Azacitidine is a chemotherapy drug used in the treatment of myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). It works by reducing the growth of abnormal blood cells in the bone marrow. Azacitidine is a type of medication known as a hypomethylating agent, which means it helps to prevent abnormal changes in DNA that could lead to cancer development. This drug is typically given via injection under the skin or into a vein. Azacitidine may also be used in combination with other medications or therapies for the treatment of certain types of blood cancers.