Oseltamivir
Pronunciation: oh-sell-TAM-ih-veer.
- Generic name
- oseltamivir
- Brand names
- Tamiflu
- Drug class
- Neuraminidase inhibitor (antiviral)
- Form
- Capsule (30 mg, 45 mg, 75 mg) or powder for oral suspension
- Route
- Oral
- Legal status
- Prescription-only medicine
Availability and supply rules vary by country
Trade names by country: United States · United Kingdom · Canada · Australia
Australia: Tamiflu (4) · Full directory
What oseltamivir is and how it works
Oseltamivir is an oral antiviral medicine that treats influenza A and B infection and can also help prevent influenza after a known exposure or during a community outbreak. It works by blocking an enzyme (neuraminidase) the influenza virus needs to spread within the body. (1) (2)
Oseltamivir's benefit for treatment is time-sensitive: it is approved for people who have had flu symptoms for 2 days (48 hours) or less. It treats influenza specifically and does not treat colds, COVID-19, or other non-influenza illnesses, and it is not a replacement for the annual flu vaccine.
Mechanism of action: how oseltamivir works
Oseltamivir phosphate is an ethyl ester prodrug requiring ester hydrolysis for conversion to the active form, oseltamivir carboxylate, which inhibits influenza virus neuraminidase, affecting release of viral particles. (1)
What oseltamivir is used for
Treatment of acute, uncomplicated influenza
For patients 2 weeks of age and older who have been symptomatic with influenza A or B for no more than 2 days (48 hours). (1)
Prevention (prophylaxis) of influenza after exposure or during an outbreak
For patients 1 year of age and older, either after close contact with someone who has influenza (post-exposure prophylaxis) or during a community outbreak (seasonal prophylaxis). It is not a substitute for annual influenza vaccination. (1)
Before taking oseltamivir
Do not take / not appropriate for
- Do not take oseltamivir if you have had a serious hypersensitivity reaction to oseltamivir or any component of the product. (all patients) (1)
Tell your clinician about
- Kidney problems, since the dose is reduced for reduced kidney function and oseltamivir is not generally recommended for people with end-stage kidney disease who are not on dialysis.
- Hereditary fructose intolerance, since the oral suspension contains sorbitol.
- Whether you have recently had or are about to have a live nasal-spray flu vaccine (such as FluMist), since timing relative to oseltamivir matters.
- Pregnancy, plans for pregnancy, or breastfeeding.
- Any history of confusion, unusual behavior, or psychiatric symptoms during a previous illness, so the care team is aware if it happens again.
How to take oseltamivir
- Start oseltamivir as soon as possible after flu symptoms begin — treatment is approved for use within 2 days (48 hours) of symptom onset.
- For treatment, the typical adult/adolescent (13 years and older) dose is 75 mg by mouth twice daily for 5 days; children 1–12 years old are dosed by body weight.
- For prevention after exposure, the typical adult/adolescent dose is 75 mg once daily for at least 10 days; for prevention during a community outbreak, dosing may continue for up to 6 weeks as directed by the prescriber.
- May be taken with or without food; taking it with food can reduce stomach upset.
- Complete the full prescribed course even if you start to feel better, unless your prescriber tells you to stop.
- Kidney function affects the correct dose — do not use a dose intended for someone else or continue a leftover course from a previous illness.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4)
Missed dose
Take the missed dose as soon as you remember, unless it is within about 2 hours of your next scheduled dose, in which case skip the missed dose and continue your regular schedule. Do not take a double dose. If you are unsure, ask your pharmacist or prescriber.
Overdose
Most reported oseltamivir overdoses have not caused adverse effects beyond those seen at normal doses, but if an overdose is suspected, call a poison control center (in the United States, 1-800-222-1222) or seek emergency medical care immediately, especially if the person collapses, has a seizure, or has trouble breathing. (1) (2)
Side effects
The most common effects are stomach-related and usually mild. Oseltamivir also carries an FDA warning about confusion and unusual behavior, reported mainly in children and teenagers with the flu itself, which needs prompt attention regardless of whether it is from the illness or the medicine.
Nausea or vomiting
What to notice: The most frequently reported side effects.
