Doxazosin is an alpha-adrenergic blocking agent used to treat hypertension and benign prostatic hyperplasia. Accordingly, Doxazosin is a selective inhibitor of the alpha1 subtype of alpha adrenergic receptors. In the human prostate, Doxazosin antagonizes phenylephrine (alpha1 agonist)-induced contractions, in vitro, and binds with high affinity to the alpha1a adrenoceptor, which is thought to be the predominant functional type in the prostate. Studies in normal human subjects have shown that Doxazosin competitively antagonized the pressor effects of phenylephrine (an alpha1 agonist) and the systolic pressor effect of norepinephrine. The antihypertensive effect of Doxazosin results from a decrease in systemic vascular resistance and the parent compound Doxazosin is primarily responsible for the antihypertensive activity.