Dexamethasone is used to treat conditions such as arthritis, blood/hormone disorders, allergic reactions, skin diseases, eye problems, breathing problems, bowel disorders, cancer, and immune system disorders. Dexamethasone injection is used to treat severe allergic reactions. It is used in the management of certain types of edema (fluid retention and swelling; excess fluid held in body tissues), gastrointestinal disease, and certain types of arthritis. Dexamethasone injection is also used for diagnostic testing