A drug used to treat chronic myelogenous leukemia (CML) that has not gotten better with other treatment. It is also used with radiation therapy and other anticancer drugs to treat certain types of head and neck cancer. It is used under the brand name Hydrea to treat these cancers. It is also used under the brand name Droxia to treat certain patients with sickle cell anemia. Hydroxyurea is also being studied in the treatment of other conditions and types of cancer. It stops cells from making DNA and may kill cancer cells. It may also make cancer cells easier to kill with radiation therapy. Hydroxyurea is a type of antimetabolite.