Prazosin and terazosin are alpha1 adrenoceptor blockers with marketed indications for the treatment of hypertension. They block the effects of noradrenaline released from sympathetic nerve endings without increasing neurotransmitter release, and produce arteriolar and venous dilation, usually resulting in postural hypotension. Heart rate is not increased during long-term use.

Postural hypotension is the major adverse effect and may be particularly dangerous in elderly patients. It is important to commence or resume therapy at the lowest dose and warn patients of this effect. Prazosin and terazosin also block alpha adrenoceptors in nonvascular smooth muscle such as the bladder neck. This results in a reduction in the resistance to urinary flow, which can present as urinary incontinence. The alpha blocker doxazosin was tested in a large controlled trial of antihypertensive therapies. The doxazosin arm of this trial was stopped early because of an excessive rate of heart failure. Alpha blockers are no longer considered as first-line agents for the management of hypertension.