You can click the blue text in this sentence to find a page listing all kinds of information about Xolair, including side effects.

After a Xolair shot, the injection site might itch, look red, sting, or hurt.

Probably the most important thing to look out for is a severe allergic reaction called anaphylaxis. Anaphylaxis symptoms can include hives, rash, trouble breathing, dizziness, chest tightness and swelling of your tongue or in your throat. Some people who experience anaphylaxis also have a terrible, frightened feeling or a feeling of "impending doom."

A person usually experiences these symptoms right away, but sometimes they might not have any symptoms until four days later!

If you have an allergic reaction to Xolair once, you can never take it again.