Xofluza (baloxavir marboxil) is a brand-name drug that’s prescribed to treat and help prevent flu in adults and certain children. As with other drugs, Xofluza can cause side effects, such as diarrhea, nausea, and headache.

Xofluza belongs to a drug class called antivirals. The drug is not available in a generic version. Xofluza is available in these forms:

  • oral tablet
  • oral liquid suspension

Read on to learn about potential common, mild, and serious side effects of Xofluza. For a general overview of the drug, including details about its uses, see this article.

Xofluza can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took Xofluza in clinical trials:

* For more information about this side effect, see “Side effect specifics” below.

Mild side effects can occur with Xofluza use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to Xofluza’s prescribing information.

Mild side effects that have been reported with Xofluza include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you develop a side effect while taking Xofluza and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Side effect specifics” below.
† An allergic reaction is possible after using Xofluza. However, this side effect wasn’t reported in clinical trials. To learn more, see the “Side effect specifics” section below.

Xofluza may cause serious side effects. The information below may not include all possible serious side effects of the drug. For more information, you can refer to Xofluza’s prescribing information.

Serious side effects that have been reported include severe allergic reaction. An allergic reaction is possible after taking Xofluza. However, this side effect wasn’t reported in clinical trials. To learn more, see the “Side effect specifics” section below.

If you develop serious side effects while 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.

Xofluza is prescribed to help prevent and treat flu in children ages 5 years and older.

In Xofluza’s clinical trials, the most common side effects reported in children were vomiting and diarrhea.

For more information about Xofluza’s side effects in children, talk with your child’s doctor or pharmacist.

Xofluza may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

Are the side effects of Xofluza similar to those seen with Tamiflu?

Tamiflu (oseltamivir) and Xofluza are both prescribed to help prevent and treat flu. These drugs can cause some similar side effects and some different ones as well.

A few common side effects of both Xofluza and Tamiflu include nausea, headache, and allergic reaction.

Tamiflu may also cause general body aches. However, this is not a reported side effect of Xofluza.

Xofluza can cause sinusitis (swelling in your sinuses). However, this isn’t a known side effect of Tamiflu.

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

How long do the side effects of Xofluza usually last?

It depends. In most cases, side effects caused by Xofluza are temporary, usually lasting only a few days. This is because Xofluza is only taken as a one-time dose.

If you experience side effects that last longer than that, bother you, or become severe, talk with your doctor or pharmacist.

Can Xofluza cause hallucinations?

It’s possible. Hallucinations weren’t reported in Xofluza’s clinical trials. However, this side effect has been reported since the drug was approved for use.

Hallucinations are when you see, hear, or experience things that aren’t really there. Rarely, the flu itself can cause hallucinations. This is also a possible side effect of certain other flu treatments. However, it’s not known for sure whether Xofluza caused hallucinations in people taking the medication.

If you experience hallucinations after taking Xofluza, contact your doctor immediately. They can recommend the best way to treat your symptoms. However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Learn more about some of the side effects that Xofluza may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for Xofluza.

Nausea

Nausea was one of the more common side effects reported in Xofluza’s clinical trials. However, it was most common among people taking a placebo instead of Xofluza. (A placebo is a pill with no active drug.)

Nausea can also be a symptom of flu. (Xofluza is prescribed to help prevent or treat flu.) There are many other possible causes of nausea as well.

What you can do

Nausea caused by Xofluza should go away on its own, especially once treatment with the drug ends. (Xofluza is taken short term to help prevent or treat the flu.)

If you experience nausea while taking Xofluza, let your doctor know. They may suggest ways to manage this symptom, such as:

Diarrhea

Diarrhea was the most common side effect reported by people taking Xofluza in clinical trials. However, it was more common in people taking a placebo instead of Xofluza.

With diarrhea, you experience watery stools. Other symptoms can include abdominal pain or cramps, bloating, and body aches.

Flu itself can cause diarrhea. (Xofluza is prescribed to help prevent or treat flu.) There are also many other possible causes of diarrhea.

What you can do

Diarrhea caused by Xofluza should go away on its own, especially once treatment ends. It’s important to drink enough fluid to avoid dehydration from diarrhea. You can also ask your doctor or pharmacist whether they recommend you take an OTC medication for diarrhea. For example, they may recommend Imodium (loperamide) or Pepto Bismol.

If you have bothersome or severe diarrhea while taking Xofluza, let your doctor know. They can review your symptoms, determine possible causes, and recommend a treatment for you.

Headache

Headache is a possible side effect of Xofluza. However, in Xofluza’s clinical trials, most people who took the drug didn’t report this side effect.

It’s important to note that flu itself can cause headache. (Xofluza is prescribed to help prevent or treat flu.) There are also many other possible factors that contribute to or cause headache.

What you can do

In most cases, headache caused by Xofluza goes away once treatment ends. Additionally, Xofluza treatment typically consists of one dose. So this side effect shouldn’t last long term.

Let your doctor know if you develop a headache that doesn’t go away or bothers you after taking Xofluza. They can suggest ways to manage your headache, such as applying an ice pack. They may also recommend you take an OTC pain reliever, such as Advil (ibuprofen) or Tylenol (acetaminophen).

Allergic reaction

As with most drugs, Xofluza can cause an allergic reaction in some people. This side effect wasn’t reported in clinical trials, but it has happened since Xofluza was approved for use.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep taking Xofluza. However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Be sure to talk with your doctor about your health history before you take Xofluza. This drug may not be the right treatment for you if you have certain medical conditions or other factors that affect your health. These are considered drug-condition or drug-factor interactions. The conditions and factors to consider include:

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

Alcohol with Xofluza

There are no known interactions between Xofluza and alcohol.

That said, your doctor may suggest avoiding alcohol consumption while you have the flu. Drinking alcohol can worsen certain flu symptoms, including headache and nausea.

Headache and nausea are also possible side effects of Xofluza. Drinking alcohol during treatment may increase your risk of these side effects or make them more severe.

If you have questions about drinking alcohol while taking Xofluza, talk with your doctor or pharmacist.

Pregnancy and breastfeeding while taking Xofluza

It’s not known whether it’s safe to take Xofluza during pregnancy or while breastfeeding.

For this reason, your doctor will likely recommend that you do not take Xofluza if you are pregnant or breastfeeding. Other flu treatments may be safer for you.

If you’re pregnant, breastfeeding, or planning for either, talk with your doctor about what flu treatments they recommend.

Xofluza is prescribed short term to help prevent or treat flu. The drug can cause mild side effects, but these should be temporary. The drug isn’t known to cause long-term side effects.

Severe allergic reaction is the only confirmed serious side effect caused by Xofluza.

If you’d like to learn more about Xofluza, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from taking the drug.

Besides talking with your doctor, you can do some research on your own. These articles might help:

  • More information about Xofluza. For details about other aspects of Xofluza, refer to this article.
  • Drug comparison. To learn how Xofluza compares with Tamiflu, read this article.
  • Dosage. For information about the dosage of Xofluza, view this article.
  • Interactions. To find out about Xofluza’s interactions, see this article.
  • A look at the flu. For details about flu, see our flu hub.

Disclaimer: Medical News Today 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.