Spironolactone: uses, potassium risks and side effects

Spironolactone is a diuretic. The NHS lists swelling caused by fluid build-up, heart failure, and high blood pressure that has not responded to other medicines as its main uses. By increasing urine output it removes surplus water from the body.

Unlike some water tablets, it tends to keep potassium in the body rather than flush it out. That makes it useful where potassium would otherwise run low, and also explains why potassium needs watching.

It comes as tablets or a liquid. Take it with food or just after food. Your dose and how long you take it for depend on why you were prescribed it, so follow the label and ask a pharmacist if anything is unclear. If you use the liquid, measure it with the equipment provided.

Miss a dose and you can take it as soon as you remember unless the next dose is due, but never take two at once to make up. If you take more than prescribed, NHS 111 can advise.

The NHS says spironolactone is unsuitable if you have had an allergic reaction to it, have severe kidney problems, cannot pass urine properly, have Addison's disease, or have had high potassium in the past.

Tell the prescriber about every medicine you use as well, because several affect potassium. Dose adjustments and extra checks are common in people with reduced kidney function.

Common effects include dizziness, nausea, muscle or leg cramps, tiredness, and breast pain or an increase in breast size, which can affect men as well as women. Mention breast changes to your doctor.

Rare but serious effects are anaphylaxis, Stevens-Johnson syndrome with blistering skin, liver problems such as jaundice, kidney problems, and high potassium. High potassium may feel like muscle weakness, tiredness, numbness and an irregular heartbeat. Call NHS 111 if you think you are having serious side effects, and 999 for anaphylaxis such as a swollen throat or tongue and difficulty breathing. It generally does not affect driving, but avoid it if you feel dizzy or have vision problems.

Because potassium is the concern, avoid salt substitutes such as LoSalt, which are high in potassium, and ask your clinician about foods rich in it such as bananas and avocados. Do not start potassium supplements unless a doctor has said so.

Named interactions on the NHS page are digoxin, eplerenone, potassium supplements, and anti-inflammatory painkillers including ibuprofen, aspirin and diclofenac. Check with a pharmacist before using any over-the-counter pain relief.

Spironolactone is not usually recommended during pregnancy because it can potentially affect a baby's development. If you are pregnant or planning to be, speak to your doctor about alternatives.

You may be able to take it while breastfeeding, but check with a doctor or healthcare professional first. Blood tests and kidney checks are part of safe long-term use, so keep your appointments.