Xolair Side Effects – The Complete List

David Fuller

Last Updated On: October 6, 2025

Like all medications, biologic therapies can bring not only benefits but also risks. With Xolair (omalizumab), most patients tolerate treatment well, but some experience side effects that range from mild skin irritation at the injection site to rare but serious reactions such as anaphylaxis. Knowing what to expect helps patients feel prepared and allows providers to respond quickly if concerns arise.

Xolair is an anti-IgE monoclonal antibody approved for conditions like allergic asthma, chronic spontaneous urticaria, nasal polyps, and IgE-mediated food allergies. While its impact can be life-changing for many, being aware of potential side effects is key to safe, confident use.

In this article, we’ll explore the complete list of Xolair side effects, explain how common or rare they are, and share practical strategies for monitoring and managing them—so patients and clinicians can work together to balance risks with the significant benefits this therapy offers.

Key Takeaways

• Xolair (omalizumab) is a biologic therapy used for allergic asthma, chronic urticaria, nasal polyps, and food allergies.
• Common side effects include injection-site reactions, headache, fatigue, joint/muscle pain, respiratory infections, and fever.
• Anaphylaxis is rare but serious, which is why injections start in a clinic with monitoring.
• Long-term safety data are reassuring, although clinicians continue to monitor for potential adverse events, such as malignancy, cardiovascular events, or thrombocytopenia.
• The risk of parasitic infection may increase slightly, particularly in regions where these infections are prevalent.
• Safe use requires monitoring, patient education, and readiness for emergencies to strike a balance between benefits and risks.
• Self-injection may be an option for some patients after training, though initiation must be clinic-based.

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Common & Expected Adverse Effects of Xolair

Most omalizumab side effects appear shortly after injection and are generally mild to moderate. These reactions often resolve without medical intervention but should always be shared with a healthcare provider to ensure proper monitoring.

• Injection-site Reactions: Pain, redness, swelling, or itching where the injection is given.
  
• Headache: Among the most frequently reported effects.
  
• Fatigue: Mild tiredness or low energy after a dose.
  
• Arthralgia and Myalgia: Discomfort in the joints or muscles.
  
• Dizziness: Temporary and usually self-limited.
  
• Upper Respiratory Tract Infections, Nasopharyngitis, and Fever: Frequently reported in clinical trials and patient resources.

These are the expected side effects most clinicians see in practice. Proper Xolair administration, such as rotating injection sites, can help reduce local discomfort, while supportive care typically manages other mild symptoms.

Moderate to Serious Risks Associated with Xolair

Less common, but more serious, side effects require medical attention and close observation. Healthcare providers must remain vigilant and educate patients about these possibilities:

• Anaphylaxis Risk: Severe allergic reactions can occur immediately or even hours after injection. Patients should be counseled to recognize symptoms like difficulty breathing, chest tightness, or sudden swelling.
  
• Delayed Hypersensitivity: Rash, hives, or serum sickness–like reactions may appear days or weeks after a dose.
  
• Cardiovascular and Thromboembolic Events: Observational studies have explored possible risks such as stroke, heart attack, or blood clots, but evidence remains inconclusive. Clinicians typically weigh individual risk factors when prescribing.
  
• Fever or Flu-like Illness: These symptoms may signal immune system involvement.

Because of these risks, patients are observed after each injection, especially when starting therapy. The duration of monitoring is based on clinical judgment, patient risk factors, and local protocols. In selected cases, trained patients may transition to self-administration under provider guidance.

Rare & Long-Term Safety Signals with Xolair

With more than 20 years of use, Xolair has a strong safety record, but rare and long-term risks are still monitored. These events are unusual but important for patients and providers to be aware of:

• Parasitic infections: Because IgE helps defend against helminths (parasitic worms), omalizumab may slightly reduce resistance. This is most relevant in regions where such infections are common. Providers may treat existing infections before starting therapy.
  
• Malignancy risk: Early studies raised concerns about cancer, but later research has not confirmed a causal link. Current evidence suggests no increased malignancy risk, though surveillance continues.
  
• Thrombocytopenia: There have been rare postmarketing reports of low platelet counts, which may lead to unusual bruising or bleeding. While routine monitoring is not necessary, patients should report unexplained symptoms.
  
• Long-term safety: Decades of cumulative data show that most adverse events occur early in treatment, with no unexpected risks emerging over time. Long-term therapy is generally considered safe when followed up properly.

Mitigation, Monitoring & Patient Counseling for Xolair Use

Ensuring safety with Xolair requires more than prescribing—it involves careful monitoring, preparedness, and patient education. A structured approach helps maximize benefits while minimizing risks:

• Observation After Injection: Patients should be closely monitored after each dose, especially during initiation. Observation time varies by risk factors and clinical protocols.
  
• Emergency Preparedness: Clinics administering Xolair must have epinephrine and resuscitation tools. Staff should have proper training on how to respond quickly in the event of anaphylaxis.
  
• Patient Counseling: Education empowers patients. Their doctors should teach them how to recognize early signs of delayed reactions or anaphylaxis and to seek immediate care.
  
• Regular Follow-up: Ongoing visits help evaluate symptom control for asthma, urticaria, or nasal polyps, adjust dosing if needed, and track any emerging side effects.

Through these strategies, clinicians create a safe environment where patients can benefit from Xolair while minimizing potential risks.

Conclusion

While Xolair side effects range from mild injection-site reactions to rare but serious complications, most patients tolerate therapy well. The benefits, such as fewer asthma flare-ups, reduced hives, and improved daily quality of life, often outweigh the risks. With proper administration, vigilant monitoring, and proactive counseling, clinicians can ensure patients receive effective and safe care with Xolair.

FAQs

1. What are the most common side effects of Xolair?

Mild issues like injection-site reactions, headache, fatigue, muscle or joint pain, and sometimes respiratory infections or fever.

2. How serious is the risk of anaphylaxis with Xolair?

It’s rare but serious. Healthcare professionals should monitor patients after injections, and maintain emergency medications on hand.

3. Does Xolair increase the risk of cancer?

Current evidence shows no proven increase in cancer risk, though monitoring continues.

4. Can Xolair affect infections or the immune system?

Yes, it may slightly raise risk for parasitic infections and cause more frequent respiratory infections, but these are usually manageable.

References

Genentech. XOLAIR® (omalizumab) Side Effects | Important Safety Information. https://www.xolair.com/important-safety-information.html

Genentech. Safety Profile – XOLAIR (omalizumab). https://www.xolairhcp.com/safety.html

Gevaert P, Omachi TA, Corren J, et al. Efficacy and safety of omalizumab in nasal polyposis: 2 randomized phase 3 trials. J Allergy Clin Immunol. 2020;146(3):595-605. doi:10.1016/j.jaci.2020.05.032