Recent Advances in the Neuropsychopharmacology of Serotonergic Hallucinogens Adam L. Halberstadt Behavioral Brain Research, 2015, 15, 277, 99–120. doi : 10.1016/j.bbr.2014.07.016   Abstract Serotonergic hallucinogens, such as (+)-lysergic acid diethylamide, psilocybin, and mescaline, are somewhat enigmatic substances. Although these drugs are derived from multiple chemical families, they all produce remarkably similar effects in animals and humans, and they show cross-tolerance. This article reviews the evidence demonstrating the serotonin 5-HT2A receptor is the primary site of hallucinogen action. The 5-HT2A receptor is responsible for mediating the effects of hallucinogens in human subjects, as well as in animal behavioral paradigms such as drug discrimination, head twitch response, prepulse [...]