Tamoxifen

Date: September 2021, Version 3

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.

Benefits

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).

Risks

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.

Alternatives

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.

No treatment

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.

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.