Ondansetron
Also known as: Zofran
What it's for
Ondansetron prevents nausea and vomiting from chemotherapy, surgery, or radiotherapy. It blocks serotonin in the gut and brain that triggers vomiting.
Comes as: Tablets, orodispersible tablets, liquid, or injection
How to take it
- Dose depends on what it is treating.
- Usually 4mg to 8mg every 8 to 12 hours.
- Orodispersible tablets dissolve on your tongue.
- Take regularly as prescribed, not just when feeling sick.
Doses here are typical. Always follow the instructions from your prescriber or on the packet — they come first.
Common side effects
- Headache
- Constipation
- Feeling flushed or warm
- Tiredness
The leaflet inside the packet lists all known side effects.
Important safety points
- Can cause constipation - drink plenty of fluids
- Can affect heart rhythm at high doses
- Tell your doctor if you have heart problems
- Tell your doctor about all other medicines
Get medical help urgently if…
- You have a fast or irregular heartbeat
- You have severe constipation
- You have signs of an allergic reaction
- You have chest pain or difficulty breathing
Call NHS 111 for urgent advice, or 999 if someone is seriously unwell.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.