Xolair (omalizumab) is a prescription drug that’s used to treat certain conditions, including asthma. Xolair can cause side effects that range from mild to serious. Examples include injection-related side effects, headache, and fatigue.

Specifically, Xolair is used to treat:

Xolair is also used to reduce the risk of a certain type of allergic reaction, including anaphylaxis from some foods in adults and children ages 1 year and older. Xolair should be used along with avoidance of known allergy-triggering foods and food ingredients for this purpose.

The active ingredient in Xolair is omalizumab. (An active ingredient is what makes a drug work.) The drug comes in a few different forms for injection under your skin.

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

Xolair has a boxed warning. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). For details, see the “Side effects explained” section later.

Below are a few of the more common side effects reported by people who took Xolair in studies. These side effects can vary depending on the condition the drug is being used to treat.

More common side effects in people receiving Xolair injections for asthma include:

More common side effects in people receiving Xolair injections for chronic sinusitis with nasal polyps include:

  • headache*
  • injection-related side effects*
  • joint pain*
  • upper abdominal pain*
  • dizziness

More common side effects in people receiving Xolair injections for hives include:

More common side effects reported in children receiving Xolair injections to reduce the risk of reactions to food allergies include fever and injection site reactions.*

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

Some people may experience mild side effects during Xolair treatment. These side effects may vary depending on the condition you’re receiving Xolair to treat.

Examples of mild side effects that have been reported in people receiving Xolair include:

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

In most cases, these side effects should be temporary. Some may be easily managed, too. But if you have any symptoms that are ongoing or that bother you, talk with your doctor or pharmacist. You shouldn’t stop Xolair treatment unless your doctor recommends it.

Xolair may cause mild side effects other than the ones listed above. See the Xolair prescribing information for details.

Note:After the 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 Xolair, visit MedWatch.

Xolair may cause serious side effects in some people. Serious side effects that have been reported with Xolair include:

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

*Xolair has a boxed warning for this side effect. This is the most serious warning from the FDA. To learn more, see the “Side effects explained” section.

Common side effects that have been reported in children receiving Xolair include:

If you have questions about side effects that your child may experience during Xolair treatment, talk with their doctor.

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

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

Injection-related side effects

During treatment with Xolair, some people may experience injection-related side effects (also called injection site reactions). These are reactions that can occur where your dose of Xolair is injected. Injection-related side effects were common in studies of Xolair.

Examples of injection-related side effects include:

  • bruising
  • redness or color changes
  • burning, stinging, or warmth in your skin
  • itching
  • rash or hives
  • pain
  • swelling

What might help

Injection-related side effects usually happen within 1 hour of an injection and last for fewer than 8 days. Most people who experienced these side effects were less likely to have them with continued use of Xolair. So your risk of this side effect may decrease over time.

If you experience injection-related side effects during treatment with Xolair, talk with your doctor or pharmacist. They may be able to recommend ways to ease these side effects.

Upper abdominal pain

Abdominal pain can occur with Xolair. In studies, upper abdominal pain was among the most common side effects in:

What might help

If you experience upper abdominal pain during Xolair treatment, talk with your doctor. They may be able to recommend ways to decrease this side effect or recommend treatment options for it.

Fatigue

You may experience fatigue during Xolair treatment. This was a common side effect reported in studies of people receiving Xolair injections for asthma. But fatigue was not reported by people receiving Xolair injections for hives, or chronic sinusitis with nasal polyps.

What might help

If you notice a decrease in your energy levels while receiving Xolair, talk with your doctor or pharmacist. They may be able to determine what’s causing your fatigue and the best way to treat it.

Headache

You may experience headaches when using Xolair. In studies, this was one of the most common side effects reported in people receiving Xolair for chronic sinusitis with nasal polyps or hives. Headaches also commonly occurred in children using Xolair for asthma.

Headache was not reported as a side effect of Xolair injections when they were used to reduce or prevent food allergies in studies. But headache is a possible side effect of Xolair when it’s used for any other purpose.

What might help

If you experience headaches that are frequent or bothersome to you, talk with your doctor or pharmacist. They may recommend over-the-counter (OTC) treatment options, such as Tylenol (acetaminophen), or they may suggest other ways to treat your headaches.

