Mercaptopurine (also known as 6-MP) is an antimetabolite and immunosuppressive drug primarily used in the maintenance chemotherapy of acute lymphoblastic leukemia (ALL).It interferes with DNA and RNA synthesis, preventing cancer cells from growing and multiplying. Mercaptopurine is a nucleoside metabolic inhibitor that interferes with the synthesis of nucleic acids, primarily DNA, disrupting the replication and proliferation of fast-growing cancer cells. It serves as a frontline, essential medicine for both pediatric and adult acute leukemia.