Aminophylline is a nonselective adenosine receptor antagonist and phosphodiesterase inhibitor. It is a serotonin 5-HT receptor antagonist. It works as an antiandrogen mainly by acting as an androgen receptor antagonist. It is a histamine H receptor antagonist. PCP works primarily as an NMDA receptor antagonist. Tolvaptan is a selective V receptor antagonist. As such, PCP is an NMDA receptor antagonist. Heroin overdose is usually treated with the opioid antagonist, naloxone. Xenon is a high-affinity glycine-site NMDA receptor antagonist. Clemastine is a selective histamine H antagonist. It acts as a nicotinic antagonist and noncompetitive NMDA antagonist. He played the roles of both the antagonist and protagonist. Dextromethorphan is an NMDA antagonist at high doses. Pyrimethamine is classified as a folic acid antagonist. He is noted for his antagonist and character roles.