A potent 5-HT2A receptor antagonist (Ki = 6.06 nM for the human receptor); selective for the human 5-HT2A receptor over human 5-HT2B and 5-HT2C and rat 5-HT2B receptors (Kis = 3,020, 1,020, and 4,700 nM, respectively); selective for 5-HT2A receptor over 5-HT1, 5-HT1A, α1- and α2-adrenergic, dopamine D2, muscarinic acetylcholine, histamine, and opiate receptors; prevents increases in acoustic startle response when administered prior to or following a stress protocol