Tamiflu starts acting against the flu virus after the first dose, but symptom relief is gradual over days rather than minutes or hours.
Onset of action
Tamiflu begins blocking the flu virus from multiplying in the body right away after you take it. Most people will not feel dramatically different immediately, but the medicine is working in the background to limit how fast the virus spreads.
When you start to feel better
Clinical data show Tamiflu usually shortens flu illness by about 1 to 2 days, sometimes up to 2 to 3 days in older adults with other health problems. Many patients start to notice that fever and body aches ease over the first 1 to 3 days after starting treatment, compared with how long symptoms would last without it.
Importance of early timing
Tamiflu works best when started within 48 hours of the first flu symptoms; after that, its benefit drops and it may not help much for otherwise healthy people. For those who are very ill or at high risk for complications (such as hospitalized or immunocompromised patients), doctors may still use it even if more than 48 hours have passed.
What to watch for
If symptoms are getting worse instead of better over the first couple of days on Tamiflu, or if you have trouble breathing, chest pain, confusion, or dehydration, medical evaluation is important. Always follow the full prescribed course (commonly 5 days) even if you feel better sooner, unless a clinician tells you to stop.
