GHK Cu is a naturally occurring tripeptide in human plasma. Levels average 200 ng ml at age 20 and drop to 80 ng ml by age 60 (Pickart et al., 2020). That decline tracks with Growth Hormone and Aging Endotext NCBI Bookshelf Nanoengineered Self Assembling Peptides with Increased Proteolytic Stability Promote Wound Healing ACS Applied Materials & Interfaces 07 MARGOLINA c_04 LORD_c Does GHK Cu Really Work? 40 Years of Research Reviewed