What it is used for
- Nausea and vomiting from chemotherapy or radiotherapy
- Nausea and vomiting after surgery
- Severe nausea and vomiting in other clinician-assessed situations
How it works
Ondansetron blocks serotonin (5-HT3) signals in the gut and brain that trigger the vomiting reflex, helping prevent and control severe nausea and vomiting.
How it is taken
Available as tablets, orally dissolving (melt) tablets, oral liquid, and an injectable form. It is taken by mouth or given by injection in healthcare settings. Use it only as a clinician prescribes, and follow the exact instructions; it is not for routine self-treatment of mild upset stomach.
No doses here on purpose. The right strength and schedule depend on you — only a doctor or pharmacist should set them. Always follow your prescription and the label.
Common side effects
- Headache
- Constipation
- Tiredness
- Flushing or warmth
- Dizziness
Serious effects — get help
- Irregular or fast heartbeat, fainting (possible heart-rhythm effect)
- Severe allergic reaction (swelling, trouble breathing)
- Signs of serotonin syndrome when combined with certain drugs (agitation, sweating, tremor, fever)
- Blurred or temporary loss of vision (rare, with injection)
- Severe constipation or signs of bowel blockage
If a reaction is severe — for example trouble breathing, swelling of the face or throat, or collapse — go to the nearest emergency room now or call your local emergency number. Do not wait for an online consultation.
Interactions to watch
- Other medicines that affect heart rhythm (QT interval)
- Certain antidepressants (SSRIs, SNRIs) — serotonin syndrome risk
- Tramadol
- Apomorphine (should not be combined)
Who should take care
- Tell your clinician about any heart-rhythm problems or a family history of them
- Mention low potassium or magnesium levels
- Discuss pregnancy carefully, especially early pregnancy, with your clinician
- Tell your clinician about liver problems
- Share all your medicines, particularly antidepressants and heart medicines