Water pills, also known as diuretics, are medications designed to reduce the amount of water and sodium in the body. They are used for a variety of conditions, including swelling due to fluid build-up, congestive heart failure, high blood pressure, glaucoma and certain kidney or liver diseases. Three main types of water pills are available: thiazide diuretics, loop diuretics and potassium-sparing diuretics. Although the mechanisms by which they work are different, the three types have several side effects in common, as well as some unique side effects.
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Increased Urination and Excessive Fluid Loss
One of the most common side effects of all diuretics is increased urination. It is particularly common in people taking loop diuretics, as these are the most powerful water pills. Increased urination may resolve over time, especially in people taking the other two types of diuretics. When urination is excessive, dehydration can occur. This may lead to low blood pressure with dizziness or lightheadedness, especially when standing up. When prolonged, dehydration can damage the kidneys.
Blood Levels of Potassium, Sodium and Chloride
Diuretics can affect the amount of potassium, sodium and chloride in the bloodstream. Thiazide and loop diuretics often lower blood levels of potassium unless people consume extra amounts of potassium-rich foods. Low potassium can cause various symptoms, including leg cramps and weakness. As their name suggests, potassium-sparing diuretics do not cause low potassium and can actually increase potassium levels. As all water pills reduce the amount of sodium in the body, blood levels of sodium may fall below normal. Chloride levels in the blood may decrease with thiazide and loop diuretics and increase with potassium-sparing diuretics.
Other Blood Test Results
Both thiazide and loop diuretics can cause blood sugar levels to increase, which may lead to the appearance of diabetes. Thiazide diuretics may increase blood levels of calcium and decrease levels of magnesium, while loop diuretics tend to decrease both calcium and magnesium levels in the blood. Both thiazide and loop diuretics may increase blood levels of uric acid. Over time, this can lead to gout, a painful form of arthritis that typically develops in the joints of the toes and feet. Thiazide and loop diuretics can also increase cholesterol and triglyceride levels in the blood.
Other Side Effects
Men taking potassium-sparing diuretics may experience impotence or decreased sexual desire, as these drugs have anti-androgen effects. Some men also develop breast enlargement. Premenopausal women who take these diuretics can experience menstrual irregularities, and postmenopausal women may develop uterine bleeding. All diuretics may cause abdominal discomfort, nausea, vomiting or diarrhea in some people. Potentially life-threatening inflammation of the pancreas called pancreatitis is a possible, but uncommon, side effect of thiazide and loop diuretics. Occasionally, thiazide diuretics can produce blurred vision and loop diuretics may cause ringing in the ears or decreased hearing. All diuretics can interact with a large number of other medications.
Reviewed by: Mary D. Daley, MD