What is azathioprine?

Azathioprine, sometimes known by other names such as Imuran or Azapress, is a disease-modifying anti-rheumatic drug (DMARD). It works by reducing the activity of the body’s immune system, which may be overactive in some conditions.


Azathioprine isn’t a painkiller, but it can reduce the damage and effects caused by your condition. Your symptoms should start to improve 6–12 weeks after you start taking it.

Azathioprine can be prescribed by a consultant rheumatologist for:

How is it taken?

Azathioprine is usually given as tablets, taken once or twice daily. They should be swallowed whole and taken with or after food.

Your doctor will advise you about the correct dose, which will depend on how much you weigh. But you’ll usually start on a low dose of about 50mg, your doctor may increase this if necessary.

Azathioprine may not work right away, so it’s important to continue taking it even if it doesn’t seem to be working at first.

You should also continue taking it as prescribed when your symptoms improve and you start to feel better, as this will keep your condition under control.

Things to know before you start

Azathioprine is a very effective drug for many patients with arthritis. But it’s not suitable for everyone.

Before prescribing azathioprine, your doctor will order a blood test for an enzyme called TPMT, also known as thiopurine methyltransferase (thio-pew-reen meth-ile-trans-fe-raise). Enzymes are proteins in your body that can help to break down certain substances or chemicals.

TPMT helps to break down and remove azathioprine from the body. Low levels of TPMT may mean there is a slightly increased risk of side effects from azathioprine, so your doctor may suggest a lower dose.

If the TPMT result is very low, azathioprine may not be the right medication for you, and your doctor will discuss other treatment options.

Azathioprine may need to be used with caution if:

  • you have severe liver or kidney problems
  • you have bone marrow problems
  • you have infections that repeatedly come and go.

Before starting azathioprine you might need to be checked for previous hepatitis B or C infections, as this drug can increase the risk of these infections starting up again. If the tests are positive you may need antiviral treatment first.

You’ll also need to have a chest x-ray before starting azathioprine. If you have any long-term lung conditions, such as fibrosis or emphysema, you’ll need tests to see how your lungs are working to check whether azathioprine is suitable for you.

If you smoke, it’s worth cutting down or ideally giving up, as smoking increases the risk of complications of your condition and its treatments.

Side-effects and risks

Most people don’t have any side effects, and for those who do, they aren’t usually serious. However, if you do have severe side effects, or are concerned about your symptoms, contact one of the healthcare professionals in charge of your care.

Azathioprine may cause:

  • nausea or feeling sick
  • vomiting
  • diarrhoea
  • loss of appetite
  • hair loss
  • skin rashes
  • sensitivity to sunlight.

Because azathioprine affects the immune system, it can make you more likely to develop infections. It can also affect your blood count or liver. So you’ll need to have blood tests before and during your course of azathioprine.

You may be asked to keep a record of your blood test results in a booklet, and you should take it with you when you visit your GP or the hospital.

You should tell your doctor or nurse specialist straight away if you develop any of the following after starting azathioprine:

  • a sore throat, fever or any other signs of infection
  • unexplained bruising or bleeding
  • yellowing of the skin or eyes, this is known as jaundice
  • any new symptoms that concern you.

Contact your rheumatology team if you get chickenpox or shingles, or if you come into come into contact with someone who has them and you’ve never had chickenpox before.

These illnesses can be worse than usual if you’re on azathioprine. You may need treatment for them, and your azathioprine may be stopped until you’re better.

Tips to reduce your risk of infection

  • Try to avoid close contact with people you know have an infection.
  • Wash your hands regularly and carry around a small bottle of antibacterial hand gel.
  • Keep your mouth clean by brushing your teeth regularly.
  • Stop smoking if you’re a smoker.
  • Make sure your food is stored and prepared properly.
  • Try to keep your house clean and hygienic, especially the kitchen, bathrooms and toilets.

Effects on other treatments

Azathioprine can interact with medications used to treat gout, such as allopurinol and febuxostat. It’s also known to interact with some medications used to control high blood pressure, such as warfarin. So make sure to discuss what medications you’re on with your rheumatology team, as they might suggest starting you on an alternative DMARD.

Check with your doctor or pharmacist before starting any new medications. And remember to mention you’re on azathioprine if you’re treated by anyone other than your usual rheumatology team.

You can carry on taking a non-steroidal anti-inflammatory drug (NSAID) or painkillers if needed, unless your doctor advises otherwise.

Don’t take over the counter preparations or herbal remedies without discussing this first with your doctor or pharmacist as some of them could react badly with azathioprine.


The pneumonia (new-mow-nee-uh) vaccine and yearly flu vaccines don’t affect azathioprine and are perfectly safe to have while you’re taking it. It’s very important to have these to reduce your risk of infection.

Avoid having live vaccines, such as MMR (measles, mumps and rubella) or yellow fever. Vaccines for chickenpox are also live and should be avoided if you're on azathioprine.

The Zostavax shingles vaccine is a live vaccine and isn’t usually recommended for people who are on azathioprine, though you may be able to have it if you're on a low dose of azathioprine. Alternatively, a non-live shingles vaccine (Shingrix) is available so you may be able to have this instead. Your healthcare team will be able to advise on this.

If you’re unsure about whether you should be having a vaccine, have a chat with your rheumatology team first.

Having an operation

If you’re due to have surgery, you might need to stop taking azathioprine or other drugs beforehand. You should speak to your doctor and surgeon about this first.


Alcohol and azathioprine can both affect your liver, so it’s important you don’t drink more alcohol than the government’s recommended limits.

Government guidelines say both men and women should have no more than 14 units of alcohol a week, and that you should spread these through the week rather than having them all in one go.

You can find out more about units of alcohol at

Some rheumatologists may suggest stricter limits. If you’re concerned, discuss your alcohol intake with your healthcare team.

Fertility, pregnancy and breastfeeding

If you’re planning a family or become pregnant while taking azathioprine, you should discuss this with your doctor as soon as possible.

Current guidelines say that azathioprine can be taken if trying for a baby and even when pregnant or breastfeeding.

Men are also fine to continue taking it when trying for a baby.