Fasenra (benralizumab) can cause side effects that range from mild to serious. More common side effects include sore throat and headache. If side effects from Fasenra become difficult to tolerate, talk with your doctor about coping tips or other treatment options.

Fasenra is used in adults and certain children ages 6 years and older to treat eosinophilic asthma. It may also be used to treat eosinophilic granulomatosis with polyangiitis (EGPA) in adults.

Keep reading to learn about the common, mild, and serious side effects Fasenra can cause. To learn more about Fasenra, including its uses, dosage, and cost, read this Fasenra overview.

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

  • sore throat
  • headache (see “Side effect specifics”)

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

  • sore throat
  • headache
  • fever
  • injection site reaction

In most cases, these side effects should be temporary. And some may be easily managed. But if you have ongoing or bothersome symptoms, talk with your doctor or pharmacist. And do not stop treatment with Fasenra unless your doctor recommends it.

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

For more information about some of these side effects, see “Side effect specifics.”

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The only serious side effect reported in studies of Fasenra was severe allergic reaction.

If you develop serious side effects during Fasenra treatment, 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.

Allergic reaction

For some people, Fasenra can cause an allergic reaction.

In general, symptoms of an allergic reaction can be mild or serious.

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 and can determine whether you should keep using Fasenra.

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.

If your doctor confirms you’ve had a serious allergic reaction to Fasenra, they may have you switch to a different treatment.

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

Headache

Headaches were the most common side effect reported in studies of Fasenra. Headache may cause symptoms such as:

  • a dull ache on the top of the head, at the eyebrows, or ears
  • a tight band feeling around the head
  • mild neck or shoulder pain
  • tiredness
  • irritability

Factors that can increase the risk of headache with Fasenra include dehydration, hunger, and lack of sleep.

What might help

If you get a headache during Fasenra treatment, it may help to drink more water, eat a healthy snack, and get some rest.

You can also try over-the-counter (OTC) acetaminophen to help relieve your symptoms. Avoid aspirin, ibuprofen, and naproxen, as these OTC products may worsen asthma symptoms. Follow package instructions and ask your pharmacist for help when choosing a product.

If your headaches become frequent or severe, talk with your doctor.

Injection site reaction

Injection site reactions were an occasional side effect reported in studies of Fasenra. This side effect may cause the following symptoms at or near your Fasenra injection site:

  • stinging or aching pain
  • discolored or darkened skin
  • swelling
  • itchiness
  • bruising
  • raised rash

What might help

Fasenra video instructions recommend setting the injection pen at room temperature for 30 minutes before using it. If the medication in the pen is too cold, the risk of injection site reactions may increase. It may also help to review the self-injection video instructions occasionally, as having the correct injection technique may help reduce site reactions.

Avoid using the same spot on your arm, stomach, or thigh for each Fasenra injection. Instead, keep a calendar or list of sites used (upper-right thigh, lower-left stomach, etc.) and choose a new spot each time. This may help reduce injection site reactions.

If you get an injection site reaction during Fasenra treatment, you can apply a cool compress to the area as frequently as needed.

If the injection site becomes swollen, painful, and hot to the touch (signs of infection) or other symptoms worsen, contact your doctor or pharmacist.

Here are answers to some frequently asked questions about Fasenra’s side effects.

Can Fasenra cause cancer?

No, Fasenra isn’t known to cause cancer. This wasn’t reported as a side effect in the drug’s studies.

It’s important to note that Fasenra belongs to a group of drugs called monoclonal antibodies. These drugs can affect the immune system. However, monoclonal antibodies have not been confirmed to cause cancer.

If you have specific concerns about your risk of cancer during treatment with Fasenra, talk with your doctor or pharmacist.

Does Fasenra have long-term side effects?

No, Fasenra isn’t expected to have any long-term side effects. In Fasenra’s studies, long-term side effects weren’t reported. And a 5-year study of Fasenra found that the drug continued to be safe and effective when used long-term.

Talk with your doctor if you notice any side effects that are persistent or bothersome during your treatment with Fasenra. They can help determine what may be causing these effects. If necessary, they can also recommend ways to manage them.

How long do Fasenra’s side effects last?

Fasenra’s side effects are typically expected to be short term. In studies of Fasenra, most side effects were reported within a few hours of injecting a dose. This includes allergic reaction, headache, and injection site reactions.

These side effects typically go away on their own after a few days, but some may require additional treatment or management.

If you experience side effects that are severe or bothersome after injecting Fasenra, talk with your doctor or pharmacist. They can recommend ways to manage certain side effects, such as taking an OTC pain reliever or antihistamine.

Keeping track of side effects

During your Fasenra treatment, consider taking notes on any side effects you’re having. 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 Fasenra affects you. They can then use this information to adjust your treatment plan if needed.

Below is important information you should consider before starting Fasenra.

Warnings

Fasenra can sometimes cause harmful effects in people with certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether Fasenra is a good treatment option for you.

Talk with your doctor about your health history before starting this medication. Be sure to tell them if any of the following factors apply to you:

For more information about these and other interactions with Fasenra, see this Fasenra interactions article.

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.