Ondansetron

(Date: April 2015. Version: 2.3)

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 it?

Ondansetron (Zofran®, Ondemet®, Setofilm®, Demorem®) is a medicine used to treat nausea and/or vomiting. It is available as a tablet (to swallow, or which dissolves in the mouth), liquid, suppository, or can be given as an injection. Ondansetron is generally only prescribed for pregnancy sickness when other treatments have not worked.

Is it safe to take ondansetron in pregnancy?

When deciding whether or not to take ondansetron during pregnancy it is important to weigh up the benefits of its use against the known or possible risks, some of which will depend on how many weeks pregnant you are.

This leaflet summarises the scientific studies relating to the effects of ondansetron on a baby in the womb. It is advisable to consider this information before taking ondansetron if you are pregnant. Your doctor is the best person to help you decide what is right for you and your baby. It is important that you do not become dehydrated or unhealthy as a result of severe vomiting in pregnancy. For some pregnant women treatment with ondansetron may be advised.

What if I have already taken ondansetron during pregnancy?

If you have taken any medicines it is always a good idea to let your doctor know that you are pregnant so that you can decide together whether you still need the medicines that you are on and to make sure that you are taking the lowest dose that works.

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.

Heart defects
It is currently unclear whether women who take ondansetron in early pregnancy may have a higher chance of having a baby with a heart defect. The first study to investigate this found no evidence of a link between ondansetron use in pregnancy and heart defects in the baby. Another group of researchers then analysed information from the same health record database using a different technique. The results of their study suggest a possible link between ondansetron use in pregnancy and heart defects in the baby. However, full details of the study have not yet been published in a scientific journal and it is therefore not possible to evaluate the reliability of this early report.
 
One further study found that around two in every hundred women who took ondansetron in pregnancy had a baby with a heart defect compared to one in every hundred pregnant women who did not take ondansetron. The heart defects in babies exposed to ondansetron were generally not severe.

In all of these studies, many of the women took ondansetron after the time in pregnancy when the baby’s heart was forming. Any heart defects in the babies of these women were therefore not caused by ondansetron. More information needs to be collected from pregnant women who took ondansetron specifically during the time that the baby’s heart was forming to accurately assess whether there is a link between ondansetron use in pregnancy and heart defects in the baby.

Cleft palate
One study which specifically investigated possible causes of cleft palate suggested that there may be a link with taking ondansetron during early pregnancy, however no cleft palates occurred in two further studies which together assessed over 3,000 babies of women who took ondansetron in pregnancy. More research is required before we can say for certain whether use of ondansetron in pregnancy may increase the risk of cleft palate in the baby.

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

There is no scientific evidence to suggest that women who take ondansetron during pregnancy are more likely to have a miscarriage, a premature baby (born before 37 weeks of pregnancy),  a low birth weight baby (weighing less than 2500g), or a stillbirth. However, because only a few studies have looked at these pregnancy outcomes, more information is needed before firm conclusions can be drawn.

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

A baby’s brain continues to develop right up until the end of pregnancy. It is therefore possible that taking certain medicines at any stage of pregnancy could have a lasting effect on a child’s learning or behaviour.

There is no known link between taking ondansetron in pregnancy and learning or behavioural problems such as ADHD or autism spectrum disorder in the child later on in life. There are, however, no scientific studies that have specifically investigated a link between ondansetron and these problems and more research is therefore required. One study has assessed children who were exposed to either ondansetron or another anti-sickness medicine in the womb. These children were no more likely to have developmental problems than children who had not been exposed to medicines in the womb. However, the children exposed to ondansetron were not analysed separately.

Will my baby need extra monitoring during pregnancy?

Taking ondansetron during pregnancy is not expected to cause any problems that would require extra monitoring of your baby. If you have had severe pregnancy sickness your doctor may wish to monitor your weight and your baby’s growth more closely.

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 health care provider. They can access more detailed medical and scientific information from www.uktis.org.  

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.

   

www.medicinesinpregnancy.org

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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