Aprepitant is a selective neurokinin 1 (NK1) receptor antagonist with high affinity for human substance P (a P-neuropeptide of the tachykinin family). Additional screening studies showed that aprepitant was at least 3000-fold more selective for NK1 receptors than for another enzyme, ion channel transporter, and receptor localization, including dopamine and serotonin receptors, which are targets for chemotherapy-induced nausea and vomiting.