- A drug used to reduce inflammation and lower the body’s immune response. It is used with other drugs to treat leukemia, lymphoma, mycosis fungoides (a type of skin lymphoma), and multiple myeloma. Dexamethasone is also used alone or with other drugs to prevent or treat many other diseases and conditions. These include conditions related to cancer and its treatment, such as anemia (a low level of red blood cells), allergic reactions, swelling in the brain, and high levels of calcium in the blood. Dexamethasone is a type of corticosteroid.