4-Thiothymidine is primarily utilized in biochemical research as a modified nucleoside. It is often incorporated into DNA or RNA strands to study nucleic acid interactions and dynamics. This modification allows researchers to probe the structure and function of nucleic acids, particularly in understanding the mechanisms of DNA replication and repair. Additionally, 4-Thiothymidine is used in photochemical studies due to its ability to absorb UV light, making it a valuable tool for investigating light-induced reactions in nucleic acids. It also serves as a potential antiviral and anticancer agent in drug development, where its unique properties are explored for therapeutic applications.