Ondansetron
Ondansetron blocks serotonin 5-HT3 receptors and is used for nausea and vomiting from chemotherapy, radiotherapy, surgery, and sometimes other causes when prescribed. It is prescription-only in many UK contexts.
This medicine is part of the Stomach acid & reflux category.
Generic name: ondansetron
Quick answers
Short replies to searches people often run before speaking to a clinician. For the overview of what the medicine is used for, see the short summary under the page title above.
What is it for?
Ondansetron blocks serotonin 5-HT3 receptors and is used for nausea and vomiting from chemotherapy, radiotherapy, surgery, and sometimes other causes when prescribed.
How long does it take to work?
Onset varies by condition and dose. Your GP or pharmacist can explain what to expect and when to review.
What are common side effects?
Constipation, headache, flushing, or mild sedation.
Can you take paracetamol or ibuprofen with it?
Ask your GP or pharmacist before taking Ondansetron with paracetamol or ibuprofen. Many adults use paracetamol for short periods when appropriate; NSAIDs such as ibuprofen need extra checks with your other medicines and health conditions.
More about what Ondansetron is used for
Ondansetron blocks serotonin 5-HT3 receptors and is used for nausea and vomiting from chemotherapy, radiotherapy, surgery, and sometimes other causes when prescribed.
It is prescription-only in many UK contexts.
How does Ondansetron work, and how long does it take to work?
It reduces vomiting signals from the gut and brainstem trigger zones.
It does not treat the underlying cause of nausea alone.
How and when should you take Ondansetron?
Tablets, melts, or injections as your prescriber directs — timing differs for chemo versus surgery.
Dissolvable films or melts go on the tongue as the leaflet describes.
What are the common side effects of Ondansetron?
Constipation, headache, flushing, or mild sedation.
Serious side effects of Ondansetron — when to get urgent help
Seek urgent help for chest pain, severe palpitations, or allergic swelling — QT prolongation is a recognised concern with other risk factors.
What if you miss a dose of Ondansetron?
For scheduled antiemetic cycles, follow your oncology or surgical plan; call the team if a dose is missed.
Who should not take Ondansetron?
Congenital long QT syndrome and some drug combinations need avoidance. Severe constipation from previous ondansetron may need review.
Can you take paracetamol or ibuprofen with Ondansetron? — other interactions
Other QT-prolonging drugs, apomorphine, and Tramadol combinations need specialist review.
Ondansetron in pregnancy and breastfeeding
Discuss with your prescriber — use when benefit outweighs risk, often in pregnancy sickness under medical care.
Blood tests and monitoring on Ondansetron
ECG may be checked if you have heart risk factors or take interacting medicines.
What might your GP prescribe instead of Ondansetron?
Cyclizine, Metoclopramide, or steroids in some settings may be used instead.
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Reviewed by UK registered pharmacists for accuracy and clarity. Content is informational only.
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Frequently asked questions about Ondansetron
People also ask — common Google searches
- What is Ondansetron used for?
- Ondansetron blocks serotonin 5-HT3 receptors and is used for nausea and vomiting from chemotherapy, radiotherapy, surgery, and sometimes other causes when prescribed. It is prescription-only in many UK contexts.
- How long does Ondansetron take to work?
- Onset varies by condition and dose. Your GP or pharmacist can explain what to expect and when to review. Always follow your prescriber’s follow-up plan.
- Can you take Ondansetron with paracetamol or ibuprofen?
- Ask your GP or pharmacist before taking Ondansetron with Paracetamol or Ibuprofen. Many adults use paracetamol for short periods when appropriate; NSAIDs such as ibuprofen need extra checks with your other medicines and health conditions.
- What are the side effects of Ondansetron?
- Constipation, headache, flushing, or mild sedation. See the sections below for more detail, including serious side effects and when to seek urgent help.
- Does ondansetron cause constipation?
- Constipation is common. Fluids, fibre, and pharmacist-suitable laxatives may help — ask if stools stop completely.
- Can ondansetron be used for morning sickness?
- Sometimes specialists prescribe it when other options fail — decisions are individual with safety checks.
Need personalised advice?
Your local pharmacist or GP surgery can help with questions about your medicines, side effects, and alternatives that may be suitable for you.
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Often used with
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