What Is Melanotan 2? The Melanocortin Peptide Explained

The short version

What is Melanotan 2? It is a man-made peptide — a short chain of amino acids — designed to copy a natural pigment-controlling hormone called alpha-MSH, but in a tougher, longer-lasting form. Scientists at the University of Arizona built it in the late 1980s to make skin tan without sun.

It works by switching on a family of cell controls called melanocortin receptors. Because it switches on all of them, it affects skin color, appetite, and sexual function together. People know it by several names: Melanotan 2, Melanotan II, MT-2, and MT-II. It is sometimes just called "melanotan," though that name is also used for a different, related compound. It has never been approved as a drug or cosmetic, and it is not the same thing as the approved medicines it is often confused with — this page explains those differences plainly.

Melanotan

The bare term melanotan is ambiguous and worth pinning down. It refers to a small family of synthetic alpha-MSH analogs developed to stimulate melanin. "Melanotan I" is the linear, more MC1R-selective analog now approved (as afamelanotide) for a rare light-sensitivity disorder. "Melanotan 2" — the subject of this site — is the cyclic, non-selective analog that was never approved and that drives the broader set of effects ^[3]. When a source says only "melanotan," it is usually the unlicensed tanning product, which in practice has most often been Melanotan 2 sold online as "sun-tan jabs" ^[40]. The two are not interchangeable, and conflating them causes real confusion in the harm literature.

Mt2

MT2 (also written MT-2 or MT-II) is shorthand for Melanotan 2 in user communities and some research notes. Chemically it is a cyclic heptapeptide of formula C50H69N15O9, molecular weight about 1024.2 Da, CAS number 121062-08-6, with the sequence Ac-Nle4-cyclo[Asp5-His6-D-Phe7-Arg8-Trp9-Lys10]-NH2. It is catalogued under identifiers including PubChem CID 92432 and FDA UNII UPF5CJ93X7. The "MT2" label appears constantly in online discussion, but it always denotes the same unapproved research peptide described here — not a branded or regulated product.

Melanotan ii

Melanotan II is simply the formal spelling of the same compound, using the Roman numeral. It is a non-selective melanocortin receptor (MC1R-MC5R) agonist ^[11], classed as a synthetic melanocortin peptide and, for structured-data purposes, a chemical substance rather than an approved drug. It is synthetic: it does not occur in the body, but it is an analog of endogenous alpha-MSH, the natural 13-amino-acid POMC-derived peptide that activates the melanocortin receptors. Whether written "Melanotan 2," "Melanotan II," "MT2," or "MT-II," it is one molecule with one mechanism, covered on the melanotan 2 mechanism of action page.

Where it came from

Melanotan 2 was designed by Victor Hruby, Mac Hadley, and colleagues at the University of Arizona in the late 1980s as a superpotent, enzyme-resistant cyclic analog of alpha-MSH, intended to promote tanning and photoprotection and so potentially reduce skin-cancer risk ^[3]. The cyclization and D-amino-acid substitution were deliberate engineering choices to make it bind harder and last longer than the natural hormone ^[1]. A preformulation study from the same era explicitly described it as a potential skin-cancer-chemopreventive peptide ^[7]. The tanning program never reached market; the compound's later life as an unlicensed internet "tanning injection" is a separate story documented in the regulatory and user-experience literature ^[40], ^[12].

How it differs from the compounds it is confused with

Melanotan 2 is routinely mistaken for two approved drugs, and the distinction matters because their safety data do not transfer. Afamelanotide (Melanotan I) is the linear, relatively MC1R-selective analog approved for erythropoietic protoporphyria, a rare inherited disorder causing painful sun reactions ^[42]; long-term observational data exist for that approved use ^[43]. Bremelanotide (PT-141) is a cyclic agonist engineered from the Melanotan 2 scaffold toward MC4R-driven sexual effects, approved for a specific sexual-desire disorder ^[39]. Neither approval applies to Melanotan 2 ^[3]. Melanotan 2 itself remains an unapproved, non-selective research peptide — broader in its effects and unstudied in late-phase trials — and confusing it with its approved relatives is exactly the error that leads people to assume a safety record it does not have.