For treating the flu, Tamiflu (oseltamivir) is taken twice a day for five days. For preventing the flu after exposure, it’s taken once a day for at least ten days. The specific dose depends on whether you’re an adult or a child, and whether you’re treating active flu symptoms or trying to avoid getting sick in the first place.
Treatment Schedule for Active Flu
Adults and teenagers 13 and older take 75 mg twice daily for five days. That means one dose in the morning and one in the evening, spaced roughly 12 hours apart. The five-day course is the same regardless of how severe your symptoms are.
Children ages 1 through 12 are dosed by body weight:
- 15 kg (33 lbs) or less: 30 mg twice daily
- 15.1 to 23 kg (33 to 51 lbs): 45 mg twice daily
- 23.1 to 40 kg (51 to 88 lbs): 60 mg twice daily
- Over 40 kg (88 lbs): 75 mg twice daily
Infants 3 months and older but younger than 1 year receive a dose calculated by their exact weight, typically 3 mg per kilogram twice daily. Children in this age group use the liquid suspension form rather than capsules.
Prevention Schedule After Exposure
If someone in your household has the flu and you’re trying to avoid catching it, the dosing schedule changes. Adults take 75 mg once daily, not twice, for at least 10 days following close contact. Children follow the same weight tiers listed above but take their dose just once a day instead of twice.
During a broader community outbreak, the once-daily prevention dose can continue for up to 6 weeks. People with weakened immune systems may take it for up to 12 weeks if their doctor recommends ongoing protection. Prevention dosing should start within 48 hours of your exposure to be most effective.
Why Timing Matters
Tamiflu works by blocking a protein on the surface of the flu virus that normally helps newly made viral copies break free from infected cells and spread. When that protein is blocked, the virus clumps together on the cell surface instead of moving on to infect neighboring cells. This slows the infection but doesn’t kill virus that’s already deeply established, which is why starting early makes a real difference.
The greatest benefit comes when you begin treatment within 48 hours of your first symptoms. In studies of children who started within five days of getting sick, symptoms lasted about one day less than in those who took a placebo (three days versus four). Starting sooner generally means a bigger benefit, but even treatment begun after the 48-hour window can still help, particularly for people at higher risk of complications.
Taking It With Food
The most common side effects are nausea and vomiting, and they tend to show up in the first two days of treatment. Taking each dose with food reduces the chance of stomach upset. A small snack or meal is enough. If you tolerate it fine on an empty stomach, that works too, but food is the simplest fix if you’re feeling queasy.
What to Do if You Miss a Dose
Take the missed dose as soon as you remember, with one exception: if your next scheduled dose is less than two hours away, skip the missed one and just take your next dose on time. Never double up to make up for a missed dose. If you miss several doses in a row, check with whoever prescribed it for guidance on whether to continue or restart.
Dose Adjustments for Kidney Problems
Because Tamiflu is processed through the kidneys, people with significantly reduced kidney function need a lower frequency. For treatment, the dose drops from 75 mg twice daily to 75 mg once daily for five days. For prevention, it drops further to 75 mg every other day or 30 mg once daily. These adjustments apply when kidney function falls below a certain threshold, so your prescriber will determine the right schedule based on your lab work.
Children’s Dosing at a Glance
Tamiflu comes in both capsules and a liquid suspension. Younger children almost always use the liquid, which allows for precise weight-based dosing. If the liquid isn’t available, capsules can be opened and mixed with a small amount of sweetened liquid to mask the bitter taste. The weight-based tiers are the same for both treatment and prevention. The only difference is frequency: twice daily for treatment, once daily for prevention.
For children under 1 year old, dosing is individualized by exact body weight rather than grouped into tiers. A pharmacist or pediatrician calculates the precise volume of liquid needed per dose.