Melanotan I, Melanotan II and PT-141: The Melanocortin Peptides Compared

The melanocortin peptides are some of the most searched research compounds in the UK, and some of the most misused. This guide sets out how they differ, and why their regulatory status matters.

The melanocortin system

Melanocortins are hormones derived from the precursor protein POMC, including α-MSH. They act on five receptors:

Receptor	Main location	Associated with
MC1R	Melanocytes (skin)	Pigmentation
MC2R	Adrenal cortex	Cortisol (ACTH receptor)
MC3R / MC4R	Brain	Energy balance, appetite, sexual function pathways
MC5R	Exocrine glands	Secretion

The three compounds

Melanotan I / afamelanotide — a linear 13-amino-acid α-MSH analogue that is relatively selective for MC1R. It is licensed in the UK only as a prescription implant for a rare light-sensitivity condition.

Melanotan II — a shorter, cyclic analogue that activates several melanocortin receptors (MC1R, MC3R, MC4R and others). It is not licensed anywhere. The MHRA and NHS have issued repeated warnings about unlicensed tanning products, including reports of changes to moles.

PT-141 / bremelanotide — developed from Melanotan II and acting mainly on central MC4R and MC3R. It is licensed in the United States for one indication but not in the UK.

Why selectivity matters

Because Melanotan II activates several receptor subtypes, its effects in models are broad. Afamelanotide's narrower MC1R profile is why it was the one developed as a licensed photoprotection medicine. Bremelanotide was refined towards central receptors and away from pigmentation.

KPV, a three-amino-acid fragment of α-MSH, is studied for anti-inflammatory signalling without pigmentation effects.

A clear warning

Research-grade melanocortin peptides are not tanning products and not medicines. Using unlicensed products on people is unsafe and is the subject of UK regulator warnings. PeptideCompare lists research-use material only.

Comparing listings

1. Make sure the listing names the compound, not just "Melanotan". MT1 and MT2 are different molecules.
2. Check the mass-spec result against the expected molecular weight.
3. Compare price per mg on each compound's own comparison page.

Summary

MT1, MT2 and PT-141 are melanocortin agonists with different receptor selectivity and very different regulatory status. PeptideCompare provides no dosing or usage guidance, and nothing here is for human or veterinary use.