source: MedlinePlus

Hydroxyurea (Hydrea) is used alone or with other medications or radiation therapy to treat a certain type of chronic myelogenous leukemia (CML; a type of cancer of the white blood cells) and certain types of head and neck cancer (including cancer of the mouth, cheek, tongue, throat, tonsils, and sinuses). Hydroxyurea (Droxia) is used to reduce the frequency of painful crises and reduce the need for blood transfusions in patients with sickle cell anemia (an inherited blood disorder in which the red blood cells are abnormally shaped [shaped like a sickle] and cannot bring enough oxygen to all parts of the body). Hydroxyurea is in a class of medications called antimetabolites. Hydroxyurea treats cancer by slowing or stopping the growth of cancer cells in your body. Hydroxyurea treats sickle cell anemia by helping to prevent formation of sickle-shaped red blood cells.