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A diuretic is any drug that tends to increase the flow of urine from the body. Some common diuretics are caffeine and alcohol.

Medically, diuretics are used to treat heart failure, cirrhosis of the liver, Hypertension and certain kidney diseases. Diuretics are able to alleviate the symptoms of these diseases by causing sodium and water loss through the urine. As more urine is produced by the kidney, sodium and water causing edema related to the disease move into the blood to replace the volume lost as urine, thereby reducing the pathological edema. Diuretics also lower blood pressure by simply reducing the volume of fluid in the body's blood vessels and are therefore frequently used in the treatment of hypertension (high blood pressure). Some diuretics such as acetazolamide help to make the urine more alkaline and are helpful increasing excretion of substances such as aspirin in cases of overdose/poisoning.

It should be noted, however, that the actions of diuretics used in the treatment of hypertension (thiazides and loop diuretics in particular) are independent of their diuretic effect. That is, the reduction in blood pressure is not due to decreased blood volume resulting from increased urine production, but occurs through other mechanisms and at lower doses than that required to produce diuresis. Indapamide was specifically designed with this is mind, and has a larger therapeutic window for hypertension (without pronounced diuresis) than most other diuretics.

Diuretics in medicine are classified into:

  1. Osmotic diuretics eg. mannitol
  2. Carbonic anhydrase inhibitors eg. acetazolamide, dorzolamide
  3. Thiazides eg. hydrochlorothiazide, bendroflumethiazide
  4. loop diuretics eg. furosemide, bumetanide, ethacrynic acid
  5. potassium-sparing diuretics eg. spironolactone, amiloride

Chemically, diuretics are a diverse group of compounds that either stimulate or inhibit various hormones that naturally occur in the body to regulate urine production by the kidneys. Key targets of these drugs include angiotensin II, aldosterone, atrial-natriuretic peptide, and vasopressin, all of which act on the kidney's nephron in various ways to control urine formation.

Excess consumption of a diuretic substance may cause diuresis. Alcohol and caffeine produce diuresis through modulation of the vasopressin system.

For more information, consult any textbook of physiology or nephrology.