Antiviral Medications for the Flu

Antiviral medications are a class of drugs typically used to prevent or shorten the severity and duration of a viral infection such as influenza. Those used for the flu are considered a second line of defense against infection (with the seasonal flu vaccine being the first). Antivirals are most effective if taken soon after flu exposure or flu symptoms appear, but they are generally reserved for severe cases and those who are at-high risk for flu-related complications, as well as those who regularly interact with them (such as caretakers).

There are four antiviral medications currently approved by the U.S. Food and Drug Administration (FDA) to treat the flu in the United States:

Two other medications, amantadine and rimantadine, have been shown to target influenza A viruses. However, they are not recommended to prevent or treat influenza at this time as the flu viruses that make people sick are resistant to these drugs.

how the flu is treated
Hilary Allison / Verywell


Antiviral medications can reduce your fever and symptoms of influenza. They have the best chance of success if you start treatment within two days of experiencing symptoms, and they can speed up your recovery by about one day.

Antiviral medications can also lessen the risk of complications including childhood ear infections, respiratory issues such as pneumonia, and potential hospitalization for adult patients.

For those at a higher risk of serious flu complications, receiving early antiviral treatment can lessen the chance of becoming severely ill and requiring a hospital visit. Research has even shown that early antiviral treatment can reduce someone's risk of death from the flu.

Antiviral drugs help reduce the amount of virus being produced within the body of the infected person. That can help limit the spread of the virus to others.

How They Work

Three of the antiviral drugs used for influenza are neuraminidase inhibitors. Neuraminidase is a glycoprotein found in the influenza virus.

After the virus infects a human cell, its genetic material (RNA) orders the cell to make more viral copies. These bud to the surface of the host cell, where the viral neuraminidase must cleave the bond to sialic acid (found on the surface of the host cell) in order for the new viruses to be released.

Tamiflu (oseltamivir phosphate), Relenza (zanamivir), and Rapivab (peramivir) block the active sites of neuraminidase and, therefore, help prevent the new viruses from being released and going out to infect more cells. The peak of this viral replication is at 24 to 48 hours after infection. So, in order to stop release of more virus, the drug needs to be administered as soon as possible. These drugs work against both influenza A and influenza B viruses.

Xofluza (baloxavir marboxil) is a cap-dependent endonuclease inhibitor. Rather than preventing the release of viral particles, it interferes with viral RNA transcription so the virus can't replicate inside the host cells. It is also effective against both influenza A and influenza B.

As viruses change year after year, they can develop resistance to these antiviral drugs. As a result, researchers are continually looking for new drugs with slightly different methods of action that might be effective. Reserving antiviral drugs for those most at risk, rather than giving them to anyone, is thought to help slow the development of viral resistance to these drugs.

Who Should Take Them

Antiviral medications are available by prescription only. They are not routinely given to every person who has a mild case of influenza but are reserved for those who have the most severe illness, are at high risk of complications, or close contacts of those at high risk. As well, they may be given to prevent influenza in a person who is at high risk of complications or their close contacts.

In All Cases

Here are the scenarios in which antiviral treatment should always be started, regardless of whether or not you have had the flu vaccine:

  • You are hospitalized with influenza.
  • You have severe or progressive flu illness but are not hospitalized.
  • You have the flu and are 65 years or older, pregnant, or have given birth in the past two weeks. Children with the flu who are age 2 or younger should also receive an antiviral.
  • Groups at higher risk include people with chronic diseases such as asthma or lung disease, and those with weakened immune systems.

Possible Use

Your healthcare provider can consider prescribing antiviral medications in these instances where you are having flu symptoms, regardless of having been immunized or being in a high-risk group:

  • You have developed flu symptoms in the past 48 hours.
  • You have flu symptoms and you live with people who are at high risk of developing flu complications.
  • You are having flu symptoms and you are work in a healthcare setting where you have contact with people who are at high risk of developing flu complications.

