What it is used for

Crohn's disease and ulcerative colitis
Rheumatoid arthritis
Preventing rejection after an organ transplant
Autoimmune hepatitis, lupus, vasculitis and some other autoimmune conditions

Read our guides:

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.

Severe eczema, under a dermatologist
Myasthenia gravis and some other nerve and muscle conditions

How it works

Azathioprine slows down the production of white blood cells called lymphocytes, which drive inflammation in autoimmune conditions. It takes 2 to 3 months to work fully.

Side effects

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

Common side effects

feeling sick
being sick
loss of appetite
tiredness
more infections
hair thinning

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:

a high temperature, sore throat, mouth ulcers or other signs of infection
unusual bruising or bleeding
yellowing of the skin or eyes
severe stomach pain, which can be a sign of an inflamed pancreas

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

You need a blood test (TPMT) before starting, and regular blood tests during treatment.
It increases the risk of skin cancer. Use sunscreen and check your skin.
It interacts with allopurinol and febuxostat. Your doctor must adjust the dose.
Avoid live vaccines.

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.