What Are Alpha Blockers?

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Alpha blockers are a type of medicine sometimes used to treat high blood pressure. They are not usually used alone, and many patients are more familiar with alpha blockers because they are used to treat other illnesses, including:

While other medicines are usually tried before considering alpha blockers, for some patients they represent an important treatment option.

How Alpha Blockers Work

Alpha blockers, also called alpha adrenergic blocking agents, work by interfering with the transfer of messages to specific parts of the body. Like other "blocker" medications, alpha blockers attach themselves to molecules in the body that serve as receptors for certain chemical messages. Because the chemical message is then prevented from reaching its target, it is said to be blocked. 

Alpha blockers block targets called alpha receptors, which are found in arteries and smooth muscle. Through their action, they keep the hormone adrenaline from exerting a tightening effect on the the muscles and the smaller arterial and venous walls. Blocking that effect causes the blood vessels to relax, thereby increasing blood flow and lowering blood pressure. 

Names of Common Alpha Blockers

Many different alpha blockers are available. Some commonly prescribed alpha blockers include:

  • Doxazosin (Cardura)
  • Phentolamine
  • Tamsulosin (Flomax)
  • Terazosin

Other alpha blockers are available, both within the U.S. and around the world. However, the vast majority of prescriptions in the U.S. are for the drugs listed above. Other types of alpha blockers are used mainly in special circumstances or controlled hospital settings.

Side Effects of Alpha Blockers

Alpha blockers tend to be well tolerated, but have some important side effects. These include:

  • Dizziness
  • Fainting
  • Low blood pressure
  • Sudden blood pressure changes when standing after sitting

In addition to these side effects, an important research study called the ALLHAT Study found that long-term use of alpha blockers seems to increase the risk of heart failure. While this risk is real, it is small, and the main reason that alpha blockers are not used as "first choice" drugs is that, unlike other high blood pressure medicines, they have not been shown to reduce the risk of stroke and heart attack.

Who Shouldn't Take an Alpha-Blocker


Women are generally not prescribed alpha-blockers because they can cause urinary stress incontinence and loss of bladder control. In addition, women who are pregnant, breastfeeding or may become pregnant should not take alpha-blockers.

Patients with a history of orthostatic ­hypotension should also not be prescribed an alpha-blocker, nor should those with a history of heart failure, problems with liver or kidney function, or Parkinson’s disease.

Only you and your doctor can decide on a proper medication for treatment of high blood pressure. Be sure to notify your doctor if you fall into any of the above categories, and to supply the names of any other medicines and/or supplements you are taking. Remember to include over-the-counter medicines like aspirin or Advil and herbal/natural supplements.

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