This medication is used to treat various conditions such as severe allergic reactions, arthritis, blood diseases, breathing problems, certain cancers, eye diseases, intestinal disorders, and skin diseases. It is also used to test for an adrenal gland disorder (Cushing's syndrome). It decreases your body's natural defensive response and reduces symptoms such as swelling and allergic-type reactions. Dexamethasone is a corticosteroid hormone (glucocorticoid). This injectable form of dexamethasone is used when a similar drug cannot be taken by mouth or when a very fast response is needed, especially in patients with severe medical conditions.