 Because of these psychotomimetic effects, NMDA receptor antagonists, especially phencyclidine, ketamine, and dextromethorphan, are used as recreational drugs.At subanesthetic doses, these drugs have mild stimulant effects and, at higher doses, begin inducing dissociation and hallucinations, though these effects and the strength thereof vary from drug to drug.Most NMDA receptor antagonists are metabolized in the liver.