AHK-Cu is a peptide with a copper ion linked to it. It is found in the blood of most mammals and is particularly important in regulating the growth, development, and death of vascular endothelial cells, the cells that line the inside of blood vessels. It is often called "copper AHK" and is of interest to researchers for its ability to improve hair growth and prevent the effects of aging as they relate to skin.

AHK-Cu is a short peptide that is complexed with (chemically linked to) a copper molecule. In the case of AHK, the copper atom is linked between the alanine and histidine residues of the alanine-histidine-lysine peptide. The copper atom is bound to three of the nitrogen atoms in the tripeptide. AHK-Cu has been heavily researched as a skin conditioning agent and has recently gained interest as a potential treatment for hair loss after promising bench-top experiments.