Diuretics

Often referred to as fluid or water pills, diuretics help reduce blood pressure by increasing the kidneys' excretion of sodium into the urine. These drugs also lower blood pressure by promoting the dilation of small blood vessels. There are three types of diuretics--thiazide diuretics, loop diuretics, and potassium-sparing diuretics. Each type of diuretic acts on a different site in the kidney.

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Thiazide diuretics are the most commonly used diuretic. These drugs are inexpensive and need to be taken only once a day. In addition, they are at least as effective--if not more effective--than other classes of antihypertensive drugs. Loop diuretics are often used in people who also have heart failure or kidney disease. Potassium-sparing diuretics are used in combination with another type of diuretic, when that diuretic results in excessive loss of potassium.

The benefits of thiazide diuretics were demonstrated in a study called ALLHAT--the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial--published in 2002 in the Journal of the American Medical Association. The study looked at more than 42,000 people with hypertension who were age 55 and older and had at least one risk factor for heart disease. The participants were randomly assigned to receive either a thiazide diuretic (chlorthalidone), an ACE inhibitor (lisinopril), a calcium channel blocker (amlodipine), or an alpha-blocker (doxazosin).

The researchers followed the participants for an average of five years. The results clearly showed that the diuretic was superior to the ACE inhibitor and calcium channel blocker in terms of lowering blood pressure and preventing certain cardiovascular events. (The alpha-blocker portion of the study was stopped early because participants on this medication had a 25 percent increase in cardiovascular events relative to the diuretic.)

Low doses of thiazide diuretics are well tolerated. However, side effects can occur, including weakness, fatigue, malaise, sexual dysfunction, increased blood levels of glucose, triglycerides, calcium, and uric acid, and reduced blood sodium and HDL cholesterol levels. Thiazide and loop diuretics can also cause loss of potassium, which can lead to serious cardiac risks.