The Effect of the Human Peptide GHK on Gene Expression Relevant to Nervous System Function and Cognitive Decline GHK Cu vs NAD+: Which Longevity Peptide Should You Take or Stack? Now introducing one of my favorite peptides.. GHK Cu This is a naturally occurring copper peptide your body already uses to repair and regenerate skin. As we age, those levels decline and that's GHK Cu Peptides: Unlocking the Copper Peptide Revolution in Skin Care