute syndrome consisting of disorientation, agitation, and delirium. It appears to be of value in treatment of stroke. PCP is relatively cheap and easy to synthesize and has been in use as an illicit drug since the 1970s. Related agents that produce similar effects include dexoxadrol and ketamine.

In illicit use PCP may be taken orally, intravenously, or by sniffing, but it is usually smoked; effects begin within 5 minutes and peak at about 30 minutes. At first, the user feels euphoria, body warmth, and tingling, floating sensations, and a feeling of calm isolation. Auditory and visual hallucinations may appear, as well as altered body image, distorted perceptions of space and time, delusions, and disorganization of thought. Accompanying neurological and physiological symptoms are dose-related and include hypertension, nystagmus, ataxia, dysarthria, grimacing, profuse sweating, hyperreflexia, diminished responsiveness to pain, muscle rigidity, hyperpyrexia, hyperacusis, and seizures. Effects usually last for 4-6 hours, although residual effects may take several days or longer to clear. During the immediate recovery period there may be self-destructive or violent behaviour. PCP delirium, PCP delusional disorder, and PCP mood disorder have been observed. As is the case with the hallucinogens, it is not known whether such disorders are specific drug effects or a manifestation of pre-existing vulnerability. In ICD-11, PCP-related disorders are classed with hallucinogens (XM5M84).

WHO ICD-11: 6C4D Disorders due to use of dissociative drugs including ketamine and phencyclidine [PCP] - Disorders due to use of dissociative drugs including ketamine and phencyclidine [PCP] are characterised by the pattern and consequences of dissociative drug use. Dissociative drugs include ketamine and phencyclidine (PCP) and their (comparatively rare) chemical analogues. Ketamine is an intravenous anaesthetic widely used in low- and middle-income countries, particularly in Africa, and in emergency situations. Ketamine is also undergoing evaluation for treatment of some mental disorders (e.g., treatment resistant Depressive Disorders). It is also a widespread drug of nonmedical use in many countries and may be taken by the oral or nasal routes or injected. It produces a sense of euphoria but depending on the dose, emergent hallucinations and dissociation are recognised as unpleasant side effects. Phencyclidine has a more restricted worldwide distribution and also has euphoric and dissociative effects. Its use may result in bizarre behaviour uncharacteristic for the individual, including self-harm. Dissociative Drug Dependence is described but a withdrawal syndrome is not recognized by most authorities. Several Dissociative Drug-Induced Mental Disorders are recognised (WHO ICD-11).