Vasodilators for high blood pressure


Generic Name Brand Name
clonidine Catapres
doxazosin Cardura
guanfacine Tenex
prazosin Minipress
terazosin Hytrin

How It Works

These medicines work by relaxing the smooth muscle of blood vessels, which opens up (dilates) the blood vessels. This allows blood to flow more easily, thereby lowering blood pressure.

Some of these medicines need to be combined with other medicines to counteract the body's natural tendency to retain fluid and increase heart rate when there is a sudden drop in blood pressure.

Vasodilators are not commonly used alone to treat ongoing high blood pressure because of the significant drop in blood pressure that they cause, which may lead to heart palpitations or rapid heartbeat. They may be used if a person is in a hypertensive crisis or when other classes of medicine are not effective in controlling high blood pressure. They also may be used if a person has certain other conditions in addition to high blood pressure—such as heart failure, asthma, impotence, or an enlarged prostate—that may benefit from the effects of vasodilators. For high blood pressure, vasodilators usually are used in combination with a beta-blocker and/or a diuretic, and in some cases with angiotensin-converting enzyme (ACE) inhibitors or calcium channel blockers.

Why It Is Used

These drugs often are used to treat high blood pressure in combination with other drugs when first-line medicines alone do not control blood pressure.

Older medicines (such as hydralazine) may be prescribed only for people who have severe high blood pressure or when blood pressure does not respond to other medicines.

Methyldopa can be used in pregnant women who have high blood pressure and in people who also have kidney disease.

Minoxidil is effective in people who have severe high blood pressure problems, which sometimes may be seen in people with severe kidney disease.

Terazosin and doxazosin are also used to treat symptoms of enlarged prostate.

Clonidine may be used in people whose high blood pressure is not lowered with other medicines.

How Well It Works

Vasodilators are effective in helping reduce blood pressure. They are usually not used as the initial medicine but are added on to other therapies.

Side Effects

Many of the side effects of these medicines are due to the significant drop in blood pressure that they cause. Side effects include:

  • Fainting.
  • Rapid heartbeat.
  • Irregular heartbeat (palpitations).
  • Headache.
  • Fluid retention (edema).
  • Gastrointestinal disturbances (hydralazine only).
  • Hair growth (minoxidil only).
  • Very low blood pressure (hypotension).
  • Drowsiness.
  • Dry mouth.
  • Erection problems (impotence).
  • Fatigue.
  • Rapid return of high blood pressure if medicines are stopped suddenly.
  • Skin irritation (clonidine patch).

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Some of the newer vasodilator medicines have fewer side effects than the older ones. Older drugs may be tried when blood pressure problems are difficult to control.

It is important to take high blood pressure medicines daily as prescribed. High blood pressure often has no symptoms, so it is easy to forget to take the pills.

If your high blood pressure medicine causes erection problems, you may want to talk to your doctor about erection-enhancing medicines such as sildenafil (Viagra).

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.

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