Along with its needed effects, omalizumab may cause some unwanted or undesirable effects. Often, people using omalizumab never experience any unwanted effects. The severity and duration of these effects are dependant on many factors including duration of therapy, dose, and individual response. Possible unwanted effects include:

• injection-site reactions (bruising, redness, warmth, burning, stinging, or other discomfort around the injection site)
• viral and respiratory tract infections
• sinus infections
• headache
• sore throat

Less common:

• pain
• dizziness
• hair loss

Rare but serious side effects - seek medical help if you experience:

• Sudden severe allergic reaction (sudden signs of allergy such as rash, itching or hives on the skin, swelling of the face, lips, tongue or other parts of the body, fast heartbeat, dizziness and light headedness, shortness of breath, wheezing or trouble breathing)
• bleeding or bruising more easily than normal
• Pain, numbness or tingling in the arms and legs, lumps or raised patches in the skin, weakness and fatigue, loss of appetite and weight loss 
• Joint pain, stiffness, rash, fever, swollen/enlarged lymph nodes 

Omalizumab blocks a substance called immunoglobulin E (IgE) which is produced by your body. If you have allergic asthma, your body makes more IgE when you breathe in an allergen that triggers your asthma. Omalizumab helps stop the allergic-inflammatory process in allergic asthma.

Omalizumab is not a rescue medication and should not be used to treat sudden asthma attacks.
It is not a substitute for the medicines you are already taking.
Adding omalizumab to treatment with inhaled steroids (e.g. fluticasone) has been shown to reduce the number of asthma attacks. It has not been proven to work in other allergic conditions.
Oral or inhaled corticosteroids (e.g. prednisone, fluticasone) should not be abruptly stopped upon starting omalizumab therapy.
Use is not recommended in the following situations:

• allergy to omalizumab or any component of the formulation

Caution is recommended in the following situations:

• diabetes
• glucose-galactose malabsorption syndrome

Use in pregnancy and breastfeeding: At this time there is limited information on use in pregnant and breastfeeding women. Consult your doctor or pharmacist before using.