Nausea & motion sickness · 5-HT3 receptor antagonist (anti-emetic)
Ondansetron
Ondansetron is a prescription anti-nausea medicine used to control nausea and vomiting from many causes.
Prescription onlyPregnancy: cautionKidney warningLiver warningAlcohol interactionPaediatric useSenior precautionOverview & typical uses
Ondansetron is a prescription anti-nausea medicine used to control nausea and vomiting from many causes.
Primary uses
- Nausea and vomiting from chemotherapy or radiotherapy
- Post-operative nausea and vomiting
- Severe gastroenteritis-related vomiting (under clinical guidance)
How it works
Blocks serotonin (5-HT3) receptors in the gut and brainstem that trigger nausea and vomiting reflexes.
Available forms & strengths
- Tablet — 4 mg, 8 mg (Oral)
- Orally disintegrating tablet — 4 mg, 8 mg (Oral)
- Oral solution — 4 mg / 5 mL (Oral)
- Injection — 2 mg / mL (Intravenous / intramuscular)
General precautions & contraindications
Do not use if
- Known long-QT syndrome
- Concurrent use with apomorphine
- Known allergy to ondansetron
Pregnancy
Use with caution — discuss with clinician. Reserve for cases where other options are unsuitable; discuss risk and benefit with a clinician.
Breastfeeding
Use with caution — discuss with clinician. Limited data; short-term use is usually acceptable under clinical guidance.
Kidney considerations
- No routine adjustment needed for standard use.
Liver considerations
- Reduce total daily amount in significant liver disease.
Paediatric use
Under clinical supervision.
Older adults
Watch for QT prolongation, especially with other QT-prolonging medicines.
Common side effects
- Headache
- Constipation
- Feeling warm or flushed
- Tiredness
Serious warnings — seek help if these appear
- Cardiac rhythm disturbance (QT prolongation) — particularly with high doses or in combination
- Serotonin syndrome when combined with other serotonergic medicines
- Serious allergic reactions
Drug interactions
Serious low blood pressure — combination contraindicated.
Additive risk of heart rhythm problems.
Possible serotonin syndrome risk.
Food & alcohol precautions
No notable food interactions recorded.
Alcohol
- Alcohol may worsen nausea.
Storage, missed dose & overdose
Storage
Store below 25 °C, out of reach of children.
If a dose is missed
Take when remembered unless close to the next dose — never double up.
Overdose
Overdose can cause vision changes, low blood pressure, and heart rhythm problems. Seek urgent medical care.
What to monitor
- Report palpitations, fainting, or unusual heartbeat while on ondansetron.
Frequently asked questions
In most countries it is prescription-only because of QT-interval and combination-medicine considerations.
Medical references
- British National Formulary — Ondansetron — BNF (NICE)
- FDA drug safety — Ondansetron — U.S. Food & Drug Administration
Content last reviewed: 2025-01-01
Medical disclaimer
This information is for educational purposes only and should not replace professional medical advice. Please consult a licensed pharmacist or clinician for advice tailored to your personal circumstances.