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GHK-Cu is a tiny copper-binding peptide found in many skin and hair products. Research links it to collagen, firmer-looking skin, wound repair and hair growth.

Melanotan II switches on the skin’s pigment signal and a brain desire signal. Small human studies showed tanning and improved erections, which is why it is known as the tanning peptide.

PT-141, or bremelanotide, works on desire signals in the brain rather than blood flow. A prescription form, Vyleesi, is approved for low sexual desire in some premenopausal women.