Spironolactone

Key facts

• Spironolactone is a potassium-sparing diuretic that helps the body remove excess fluid while holding onto potassium.
• You usually take it once or twice daily, with food to reduce stomach upset, and it can take a few weeks to reach its full effect on blood pressure.
• Its main risk is hyperkalaemia, dangerously high blood potassium, so your doctor checks blood potassium and kidney function before starting and periodically during treatment.
• Seek urgent care for muscle weakness, an irregular or slow heartbeat, or tingling, which can signal high potassium.

What spironolactone treats

Spironolactone treats fluid retention (oedema) from heart failure, liver cirrhosis, or kidney disease, and high blood pressure that has not responded fully to other treatments. It is also used for primary hyperaldosteronism, and, at lower doses, for hormone-related acne and unwanted hair growth (hirsutism) in women, since it blocks the effects of androgens.

How spironolactone works

Spironolactone blocks aldosterone, a hormone that normally tells the kidneys to hold onto sodium and water while excreting potassium. By blocking it, spironolactone increases sodium and water loss in urine, reducing fluid buildup and blood pressure, while sparing potassium. At higher doses it also blocks androgen receptors, which is why it can reduce acne and excess hair growth.

Before you take it

• Do not take spironolactone if you already have high blood potassium, Addison's disease, or severe kidney impairment.
• Avoid combining it with potassium supplements, salt substitutes (many contain potassium chloride), other potassium-sparing diuretics, or ACE inhibitors and ARBs unless your doctor is monitoring you closely, since these combinations raise potassium further.
• NSAIDs can reduce spironolactone's effect and raise potassium; tell your doctor if you take them regularly.
• Avoid it in pregnancy; discuss any plan to become pregnant with your doctor.

Side effects

Common effects include increased urination, dizziness on standing, breast tenderness, and menstrual changes.

Stop and seek urgent medical care for:

• Muscle weakness, cramping, or tingling, which can signal high potassium.
• An irregular, slow, or pounding heartbeat.
• A severe allergic reaction: rash, swelling, or difficulty breathing.
• Yellowing of the skin or eyes.

Safety essentials

• Hyperkalaemia is spironolactone's defining risk: blood potassium and kidney function are checked before starting, after any dose change, and periodically during long-term treatment.
• Do not combine it with other potassium-raising medicines or supplements without medical supervision.
• Report any symptoms of high potassium, such as muscle weakness or an irregular heartbeat, immediately rather than waiting for your next test.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.