NL GHK Cu (TETRAPEPTIDE + CU) Synthagen Synthagen PL Defy GHK Cu (glycyl L histidyl L lysine) is a naturally occurring copper binding peptide found in human plasma. As levels decline with age, so may its support of the biological processes involved in collagen production, skin GHK Copper Peptide Concentrate, cumpr ingredient cosmetic GHK Cu (copper peptide) is a science backed anti aging compound that supports collagen production, skin regeneration, and overall skin health. Used in both topical serums and subcutaneous