For Prevention

In these cases, your healthcare provider may prescribe antiviral medications to prevent influenza, even though you have not knowingly been exposed:

  • Antivirals may be given throughout the flu season if you are in a very high-risk group and cannot receive the flu vaccination or it's expected you won't respond to the flu vaccine. This group includes those who are severely immunocompromised or who have had a stem cell or lung transplant in the past 12 months.
  • Short-term treatment with antiviral medication may be prescribed if you did not get the flu vaccine, flu is circulating in your community, and you are in a high-risk group or you are in close contact with those who are in a high-risk group (such as a family member or you work in a healthcare setting). You will also be given the flu vaccine.

If you have been exposed to someone with influenza and you haven't been vaccinated, you might be given a short-term course of treatment in these instances:

  • You are in a high-risk group and have had exposure to influenza from someone in your household.
  • You care for or live with someone who is in a high-risk group and you have been exposed to influenza. In this case, you will also be given the flu vaccine.
  • You work in a long-term care facility where influenza has been detected. In this case, you might even receive antivirals if you have been vaccinated as an additional level of precaution to reduce the spread and to keep staff healthy.


Any antiviral flu drug is contraindicated if you have previously had a serious reaction to the drug or any of its components.

Relenza (zanamivir) is not recommended for those with underlying airway disease due to risk of bronchospasm, which may be serious or fatal. It is warned that this drug has not been demonstrated to be safe and effective in those at high risk for flu complications due to underlying medical conditions.

Xofluza (baloxavir marboxil) has only been established as safe and effective for those under 12 years of age and older.

How to Use Antiviral Medications

Each medication is given in a different way and may not be appropriate for certain groups of people. Your healthcare provider can determine which medication is right for you and your situation.

  • Rapivab (peramivir) is given through an IV as a one-day treatment for those aged 6 months and over. It is not given as a preventative medication.
  • Relenza (zanamivir) is an inhaled powder. It is used twice daily for five days for the treatment of children and adults age 7 years and older. It's used once daily for as a preventative medication for those age 5 and older.
  • Tamiflu (oseltamivir phosphate) is available as a pill or liquid. It may be used as a five-day treatment for any age group, or to prevent the flu after contact with someone who has the flu in people 1 year and over 
  • Xofluza (baloxavir) is a pill given as a one-day treatment for those age 5 and over. It is not given as a preventative medication.

Oral Tamiflu (oseltamivir) is the preferred treatment for those who are pregnant as its safety is supported by more studies.

If your symptoms worsen while you are on these mediations or after you complete a course, contact your healthcare provider immediately.

Potential Side Effects

According to the Centers for Disease Control and Prevention (CDC), side effects can vary for each of these antiviral medications. For example:

  • The most common side effects of oseltamivir are nausea and vomiting, which may be reduced if you take it with food.
  • Zanamivir can cause bronchospasm.
  • Peramivir can cause diarrhea.

There have been rare cases of anaphylaxis and serious skin reactions such as Stevens-Johnson syndrome and erythema multiforme with Tamiflu (oseltamivir) and Rapivab (peramivir).

The prescribing information Tamiflu, Relenza, and Rapivab notes that there have been neurologic and behavioral symptoms reported after these neuraminidase inhibitors were taken. However, these symptoms can also occur during the course of influenza, so a specific tie to drugs' use has not been established. Manufacturers note that people who take these medications should be monitored for such symptoms.

You should talk to your healthcare provider about other potential side effects and/or review the medication package insert for more information.

Drug Interactions

Combining antivirals with other medications may reduce efficacy, so talk to your healthcare provider about everything you are taking before beginning a course.

It's recommended that baloxavir not be given along with certain laxatives, antacids, or oral supplements (including calcium, iron, magnesium, selenium, or zinc), as these reduce the blood levels and effectiveness of the antiviral medication. You should not take it along with dairy products or calcium-fortified drinks.

These antiviral medications will reduce the effectiveness of the live-attenuated influenza vaccine, so they should not be given at the same time.

A Word From Verywell

Antiviral medications can be very useful in helping to prevent or shorten the duration of the flu. However, they should not replace flu vaccination as your primary means of prevention. Because all of the antiviral medications are available only by prescription, it is important to see your healthcare provider if you believe you have the flu or may need antiviral medications to prevent it. Only your healthcare provider can determine what is best for you and your situation.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Kristina Duda, RN
Kristina Duda, BSN, RN, CPN, has been working in healthcare since 2002. She specializes in pediatrics and disease and infection prevention.