Constrained peptides are peptides with cyclic portions that contain the biologically active site necessary for intracellular protein to protein interactions. The theory is that once the peptide has been locked into a specific conformation by either lactam bridge or stapling, the conformation freedom is decreased, resulting in increased binding affinity and biological activity to the targeted areas. When these constraints are strategically placed on a peptide, the constrained peptide may have a higher biological activity and efficient cell permeability, which is not the case with unconstrained peptides. In addition, these peptides have longer circulation life time in the body because their structure blocks proteolysis, which is one of the shortcomings in therapeutic application of native peptides.