Copper Peptides 2026 (GHK Cu): What They Do for Skin & Hair GHK Cu vs NAD+: Which Longevity Peptide Should You Take or Stack? GHK Cu is a naturally occurring tripeptide in human plasma. Levels average 200 ng ml at age 20 and drop to 80 ng ml by age 60 (Pickart et al., 2020). That decline tracks with OBM Geriatrics The Effect of the Human Plasma Molecule GHK Cu on Stem Cell Actions and Expression of Relevant Genes