A diuretic is a chemical substance. This substance is either in a herb (such as dandelions), or it has been separated and made into a drug. Diuretics increase the amount of urine that is secreted from the body. Diuretics are used as a treatment for heart failure, liver cirrhosis, hypertension and certain problems with the kidneys. Diuretics are often abused by people suffering form bulimia nervosa as a way to lose weight. 