(Date: September 2021. 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.

What is it?

Tamoxifen is a medicine most commonly used to treat breast cancer and works by blocking the effect of the hormone oestrogen in breast tissue.

What are the benefits of using tamoxifen in pregnancy?

Tamoxifen is an effective treatment for some types of breast cancer. It can also help to reduce the chance of developing breast cancer in women who are at high risk (such as those with a family history of breast cancer). 

Are there any risks of using tamoxifen in pregnancy?

Tamoxifen is generally not recommended during pregnancy or in women who are trying to conceive. There is not much information available about pregnant women who took tamoxifen so it is unclear how much of a risk it might pose to the baby. While there are case reports of babies being born with birth defects following tamoxifen exposure, there are also reports of babies being born without malformations. Because tamoxifen interferes with the hormone oestrogen, there are concerns that it may affect genital development in girls.

Are there any alternatives to using tamoxifen in pregnancy?

Possibly; some women may be able to pause their tamoxifen treatment for a while if they are planning a pregnancy. Women using tamoxifen who want to have a baby can speak to their doctor or specialist so that their medication can be reviewed, and the risks and benefits of stopping for a while can be weighed up. Tamoxifen should ideally be stopped three months prior to conceiving so that there is none left in the body during the baby’s early development.

What if I prefer not to take medicines during pregnancy?

Your doctor will only prescribe medicines when absolutely necessary and will be happy to talk with you about any concerns that you might have.

Will my baby need extra monitoring?

As part of routine antenatal care, most women will be offered a very detailed scan at around 20 weeks of pregnancy to check the baby’s development. Women who have taken tamoxifen in 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.

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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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