Are LSD and other hallucinogenic drugs antagonists?

Depending on the hallucinogen, it may be either an agonist or an antagonist at certain receptors. Classic psychedelics such as LSD and psilocybin are 5-HT2A receptor agonists, whereas dissociatives (PCP, DXM, ketamine, etc.) are NMDA receptor antagonists. Deliriants, such as atropine and scopolamine, are muscarinic antagonists.