Anti-sicknessPrescription only
Ondansetron
Tablet, melt or injection
Quick Summary
Ondansetron blocks serotonin signals that trigger vomiting.
Chemotherapy and surgery
Gastroenteritis
Severe morning sickness
Medical Uses
Chemotherapy and surgery: Preventing nausea.
Gastroenteritis: To help children keep fluids down, as prescribed.
Severe morning sickness: Sometimes, under medical advice.
How it's taken
Melt tablets dissolve on the tongue. Take as prescribed.
Your doctor decides the right dose for you and how long to take it.
Your doctor decides the right dose for you. Follow their instructions and the label.
Common Side Effects
Headache
Common.
Constipation
Sometimes.
Heart rhythm effects
Rarely.
Interactions
Antidepressants and some painkillers
Risk of serotonin syndrome.
Heart rhythm medicines
Rhythm risk.
Critical Warnings
Heart rhythm
Use with care in heart conditions.
Pregnancy
Discuss with your doctor.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Ondansetron: drug information(opens in a new tab) · MedlinePlus, US National Library of Medicine