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, and other types of cancer. Dexamethasone is also used to prevent or treat many other diseases and conditions. These include conditions related to cancer and its treatment, such as anemia, allergic reactions, swelling in the brain, and high levels of calcium in the blood. Dexamethasone is a type of corticosteroid.