Potent, selective 5-HT2 receptor antagonist; displays some selectivity for 5-HT2A receptors (Ki = 1.6 nM). IC50 values are 2.2, 310, 2400, 3700, > 5000 and > 5000 nM for 5-HT2, α1-adrenergic, D2 dopamine, 5-HT1, 5-HT3 and β-adrenergic receptors respectively. Inhibits 5-HT-induced platelet aggregation and pressor responses in vivo.