Diuretics are medicines that aid the elimination of sodium (salt) and water from the body. The oral forms of these drugs are sometimes referred to as "water pills." Diuretics act by increasing the excretion by the kidneys of sodium in the urine. When the kidneys excrete sodium, they excrete water from the blood along with it. That decreases the amount of fluid flowing through the blood vessels, which reduces pressure on the walls of the arteries.

doctor and patient
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If you have high blood pressure or heart failure, your doctor may prescribe diuretics.

Diuretics are used to treat a number of conditions, including:

  • High blood pressure. Most patients with high blood pressure (hypertension) are effectively treated with diuretics. Patients taking a diuretic for high blood pressure will probably be advised to stick to a low-sodium diet. Diuretics act to lower blood pressure primarily by reducing blood volume; however, some diuretics can lower blood pressure in other ways and at lower doses than that required to produce increased urine output.
  • Heart failure. By flushing excess fluids from the body, diuretics can relieve the edema (swelling from excess fluids) that commonly occurs with heart failure. Most patients with heart failure are treated with diuretics in addition to a low-sodium diet. It's important for heart failure patients taking diuretics to have their salt (electrolyte) levels carefully monitored. Heart failure patients who are prescribed diuretics will often be on the medications for the rest of the lives.
  • Renal insufficiency. Diuretics are sometimes used to treat patients whose kidneys are unable to function normally, although they can also sometimes worsen this condition.
  • Liver disease. Diuretics can treat destruction and scarring of liver tissues­ when it is complicated by fluid buildup in the liver.
  • Hypercalcemia. Diuretics can treat excessive levels of calcium in the blood.
  • Diabetes insipidus. This disorder is marked by the excessive excretion of urine and persistent thirst. Some types of diuretics actually decrease urine volume in these patients.
  • Glaucoma. Some diuretics can be used to treat this eye disease, in which increased pressure within the eye causes damage and gradual loss of sight.
  • Cerebral edema. Some diuretics can treat potentially fatal brain swelling caused by hemorrhage, trauma, disease or surgery.
  • ­­Polycystic ovarian syndrome (PCOS). A disorder marked by irregular menstruation, obesity, increased hair growth, cystic ovaries and infertility.

On the next page, we'll find out about the different kinds of diuretics.­