Does Xolair cause weight gain? (3+ facts)

In this article, we will discuss whether Xolair causes weight loss. We will also talk about the factors contributing to weight gain along with the use of Xolair and its side effects. 

Does Xolair cause weight gain? 

No, Xolair does not cause weight gain. There are no research studies which report that Xolair induces weight loss. Xolair (omalizumab) is a humanized IgG1 monoclonal antibody which acts on IgE antibodies in humans. Omalizumab disrupts the allergic cascade and reduces inflammatory cells and peripheral eosinophilia, hence reducing the symptoms of allergy, such as inflammation, itching, swelling, etc. (1)

Xolair also prevents the activation of basophils and mast cells, which helps reduce the autoimmune response which occurs in asthma and urticaria. (1) There are other factors which can contribute to weight gain while taking Xolair. If you notice any unexplained weight gain, consult your physicain for a proper evaluation and assessment. 

What factors contribute to weight gain while taking Xolair? 

Xolair is a medication used to treat allergic conditions such as asthma, urticaria, nasal polyps, food allergies, etc. Xolair was not associated with weight gain during clinical trials nor during post-marketing surveillance. However, there are other factors which can contribute to weight gain during Xolair therapy, such as: 

  • High-calorie intake: Consuming more calories, junk food, a diet high in processed foods and unhealthy fats can contribute to weight gain. 
  • Reduced physician activities: Little or no physical activity can contribute to weight gain. 
  • Metabolism: If you have a slow metabolism, you may gain weight more easily. Metabolism can impact how your body burns calories.
  • Genetics: Genetic factors can influence fat distribution and weight. If obesity runs in your family, you may have a higher chance of gaining weight. 
  • Hormonal factors: Changes in hormones during menstruation, pregnancy and menopause can affect body weight. 
  • Medical conditions: Conditions such as polycystic ovarian syndrome (PCOD), hyperthyroidism, psychiatric illnesses, etc., can cause fluctuations in weight. 
  • Medications: Drugs such as antipsychotics (clozapine, valproate, lithium), antidepressants (duloxetine, citalopram), antidiabetic medication, antihypertensives, etc can cause weight gain. 
  • Emotional factors: Stress, depression and anxiety can lead to binge eating, which can lead to an increase in weight. 

What are the side effects associated with Xolair? 

Xolair (omalizumab) is associated with side effects which include: (1,2)

  • Injection site reaction
  • Viral infection
  • Upper respiratory tract infection
  • Sinusitis
  • Headache
  • Pharyngitis
  • Hypersensitivity
  • Parasitic infection
  • Hair loss
  • Nausea
  • Fatigue
  • Headache
  • Dermatitis
  • Pruritus
  • Pain

It is important to note that not all individuals who take Xolair experience these side effects. It is essential to seek medical help if you experience any unwanted side effects. 

What are the measures to be taken while consuming Xolair? 

There are some general precautionary measures to follow while consuming Xolair. 

  • Always take medication as prescribed by your physician. 
  • Xolair is a medication given subcutaneously, so make sure you know how to use it properly. 
  • Always wash your hands and sanitize your skin before injecting the medication into your body.  
  • Hold the syringe at 45° and pinch a 2-inch fold skin before injecting the medication.
  • After you place the syringe in the position, gently pull the plunger a little back. Look for blood; if you notice any blood in your syringe, do not inject the medication; instead, choose a different site and repeat the procedure. 
  • If you do not know how to inject Xolair, visit a healthcare provider. 
  • Monitor for any side effects and seek medical help if you experience any discomfort. 

In my experience

As per my knowledge, Xolair is not associated with weight loss. However, individual variability, age, underlying disorder and medication can contribute to weight changes during Xolair treatment. Hence, it is important to get a thorough evaluation to rule out the cause of weight gain. 

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Kumar C, Zito PM. Omalizumab. [Updated 2023 Aug 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: 


Xoliar [package insert]. South San Francisco, Genentech, Inc. 2016. Available from: