Spironolactone, sold under the brand name Aldactone, is a diuretic used in the treatment of heart disease and high blood pressure. It is generally not a first line medication for the conditions it is used to treat, but because of it's unique action in blocking aldosterone and testosterone, it is used when these hormones are the root cause of a condition. It is also used to treat kidney disease and hypokalemia. In addition, because of its effect on hormones, it can be used to treat precocious puberty and by persons undergoing gender reassignment.

However, it does have numerous side effects, such as hyperkalemia, nausea and decreased sex drive.

It is currently available as a generic and a typical dose costs about U.S. $0.50.

Spironolactone at Wikipedia