Ondansetron is a medicine which prevents your child feeling sick (nausea) and being sick (vomiting). This type of drug is called an anti-emetic.

It is used mainly for nausea and vomiting caused by chemotherapy or radiotherapy. It is also used for nausea and vomiting after an operation or caused by some pain-killing medicines.

How is ondansetron given?

It may be given by mouth in the form of a tablet, melt or a syrup.

It may also be given as an injection into a vein (intravenously or IV), through a cannula, central venous catheter, implantable port or PICC line.

It may be given every eight to 12 hours and can be combined with other drugs which prevent sickness.

If it is being given after an operation or while our child is having pain-killing medicines, it will usually be given just while your child is in hospital. If it is being given for sickness caused by chemotherapy, it should be started before the first dose of chemotherapy and continued for up to three days after the end of chemotherapy. If your child is still feeling sick after this time, tell your doctor as other anti-sickness medicines may be more effective at this point.

What are the side effects of ondansetron?

Warm flushes

Your child may complain or talk about sensations of warmth or feeling flushed, particularly in the head or over the stomach.


Some children find that ondansetron gives them headaches. Tell your doctor if your child complains of headaches while having treatment with ondansetron.


Your child may become constipated. This can generally be helped by drinking lots of fluids and eating a high fibre diet. Sometimes the doctor may prescribe medicines to stimulate your child’s bowel function.

Ondansetron and interactions with other medicines

Some medicines can react with ondansetron, altering how well it works. Always check with your doctor or pharmacist before giving your child any other medicine, including medicines on prescription from your family doctor (GP), medicines bought from a pharmacy (chemist) or any herbal or complementary medicines.

Important information you should know about ondansetron

  • Keep all medicines and tablets in a safe place where children cannot reach them.
  • Store this medicine in a cool, dry place away from direct sunlight or heat.
  • Ondansetron should be taken as directed by your doctor, nurse or pharmacist.
  • If your child vomits after taking the dose, inform the doctor or nurse as your child may need to take another dose. Do not give your child another dose without first informing your doctor.
  • If you forget to give your child their dose, do not give them a double dose. Inform your doctor or nurse and keep to your child’s regular dose schedule.
  • If your doctor decides to stop treatment, return any unused tablets or medicine to the pharmacist. Do not flush or throw them away.
Last review date: 
November 2014


Please read this information sheet from GOSH alongside the patient information leaflet (PIL) provided by the manufacturer. If you do not have a copy of the manufacturer’s patient information leaflet please talk to your pharmacist. A few products do not have a marketing authorisation (licence) as a medicine and therefore there is no PIL.

For children in particular, there may be conflicts of information between the manufacturer’s patient information leaflet (PIL) and guidance provided by GOSH and other healthcare providers. For example, some manufacturers may recommend, in the patient information leaflet, that a medicine is not given to children aged under 12 years. In most cases, this is because the manufacturer will recruit adults to clinical trials in the first instance and therefore the initial marketing authorisation (licence) only covers adults and older children.  

For new medicines, the manufacturer then has to recruit children and newborns into trials (unless the medicine is not going to be used in children and newborns) and subsequently amend the PIL with the approved information. Older medicines may have been used effectively for many years in children without problems but the manufacturer has not been required to collect data and amend the licence. This does not mean that it is unsafe for children and young people to be prescribed such a medicine ‘off-licence/off-label’. However, if you are concerned about any conflicts of information, please discuss with your doctor, nurse or pharmacist.