GHK Cu is one of my personal favorites for a lot of reasons, but I can say without a doubt that it's use effectively stopped and reversed, my receiving hairline. However, there are GHK Cu vs AHK Cu: Which Copper Peptide Is More Effective? How HGH and Testosterone Can Help Reverse Muscle Loss GHK Cu as a multifunctional copper peptide: synthesis routes, process engineering and emerging applications Systems Microbiology and Biomanufacturing Springer Nature Link