Mercaptopurine drug class is typically prescribed to treat cancer and autoimmune illnesses. It acts by blocking some important cellular functions. Mercaptopurine inhibits the production of DNA and RNA, both necessary for cell development and replication. By acting as a fake metabolite, it is absorbed into DNA and RNA, preventing normal synthesis. Furthermore, mercaptopurine inhibits de novo purine synthesis (DNPS), a mechanism required for the production of purines, the building blocks of DNA and RNA. This comprehensive inhibition successfully stops cancer cells from proliferating and spreading. Mercaptopurine metabolites, such as 6-thioguanosine-5′-phosphate (6-thioGMP), might hinder cell development by inhibiting nucleotide interconversion. Because of these activities, mercaptopurine is an effective drug for inhibiting the proliferation of malignant cells.