What is Melanocortin? (Peptide Glossary)

The melanocortin system is a network of peptide hormones (derived from the POMC precursor, including alpha-MSH and ACTH) and five receptors, MC1R through MC5R, distributed across skin, brain, and other tissues. Different receptors mediate different effects: MC1R drives melanin production (pigmentation), MC3R and MC4R regulate energy balance and appetite, and MC4R also influences sexual function pathways.

The research peptides in this family map directly onto receptor selectivity. Melanotan II is non-selective - it activates all melanocortin receptors, which is why its research literature spans pigmentation, appetite, and sexual function. PT-141 (bremelanotide) was developed from Melanotan II to isolate MC4R-mediated effects, and became an FDA-approved drug. Melanotan I (afamelanotide) is more MC1R-selective and is approved for a photosensitivity disorder.

For researchers, the melanocortin family demonstrates why receptor selectivity matters in compound selection - and why COAs matter: the cyclic structure of Melanotan II makes its synthesis failure-prone, and purity varies more between vendors for this compound than for simple linear peptides.