Lyng Pharmacy
Medicines A–Z · Aldosterone antagonist / diuretic

Spironolactone

A potassium-sparing diuretic · Written by the Lyng Pharmacy team, based on NHS and BNF guidance · Updated August 2026
Also sold asAldactone
Type of medicineAldosterone antagonist / diuretic
Available asTablets, oral suspension
How you get itPrescription only

Spironolactone is a diuretic that, unlike most, holds on to potassium rather than losing it. That makes it valuable in heart failure and liver disease, and it also makes high potassium the main thing to watch for.

What it is used for

Heart failure, fluid retention in liver disease, resistant high blood pressure, and primary hyperaldosteronism. It is also used at low doses for acne and hirsutism in women, though that is off-label.

How to take it

Once daily, usually in the morning, with or after food. Taking it later in the day means being up at night.

Blood tests check kidney function and potassium before starting and regularly afterwards — these are the point of the monitoring, not a formality.

Potassium — the main risk

Contact your doctor promptly for muscle weakness, tingling or numbness, an irregular or slow heartbeat, or unusual tiredness — possible signs of high potassium, which can affect heart rhythm.

Avoid potassium-based salt substitutes such as LoSalt, and do not take potassium supplements unless specifically told to.

Risk rises alongside ACE inhibitors, sartans, anti-inflammatories such as ibuprofen, and in kidney impairment or dehydration. Tell any prescriber you take spironolactone.

Pause it during dehydrating illness — vomiting, diarrhoea, fever — and ask for a sick day rules card.

Other side effects

Breast tenderness or enlargement in men (gynaecomastia) is a well-recognised effect and a common reason for switching. It is worth reporting rather than living with.

Also common: dizziness on standing, headache, nausea, and in women irregular periods.

It is generally avoided in pregnancy — speak to your prescriber if you are planning one.

Always read the label. This page is general information, not advice for your situation. Doses, warnings and interactions differ between products and between people. Check the leaflet inside your medicine, and ask our pharmacist if anything is unclear — that conversation is free and takes two minutes.

Questions about Spironolactone?

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Frequently asked questions

Why is potassium checked on spironolactone?
Unlike most diuretics it retains potassium, and high potassium can affect heart rhythm. Blood tests before and during treatment are essential.
Can I use LoSalt on spironolactone?
No. Potassium-based salt substitutes add to the potassium your body is already retaining. Avoid them.
Why has spironolactone caused breast tenderness?
Gynaecomastia is a recognised effect in men. It is a common reason for switching — report it rather than putting up with it.
Should I stop spironolactone if I am ill?
Pause it during dehydrating illness such as vomiting or diarrhoea, and ask us or your GP for a sick day rules card.

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