(Date: September 2020. Version: 4)

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?

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.

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.

Feedback request 

WE NEED YOUR HELP! Do you have 3 minutes to complete a short, quick and simple 12 question user feedback form about our bumps information leaflets? To have your say on how we can improve our website and the information we provide please visit here.

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.

My bump’s record

Create your own ‘My bump’s record’.

Provide information about your pregnancy to help women in the future.

Login to my bumps

Join my bumps