Does GHK Cu Really Work? 40 Years of Research Reviewed 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 GHK Cu: The Regenerative Peptide for Skin, Hair, and Healing Pulse & Remedy Why Collagen Loss Accelerates After 40: The Role of GHK Cu in Menopaus Pure & Cimple