(Date: December 2019. Version: 3)

This factsheet has been written for members of the public by the UK Teratology Information Service (UKTIS). UKTIS is a not-for-profit organisation funded by the UK Health Security Agency (UKHSA) on behalf of UK Health Departments. UKTIS has been providing scientific information to health care providers since 1983 on the effects that medicines, recreational drugs and chemicals may have on the developing baby during pregnancy.

Quick read

Azathioprine and mercaptopurine can be used in pregnancy if needed to control an inflammatory condition or prevent rejection of a transplanted organ.

What is it?

Azathioprine (Imuran®) is used to treat severe eczema, a number of auto-immune illnesses such as lupus, inflammatory bowel disease, rheumatoid arthritis and psoriasis, and to prevent the rejection of transplanted organs. Another form of the same medicine called mercaptopurine (Hanixol®, Xaluprine®) is used to treat certain forms of leukaemia, and occasionally inflammatory bowel disease.

What are the benefits of using azathioprine/mercaptopurine in pregnancy?

Azathioprine and mercaptopurine reduce inflammation by stopping the immune system from attacking the body’s tissues. This is important to reduce unpleasant symptoms and prevent long-term damage. It may also lower the chance of some pregnancy problems linked to uncontrolled inflammation, including miscarriage and lower birth weight. It is also vital for both mother and baby that a transplanted organ continues to function well during pregnancy.

What are the risks of using azathioprine/mercaptopurine in pregnancy?

There is no evidence that use of azathioprine or mercaptopurine harm the baby if taken in pregnancy.

Are there any alternatives to using azathioprine/mercaptopurine in pregnancy?

Possibly. Other medicines can often be used to treat inflammatory conditions during pregnancy. However, azathioprine and mercaptopurine are usually considered to be among the safest options, as several studies have shown that they do not harm the baby.
Some women may find that their symptoms improve during pregnancy; if so, their specialist may advise that their medicine(s) can be altered. However, women should not change or stop their medication without speaking to their doctor.
Women who are planning a pregnancy should speak to their specialist to determine which medicine is best. This can be arranged through the GP or specialist clinic.
If a woman becomes pregnant while taking azathioprine or mercaptopurine she should be reviewed by her doctor as soon as possible.

What if I prefer not to take medicines during pregnancy?

It is important that inflammatory conditions are well-treated during pregnancy in order to avoid a flare-up of symptoms and to reduce the chance of certain pregnancy complications. Similarly, preventing rejection of a transplanted organ is vital to the health of the woman and her baby. A doctor will be happy to discuss any concerns.

Will I or my baby need extra monitoring during pregnancy?

As part of routine antenatal care in the UK, women are invited for a very detailed scan at around 20 weeks of pregnancy to check the baby’s development. No further scans to check for birth defects will be required due to use of azathioprine or mercaptopurine. However, women with inflammatory illnesses or a transplanted organ will usually be offered closer monitoring during pregnancy.

Are there any risks to my baby if the father has taken azathioprine/mercaptopurine?

There is currently no evidence that azathioprine or mercaptopurine used by the father can harm the baby through effects on the sperm.

Who can I talk to if I have questions?

If you have any questions regarding the information in this leaflet please discuss them with your health care provider. They can access more detailed medical and scientific information from

How can I help to improve drug safety information for pregnant women in the future?

Our online reporting system allows women with a current or previous pregnancy to create a digitally secure ‘my bumps record’. You will be asked to enter information about your health, whether or not you take any medicines, and your pregnancy outcome. You can update your details at any time during pregnancy or afterwards. This information will help us better understand how medicines affect the health of pregnant women and their babies. Please visit to register.

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General information 

Up to 1 out of every 5 pregnancies ends in a miscarriage, and 1 in 40 babies are born with a birth defect. These are referred to as the background population risks.  They describe the chance of these events happening for any pregnancy before taking factors such as the mother’s health during pregnancy, her lifestyle, medicines she takes and the genetic make up of her and the baby’s father into account.

Medicines use in pregnancy

Most medicines used by the mother will cross the placenta and reach the baby. Sometimes this may have beneficial effects for the baby.  There are, however, some medicines that can harm a baby’s normal development.  How a medicine affects a baby may depend on the stage of pregnancy when the medicine is taken. If you are on regular medication you should discuss these effects with your doctor/health care team before becoming pregnant.

If a new medicine is suggested for you during pregnancy, please ensure the doctor or health care professional treating you is aware of your pregnancy.

When deciding whether or not to use a medicine in pregnancy you need to weigh up how the medicine might improve your and/or your unborn baby’s health against any possible problems that the drug may cause. Our bumps leaflets are written to provide you with a summary of what is known about use of a specific medicine in pregnancy so that you can decide together with your health care provider what is best for you and your baby.   

Every pregnancy is unique. The decision to start, stop, continue or change a prescribed medicine before or during pregnancy should be made in consultation with your health care provider. It is very helpful if you can record all your medication taken in pregnancy in your hand held maternity records.

Disclaimer: This information is not intended to replace the individual care and advice of your health care provider. New information is continually becoming available. Whilst every effort will be made to ensure that this information is accurate and up to date at the time of publication, we cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes following decisions made on the basis of this information. We strongly advise that printouts should NOT be kept for any length of time, or for “future reference” as they can rapidly become out of date.

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