Xofluza (baloxavir marboxil) is a prescription drug that’s used to treat and help prevent influenza (the flu). Xofluza can cause side effects that range from mild to serious. Examples include headache, nausea, and diarrhea.

Xofluza is used in adults and certain children to:

  • treat influenza (the flu) when taken within 48 hours after symptoms begin
  • help prevent the flu after contact with a person who has it

The active ingredient in Xofluza is baloxavir marboxil. (An active ingredient is what makes a drug work.) The drug comes as a tablet and liquid suspension, both of which are swallowed.

Keep reading to learn about the common, mild, and serious side effects Xofluza can cause. For a general overview of the drug, including details about its uses, see this article.

Some people may experience mild to serious side effects during their Xofluza treatment. Examples of the drug’s commonly reported side effects include:

  • diarrhea*
  • bronchitis (swelling in your airways)*
  • nausea*
  • sinusitis (swelling in your sinuses)*
  • headache

* To learn more about this side effect, see the “Side effects explained” section below.

Mild side effects have been reported with Xofluza. These include:

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist.

Xofluza may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

* To learn more about this side effect, see the “Side effects explained” section below.

To date, the only serious side effects reported with Xofluza are allergic reactions. While allergic reactions weren’t reported in Xofluza’s studies, they have been reported since this drug was approved for use. To learn more about this side effect, see the “Side effects explained” section below.

If you develop serious side effects after taking Xofluza, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Xofluza, visit MedWatch.

Xofluza is prescribed to treat, as well as help prevent, the flu in children ages 5 years and older. In the drug’s studies, vomiting and diarrhea were the most common side effects reported in children. Other side effects were similar to those reported in adults (see the sections above).

If you have more questions about Xofluza’s side effects in children, talk with your child’s doctor.

Get answers to some frequently asked questions about Xofluza’s side effects.

Are side effects of Xofluza similar to those of Tamiflu?

Yes, Xofluza and Tamiflu are both prescribed to treat and help prevent the flu and can cause some of the same side effects. They can also cause some different ones.

A few common side effects reported in both drug’s studies were allergic reaction, headache, and nausea. But there were some different side effects reported as well:

  • Swelling in the sinuses was reported with Xofluza but not Tamiflu.
  • General body pain was reported with Tamiflu but not Xofluza.

If you’d like to learn more about how Xofluza and Tamiflu compare, check out this article. You can also talk with your doctor or pharmacist.

How long do side effects of Xofluza usually last?

Side effects caused by Xofluza are usually temporary, only lasting a few hours to days.

If you experience side effects from Xofluza that are bothersome, severe, or ongoing, let your doctor or pharmacist know. They can review your symptoms and suggest ways to manage them.

Can Xofluza cause hallucinations?

It’s possible. Hallucinations (seeing or hearing things that aren’t really there) weren’t reported in studies of Xofluza. But there have been rare reports of this side effect since Xofluza came on the market.

In rare instances, hallucinations can happen as a symptom of the flu. (Xofluza is prescribed to treat and help prevent the flu.) So it’s not known whether hallucinations reported by people taking Xofluza were caused by the drug, the flu, or another factor.

If you experience hallucinations during or after taking Xofluza, immediately contact your doctor. They can recommend the best treatment for your symptoms.

Learn more about some of the side effects Xofluza may cause.

Bronchitis (swelling in your airways)

Xofluza may cause bronchitis as a side effect. This makes it harder for air to pass through your lungs. However, in the drug’s studies, bronchitis was actually more common in people taking a placebo (pill with no active drug) than in those taking Xofluza.

Symptoms of bronchitis include:

It’s important to note that the flu can also cause bronchitis symptoms. (Xofluza is prescribed to help prevent and treat the flu.)

What might help

Bronchitis caused by Xofluza should go away on its own, especially once you finish treatment. Let your doctor know if your bronchitis symptoms become severe or continue after you finish taking Xofluza. They can review your symptoms and suggest the best way to treat them.

Sinusitis (swelling in your sinuses)

Sinusitis is a possible side effect of Xofluza. However, in the drug’s studies, sinusitis was more common in people taking a placebo (pill with no active drug) than in those taking Xofluza.

