Antihypertensives are medications used to treat high blood pressure (hypertension). Blood pressure is a measure of the force of the blood pushing against the walls of the arteries. When this force is elevated beyond a normal level, a patient will be diagnosed with either pre-hypertension or hypertension.

Nearly one in three adult Americans suffer from hypertension, which often occurs without symptoms and for unknown reasons (called essential hypertension). High blood pressure is a major risk factor for stroke, heart attack and heart failure. It frequently occurs in patients with diabetes and is a major contributor to diabetes-related complications, such as kidney failure and eye disease.

Hypertension is an indication that the heart and the blood vessels are being overworked. Antihypertensives lower blood pressure by opening and widening the blood vessels, preventing the blood vessels from closing and tightening, or reducing the workload of the heart. These medications include:

• Vasodilators. Medications that expand or widen blood vessels, reducing blood pressure against the walls of the vessels. This allows blood to flow more freely and the heart to pump more efficiently. Vasodilators include:
  
  
• ACE inhibitors (angiotensin-converting enzyme inhibitors). Vasodilators block the production of a substance (angiotensin II) that causes blood vessels to tighten. This results in lowering the resistance of the blood vessel to the flow of blood from the heart.
  
  
• Angiotensin II receptor blockers (ARBs). Vasodilators that produce the same effect as ACE inhibitors but by a different mechanism. Instead of preventing the production of angiotensin II, they inhibit the action of this substance by blocking it from entering angiotensin II receptors in the body.
  
  
• Calcium channel blockers. Vasodilators that reduce the workload of the heart by blocking calcium ions from signaling the blood vessels to constrict or tighten.
  
  
• Central adrenergic inhibitors. Vasodilators that act directly on the brain to prevent it from signaling the central nervous system to increase heart rate or narrow blood vessels.

The choice of which drug to use first is not settled, especially because the various drugs are roughly equally effective. A number of clinical trials have proven this by comparing the drugs in head-to-head studies among various patient groups. The most well-known antihypertensive trial is the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial, or ALLHAT.

The ALLHAT trials began in 1994 and involved more than 42,000 individuals, making it the largest such trial to date. The study showed that “traditional” diuretics about as effective as newer calcium channel blockers and ACE inhibitors but had the added advantage of reducing the development of heart failure and stroke. The researchers concluded that medication therapy to lower blood pressure should begin with diuretics.

Because of ALLHAT, most physicians will begin antihypertensive therapy with a thiazide diuretic and closely monitor its results. However, it's also important to note that the choice of which antihypertensive to use first depends on each patient's medical history and other factors. For example, black Americans tend to respond better to thiazide diuretics and relatively poorly to ACE inhibitors or beta blockers.

If the use of a single antihypertensive does not lower blood pressure sufficiently, physicians may prescribe two or more types of antihypertensives to work in combination. Combination therapies are usually not first-line treatments, but offer a valuable alternative when single-drug therapy is not effective. They allow for lower, better-tolerated doses of each antihypertensive. Some combinations are available in single fixed-dose pills, so that while patients are taking more than one medication, they are only taking one pill. The most common combination therapies include:

• ACE inhibitors and thiazide diuretics
• Angiotensin II receptor blockers, thiazide diuretics and potassium-sparing diuretics
• Beta blockers and thiazide diuretics
• Thiazide diuretics and potassium-sparing diuretics
• Calcium channel blockers and ACE inhibitors

Whether or not medication is required to control hypertension, patients may be advised to make lifestyle modifications to help control their condition.