Can I take azathioprine while pregnant or breastfeeding?
A plain-words look at what the NHS, the US drug label and LactMed say about azathioprine.
In short
Pregnancy: Azathioprine can be taken while you're pregnant.
Breastfeeding: You can take azathioprine while breastfeeding, as long as your doctor, midwife or health visitor says your baby is healthy.
Your doctor, midwife or pharmacist can help you decide.
What this means for you
Pregnancy
- Keeping on with azathioprine matters especially if you've had an organ transplant or you have an autoimmune condition, because you need it to stay healthy.
- Do not stop taking azathioprine without talking to your doctor.
- Because azathioprine affects the immune system, there's a very small risk that, once your baby is born, it can affect how well they fight infections.
- If your baby is unwell, get advice from a doctor, your midwife or your health visitor, and make sure you tell them you took azathioprine while pregnant.
- Azathioprine can occasionally affect your liver.
- If you notice itching while on azathioprine, let a doctor or your midwife know, because you may need some tests.
Breastfeeding
- Carrying on with azathioprine is important to keep you well, and breastfeeding also has benefits for both you and your baby.
- Tiny amounts of azathioprine get into breast milk.
- Many breastfeeding mothers have taken it, and it does not usually cause side effects in their babies.
- If you're on a high dose of azathioprine, extra blood tests might be needed for your baby as a precaution.
- If you have any worries about your baby, contact your health visitor, midwife, doctor or pharmacist promptly.
- This includes if your baby is not feeding as well as they usually do, or keeps getting infections.
Talk to your doctor or pharmacist
This page is educational, not advice for your own situation. Talk to your doctor, midwife or pharmacist before you start, stop or change any medicine in pregnancy or while breastfeeding.
The details: what each source says
Azathioprine in pregnancy
The NHS says
Azathioprine can be taken while you're pregnant.
Keeping on with azathioprine matters especially if you've had an organ transplant or you have an autoimmune condition, because you need it to stay healthy. Do not stop taking azathioprine without talking to your doctor.
Because azathioprine affects the immune system, there's a very small risk that, once your baby is born, it can affect how well they fight infections.
If your baby is unwell, get advice from a doctor, your midwife or your health visitor, and make sure you tell them you took azathioprine while pregnant.
Azathioprine can occasionally affect your liver. If you notice itching while on azathioprine, let a doctor or your midwife know, because you may need some tests.
In our words, from the NHS page Azathioprine (nhs.uk). Contains public sector information licensed under the Open Government Licence v3.0 (OGL v3.0). The NHS does not endorse this site.
Azathioprine while breastfeeding
The NHS says
You can take azathioprine while breastfeeding, as long as your doctor, midwife or health visitor says your baby is healthy.
Carrying on with azathioprine is important to keep you well, and breastfeeding also has benefits for both you and your baby.
Tiny amounts of azathioprine get into breast milk. Many breastfeeding mothers have taken it, and it does not usually cause side effects in their babies.
If you're on a high dose of azathioprine, extra blood tests might be needed for your baby as a precaution.
If you have any worries about your baby, contact your health visitor, midwife, doctor or pharmacist promptly. This includes if your baby is not feeding as well as they usually do, or keeps getting infections.
In our words, from the NHS page Azathioprine (nhs.uk). Contains public sector information licensed under the Open Government Licence v3.0 (OGL v3.0). The NHS does not endorse this site.
LactMed says
Studies in women with inflammatory bowel disease, systemic lupus erythematosus or transplantation taking doses of azathioprine up to 200 mg daily for immunosuppression have found either low or unmeasurable levels of the active metabolites in milk and infant serum. Some evidence indicates a lack of adverse effects on the health and development of infants exposed to azathioprine during breastfeeding up to 4.6 years of age, but long-term follow-up for effects such as carcinogenesis have not been performed. Azathioprine has been extensively used by nursing mothers and numerous experts and professional guidelines have stated that the drug is a low risk to the nursing infant and acceptable to use during breastfeeding.[1-7]
Mothers with decreased activity of the enzyme that detoxifies azathioprine metabolites may transmit higher levels of drug to their infants in breastmilk. Poorly documented cases of mild, asymptomatic neutropenia and increased rates of infection have been reported occasionally. It might be desirable to monitor exclusively breastfed infants with a complete blood count with differential, and liver function tests if azathioprine is used during lactation, although some authors feel that monitoring is unnecessary.[8] Avoiding breastfeeding for 4 hours after a dose should markedly decrease the dose received by the infant in breastmilk.[9]
“Summary of Use during Lactation”, LactMed record “Azathioprine” (LM20), quoted verbatim. Everything LactMed reports about Azathioprine while breastfeeding.
What these words mean
- metabolite
- a substance made when the body breaks down a medicine
Definitions adapted from the NCI Dictionary of Cancer Terms (National Cancer Institute).
The US prescribing label says
NURSING MOTHERS The use of azathioprine in nursing mothers is not recommended. Azathioprine or its metabolites are transferred at low levels, both transplacentally and in breast milk. 8, 9, 10 Because of the potential for tumorigenicity shown for azathioprine, a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
Prescribing label, section “Nursing Mothers”: Azathioprine (oral), NuCare Pharmaceuticals,Inc. Label on DailyMed. Quoted verbatim; US labels are written for US prescribers and patients.
Other names
UK brand names (per the NHS): Imuran.
Sources
- NHS, Azathioprine (nhs.uk), page last reviewed 9 March 2023. Paraphrased. Contains public sector information licensed under the Open Government Licence v3.0.
- US drug label: Azathioprine (oral), NuCare Pharmaceuticals,Inc., human prescription drug, label effective 5 May 2026, set ID 5116b22b-1460-5535-e063-6394a90acbe5. DailyMed (National Library of Medicine). Public domain; quoted verbatim.
- Drugs and Lactation Database (LactMed), National Institute of Child Health and Human Development (NICHD), via NCBI Bookshelf, record “Azathioprine” (LM20), bulk release of 22 September 2026. LactMed on NCBI Bookshelf. Public domain; quoted verbatim. LactMed is a registered trademark of the U.S. Department of Health and Human Services.
Sources checked 26 September 2026. How we source and check every page.
Educational summary of named sources, not medical advice.