A medication that is inactive when administered but gets converted into the active drug inside your body.A prodrug is a pharmacologically inactive compound that undergoes biotransformation in vivo to release the active drug. Prodrug strategies for peptides address bioavailability, stability, or targeting challenges. Palopegteriparatide (TransCon PTH) is a peptide prodrug: PTH(1-34) is conjugated to a PEG carrier via a transient linker that slowly hydrolyzes, providing sustained PTH release from a weekly injection. Melflufen uses a peptide-conjugated prodrug approach where aminopeptidase cleavage releases the cytotoxic alkylating agent preferentially inside tumor cells.