What to do: Taking the dose with food can help; tell the prescriber if it is severe or persistent. (1)
Headache
What to notice: A commonly reported effect.
What to do: Tell the prescriber if bothersome or persistent. (1)
Allergic-type or serious skin reaction
What to notice: Rash, hives, swelling of the face/lips/tongue/throat, or difficulty breathing; or a severe skin reaction with blistering or peeling.
What to do: Seek urgent medical care immediately; a clinician or emergency service will decide whether Oseltamivir needs to be stopped; cases of anaphylaxis and serious skin reactions (including Stevens-Johnson syndrome and toxic epidermal necrolysis) have been reported. (1)
Serious warnings
Confusion, delirium, or abnormal behavior (neuropsychiatric events) — urgent
Symptoms: Sudden confusion, delirium, hallucinations, agitation, or unusual/dangerous behavior — reported mainly, but not only, in children and teenagers with influenza, sometimes with abrupt onset.
Action: Anyone with the flu, especially children and teenagers, should be closely watched for signs of unusual behavior for the first few days of illness, whether or not they are taking oseltamivir. If these symptoms occur, contact the prescriber or seek emergency care immediately. Do not decide on your own whether to continue the medicine — the prescriber weighs this based on the individual situation. (1) (2)
Anaphylaxis or serious skin reaction — emergency
Symptoms: Swelling of the face, lips, tongue, or throat; difficulty breathing; widespread hives; or a severe blistering/peeling skin reaction.
Action: Seek emergency care immediately; a clinician or emergency service will decide whether oseltamivir needs to be continued or stopped. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Live attenuated influenza vaccine (nasal-spray flu vaccine, e.g. FluMist) | Oseltamivir may reduce the effectiveness of the live nasal-spray vaccine if given too close together. | Avoid the live nasal-spray vaccine within 2 weeks before or 48 hours after taking oseltamivir, unless the prescriber advises otherwise. The injected (inactivated) flu vaccine can be given at any time relative to oseltamivir. (1) (2) |
| Common medicines checked for interaction (amoxicillin, acetaminophen/paracetamol, aspirin, cimetidine, antacids, warfarin, and others) | No clinically significant interaction has been identified in FDA-reviewed data. | Still tell the prescriber and pharmacist about all medicines being taken, since individual situations can differ. (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Reduced kidney function
The dose is reduced for moderate or severe kidney impairment, and oseltamivir is generally not recommended for people with end-stage kidney disease who are not on dialysis; specific dosing exists for people on hemodialysis or peritoneal dialysis. This adjustment must be made by the prescriber, not the patient. (1)
Pregnancy
Published epidemiological data have not shown an increased risk of birth defects with oseltamivir use in any trimester, and no dose adjustment is recommended for pregnancy. Discuss your individual situation with the prescriber. (1)
Breastfeeding
Limited data show oseltamivir and its active form pass into breast milk at low levels considered unlikely to harm a breastfed infant, but this should still be discussed with the prescriber. (1)
Children
Treatment is approved from 2 weeks of age and prevention from 1 year of age, with weight-based dosing for children 1–12 years old. Dosing for infants and children must be set by the prescriber; do not estimate a child's dose from an adult dose. (1)
Older adults
Specific comparative safety/effectiveness data for older versus younger adults were not found in the sources reviewed for this page. Kidney function, which can decline with age, is still checked before dosing, since the dose depends on it. (2)
Monitoring
Before starting
- Confirm treatment can start within 48 hours of symptom onset.
- Check kidney function, since the dose depends on it.
- Ask about hereditary fructose intolerance if the oral suspension is being considered, and about recent or planned live nasal-spray flu vaccination.
During treatment
- Watch for signs of confusion or unusual behavior, especially in children and teenagers, for the first few days of illness.
- Watch for signs of an allergic or serious skin reaction and seek urgent care if these occur.
- Complete the full course as prescribed; do not stop early without checking with the prescriber, and do not extend or repeat a course without new medical advice.
Storage
Store capsules at room temperature away from moisture. Commercially prepared oral suspension can be kept at room temperature for up to 10 days or refrigerated for up to 17 days; pharmacist-compounded suspension has shorter limits (5 days room temperature, 35 days refrigerated) — follow the exact expiration written on your bottle. Do not freeze the suspension. Keep out of reach of children.
