While some of the metabolites are active, most of the pharmacological effects are due to the parent compound itself. Only a small amount of the drug is excreted unchanged. The half-life of the phencyclidine is about 3 days, but can be reduced significantly by gastric suction and acidification of the urine. The amount of drug in a cigarette varies from 1 to 100 mg and chronic users may ingest up to 1 g in 24 hours. In animals tolerance develops to the behavioral and toxic effects of phencyclidine.
Abrupt withdrawal is followed by tremors, facial twitches and fearfulness.