Relenza (zanamivir inhalation powder) can cause mild to serious side effects. More common side effects include sinus infection and fever. If Relenza side effects become difficult to tolerate, ask your doctor about coping tips or treatment options.

Doctors prescribe Relenza for the following uses:

  • to treat influenza types A and B infections (flu) in adults and children ages 7 years and older who have had flu symptoms for no more than 2 days
  • to help prevent flu in adults and children ages 5 years and older

Relenza belongs to the drug classification influenza virus neuraminidase inhibitor (NAI). It should not be used in people who have an airway condition, such as chronic obstructive pulmonary disease (COPD) or asthma.

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

Note: Relenza is an oral medication that you take using an inhaler device. It should not be taken or given by any other method.

The following lists contain a few of the more common side effects reported by people who took Relenza in studies. Side effects of this drug can vary depending on the condition it’s treating or preventing.

More common side effects in people taking Relenza to treat influenza include:

More common side effects in people taking Relenza to help prevent influenza include:

  • fever
  • chills
  • joint pain
  • articular rheumatism, which is a type of joint inflammation

For more information about some of these side effects, see “Tips for managing side effects.”

Mild side effects have been reported with Relenza. 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. Do not stop Relenza treatment unless your doctor recommends it.

Relenza 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 “Tips for managing side effects.”

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

If you develop serious side effects while taking Relenza, 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 call your local emergency number right away.

Serious side effects that have been reported include:

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Sharing your experience helps make medication safer for everyone. It gives doctors and researchers more information about how the drug works in real life. If you develop a side effect during treatment with Relenza and want to tell the FDA about it, visit MedWatch or call 800-FDA-1088.

Allergic reaction

For some people, Relenza can cause an allergic reaction. This side effect wasn’t reported in the drug’s studies, but it has occurred since the drug became available.

In general, symptoms of an allergic reaction can be mild or serious. But a mild reaction can develop into a serious or severe reaction, so you should be watchful.

Mild allergic reaction and what to do

If you have mild symptoms of an allergic reaction, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should continue Relenza treatment.

Watch for symptoms such as:

  • mild rash
  • mild itching

Serious or severe allergic reaction and what to do

If you have symptoms of a serious or severe allergic reaction, call 911 or your local emergency number right away. These symptoms could be life threatening. They can also progress to anaphylaxis, a severe reaction requiring immediate medical treatment.

Watch for symptoms such as:

  • swelling of the face or mouth, especially the back of the mouth
  • difficulty breathing
  • difficulty swallowing
  • wheezing
  • coughing
  • serious rash
  • anxiety or confusion
  • slurred speech
  • abdominal pain
  • weak pulse

Your doctor can confirm whether you’ve had a serious allergic reaction to Relenza. If you have, they may switch you to a different treatment.

You can do certain things to help make some Relenza side effects more manageable. If you have ongoing, worsening, or bothersome side effects, talk with your doctor or pharmacist. They can suggest tips for managing them or recommend other treatment options for your condition.

Sinus infection

Sinus infection was a common side effect reported in studies of Relenza. Symptoms can include:

Steps you can take to manage symptoms associated with this side effect include:

  • applying a warm, damp cloth to your forehead and face throughout the day
  • staying hydrated
  • using a humidifier to add moisture to the air
  • spraying a nasal saline rinse into your nostrils to help keep them clear
  • taking over-the-counter medications, such as:
    • guaifenesin (Mucinex), to treat congestion and cough
    • nasal corticosteroid spray, to reduce nasal swelling and inflammation
    • decongestant, to relieve stuffy nose
    • acetaminophen (Tylenol) or ibuprofen (Advil, Motrin), to relieve pain
  • seeing your doctor, who might prescribe antibiotics

Joint pain

Joint pain was a common side effect reported in studies of Relenza.

Steps you can take to manage symptoms associated with this side effect include:

  • taking over-the-counter pain medications, such as ibuprofen or topical capsaicin
  • resting the affected joint
  • applying ice packs to the affected joint
  • wrapping the affected joint with an elastic bandage
  • elevating the affected joint to lessen swelling
  • seeing your doctor

Before taking Relenza, discuss your health history with your doctor. Relenza may not be right for you if you have certain medical conditions or other factors affecting your health, including contraindications. These are factors or conditions that could prevent your doctor from prescribing a drug due to the risk of harm.

Be sure to talk with your doctor if any of the following apply to you:

  • airway condition, such as COPD or asthma
  • reside in a nursing facility
  • recent live vaccination, especially the intranasal attenuated influenza vaccine
  • past allergic reaction to this or a similar drug
  • pregnancy
  • breastfeeding
  • alcohol consumption

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.