What it is used for

Preventing gout attacks (it does not treat an attack that has already started)
Preventing kidney stones made of uric acid or calcium oxalate
Preventing high uric acid levels during some cancer treatments

Read our guides:

Gout

Off-label uses

Doctors sometimes prescribe a medicine for a condition it is not officially licensed for. This is called off-label use. It is legal and common when there is good evidence it helps, and your doctor should explain why they are suggesting it.

Allopurinol is not commonly used off-label.

How it works

Allopurinol blocks an enzyme called xanthine oxidase, which the body uses to make uric acid. Lower uric acid levels mean crystals stop forming in joints and existing crystals slowly dissolve.

Side effects

Like all medicines, Allopurinol can cause side effects, although not everyone gets them. Many are mild and ease after the first few weeks.

Common side effects

skin rash
more gout flares in the first few months

Tell your doctor or pharmacist if these bother you or do not go away.

Serious side effects

These are rare. Call 111 or contact your doctor straight away if you get:

any skin rash, especially with a high temperature, sore mouth, blisters or peeling skin. Stop and get help straight away
yellowing of the skin or eyes
unusual bleeding or bruising

Call 999 if you have signs of a serious allergic reaction, such as swelling of your lips, mouth, throat or tongue, or trouble breathing.

You can report any side effect to the Yellow Card scheme, run by the medicines regulator.

Stopping and withdrawal

Important safety information

Keep taking it during a gout attack once you have started it.
A rash can be a sign of a rare but serious reaction. Get medical help straight away.
It interacts with azathioprine and mercaptopurine. Your doctor must adjust these.
Drink plenty of fluids.

Questions about your medicine?

A pharmacist can answer questions about your medicines for free, without an appointment. You can also ask your GP for a medication review. Check if you can get free prescriptions.