Medicines used by men around the time of conception (‘paternal exposure’)

Date: March 2024, Version 3.0

Quick read

Most medicines taken by men around the time of conception are unlikely to affect a baby’s development in the womb. However, men receiving drugs that can damage DNA (such as some medicines for chemotherapy and/or inflammatory illnesses) might be advised to avoid fathering a pregnancy for up to six months after treatment has finished.

Can medicines affect male fertility?

Some medicines can reduce male fertility by lowering the sperm count or affecting the way that sperm move and swim (sperm motility); other medicines affect the amount of semen produced. Some medicines can also affect a man’s libido (sex drive) or cause erectile dysfunction. These effects usually disappear once the medicine is stopped.

Can a medicine taken by the father around the time of conception affect the baby?

Sperm cells take around three months to fully develop, so in theory, medicines taken up to three months before conception could affect a pregnancy.

There are very few studies about whether medicines taken by a man can impact on a baby’s development. However, most medicines work in ways that are not expected to cause problems with sperm and the studies that have been carried out generally do not raise concern.

The types of drugs that could possibly affect sperm are mainly those that damage DNA, including some medicines used for chemotherapy and/or to treat inflammatory illness. To be safe, men taking these drugs may be advised by their doctor to avoid fathering a pregnancy until three to six months after treatment has finished.

Please see individual bumps leaflets for advice on use of medicines in men who want to father a pregnancy.

What about exposure to medicine in semen through sexual intercourse?

Medicines taken by men can pass in small amounts into semen. In theory, medicine could therefore be absorbed into a woman’s bloodstream following unprotected sex and could reach a baby in the womb. In practice, only tiny amounts of drugs in semen would ever reach a baby in the womb and it is therefore very unlikely that this could cause problems.

As a precaution, the manufacturers of a number of medicines that could cause birth defects through exposure in early pregnancy recommend that men taking them avoid unprotected sex with pregnant women. Examples include thalidomide, mycophenolate mofetil and leflunomide. 

Men who have recently had Zika virus or travelled to an area with Zika virus should avoid unprotected sex with pregnant women as the virus might be passed on via sperm. For more information see the Zika virus BUMP leaflet. 

What if the father of my baby was taking a drug that might affect sperm when I got pregnant?

Let your doctor know if you became pregnant while the father was taking a medicine that is recommended to be stopped before conception. It is unlikely that any extra monitoring of the pregnancy/baby will be needed but this information might be recorded in your notes.

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 (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.