Date: September 2020, Version 4

What is it?

Ondansetron is an anti-sickness drug (sometimes called an anti-emetic). It is most commonly used in pregnancy to treat a severe form of sickness called hyperemesis gravidarum.

For general information please see the bump leaflet on treatment of nausea and vomiting in pregnancy.


What are the benefits of taking ondansetron in pregnancy?

Ondansetron is a very effective medicine that works by blocking the action of chemicals in the body that trigger nausea and vomiting. Ondansetron can greatly improve quality of life in women with hyperemesis gravidarum, as well as helping to prevent the serious complications that can be caused by this condition.


Are there any risks of taking ondansetron during pregnancy?

Some studies have suggested that heart defects and cleft lip and palate may be more common in babies exposed to ondansetron in early pregnancy. However, these findings need to be confirmed with further research. The available evidence shows that the vast majority of babies exposed in the womb to ondansetron do not have these birth defects. Ondansetron used after around week 10 of pregnancy would not be able to cause these problems as the baby is fully developed by this stage.

There are no concerns that ondansetron use in pregnancy affects the chance of miscarriage, stillbirth, preterm delivery or low infant birth weight.


Are there any alternatives to taking ondansetron?

Possibly. Other medicines can be used to treat hyperemesis, but generally will already have been tried before a doctor prescribes ondansetron. Where ondansetron use is being considered, your doctor will speak to you about the possible risks and you will decide together whether these are outweighed by the benefits of treatment.

No treatment

What if I prefer not to take medicines during pregnancy?

Some women with milder pregnancy sickness may be able to cope without use of medicines. However, anti-sickness treatment is generally advisable in pregnant women experiencing uncontrolled vomiting. These women are likely to be extremely unwell and unable to cope with the activities of daily living. Additionally, uncontrolled vomiting can lead to malnutrition, severe dehydration, and electrolyte imbalance. This is where the levels of salts in the bloodstream are altered, leading to adverse effects on the muscles and nervous system, and might require admission to hospital for rehydration through a drip.

Your doctor will be happy to talk to you about any concerns that you might have when considering use of a medicine in pregnancy.

Will my baby need extra monitoring?

All pregnant women in the UK should be offered a very detailed anomaly scan at around 20 weeks of pregnancy as part of their routine antenatal care. No extra monitoring for major birth defects is required following ondansetron use in pregnancy.

Are there any risks to my baby if the father has taken ondansetron?

We would not expect any increased risk to your baby if the father took ondansetron before or around the time you became pregnant.

Who can I talk to if I have questions?

If you have any questions relating to 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.

The charity Pregnancy Sickness Support provides resources, information and advice for women experiencing hyperemesis gravidarum.

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.