An endopeptidase inhibitor is a drug that inhibits one or more endopeptidase enzymes. Endopeptidases are one of two types of proteases (enzymes that break down proteins and peptides), the other being exopeptidases. Endopeptidases cleave peptide bonds of non-terminal amino acids (that is, they cut proteins/peptides into two chains), whereas exopeptidases break terminal bonds, resulting in the release of a single amino acid or dipeptide from the peptide chain.