Ondansetron is a medicine which prevents your child feeling sick (nausea) and being sick (vomiting). This type of drug is called an anti-emetic. This page from Great Ormond Street Hospital (GOSH) explains what ondansetron is, how it is given and some of the possible side effects. Each person reacts differently to medicines, so your child will not necessarily suffer from every side effect mentioned.

Ondansetron 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 it 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 or implantable port.

It may be given every 8 to 12 hours and can be combined with other drugs which prevent sickness.

If it is being given after an operation or while your 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?

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 laxative medicines to stimulate your child’s bowel function.

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.


  • Keep all medicines in a safe place where children cannot reach them.
  • Store this medicine in a cool, dry place away from direct sunlight or heat. 
  • If your child is taking ondansetron liquid, check how long it can be used for after opening. Your pharmacist will be able to advise on this and it will also be written on the pharmacy Label.
  • 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. 
Compiled by:
The Pharmacy department in collaboration with the Child and Family Information Group
Last review date:
May 2020