What Is Oseltamivir?

Oseltamivir (brand name Tamiflu) is a prescription antiviral medication used to treat and prevent influenza (the flu). It belongs to a class of drugs called neuraminidase inhibitors and is one of the most commonly prescribed flu treatments in the world.

Oseltamivir is available as a generic medication and under the brand name Tamiflu, made by Genentech/Roche. Generic versions are manufactured by companies including Alvogen, Amneal, Aurobindo, Dr. Reddy's, and Teva.

What Does Oseltamivir Treat?

Oseltamivir is FDA-approved for two main uses:

1. Treatment of influenza A and B — for patients 2 weeks of age and older who have been experiencing symptoms for no more than 48 hours
2. Prevention (prophylaxis) of influenza A and B — for patients 1 year of age and older who have been exposed to the flu

It's important to understand that Oseltamivir only works against influenza viruses. It does not treat:

• The common cold
• COVID-19
• Bacterial infections
• Stomach flu (gastroenteritis)

If you're unsure whether you have the flu, a rapid flu test at your doctor's office or urgent care can confirm the diagnosis. Learn more about finding a doctor who can prescribe Oseltamivir.

How Does Oseltamivir Work?

Oseltamivir works by blocking an enzyme called neuraminidase on the surface of the flu virus. This enzyme helps new virus particles escape from infected cells and spread throughout your body. By blocking neuraminidase, Oseltamivir slows the spread of the virus and gives your immune system a better chance to fight it off.

For a more detailed explanation, read our guide on how Oseltamivir works.

How to Take Oseltamivir

Dosage Forms

Oseltamivir comes in two forms:

• Oral capsules: 30 mg, 45 mg, and 75 mg
• Oral suspension (liquid): 6 mg/mL (powder that the pharmacist mixes with water)

The liquid form is typically used for young children or anyone who has difficulty swallowing capsules.

Standard Adult Dosage

Pediatric Dosage

Children's doses are based on weight. Your child's doctor will determine the correct dose. Oseltamivir is approved for treatment in children as young as 2 weeks old and for prevention in children 1 year and older.

Kidney Impairment

If you have kidney problems (CrCl 30-60 mL/min), your doctor will likely prescribe a reduced dose of 30 mg twice daily for treatment. For more severe kidney impairment, talk to your doctor about whether Oseltamivir is appropriate.

Important Instructions

• Take with or without food. Taking it with food may reduce nausea.
• Start within 48 hours of symptom onset for treatment to be most effective.
• Complete the full course even if you start feeling better before it's done.
• If you miss a dose, take it as soon as you remember. If it's almost time for your next dose, skip the missed one — don't double up.

How Well Does Oseltamivir Work?

Clinical studies show that Oseltamivir can:

• Reduce the duration of flu symptoms by about 1-2 days when started within 48 hours
• Reduce the risk of flu complications (like pneumonia) in high-risk patients
• Reduce the risk of getting the flu by 70-90% when used for prevention after exposure

Oseltamivir is most effective when started as early as possible. However, doctors may still prescribe it beyond the 48-hour window for hospitalized patients or those at high risk for complications.

Who Should Take Oseltamivir?

While anyone with confirmed influenza can benefit from Oseltamivir, treatment is especially important for people at higher risk of flu complications:

• Adults 65 years and older
• Children under 5 (especially under 2)
• Pregnant women
• People with chronic conditions (asthma, diabetes, heart disease, weakened immune system)
• Residents of nursing homes or long-term care facilities

Even if you're not in a high-risk group, Oseltamivir can help you feel better faster and reduce the chance of spreading the flu to others.

Side Effects

The most common side effects are nausea, vomiting, headache, and stomach pain. Most are mild and can be reduced by taking the medication with food. Serious side effects are rare but include neuropsychiatric events (confusion, hallucinations, abnormal behavior) and severe allergic reactions.

For a complete breakdown, read our detailed guide on Oseltamivir side effects.

Drug Interactions

Oseltamivir has relatively few drug interactions, but there are some important ones to know about — including the live nasal flu vaccine (FluMist) and Probenecid. Check our full guide on Oseltamivir drug interactions.

How Much Does Oseltamivir Cost?

The cost depends on whether you get the generic or brand-name version:

• Generic Oseltamivir with a coupon: as low as $25-$55 for a 5-day course (10 capsules)
• Generic without a coupon: up to $160 retail
• Brand-name Tamiflu: $175-$200
• With insurance: typical copay of $10-$75

Oseltamivir is covered by about 68% of insurance plans. Most plans do not require prior authorization for a standard treatment course. For tips on getting the best price, read our guide on saving money on Oseltamivir.

Oseltamivir Availability in 2026

The severe 2025-2026 flu season has caused an active shortage of Oseltamivir. Multiple generic manufacturers have reported back orders, and some capsule strengths and the oral suspension are particularly affected.

If you're having trouble filling your prescription, try these resources:

• How to find Oseltamivir in stock near you
• How to check pharmacy stock without calling
• Alternatives to Oseltamivir

Key Takeaways

• Oseltamivir is a prescription antiviral that treats and prevents influenza A and B
• It works best when started within 48 hours of symptoms
• The standard adult dose is 75 mg twice daily for 5 days
• Common side effects are mild and include nausea, vomiting, and headache
• Generic versions are available and can cost as little as $25 with a coupon
• There is currently a shortage — use the tools and guides above to find it near you