The GH IGF 1 axis in obesity: pathophysiology and therapeutic considerations Nature Reviews Endocrinology The Effect of the Human Peptide GHK on Gene Expression Relevant to Nervous System Function and Cognitive Decline Synergy of GHKCu and hyaluronic acid on collagen IV upregulation via fibroblast and exvivo skin tests Jiang 2023 Journal of Cosmetic Dermatology Wiley Online Library Before vs. after 3 months of GHK Cu peptide therapy smoother texture, more even tone, and skin that looks healthier overall. Small peptide, big difference