Joint pain (arthralgia)

Some people may develop joint pain (arthralgia) during treatment with Xolair. Joint pain was a common side effect reported by people receiving Xolair in studies.

What might help

If you develop joint pain, talk with your doctor. In some cases, joint pain can be a symptom of a more serious condition called serum sickness. This condition usually causes fever and rash along with joint pain. If you develop serum sickness, your doctor will recommend that you stop Xolair treatment. They can discuss other treatment options for your condition.

If your joint pain is not associated with serum sickness, your doctor may recommend OTC pain relievers, such as Tylenol. Or they may suggest other ways to decrease your joint pain.

Allergic reaction including anaphylaxis

Like most drugs, Xolair can cause an allergic reaction in some people. In fact, Xolair has a boxed warning for the risk of anaphylaxis, which is a severe allergic reaction that can be life threatening.

When you receive your first dose of Xolair, your doctor will monitor you after the injection. This is done to be sure you don’t develop symptoms of anaphylaxis. Some people who experienced anaphylaxis had reactions after their first dose. But in some cases, anaphylaxis may not occur until a year or more after starting Xolair treatment.

For safety, your doctor may prescribe an EpiPen (epinephrine) for you to keep with you or at home for emergency treatment of an anaphylactic reaction to Xolair.

It’s important to understand the symptoms of a mild and serious allergic reaction, including anaphylaxis, so you can get help right away if you develop symptoms.

Symptoms of a mild allergic reaction can include:

Symptoms of a more serious allergic reaction, including anaphylaxis, can include:

  • hives
  • constriction (tightening) of the airways in your lungs, which can cause:
    • shortness of breath
    • wheezing or a whistling sound when you inhale
    • coughing
    • pain or tightness in your chest and back
  • fainting
  • 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

You should not use Xolair if you have ever had an allergic reaction to Xolair or any of its ingredients, including latex.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. To manage your symptoms, they may suggest:

  • an OTC antihistamine that you swallow, such as Benadryl (diphenhydramine)
  • a product you apply to your skin, such as hydrocortisone cream

If your doctor confirms you had a mild allergic reaction to Xolair, they’ll decide whether you should continue receiving it.

If you have symptoms of a severe allergic reaction, such as swelling or difficulty 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 had a serious allergic reaction to Xolair, they may have you switch to a different treatment.

Keeping track of side effects

During your Xolair treatment, consider keeping notes on any side effects you’re having. Then, you can share this information with your doctor. This is especially helpful to do when you first start taking new drugs 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 after starting that dose you had the side effect
  • what your symptoms were from the side effect
  • how it affected your daily activities
  • what other medications you were also taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help your doctor learn more about how Xolair affects you. Your doctor can use this information to adjust your treatment plan if needed.

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

Can Xolair be dangerous?

Xolair injections are generally safe and effective when used as directed for the indications in the drug’s prescribing information. But certain serious side effects can occur in some people.

For example, Xolair has a boxed warning for anaphylaxis. A boxed warning is the most serious warning from the FDA. For details, see the “Side effects explained” section later in the article. To learn about other potentially dangerous side effects of Xolair, see the “What are the serious side effects of Xolair?” section.

If you have concerns about the safety and potential dangers of Xolair injections, talk with your doctor.

Does Xolair cause weight gain or weight loss?

No, you shouldn’t experience weight gain or weight loss during Xolair treatment. Changes in weight were not side effects reported by people receiving Xolair in studies.

If you have unexplained weight changes during treatment with Xolair, talk with your doctor. They can try to determine what may be causing your weight changes.

Does Xolair cause any long-term side effects?

Yes, it’s possible that Xolair may cause long-term side effects. For example, this medication may raise your risk of heart attack, stroke, or cancer, which can all have long-term complications. But these side effects are rare.

Short-term, mild side effects are much more common with Xolair than long-term side effects. But if you’re concerned about long-term side effects with this drug, talk with your doctor or pharmacist.

How long do side effects from Xolair typically last?