Symptoms of sinusitis include:

It’s important to note that the flu can also cause symptoms of sinusitis. (Xofluza is prescribed to treat or help prevent the flu.)

What might help

In most cases, sinusitis caused by Xofluza goes away on its own. That said, your symptoms may continue after you finish taking Xofluza. It’s also possible for these symptoms to become severe. In either instance, let your doctor know. They can review your symptoms and suggest the best way to treat them.

Diarrhea

Diarrhea was the most commonly reported side effect in studies of Xofluza. However, diarrhea was more common among people taking a placebo (pill with no active drug) than in people taking Xofluza.

It’s important to note that there are many other possible causes of diarrhea, including the flu. (Xofluza is prescribed to treat and help prevent the flu.)

Symptoms of diarrhea include:

What might help

Diarrhea caused by Xofluza usually goes away on its own.

To help avoid dehydration (low fluid level) from diarrhea, drink plenty of fluids. If your doctor or pharmacist agrees that it’s safe for you, they may recommend an over-the-counter treatment for diarrhea, such as Pepto Bismol (bismuth subsalicylate) or Imodium (loperamide).

Serious diarrhea wasn’t reported in Xofluza’s studies, but you should let your doctor know if this side effect becomes bothersome or doesn’t go away. They can review your symptoms and recommend the best way to treat them.

Nausea

Nausea is a possible side effect of Xofluza. However, in the drug’s studies, nausea was actually more common in people taking a placebo (pill with no active drug) than in people taking Xofluza. There are many other possible causes of nausea, including the flu, which Xofluza is taken to help prevent or treat.

What might help

If you develop nausea after taking Xofluza, this side effect should go away on its own. This usually occurs shortly after finishing treatment.

There are ways to help manage nausea using home remedies, such as consuming peppermint or ginger. If your doctor or pharmacist tells you it’s safe, you can also try an over-the-counter drug such as Pepto Bismol (bismuth subsalicylate).

Allergic reaction

Like most drugs, Xofluza can cause an allergic reaction in some people. This side effect wasn’t reported in studies but has happened since Xofluza came on the market.

Symptoms can be mild to serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin (usually in your eyelids, lips, hands, or feet)
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms. Examples include:

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

Keeping track of side effects

Consider taking notes on any side effects you experienced from Xofluza treatment. You can then share this information with your doctor. This is especially helpful when you first start taking a new drug or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help them learn more about how Xofluza affects you.

Xofluza may not be right for you if you have certain medical conditions. This is known as a drug-condition interaction. Other factors may also affect whether this drug is a good treatment option for you. Talk with your doctor about your health history before starting Xofluza. Factors to consider include those described below.

Allergic reaction. If you’ve had an allergic reaction to Xofluza or any of its ingredients, your doctor will likely not prescribe it for you. Ask them about other medications that might be better options.

Alcohol and Xofluza

Alcohol and Xofluza aren’t known to interact with one another. But your doctor may suggest that you avoid consuming alcohol while you have the flu. (Xofluza is prescribed to treat and help prevent the flu.)

Drinking alcohol can worsen certain flu symptoms, including nausea and headache. And Xofluza can cause nausea and headache as a side effect. So drinking alcohol could increase your risk of these side effects from the drug.

Talk with your doctor or pharmacist if you have questions about drinking alcohol during treatment with Xofluza.

Pregnancy and breastfeeding with Xofluza

It’s unknown whether it’s safe to take Xofluza while pregnant or breastfeeding a child. Due to the lack of research, the Centers for Disease Control and Prevention (CDC) recommend against taking Xofluza in these situations. They recommend other flu treatments instead.

Talk with your doctor to learn more about other treatments for the flu that are considered safer to take if you’re pregnant or breastfeeding a child.

Side effects from taking Xofluza are rare but may still occur. If you have questions about side effects Xofluza can cause, talk with your doctor. Examples of questions to help get you started include:

  • Are Xofluza’s side effects similar to those of other drugs prescribed to help treat or prevent the flu?
  • Do any of the medications I take increase my risk of side effects from Xofluza?
  • Does my health history increase my risk of side effects from Xofluza?

To learn more about Xofluza, see these articles:

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Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.