Alpha blockers, also called alpha-adrenergic antagonists, treat a variety of conditions, such as high blood pressure, benign prostatic hyperplasia and Raynaud's disease. Find out more about this class of medication. By Mayo Clinic Staff

Alpha blockers relax certain muscles and help small blood vessels remain open. They work by keeping the hormone norepinephrine (noradrenaline) from tightening the muscles in the walls of smaller arteries and veins. Blocking that effect causes the vessels to remain open and relaxed. This improves blood flow and lowers blood pressure.

Because alpha blockers also relax other muscles throughout the body, these medications can help improve urine flow in older men with prostate problems.

Many alpha blockers are available, in either short-acting or long-acting forms. Short-acting medications work quickly, but their effects last only a few hours. Long-acting medications take longer to start working, but their effects last longer. Which one is best for you depends on your health and the condition being treated.

Alpha blockers are also called alpha-adrenergic blocking agents, alpha-adrenergic antagonists, adrenergic blocking agents and alpha-blocking agents.

Examples of alpha blockers used to treat high blood pressure include:

  • Doxazosin (Cardura)
  • Prazosin (Minipress)

Doctors prescribe alpha blockers to prevent, treat or improve symptoms in conditions such as:

  • High blood pressure
  • Enlarged prostate (benign prostatic hyperplasia)
  • Some circulatory conditions, such as Raynaud's disease
  • Hardening and thickening of the skin (scleroderma)
  • Adrenal gland tumors (pheochromocytoma)

Though alpha blockers are commonly used to treat high blood pressure, they're typically not preferred as the first treatment option. Instead, they're used in combination with other drugs, such as diuretics, when your high blood pressure is difficult to control.

Alpha blockers may have what's called a "first-dose effect." When you start taking an alpha blocker, you may develop pronounced low blood pressure and dizziness, which can make you suddenly faint when you rise from a sitting or lying position. As a result, the first dose is often taken at bedtime.

Other side effects include headache, pounding heartbeat, nausea, weakness, weight gain and small decreases in low-density lipoprotein (LDL) cholesterol (the "bad" cholesterol).

Alpha blockers can increase or decrease the effects of other medications you take. Tell your doctor if you take any other medications, such as beta blockers, calcium channel blockers or medications used for erectile dysfunction, if you're prescribed an alpha blocker.

Some research has found that some alpha blockers can increase the risk of heart failure with long-term use. While more research is needed to confirm this finding, talk to your doctor if you're concerned.

Feb. 01, 2014