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Alpha-adrenoreceptor antagonists bind to and block alpha-1 receptors. They are mostly used to treat high blood pressure or symptomatic benign prostatic hypertrophy (BPH) because alpha-1 receptors are located in the smooth muscle lining blood vessels, in the prostate, and in the neck of the bladder.

These conditions are characterized by a tightening (contraction) of smooth muscle because the alpha-1 receptors are stimulated. If this occurs in smooth muscle located in the prostate and neck of the bladder, this tightening can detrimentally affect urine flow and frequency, causing symptoms such as those seen in BPH. Alpha-adrenoreceptor antagonists block these receptors, allowing this muscle to relax and resolving symptoms.

Alpha-adrenoreceptor antagonists can also lower blood pressure by selectively blocking alpha-1 receptors located in the smooth muscle lining blood vessels, allowing the blood vessels to widen (dilate). They may also block the nerve receptors responsible for the contraction (narrowing) of the blood vessels.

Common side effects may include low blood pressure and dizziness, particularly when starting this type of medication and when rising from a sitting or lying position. The first dose is often taken at bedtime. Other side effects might include a headache, pounding heartbeat, and tiredness.