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. Dexamethasone injection is also used to treat certain conditions that affect the blood, skin, eyes, thyroid, kidneys, lungs, and nervous system. It is sometimes used in combination with other medications to treat symptoms of low corticosteroid levels (lack of certain substances that are usually produced by the body and are needed for normal body functioning) and in the management of certain types of shock. Dexamethasone injection is in a class of medications called corticosteroids. It works to treat people with low levels of corticosteroids by replacing steroids that are normally produced naturally by the body. It also works to treat other conditions by reducing swelling and redness and by changing the way the immune system works.