It depends on which side effects you’re experiencing. For example, injection-related side effects usually go away within 8 days after an injection. These side effects are less likely to happen as your condition is treated with Xolair for a longer period of time.

Other side effects of Xolair, such as joint pain, may last longer. Some side effects may even last throughout Xolair treatment. If you’re concerned about how long a specific side effect could last, talk with your doctor or pharmacist. They may be able to recommend treatment for your side effects.

Before you start treatment with Xolair, talk with your doctor about any other medical conditions you have or other medications you’re taking. They can determine whether Xolair may be a safe treatment option for your condition.

Boxed warning: Risk of anaphylaxis

Xolair has a boxed warning for the risk of anaphylaxis, which is a severe allergic reaction. A boxed warning is the most serious warning from the FDA.

If you’ve had an allergic reaction to any of the ingredients in Xolair, including latex, you should not receive this medication. Symptoms of anaphylaxis may include trouble breathing, swelling of the throat or tongue, and low blood pressure.

To learn more, see the “Side effects explained” section.

Other warnings

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

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

Asthma attack or bronchospasm: If you’re experiencing difficulty breathing, bronchospasm, or any other symptoms of an asthma attack, you should not use Xolair to treat it. Xolair may not be an effective medication to treat asthma attacks or bronchospasm. If you’re experiencing these symptoms, talk with your doctor about the best treatment option for your condition.

Allergic reaction: If you’ve had an allergic reaction to Xolair or any of its ingredients, including latex, your doctor likely won’t prescribe Xolair. Ask your doctor what other medications are better options for your condition.

Parasitic infection: If you have a parasitic infection (such as hookworm or roundworm), tell your doctor before you start using Xolair. This drug may raise your risk of a parasitic infection. If you already have this type of infection, Xolair may make your condition worse. Your doctor will likely recommend treating the infection before you start receiving Xolair.

Cancer: Xolair may increase your risk of cancer. If you have cancer or have had it in the past, tell your doctor before you start Xolair treatment. Your doctor may recommend monitoring you more closely during your Xolair treatment. Or they may recommend a different treatment for your condition.

Current steroid treatment: If you currently take a steroid medication for asthma or nasal polyps, tell your doctor. They’ll recommend that you don’t suddenly stop taking the steroid when starting Xolair. Instead, your doctor will have you slowly decrease your dosage until you can safely stop taking the steroid if needed.

Alcohol and Xolair

There are no known interactions between alcohol and Xolair. But drinking alcohol during Xolair treatment could raise your risk of certain side effects. For example, both alcohol and Xolair may cause a headache or nausea. So drinking alcohol with Xolair may make these side effects worse.

If you drink alcohol, talk with your doctor about how much (if any) may be safe for you to drink during treatment with Xolair.

Pregnancy and breastfeeding while receiving Xolair

It’s not known whether Xolair is safe to use during pregnancy or while breastfeeding.

If you’re pregnant or breastfeeding, or planning to become pregnant or to breastfeed, talk with your doctor before starting Xolair treatment.

You may experience side effects during treatment with Xolair. But most side effects are mild. Before starting Xolair treatment, talk with your doctor about your risk of side effects with this drug.

Questions that you may want to ask include:

  • Do I have a higher risk of side effects due to my medical conditions?
  • How should I treat side effects that I experience?
  • What should I do if I become pregnant during treatment with Xolair?

To learn more about Xolair, see these articles:

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Q:

Can Xolair weaken my immune system and raise my risk of side effects?

Anonymous

A:

Based on how Xolair works, it’s thought that the drug doesn’t weaken your immune system.

Infection can occur during Xolair treatment. This may make it seem like the drug weakens your immune system’s ability to fight infection. But it’s important to keep in mind that people with asthma and chronic sinusitis with nasal polyps (two conditions Xolair is used to treat) have a higher risk of infection.

Xolair is a biologic (a drug made from living cells). Other biologics, including those used to treat autoimmune conditions such as psoriasis and rheumatoid arthritis, work by weakening your immune system. But Xolair works differently to treat asthma, hives, and chronic sinus infection with nasal polyps.

If you have questions about how Xolair could affect your immune system, talk with your doctor or pharmacist.

The Healthline Pharmacist TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

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.