2’,3’-Didehydro-3’-deoxythymidine-5’-triphosphate (d4T-TP) is an analog of thymidine which inhibits activity of HIV reverse transcriptase by competing with its substrate deoxythymidine triphosphate. When incorporated, it causes termination of DNA chain elongation. d4T-TP also inhibits cellular DNA polymerase and reduces synthesis of mitochondrial DNA.