Spironolactone is a diuretic and is used as an antiandrogen.

It is a synthetic 17-lactone drug which is a renal competitive aldosterone antagonist in a class of pharmaceuticals called potassium-sparing diuretics, used primarily to treat heart failure, ascites in patients with liver disease, low-renin hypertension, hypokalemia, and Conn's syndrome as well as high blood pressure. On its own, spironolactone is only a weak diuretic, but it can be combined with other diuretics. About one person in one hundred with hypertension has elevated levels of aldosterone; in these persons the antihypertensive effect of spironolactone may exceed that of complex combined regimens of other antihypertensives. Due to its anti-androgen effect, it can also be used to treat hirsutism, and is a common component in hormone therapy for male-to-female transsexual and transgendered people. It is also used for treating hair loss and acne in women and can be used as a topical medication for treatment of male baldness.