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HEALTH GUIDE / Prescription Drugs / Alpha Blockers

Alpha Blockers

Alpha Adrenergic Antagonists, Alpha 1 Blockers, Alpha 2 Blockers


About alpha blockers

Alpha blockers are non-habit-forming medications. They block the effects of certain hormones in the body (e.g., the stress hormones) that could lead to a rapid heartbeat.

They are called alpha blockers because they block the microscopic areas in the heart called alpha receptors. These alpha receptors are normally activated by certain chemicals in the brain, such as the hormones released during stress (e.g., adrenaline). When activated by these chemicals, the alpha receptors trigger a reaction that speeds the heart rate, increases the force of the heartbeat and constricts the blood vessels. However, this reaction cannot be triggered if the chemicals are blocked by alpha blockers from activating or binding to the alpha receptors.

Therefore, alpha blockers relieve cardiac stress by slowing the heart rate and reducing the force of heart muscle contractions (the pumping action). They also reduce blood vessel constriction in the heart, brain and other parts of the body and therefore belong to a class of drugs called vasodilators.

Because they affect stress hormones, alpha blockers result in a lowering of blood pressure (the force of blood against artery walls). However, they are less commonly used in the treatment of high blood pressure (hypertension) because they may increase the risk of heart failure with long-term use and are associated with relatively strong side effects.

The link between heart failure risk and alpha blocker use was one of the findings of the landmark ALLHAT study (Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial). The largest antihypertensive trial to date with more than 42,000 participants, ALLHAT determined that thiazide diuretics were the preferred “first line” treatment for high blood pressure because they were the most effective at also lowering the risk of heart attack, stroke and other heart diseases. Calcium channel blockers or ACE inhibitors were recommended for patients who could not take diuretics. ALLHAT also noted that many patients need a combination of multiple antihypertensive medications.

There are two types of alpha blockers, which are classified according to the type of alpha receptor that they block (alpha 1 or alpha 2):

  • Selective alpha antagonists only block alpha 1 receptors and are more commonly used for treatment of cardiac conditions.
  • Nonselective alpha antagonists can bind with both types of receptors and are generally not used for cardiology treatments because blocking both receptors can cause tachycardia (rapid heart beat) and palpitations (pounding heart beat).

Alpha blockers include medications such as the following:

dihydroergotamine mesylate
phentolamine mesylate



Conditions treated

Selective alpha antagonists (alpha 1 blockers) include prazosin, terazosin and doxazosin. These drugs are sometimes used to treat high blood pressure, as well as benign prostatic hyperplasia (BPH), an enlargement of the prostate that may cause the urethra to constrict, inhibiting urination. They may also be used in the treatment of pheochromocytoma, a rare blood pressure-related condition.

Alpha 1 blockers decrease resistance within blood vessels and increase vein capacity, increasing the flow of blood in the heart and reducing cardiac output – a measure of the heart’s workload. They are among the only antihypertensive drugs that have been shown to lower LDL cholesterol, raise HDL cholesterol and improve the body's ability to use insulin, which reduces the risk of diabetes. Alpha 1 blockers have also been found effective in the prevention and treatment of post-traumatic stress disorder, particularly in reducing trauma-related nightmares.

However, alpha 1 blockers may also have pronounced side effects and, as shown in the ALLHAT trials, doxazosin may increase the risk of heart failure over long-term use.

Nonselective alpha antagonists (alpha 1 and alpha 2 blockers) are used in the treatment of various types of peripheral vascular disease, which include the following:

  • Raynaud syndrome. A painful condition caused by the temporary constriction of the small arteries in the hands and feet.
  • Acute arterial occlusion. The blockage or obstruction of an artery, usually by a build-up of cholesterol-rich plaque or a blood clot.
  • Phlebitis. Inflammation of the veins that is often associated with the formation of blood clots (thrombophlebitis).
  • Diabetic gangrene. The death of body tissue (necrosis) resulting from a diabetes-related lack of blood supply due to poor circulation.
  • Acrocyanosis. A bluish tinge to the skin (cyanosis) caused by a disorder of the arterioles (very small arteries) in the hands and feet.

In addition, nonselective alpha antagonists are sometimes prescribed to treat migraine headaches or frostbite.

None of the forms of alpha blockers are typically used as first-line treatment for high blood pressure (hypertension). While they do lower blood pressure, alpha blockers also have relatively bothersome side effects and certain alpha blockers have been shown to increase the risk of heart failure with long-term use. Other antihypertensive medications not only lower blood pressure, but also reduce the risk of cardiovascular disease or death and are therefore a better choice for the treatment of hypertension.

Conditions of concern

Patients with the following conditions should discuss the benefits and risks of alpha blocker use with their physicians:

  • Low blood pressure (hypotension)
  • Prostate cancer
  • Arrhythmia (heart rhythm disorder)
  • Liver or kidney disease
  • Asthma or other lung disease
  • Blood vessel disease (e.g. atherosclerosis, coronary artery disease)
  • Hyperthyroidism (overactive thyroid gland)
  • Pheochromocytoma (a rare tumor)
  • Heart failure
  • Central nervous system diseases
  • Depression
Side effects

Potential side effects of alpha blockers

Selective alpha antagonists (alpha 1 blockers) can cause one or more of the following side effects:

  • Fainting (syncope)
  • Dizziness or lightheadedness, especially after getting up from a standing or lying position
  • Headache
  • Weakness

Nonselective alpha antagonists (which block both alpha receptors) typically cause:

