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Spironolactone (marketed as Aldactone®, Novo-Spiroton®, Spiractin®, Spirotone®, or Berlactone®) is a synthetic 17-lactone steroid which is a renal competitive aldosterone antagonist in a class of pharmaceuticals called potassium-sparing diuretics, used primarily to treat low-renin hypertension, hypokalemia, and Conn’s syndrome. On its own, spironolactone is only a weak diuretic, but it can be combined with other diuretics. Due to its anti-androgen effect, it can also be used to treat hirsutism, and is a common component in hormone therapy for trans women people.

Mechanism of action

Spironolactone inhibits the effect of aldosterone by competing for intracellular aldosterone receptor in the distal tubule cells. This increases the secretion of water and sodium, while decreasing the excretion of potassium. Spironolactone has a fairly slow onset of action, taking several days to develop and similarly the effect diminishes slowly.


Spironolactone is fairly rapidly absorbed from the gastrointestinal tract. It is also rapidly metabolised and bound in plasma proteins. Many of its metabolites are also active and one of them, canrenone as potassium canrenoate, is used parenterally when rapid effect is needed. Spironolactone’s half-life is only 10 minutes, but canrenone’s half-life is 10 to 35 hours, depending on the dose. The main elimination route is in the urine and some also in the bile.

Adverse effects

Spironolactone can cause gastrointestinal problems fairly often. Since it also affects steroid receptors elsewhere in the body, it can cause gynecomastia, menstrual irregularities and testicular atrophy. Other side effects include ataxia, impotence, drowsiness and rashes. A carcinogenic effect has been demonstrated in rats.

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