GHK-Cu — glycine-histidine-lysine complexed with copper — is one of the most structurally simple compounds in this series and one of the most mechanistically interesting. It is a tripeptide: three amino acids, naturally present in human plasma, saliva, and urine, with plasma concentrations that fall from roughly 200 nanograms per millilitre in young adults to near-undetectable levels by the time most people reach 60. That decline, and what it may mean for tissue maintenance and repair capacity across the lifespan, is the central biological question this episode addresses.

The compound was first characterised in the early 1970s by Loren Pickart, who identified it in human plasma albumin fractions and noted its capacity to stimulate liver tissue regeneration in vitro. Subsequent decades of research — predominantly preclinical, predominantly i ...