Tamoxifen

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Date: June 2026, Version 4.0

Quick read

Tamoxifen should not be used during pregnancy. Women planning to conceive should speak to their specialist about stopping tamoxifen.

What is it?

Tamoxifen is most commonly used to treat breast cancer. It works by blocking the effects of the hormone oestrogen in breast tissue.

Benefits

What are the benefits of using tamoxifen?

Tamoxifen is an effective treatment for some types of breast cancer. It can also reduce the chance of breast cancer developing in women at higher risk, such as those with a family history.

Risks

Are there any risks of using tamoxifen in pregnancy?

Tamoxifen should not be used during pregnancy or when trying to conceive. There is not much information about pregnant women who have taken tamoxifen, so it is unclear whether it may harm your baby. There have been reports of babies being born both with and without birth defects after their mothers took tamoxifen during pregnancy. Because tamoxifen interferes with the hormone oestrogen, there are concerns that it may affect genital development in female babies.

Alternatives

Are there any alternatives to using tamoxifen in pregnancy?

Yes. If you are planning a pregnancy, your specialist will usually advise you to pause tamoxifen treatment. Tamoxifen should be stopped three months before trying to conceive so that it has time to leave your body before the early stages of your baby’s development. Do not stop tamoxifen treatment without speaking to your specialist.

No treatment

What if I prefer not to take medicines during pregnancy?

Your doctor will be happy to discuss any concerns about medicines prescribed during pregnancy to help you decide what is best for you and your baby.

Will my baby need extra monitoring?

As part of routine antenatal care, most women will be offered a detailed scan at around 20 weeks of pregnancy to check the baby’s development. Women who have taken tamoxifen during pregnancy may be offered some extra monitoring of the baby as a precaution.

Who can I talk to if I have questions? 

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

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

Our online reporting system (MyBump Portal) allows women who are currently pregnant to create a secure record of their pregnancy, collected through a series of questionnaires. You will be asked to enter information about your health, whether or not you take any medicines, your pregnancy outcome and your child's development. 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 the MyBump Portal to register.

General information
Sadly, miscarriage and birth defects can occur in any pregnancy.

Miscarriage occurs in about 1 in every 5 pregnancies, and 1 in every 40 babies are born with a birth defect. This is called the ‘background risk’ and happens whether medication is taken or not.

Most medicines cross the placenta and reach the baby. For many medications this is not a problem. However, some medicines can affect a baby’s growth and development.

If you take regular medication and are planning to conceive, you should discuss whether your medicine is safe to continue with your doctor/health care team before becoming pregnant. If you have an unplanned pregnancy while taking a medicine, you should tell your doctor as soon as possible.

If a new medicine is suggested for you during pregnancy, please make sure that the person prescribing it knows that you are pregnant. If you have any concerns about a medicine, you can check with your doctor, midwife or pharmacist.

Our Bumps information leaflets provide information about the effects of medicines in pregnancy so that you can decide, together with your healthcare provider, what is best for you and your baby.