AntiviralPrescription only
Oseltamivir
Capsule or syrup
Quick Summary
Oseltamivir works best when started within 48 hours of flu symptoms.
Influenza treatment
Flu prevention
Medical Uses
Influenza treatment: Especially in high-risk people or severe illness.
Flu prevention: After exposure in some people.
How it's taken
Take it with food to reduce nausea, for the course 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
Nausea and vomiting
Common.
Headache
Sometimes.
Behaviour changes
Rarely, especially in children.
Interactions
Live flu vaccine
Oseltamivir can stop it working.
Critical Warnings
Unusual behaviour
Watch children for confusion or unusual behaviour.
Not a substitute for vaccination
The yearly vaccine is the best prevention.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Oseltamivir: drug information(opens in a new tab) · MedlinePlus, US National Library of Medicine