Ki: 3.91 nM (α1a-adrenoceptor), 0.79 nM (α1b-adrenoceptor) and 1.16 nM (α1d-adrenoceptor); 729 nM (α2a-adrenoceptor), 3.5 nM (α2Ba-adrenoceptor) and 46.4 nM (α2c-adrenoceptor)

The racemic compound and its enantiomers show high and apparently equal affinity for subtypes of α1-adrenoceptors with K _i values in the low nanomolar range, and showed potent antagonism of α1-adrenoceptors 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 antagonism of at rat atrial α2B receptor with a 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.