Diuretic, chemical compound that increases the flow of urine and thus eliminates accumulations of water in cells, tissues, blood, and organs. The retention of excess water may occur following injury, as when water accumulates in the knee; in congestive heart failure, when the heart pumps insufficient blood to eliminate a normal volume of fluid; and in a variety of other disabilities, including hypertension, cirrhosis of the liver, and kidney diseases. Heart stimulants, such as digitalis, produce a diuretic effect by increasing blood pressure and thus increasing the flow of blood through the kidneys. Certain alkaloids found in coffee and tea (caffeine, theobromine, and theophylline, in increasing order of strength) increase urine output by counteracting the tendency of blood proteins to prevent the removal of water from the blood by the kidneys. A class of drug known as loop diuretics, such as furosemide, are extremely effective when taken orally. All diuretics may have severe side effects, may cause abnormal excretion of sodium, potassium, and chloride, and may become ineffective after repeated use.