Dexamethasone is used to treat conditions such as arthritis, blood/hormone/immune system disorders, allergic reactions, certain skin and eye conditions, breathing problems, certain bowel disorders, and certain cancers. It is also used as a test for an adrenal gland disorder (Cushing's syndrome). This medication is a corticosteroid hormone (glucocorticoid). It decreases your body's natural defensive response and reduces symptoms such as swelling and allergic-type reactions.