What Is Melanotan 2? The Melanocortin Peptide Explained

In plain English

What is Melanotan 2? It is a small lab-made molecule — a ring of seven amino acid building blocks — designed to copy a natural body hormone that tells skin to make pigment. Because the lab version is built into a tight ring, it lasts longer and works harder than the natural one. People inject it to tan with little sun, and it also tends to cut appetite and, in men, cause erections.

It goes by several names. 'Melanotan' on its own usually means this molecule; 'MT2' is shorthand; 'Melanotan II' is the formal spelling. There is also a separate, earlier molecule called Melanotan 1, and a related approved drug — these are not the same thing and are explained below. The short answer: Melanotan 2 is an unapproved research chemical that acts on the body's pigment-and-appetite signaling system, with real effects and real, documented risks.

The molecule

Melanotan 2 is a cyclic (lactam-bridged) heptapeptide analog of alpha-MSH, the 13-amino-acid hormone derived from proopiomelanocortin that naturally activates the melanocortin receptors ^[3]. Its structure is Ac-Nle4-cyclo[Asp5-His6-D-Phe7-Arg8-Trp9-Lys10]-NH2 — a truncated, cyclized, D-Phe-substituted core of alpha-MSH, with molecular formula C50H69N15O9 and a molecular weight near 1024.2 Da (CAS 121062-08-6). The internal lactam bridge — an amide bond closing the chain into a ring — constrains the shape, which both raises potency and makes the peptide far more resistant to enzymatic breakdown than the linear hormone it mimics ^[3]. The first preparative solution-phase total synthesis was reported in 2008, characterizing it as a synthetic cyclic heptapeptide that stimulates the skin-tanning process ^[15].

Melanotan, MT2, and Melanotan II — the names

The naming is a frequent source of confusion. 'Melanotan' is used loosely; in current usage it most often refers to this cyclic compound. 'MT2' and 'MT-II' are common shorthand, and 'Melanotan II' is the formal written form — all the same molecule ^[3]. The synonym list runs MT-2, MT-II, MTII, and the full sequence name above.

The term matters because a different, earlier molecule, Melanotan I (afamelanotide), is a linear analog with relatively selective MC1R activity, and it is the only melanocortin tanning-class analog with any regulatory approval — for the rare light-sensitivity disorder erythropoietic protoporphyria, not for cosmetic tanning ^[3]. A third relative, bremelanotide (PT-141), was derived from the Melanotan 2 scaffold and optimized toward MC4R-mediated sexual effects; it carries its own separate approval for a sexual-desire disorder in premenopausal women ^[3]. None of those approvals applies to Melanotan 2 itself.

Where it came from and what it is now

Melanotan 2 was designed in the late 1980s by Victor Hruby, Mac Hadley, and colleagues at the University of Arizona as a superpotent analog intended to promote tanning and photoprotection, with the original hope of reducing skin-cancer risk ^[3]. Early human work showed it could darken skin; researchers then noticed it triggered erections, which led to the small erectile-dysfunction study and, eventually, the PT-141 spin-off ^[2][3].

The original tanning program never reached the market. From the mid-2000s an illicit trade emerged, with the peptide sold online as unlicensed tanning injections — the so-called 'Barbie drug' or 'sun-tan jabs' — despite repeated regulator warnings ^[4]. Today it remains a non-selective melanocortin agonist (MC1R-MC5R) sold as a research chemical, approved nowhere, and that status is the backdrop to everything on the effects page and the Melanotan 2 references.