Potent and selective 5-HT1B/1D receptor antagonist (pKi values are 8.5 for both guinea pig 5-HT1D and rat 5-HT1B receptors). Displays > 100-fold selectivity over 5HT1A, 5-HT2A, 5-HT2C receptors and other receptor types. Centrally active following oral administration.