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 Role of IGF 1 in the Growth Hormone IGF Axis Therapeutic Peptides in Aesthetic, Metabolic and Endocrine Conditions: Effects, Safety, Clinical Applications, and Future Perspectives Human conditions of insulin like growth factor I (IGF I) deficiency Journal of Translational Medicine Springer Nature Link Normal Physiology of Growth Hormone in Normal Adults Endotext NCBI Bookshelf