(Date: September 2019. 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 Public Health England 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 ondansetron?

Ondansetron is a medicine used to treat nausea and/or vomiting. Ondansetron is normally prescribed for severe pregnancy sickness when other treatments have not worked.

Is it safe to take ondansetron in pregnancy?

Although a possible link between ondansetron use in early pregnancy and cleft lip and/or palate in the baby has been suggested, current research suggests that the chance of this occurring is very small. Women can be substantially affected by severe pregnancy sickness (hyperemesis gravidarum). Without treatment, they are at risk of dehydration and poor mental and physical health. Ondansetron may be offered in these circumstances, in which case their doctor/obstetrician will help them to weigh up the benefits of its use against the possible risks.

What if I have already taken ondansetron during pregnancy?

There is no need to worry if you have already taken ondansetron, since the risk to the baby is very small. However, you may wish to discuss this further with your midwife, GP or obstetrician.

Can taking ondansetron in pregnancy cause my baby to be born with birth defects?

A baby’s body and most internal organs are formed during the first 12 weeks of pregnancy. It is mainly during this time that some medicines are known to cause birth defects. Use of a medicine after week 12 of pregnancy would not be expected to cause structural problems in the baby.

Cleft lip and/or palate
Research suggests that babies whose mothers are taking ondansetron between weeks six and twelve of pregnancy may have a slightly higher chance of cleft lip and/or palate than unexposed babies. Around 11 in every 10,000 babies are born with cleft lip and/or palate every year (this is called the background rate). This increases to 14 in every 10,000 babies exposed to ondansetron in the womb.

The vast majority of babies exposed to ondansetron in the womb (at least 998 out of every 1,000) are born without cleft lip and/or palate.

Heart defects
There has been some evidence that babies exposed to ondansetron may have a higher chance of having a heart defect. However, a large study did not show any increase in structural heart disease, more evidence is still needed.

Can taking ondansetron in pregnancy cause miscarriage, preterm birth, my baby to be small at birth (low birth weight), or stillbirth?

There is no evidence that women who take ondansetron during pregnancy are more likely to have a miscarriage, a premature baby, a low birth weight baby or a stillbirth.

Can taking ondansetron in pregnancy cause learning or behavioural problems in the child?

Two studies have investigated learning and behaviour in a total of 350 children exposed to ondansetron in the womb and neither study identified any significant problems. While this is reassuring, ongoing research is required.

Will my baby need extra monitoring during pregnancy?

No extra monitoring of your baby is needed.

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 regarding the information in this leaflet please discuss them with your healthcare 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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