Are there any major side effects of xolair?

Anaphylaxis. Biggest is-warning for Anaphylaxis, But newer studies show that just having severe asthma puts you at a risk for anaphylaxis that is greater than the risk of Xolair. Also, the definition for anaphylaxis in the Xolair studies was very broad. Because of this, they recommend you receive it in a doctors office and have injectable epinephrine available. Don't let that scare you. It's very effective.