(S)-Terazosin is an active S-enantiomer of Terazosin and acts as a potent, high-affinity antagonist of α-adrenoceptors [α1a, α1b, and α1d-adrenoceptors] with Ki values of 3.91 nM, 0.79 nM, and 1.16 nM, respectively.

α2B-adrenoceptor:3.5 nM (ki), α1B-adrenoceptor:0.79 nM (ki), α2C-adrenoceptor:46.4 nM (ki), α1D-adrenoceptor:1.16 nM (ki), α1A-adrenoceptor:ki： 3.91 nM , α2A-adrenoceptor: 729 nM (ki)

(S)-Terazosin and its enantiomers show high and apparently equal affinity for subtypes of α1-adrenoceptors, and showed potent α1-adrenoceptors antagonist in isolated tissues, with the enantiomers approximately equipotent to the racemate at each α1-adrenoceptor subtype. At α2b sites, (R)-Terazosin binds less potently than either the (S)-Terazosin or racemate.

(S)-Terazosin shows α2B receptor antagonist at rat atrial(pEC30 of 6.93). (s)-Terazosin shows antagonism of at rat vas deferens α1A and α2A receptor with pA2 values of 8.3 and 6.12, respectively.