A 5-HT1D antagonist; selective over 5-HT1B, where it inhibits binding of radiolabeled citalopram by only 32% at a concentration of 1,000 nM; potentiates 5-HT release stimulated by potassium in guinea pig cortex (EC50 = 31 nM); reverses vasodilation induced by 5-HT in phenylephrine-perfused rat kidney when administered at a dose of 1 mg/kg