Ondansetron for sickness

Authored by Helen Allen, 28 Dec 2016

Patient is a certified member of
The Information Standard

Reviewed by:
Dr John Cox, 28 Dec 2016

Ondansetron is an anti-sickness medicine.

It will start to work within 1-2 hours.

The most common side-effects are a headache, constipation, and feeling flushed.
Type of medicineAn anti-sickness medicine - a serotonin (5HT3) receptor antagonist
Used forPrevention or treatment of sickness associated with chemotherapy, radiotherapy or surgery
Also calledOndemet®; Setofilm®; Zofran®
Available asTablets, orodispersible (melt in the mouth) tablets, oral liquid medicine, suppositories, and injection

Ondansetron is an anti-sickness medicine. It is known as a serotonin receptor antagonist. It is prescribed to stop you from feeling sick. It works by blocking the effect of a naturally produced chemical in your body, called serotonin. Serotonin is also referred to as 5HT3.

Chemotherapy, radiotherapy and surgery can all cause the release of an increased amount of serotonin in your body. There are tiny areas in your small intestine and brain called 5HT3 receptors. Serotonin acts on these receptors and causes you to feel sick. Ondansetron works by blocking serotonin from acting on the receptors, and this stops you from feeling (or being) sick.

Some medicines are not suitable for people with certain conditions, and sometimes a medicine can only be used if extra care is taken. For these reasons, before you start taking ondansetron it is important that your doctor knows:

  • If you are pregnant or breast-feeding.
  • If you have any problems with the way your liver works.
  • If you have been told you have an irregular heartbeat.
  • If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.
  • If you have ever had an allergic reaction to a medicine.
  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about ondansetron, and it will also provide you with a full list of the side-effects which you could experience from taking it.
  • Take ondansetron exactly as your doctor tells you to. The way you have been told to take it will depend upon the reason why you are taking it:
    • If you are due to have a chemotherapy or radiotherapy treatment that could cause you to feel sick, your doctor will prescribe you a dose of ondansetron to take an hour or so before the treatment. You will then be asked to continue to take ondansetron for up to five more days - tablets and liquid medicine are usually prescribed to take twice daily (every 12 hours), whereas suppositories are inserted just once daily.
    • If you are being prescribed ondansetron because you are due to have surgery, you will be given a dose to take shortly before the operation.
    • Ondansetron can also be given by injection. If this is the treatment prescribed for you, a doctor or nurse will administer the injections to you.
  • If you have been prescribed a brand of tablet called either Zofran® Melt or Setofilm® tablets, these tablets are designed to dissolve very quickly in your mouth when you put them on the top of your tongue. Take out a tablet from the packaging - the tablets are quite fragile so you need to peel off the foil rather than try to push the tablet through it. Place the tablet on the top of your tongue and allow it to dissolve there for a few moments before you swallow.

How to use ondansetron suppositories

  1. Remove the suppository from the wrapping.
  2. You may find that inserting the suppository is easier if you squat or bend forward.
  3. Using a finger, gently push the suppository pointed end first into your back passage (rectum).
  4. Remove your finger and then remain still for a little while to help you hold the suppository in place.
  5. Then, wash your hands.
  • Ondansetron should start to work within an hour or so. If you are taking tablets or liquid medicine and you are sick within one hour of taking a dose, you should take the same dose again. This does not apply, however, if you are using suppositories or if you have been given an injection, as being sick will not prevent these from being absorbed by your body.
  • Even if you do not feel like eating or drinking, try to sip water regularly to prevent you from becoming lacking in fluids (dehydrated). Also, rather than trying to eat three main meals a day, try eating small, simple but nourishing snacks, every few hours.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the more common ones associated with ondansetron. The best place to find a full list of the side-effects which can be associated with your medicine, is from the manufacturer's printed information leaflet supplied with the medicine. Alternatively, you can find an example of a manufacturer's information leaflet in the reference section below. Speak with your doctor or pharmacist if any of the following continue or become troublesome.

Very common ondansetron side-effects (these affect more than 1 in 10 people)
What can I do if I experience this?
HeadacheDrink plenty of water and ask your doctor to prescribe/recommend a suitable painkiller
Common ondansetron side-effects (these affect less than 1 in 10 people)What can I do if I experience this?
ConstipationTry to eat a well-balanced diet, and drink several glasses of water each day. Let your doctor know if this continues
Feeling warm or flushedWear light, cool clothes

If you experience any other symptoms which you think may be due to the medicine, speak with your doctor or pharmacist for further advice.

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

If you are having an operation or any dental treatment, tell the person carrying out the treatment which medicines you are taking.

If you buy any medicines, check with a pharmacist that they are suitable to take with your other medicines.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Further reading and references

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