A diuretic is any drug that tends to increase the flow of urine from the body (diuresis). They also decrease the extracellular fluid volume, and are primarily used to produce a negative extracellular fluid balance. Some common diuretics are caffeine, cranberry juice and alcohol.

In medicine, diuretics are used to treat heart failure, liver cirrhosis, 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 – which cause edema related to the disease – move into the blood to replace the volume lost as urine, thereby reducing the pathological edema. Diuretics are also 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 in increasing excretion of substances such as aspirin in cases of overdose or poisoning.

It should be noted, however, that the antihypertensive actions of some diuretics (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 (e.g., mannitol)
2. Carbonic anhydrase inhibitors (e.g., acetazolamide, dorzolamide )
3. Thiazides (e.g., hydrochlorothiazide, bendroflumethiazide)
4. loop diuretics (e.g., furosemide, bumetanide, ethacrynic acid )
5. Potassium-sparing diuretics (e.g., 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.

Alcohol and caffeine produce diuresis through modulation of the vasopressin system.

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