What Is Melanotan 2? The Melanocortin Peptide Explained

The short version

What is Melanotan 2? It is a small, lab-made peptide — a short chain of amino acids — built to copy a natural body hormone called alpha-MSH that tells skin to make pigment. The lab version is stronger and longer-lasting. Injected, it darkens skin without sun, cuts appetite, and (in men) can trigger erections.

It goes by several names. Melanotan, Melanotan II, MT-2, and MT2 all point to the same compound. It is not a tanning product and not a medicine — no regulator has approved it for any use ^[4]. It was designed by university scientists in the 1980s, never finished clinical development, and now circulates as an unregulated research chemical. Below: the chemistry in plain words, the origin story, and how it differs from the two related compounds that did get approved.

Melanotan, MT2, and Melanotan II — the names

The naming is a common source of confusion, so here it is plainly.

Melanotan on its own usually means this compound, though it is sometimes used loosely for the whole family. Melanotan II is the precise name. MT-2 and MT2 are the everyday short forms. Chemically it is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 — a cyclic (ring-shaped) seven-unit peptide, molecular weight about 1024 Da, CAS 121062-08-6.

What MT2 is not: it is not Melanotan I, and it is not the approved sexual-function drug derived from this scaffold. Those are separate compounds with separate profiles, covered below. And searching Melanotan II will surface both the legitimate research literature and a large illicit market — this site digests only the former ^[22].

Where it came from

Melanotan 2 was designed in the late 1980s by Victor Hruby, Mac Hadley, and colleagues at the University of Arizona ^[29]. The idea was elegant: if you could darken skin with a drug instead of sun, you might cut UV exposure and skin-cancer risk. They built a superpotent cyclic analog of alpha-MSH, resistant to the enzymes that chew up the natural hormone.

A pilot Phase I study showed it worked — skin darkened ^[1]. Researchers also noticed it triggered erections, which spun off a small erectile-dysfunction study and, eventually, a separate MC4R-focused agonist for sexual dysfunction ^[29]. The original tanning program never reached the market. From the mid-2000s, an illicit "melanotan" trade filled the gap, selling unlicensed tanning injections despite regulator warnings ^[30].

Melanotan 2 vs Melanotan I vs PT-141

Three compounds, one family, easy to confuse.

• Melanotan 2 (this compound): non-selective melanocortin agonist — hits MC1R through MC5R. Broadest effect (pigment plus appetite, sexual, behavioral). No regulatory approval anywhere ^[4].
• Afamelanotide (Melanotan I): a linear analog, more selective toward MC1R, so its action leans pigment-only. It is the one melanocortin tanning-type analog with regulatory approval — for the rare inherited disorder erythropoietic protoporphyria (EPP), which causes painful sun reactions ^[27]. That approval does not extend to Melanotan 2.
• Bremelanotide (PT-141): a cyclic agonist derived from the Melanotan 2 scaffold, optimized toward MC4R for sexual effects with reduced pigment activity. It is approved for hypoactive sexual desire disorder in premenopausal women ^[28]. That approval does not extend to Melanotan 2 either.

The takeaway: two relatives crossed the regulatory finish line; Melanotan 2 did not. Its controlled human data is limited to small Phase I studies, and its long-term safety remains unknown ^[6]. For how the receptors produce these differences, see the melanotan 2 mechanism of action page.