Sounds like 'ay-za-THYE-oh-preen'

Key points about azathioprine

  • Azathioprine is used to treat autoimmune conditions such as Crohn's disease, ulcerative colitis and rheumatoid arthritis.
  • Azathioprine is commonly called Imuran or Azamun.
  • Find out how to take it safely and possible side effects. 
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Azathioprine is an immunosuppressant medicine, which means it weakens your bodys defence (immune) response. It belongs to a class of medicines known as disease-modifying antirheumatic drugs (DMARDs).

It is used to treat a number of autoimmune conditions related to an ‘overactive’ immune system, such as Crohn's disease, ulcerative colitis and rheumatoid arthritis. Autoimmune means that your body ‘attacks’ itself, without any real known cause or reason.

Azathioprine is also used to stop transplant rejection for people who have had transplant surgery. 

In Aotearoa New Zealand azathioprine is available as tablets (25 mg and 50 mg) and as an injection (but this is usually only given in hospital). 

  • The dose of azathioprine is different for different people, depending on your condition, weight and response to treatment.
  • Always take your azathioprine exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much azathioprine to take, how often to take it and any special instructions.

  • Timing of your doses: Try to take your dose at the same time each day. Azathioprine is best taken on an empty stomach, at least 1 hour before or 3 hours after food or milk. 
  • Swallow your tablets whole with a drink of water. Do not break, chew or crush the tablets.
  • Missed dose: If you forget to take your azathioprine dose, take it as soon as you remember. But if it is nearly time for your next dose, take the next dose at the right time. Do not take double the dose.    
  • Keep taking azathioprine regularly. Azathioprine does not work straight away. It usually takes a few weeks or months before you notice the full benefits.   

Here are some things to know when you're taking azathioprine. Other things may be important as well, so ask your healthcare provider what you should know about.

  • You will need to have regular blood tests to monitor for side effects and to check whether the treatment is effective. Blood tests are very important during the first few months of treatment.
  • Azathioprine weakens your bodys defence (immune) system, so you are more likely to pick up infections. It is important to avoid anyone who has chickenpox or shingles.    
  • Azathioprine makes your skin more sensitive to the sun. Protect your skin when you are in the sun, especially between 10am and 3pm. Wear protective clothing and use a high factor sunscreen (SPF 30+).
  • You should avoid becoming pregnant while you or your partner are taking azathioprine. Discuss with your healthcare provider which types of contraception are suitable for you and your partner.  
  • Some vaccines should not be taken if you are on azathioprine. Always check with your doctor or pharmacist first. It is safe for you to have the annual flu vaccine.
  • Azathioprine may interact with a few medicines and herbal supplements, so check with your doctor or pharmacist before starting azathioprine or before starting any new medicines, including those you may buy over the counter.

Like all medicines, azathioprine can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.


Side effects What should I do?
  • Feeling sick (nausea)
  • Vomiting (being sick)
  • Loss of appetite (don't feel like eating) 
  • This is quite common when you first start taking azathioprine.
  • Tell your doctor if these bother you.
  • Signs of getting an infection, such as feeling unwell, fever or chills  
  • Tell your doctor immediately or phone Healthline on 0800 611 116.
  • Signs of changes in your blood cells, such as a severe sore throat, mouth ulcers, easy bruising, nosebleeds, bleeding gums, shortness of breath or fever
  • Tell your doctor immediately as you may need a blood test.
  • Signs of problems with your liver, such as sudden pains in your stomach, loss of appetite or yellowing of your skin and eyes
  • Tell you doctor immediately or phone Healthline on 0800 611 116.
For more information on side effects, see the Medsafe consumer information leaflets Azamun(external link) and Imuran(external link).

Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product(external link)

The following links have more information about azathioprine. Be aware that websites from other countries may have information that differs from New Zealand recommendations.

Azathioprine(external link) (Azathioprine for transplant patients(external link)NZ Formulary
Azathioprine(external link) RheumInfo
Azamun(external link) Consumer Information Sheet, Medsafe, NZ
Azathioprine(external link) Arthritis Australia


  1. Azathioprine(external link) NZ Formulary
  2. Azamun(external link) Data Sheet, Medsafe, NZ

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Credits: Sandra Ponen, Pharmacist, Healthify He Puna Waiora. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Maya Patel, Pharmacist, Auckland

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