Spironolactone is a potassium-sparing diuretic used for heart failure, fluid in liver disease, resistant high blood pressure and primary aldosteronism. It is also used for acne and hirsutism in women. It raises potassium, so blood tests are part of the treatment.
What is Spironolactone?
Spironolactone is a potassium-sparing diuretic and an aldosterone antagonist. Common strengths are 25 mg, 50 mg and 100 mg, and it is a Schedule 3 medicine.
Aldosterone is a hormone that tells the kidney to retain sodium and water and to excrete potassium. Spironolactone blocks its receptor. Sodium and water are lost, and — unlike most diuretics — potassium is retained rather than flushed out.
That reversal is the whole point of the medicine, and it explains both its uses and its main risk. Loop diuretics such as furosemide and thiazides such as Ridaq deplete potassium; spironolactone conserves it, which is why the two are so often prescribed together — they balance each other.
Spironolactone also blocks androgen receptors, an effect unrelated to the kidney. That produces some of its side effects in men, and is the basis of a completely separate use in women, covered below.
In heart failure, spironolactone is not really working as a diuretic at all. At the low amounts used there, its benefit comes from blocking aldosterone’s effects on the heart muscle itself — aldosterone drives fibrosis and scarring. That is why it improves survival, and why the amount used for heart failure is far smaller than the amount used to shift fluid.
What is Spironolactone commonly used for?
- Heart failure, where it reduces hospital admissions and improves survival — one of the medicines that changes the course of the illness.
- Ascites in liver cirrhosis — fluid in the abdomen — where it is the diuretic of first choice, because the condition involves excess aldosterone.
- Resistant high blood pressure, where three other medicines have not achieved control. It is notably effective in this situation.
- Primary aldosteronism (Conn’s syndrome), a treatable cause of high blood pressure produced by too much aldosterone.
- Oedema from cardiac, hepatic or renal causes, often with a loop diuretic.
- Acne in women, particularly hormonal acne along the jawline that has not responded to other treatment.
- Hirsutism and female pattern hair loss, through the same anti-androgen effect.
- Gender-affirming hormone therapy, as an androgen blocker.
The acne and hirsutism uses often surprise people handed a “water tablet” for their skin. Spironolactone blocks androgen receptors in the skin, reducing oil production — which is why it works for hormonal acne where antibiotics have not. It is used in women and must not be used in pregnancy, since blocking androgens can affect development of a male fetus.
How Spironolactone fits into this medicine category
| Group | Examples | Effect on potassium |
|---|---|---|
| Potassium-sparing | Spironolactone, amiloride, eplerenone | Retains potassium |
| Loop diuretics | Furosemide | Strongly depletes potassium |
| Thiazide diuretics | Hydrochlorothiazide (Ridaq) | Depletes potassium |
| ACE inhibitors / ARBs | Enalapril, losartan | Raises potassium |
| Calcium channel blockers | Amlodipine (Ciplavasc) | No significant effect |
Note that ACE inhibitors also raise potassium — and someone with heart failure is commonly on both an ACE inhibitor and spironolactone. That combination is deliberate and beneficial, and it is exactly why potassium is monitored. See the heart, blood pressure and circulation medicines hub.
What to check before using Spironolactone
Do not take potassium supplements or use a salt substitute unless specifically told to. Most salt substitutes are potassium chloride, and combining one with spironolactone is a well-recognised route to dangerously high potassium.
Blood tests are part of the treatment, not optional. Potassium and kidney function are checked before starting, within a week or two of starting or any increase, and periodically thereafter.
Take it in the morning, with food.
Tell your prescriber or pharmacist if:
- You have kidney disease. This is the main determinant of whether spironolactone is safe for you.
- You have high potassium, or have had it before.
- You have Addison’s disease.
- You take an ACE inhibitor, an ARB, another potassium-sparing diuretic, trimethoprim or co-trimoxazole (Purbac) — all of which also raise potassium.
- You take an anti-inflammatory such as ibuprofen or diclofenac, which raises potassium further and reduces the diuretic effect.
- You take digoxin or lithium.
- You are pregnant or planning pregnancy. Spironolactone is avoided in pregnancy.
- You have liver disease.
Follow the dispensing label. This page does not set doses, and the amount differs greatly between heart failure and ascites.
Possible cautions and when to ask a pharmacist or doctor
High potassium is the risk that matters. It often causes no symptoms until it becomes dangerous, and severe hyperkalaemia can cause life-threatening heart rhythm disturbances. This is why the blood tests are non-negotiable — they detect a problem you cannot feel.
Report muscle weakness, numbness or tingling, palpitations or an irregular heartbeat promptly.
Pause it during illness. During vomiting, diarrhoea or dehydration, potassium can rise sharply and kidney function fall. Ask your doctor whether to hold it — this is one of the more common scenarios in which people come to harm.
Breast tenderness and enlargement in men (gynaecomastia) is a well-known effect at higher amounts, caused by the anti-androgen action. It is reversible on stopping and is worth raising — eplerenone is an alternative without this effect.
Menstrual irregularity can occur in women.
Do not stop it on your own in heart failure. Like an ACE inhibitor, it produces no sensation while doing something important.
Seek urgent medical attention for palpitations or an irregular heartbeat, marked muscle weakness, numbness or tingling, fainting, confusion, a significant reduction in urine, severe dizziness, or yellowing of the skin or eyes.
Related medicine guides
- Browse Heart, Blood Pressure & Circulation Medicines guides
- Read: Ciplavasc used for
- Read: Ridaq used for
Frequently asked questions
What is spironolactone used for? Heart failure, fluid in liver disease, resistant high blood pressure and primary aldosteronism — and in women, hormonal acne and hirsutism.
Why has it been prescribed for my acne? Spironolactone blocks androgen receptors in the skin, reducing oil production. It is used in women for hormonal acne that has not responded to other treatment.
How is it different from other water tablets? Most diuretics flush potassium out; spironolactone retains it. That is why it is often paired with a loop or thiazide diuretic.
Why do I need blood tests? To check potassium and kidney function. High potassium usually causes no symptoms until it is dangerous, so it can only be detected by testing.
Can I use a salt substitute? No, unless specifically told to. Most are potassium chloride, and spironolactone already raises potassium.
Why is my chest tender? Breast tenderness or enlargement is a recognised effect in men, from the anti-androgen action. Raise it with your prescriber — an alternative without this effect exists.