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

Azathioprine is used to treat autoimmune conditions such as Crohn's disease, ulcerative colitis and rheumatoid arthritis. Find out how to take it safely and possible side effects. Azathioprine is commonly called Imuran or Azamun.

Type of medicine Also called
  • Immunosuppressant medicine (it weakens your body's immune response)
  • Belongs to a class of medicines known as disease-modifying antirheumatic drugs (DMARDs)
  • Imuran®
  • Azamun®

What is azathioprine?

Azathioprine is an immunosuppressant medicine, which means it weakens your bodys defence (immune) response. 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. By weakening your immune system, it helps your body accept the new organ as if it were your own. Azathioprine is prescribed by a specialist doctor who is experienced in treating the condition. Azathioprine is available as tablets and as an injection.


  • In New Zealand there are 2  strengths of azathioprine tablets – 25 mg and 50 mg. 
  • Always take your azathioprine exactly as your doctor has told you. 
  • The dose of azathioprine is different for different people.
  • Your doctor will work out your dose based on your condition, your weight and your response to treatment.
  • The pharmacy label on your medicine will tell you how much azathioprine to take, how often to take it and any special instructions.

How to take azathioprine

  • Timing: Take your azathioprine dose 1 or 2 times a day, as directed by your doctor. 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. But if azathioprine makes you feel nauseous (sick), try taking it after food or at bedtime, or ask your doctor if you can divide your dose and take it twice a day.    
  • Swallow your tablets whole with a drink of water. Do not break, chew or crush the tablets.
  • Avoid or limit alcohol. Heavy drinking can increase your risk of side effects, such as problems with your liver. 
  • 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.   

Precautions when taking azathioprine

Before starting azathioprine

  • Are you pregnant, planning a pregnancy or breastfeeding?
  • Do you have problems with the way your liver or kidneys work?
  • Have you had chickenpox or shingles?
  • Are you taking other medicines?
  • Have you recently had any vaccinations?

If so, it’s important that you tell your doctor or pharmacist before you start azathioprine. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

While taking azathioprine

Extra care is needed when taking azathioprine.

  • Blood tests: You will need to have regular blood tests to monitor for side effects and to work out whether the treatment is effective. Blood tests are very important during the first few months of treatment.
  • Risk of infections: Because azathioprine weakens your bodys defence (immune) system, you are more likely to pick up infections. It is important to avoid anyone who has chickenpox or shingles.    
  • Sun protection: 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+).
  • Pregnancy: Make sure you or your partner do not get pregnant if either of you are taking azathioprine. Speak to your doctor about contraception.
  • Vaccines: 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.

What are the side effects of azathioprine?

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.
  • Take your azathioprine with food, or ask your doctor about splitting your dose and taking it twice a day instead of all at once.
  • Tell your doctor if troublesome.
  • 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 and Imuran.

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


Azathioprine interacts with some medicines and herbal supplements, so check with your doctor or pharmacist before you start taking anything new. Check with a pharmacist before taking over-the-counter anti-inflammatories such as diclofenac (eg, Voltaren Rapid), ibuprofen (eg, Nurofen) or naproxen (eg, Naprogesic). Taking these together with azathioprine may increase your risk of side effects.

Learn more

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 (Azathioprine for transplant patientsNZ Formulary
Azathioprine RheumInfo
 Consumer Information Sheet, Medsafe, NZ 
Azathioprine Arthritis Australia


  1. Azathioprine NZ Formulary
  2. Azamun Data Sheet, Medsafe, NZ

Additional resources for healthcare professionals

Imuran Medsafe, NZ
Immunomodulatory medicines and risk of progressive multifocal leukoencephalopathy Medsafe, NZ, 2016

Credits: Sandra Ponen, Pharmacist. Reviewed By: Maya Patel, Pharmacist, Auckland Last reviewed: 06 Sep 2021