GHK Cu vs NAD+: Which Longevity Peptide Should You Take or Stack? GHK Peptide as a Natural Modulator of Multiple Cellular Pathways in Skin Regeneration Pickart 2015 BioMed Research International Wiley Online Library Peptide Series #6 GHK Cu Tighter Smoother Skin. Your body naturally produces this copper binding peptide. At age 20, your plasma levels are around 200 ng mL. By age 60 they've dropped Peptide Series #6 GHK Cu Tighter Smoother Skin. Your body naturally produces this copper binding peptide. At age 20, your plasma levels are around 200 ng mL. By age 60 they've dropped