  • Rapid heart rate (tachycardia)
  • Pounding or “galloping” heart beat (palpitations)
  • Fluid retention
  • Nasal (nose) and ocular (eye) congestion.
  • Aggravation of respiratory infection (if one is present)

Side effects associated with both forms of alpha blockers include:

  • Low blood pressure (hypotension)
  • Allergic reaction
  • Swelling (edema) of feet, legs or ankles
  • Chest pain
  • Shortness of breath (dyspnea) or wheezing
  • Weight gain
  • Nausea or upset stomach
  • Vomiting
  • Irritability, nervousness or restlessness
  • Trouble sleeping
  • Nightmares and vivid dreams
  • Loss of bladder control
  • Painful, continuous erection or impotence
  • Back or joint pain
  • Blurred vision
  • Runny or stuffy nose

Side effects of alpha blockers typically diminish with regular use. Because of these side effects, however, alpha blockers are generally not the first choice of medications to treat high blood pressure or other conditions.

Individuals who have been using an alpha blocker for an extended period of time may notice unpleasant or harmful effects if they discontinue the use of the medication suddenly. Patients using alpha blockers should discuss discontinuing the drug with their physician.


Drug or other interactions

Patients should consult their physician before taking any other medication (either prescription or over-the-counter), nutritional supplements or herbal remedies. Of particular note to individuals taking alpha blockers are substances such as the following:

  • Other antihypertensives (drugs that slow heart rate or lower blood pressure) such as calcium channel blockers or ACE inhibitors. Combined, these medications may lower blood pressure to unsafe levels. However, lower doses of these medications are routinely prescribed along with alpha-blockers in patients who do not respond to other therapies. Some medications even combine more than one antihypertensive into a single pill.
  • NSAIDs (nonsteroidal anti-inflammatory drugs). Mixing these medications may reduce the effectiveness of the antihypertensive.
  • Some antiarrhythmics (medications that treat abnormal heart rhythms (arrhythmias).
  • Impotence therapy agents. Mixing alpha blockers and impotence therapy agents could result in a sudden and unsafe drop in blood pressure.
  • Some antibiotics.
  • Some anti-fungal medications.
  • Protease inhibitors or anti-viral medications used in the treatment of HIV.
  • Some antidepressants or anti-anxiety drugs.
  • Insulin and other diabetic medications.
  • Some immunodepressants.
  • Some medications used in the treatment of conditions such as heartburn, ulcers, asthma and endometriosis.
  • Grapefruit juice.
  • Over-the-counter (OTC) medications. Patients taking alpha blockers for high blood pressure (hypertension) should avoid OTC products that may increase blood pressure (vasoconstrictors), including diet pills and asthma, cold, cough, sinus or hay fever medications. People should also be careful about using eye drops that treat bloodshot eyes.

Patients should carefully adhere to their physician’s instructions regarding exercise, activity levels and diet. People taking alpha blockers are more likely to experience side effects if they engage in the following:

  • Alcohol use
  • Smoking
  • Spending too much time in the heat
  • Spending too much time standing
  • Overly strenuous exercise

Lifestyle considerations

When first taking an alpha blocker, patients should avoid operating heavy machinery (e.g., driving) until they know how the medication will affect them. Some patients on alpha blockers to treat high blood pressure (hypertension) will be taking the medication for the rest of their lives, provided no serious side effects occur.

Patients should remember that alpha blockers control high blood pressure, but do not cure it. Even if all their symptoms are relieved, patients should continue to take their medication exactly as directed and to keep all scheduled follow-up appointments with their physicians.

Patients should take and record their blood pressure readings regularly, reporting anything unusual to their physician.

How to use

Pregnancy use issues

Women are advised against taking alpha blockers during pregnancy, especially during the second and third trimesters. Patients taking alpha blockers should inform their physician immediately if they become pregnant or are planning to become pregnant, so that they can start alternative therapy.

When breast feeding, some alpha blockers will pass into breast milk. While this has not been found to cause problems in nursing infants, an alternative feeding method may be recommended when alpha blockers are being used by the mother. Parents should weigh the benefits and risks with their physicians.

Child use issues

Currently, there is no evidence that the risk of children’s side effects from alpha blockers is different from those of adults. However, the safety of alpha blocker use in children has not yet been scientifically established. Parents are encouraged to discuss the potential risks and benefits with a pediatric cardiologist before their child begins any alpha blocker treatment.

Elderly use issues

Aged adults have a higher frequency and intensity of side effects, such as lightheadedness, dizziness and fainting (syncope). Generally, older patients require lower doses of alpha blockers.

Symptoms of alpha blocker overdose

Patients exhibiting any of these symptoms should contact their physician immediately:

  • Severe low blood pressure (hypotension)
  • An abnormally fast heart rate tachycardia
  • Severe dizziness, drowsiness or fainting (syncope)

Questions for your doctor

Patients may wish to ask their doctor the following questions about alpha blockers:
  1. Is it true that, while treating my high blood pressure, alpha blockers may increase my risk for heart failure?
  2. How long can I expect my dizziness to last?
  3. When is the best time of day to take alpha blockers?
  4. Could alpha blockers be reponsible for me not sleeping well?
  5. Will I gain weight from taking alpha blockers?
  6. Are alpha blockers contributing to my loss of bladder control?
  7. Which over the counter drugs should I avoid while on alpha blockers?
  8. Is it safe to take alpha blockers while breast-feeding?

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