Copper Peptides 2026 (GHK Cu): What They Do for Skin & Hair Quantitation of Copper Tripeptide in Cosmetics via Fabric Phase Sorptive Extraction Combined with Zwitterionic Hydrophilic Interaction Liquid Chromatography and UV Vis Detection 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 GHK Cu vs NAD+: Which Longevity Peptide Should You Take or Stack? The Effect of the Human Peptide GHK on Gene Expression Relevant to Nervous System Function and Cognitive Decline