Four prescription antiviral medications are currently approved to treat influenza, and the one you’re most likely to receive is oseltamivir (sold as Tamiflu and generics). It’s the most widely prescribed option because it works against both influenza A and B, comes as a pill or liquid, and is safe for a broad range of patients including young children and pregnant women. The other three approved antivirals are baloxavir (Xofluza), zanamivir (Relenza), and peramivir (Rapivab), each with different advantages depending on your situation.
The 48-Hour Window
All flu antivirals work best when started within 48 hours of your first symptoms. Clinical trials show that early treatment shortens fever and illness by roughly one day. That might not sound dramatic, but for someone with a high fever, body aches, and exhaustion, cutting a day off the worst stretch matters. It also reduces the risk of complications like pneumonia, especially for people in high-risk groups.
This tight window is why doctors sometimes prescribe antivirals based on symptoms alone, without waiting for a lab test to confirm influenza. A negative rapid flu test doesn’t rule out infection, and delaying treatment reduces how well the medication works.
Oseltamivir: The Most Common Prescription
Oseltamivir is taken as a pill or liquid twice a day for five days. It works by blocking a protein on the surface of the virus that newly formed viral particles need to break free from infected cells and spread. Without that protein functioning, the virus gets trapped and can’t replicate efficiently.
Adults take 75 mg twice daily. Children’s doses are based on weight, ranging from 30 mg to 75 mg twice daily for kids over age one. Infants under one year can also be treated, with dosing based on body weight. The most common side effect is nausea, reported in about 10% of adults (compared to 6% on placebo). Vomiting occurs in roughly 9% of adults and 14% of children. These symptoms are usually mild enough that only about 1% of people stop the medication because of them. Taking it with food helps.
Rare reports of neuropsychiatric effects like confusion or agitation have surfaced during post-marketing monitoring, primarily among Japanese adolescents and adults. These events appear to be uncommon and temporary.
Baloxavir: One Dose, One Day
Baloxavir stands out because it requires just a single dose. Instead of blocking viral release the way oseltamivir does, it interferes with the virus’s ability to copy its genetic material in the first place. This different mechanism means it attacks the virus at an earlier stage of replication.
It’s approved for people five and older who have been sick for no more than 48 hours. Dosing is weight-based: one 40 mg tablet for people between 20 and 80 kg (roughly 44 to 176 pounds), and one 80 mg tablet for those 80 kg and above. A liquid suspension is available for children who can’t swallow tablets.
For influenza B infections specifically, baloxavir shortened symptom duration by more than 24 hours compared to oseltamivir, making it a particularly strong option during seasons when influenza B is circulating heavily. However, it is not recommended during pregnancy or breastfeeding because safety data for those groups don’t yet exist.
Zanamivir and Peramivir
Zanamivir is an inhaled powder, delivered through a disk inhaler. It uses the same viral-blocking mechanism as oseltamivir but goes directly to the respiratory tract. The catch: it’s not appropriate for people with asthma or chronic lung disease, since inhaling the powder can trigger bronchospasm. It’s approved for people seven and older for treatment.
Peramivir is the only flu antiviral given intravenously, as a single infusion. It’s typically reserved for hospitalized patients or people who can’t take medications by mouth, whether due to vomiting, being on a ventilator, or other reasons. It’s approved for people two and older.
Who Gets a Prescription
Any adult or child with confirmed or suspected flu can be prescribed antivirals, but treatment is most strongly recommended for people at higher risk of serious complications. That includes children under five (especially under two), adults 65 and older, pregnant women and those up to two weeks postpartum, and people with chronic conditions like asthma, heart disease, diabetes, or weakened immune systems. Residents of nursing homes and long-term care facilities also fall into this group.
For otherwise healthy adults with mild symptoms, the decision is more case-by-case. The medication still shaves about a day off illness, but some doctors weigh that benefit against cost and side effects. If you’re within the 48-hour window and feeling miserable, it’s worth asking.
Flu Treatment During Pregnancy
Pregnant women are at heightened risk for flu-related hospitalization, and that elevated risk extends up to two weeks after delivery or pregnancy loss. Oseltamivir is the preferred antiviral during pregnancy because it has the most safety data. It can be taken during any trimester, and treatment should start as soon as flu is suspected rather than waiting for test results.
Pregnancy changes how the kidneys filter medications, so some women may need a slightly higher dose to achieve the same drug levels. Standard dosing is still the default, but your provider may adjust based on the circumstances.
What About Antibiotics?
Antibiotics do not treat the flu. Influenza is caused by a virus, and antibiotics only work against bacteria. Prescribing antibiotics for uncomplicated flu provides no benefit and contributes to antibiotic resistance.
The exception is when the flu leads to a secondary bacterial infection, most commonly bacterial pneumonia, sinus infections, or ear infections. Signs that a bacterial complication may be developing include a fever that returns after improving, worsening cough with thick or discolored mucus, or new ear pain. In those cases, your doctor may add an antibiotic alongside the antiviral, sometimes using lab cultures to identify the specific bacteria involved.
Older Drugs No Longer Recommended
Two older medications, amantadine and rimantadine, were historically used against influenza A. They targeted a different viral protein and were never effective against influenza B. The CDC no longer recommends them because most circulating flu strains, including the H1N1 virus that emerged in 2009, are resistant to both drugs. They could theoretically return to use if a future strain showed susceptibility, but for now they sit on the shelf.