Professional information
Clinician-facing context only. Use the current local label and dosing table, especially for renal-impairment and pediatric weight-based dosing.
United States (FDA label)
Indication: Treatment and prophylaxis of influenza A and B
Dose summary: Treatment (≥13 years): 75 mg twice daily x5 days, started within 48 hours of symptom onset. Treatment (2 weeks–<1 year): 3 mg/kg twice daily x5 days. Treatment (1–12 years): weight-banded dosing (≤15 kg: 30 mg; 15.1–23 kg: 45 mg; 23.1–40 kg: 60 mg; >40 kg: 75 mg, twice daily x5 days). Prophylaxis (≥13 years): 75 mg once daily for ≥10 days (post-exposure) or up to 6 weeks (outbreak). Prophylaxis (1–12 years): same weight bands, once daily.
Renal context: CrCl 60-90: standard dose. CrCl 30-60: 30 mg twice daily (treatment) / 30 mg once daily (prophylaxis). CrCl 10-30: 30 mg once daily (treatment) / 30 mg every other day (prophylaxis). ESRD on hemodialysis: 30 mg immediately then after each dialysis cycle, max 5 days (treatment) / 30 mg immediately then after alternate cycles (prophylaxis). ESRD on CAPD: single 30 mg dose (treatment) / 30 mg immediately then weekly (prophylaxis). ESRD not on dialysis: not recommended. (1)
Hepatic guidance
The U.S. label's dose adjustments are renal-function-based; no specific hepatic-impairment dose adjustment is described in the reviewed label.
Overdose note
Most reported overdoses have not produced adverse reactions beyond those seen at therapeutic doses; manage supportively per current poison-control guidance. (1)
Frequently asked questions
Does it matter when I start taking oseltamivir after flu symptoms begin?
Yes. Treatment is approved for people who have had symptoms for 2 days (48 hours) or less, and starting within that window is when the labeled benefit has been shown. Contact your prescriber as soon as flu symptoms start if you think you may need treatment. (1)
Can oseltamivir treat a cold, COVID-19, or other non-flu illness?
No. Oseltamivir works specifically against influenza A and B viruses. It is not effective against bacterial infections or other, non-influenza viral illnesses. (1)
Should I worry about confusion or unusual behavior while taking oseltamivir?
Influenza itself, with or without oseltamivir, has been linked to confusion or unusual behavior, reported mainly in children and teenagers. Watch closely for these signs during the first few days of illness and contact the prescriber or seek emergency care immediately if they occur. (1) (2)
What is the mechanism of action of oseltamivir?
Oseltamivir phosphate is an ethyl ester prodrug requiring ester hydrolysis for conversion to the active form, oseltamivir carboxylate, which inhibits influenza virus neuraminidase, affecting release of viral particles. (1)
References
- TAMIFLU (oseltamivir phosphate) capsule and powder for oral suspension — prescribing informationDailyMed, U.S. National Library of Medicine (FDA-approved label, packager Genentech, Inc.) · United States · accessed 2026-07-26 · source 1
- OseltamivirMedlinePlus, U.S. National Library of Medicine (patient-facing monograph) · United States · accessed 2026-07-26 · source 2
- Tamiflu 75 mg Hard Capsules — Summary of Product Characteristics (SmPC)electronic Medicines Compendium (UK) — Summary of Product Characteristics · United Kingdom · accessed 2026-07-26 · source 3
- TAMIFLU oseltamivir (as phosphate) 75 mg capsule blister pack — ARTG entry 76017Therapeutic Goods Administration (TGA), Australia — Australian Register of Therapeutic Goods · Australia · accessed 2026-07-26 · source 4
Brand names by country
Single-ingredient oseltamivir names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- oseltamavir phosphate75 mg, 45 mg · nucare pharmaceuticals,inc.
- Tamiflu75 mg, 30 mg, 6 mg/mL · genentech, inc.
United Kingdom
- Tamiflu (3)verified
Canada
- TAMIFLU
Australia
- Tamiflu (4)verified