# What Is Melanotan 2? The Melanocortin Peptide Explained > What is Melanotan 2? A lab-made melanocortin peptide studied for tanning, appetite, and sexual function. Plain-English explainer of MT2 and Melanotan II, fully cited. A clear, cited introduction to the molecule, its names, where it came from, and what it does. ## The gist So, what is Melanotan 2? It is a lab-made peptide — a short chain of seven amino acids closed into a ring — that copies a natural hormone called alpha-MSH, the signal your body uses to make skin pigment. Because it copies that hormone but is far stronger and longer-lasting, it powerfully switches on a family of cell receptors called melanocortin receptors. Those receptors control four very different things: skin color, appetite, sexual arousal, and how the body burns energy. So a single peptide originally built to help people tan turned out to also suppress hunger and trigger erections. It was designed at the University of Arizona in the late 1980s, was tested in a few small human studies, and was never approved as a medicine. Today it is sold illegally online as a tanning injection — but it remains an unapproved research chemical with documented risks. ## Melanotan The word Melanotan refers to a small family of synthetic peptides built to mimic alpha-MSH and stimulate tanning. There are two: a linear version (often called Melanotan I, the basis of an approved drug for a rare light-sensitivity disorder) and the ring-shaped version that is the subject of this site. When people say 'melanotan' casually they often mean the second one, but the two are chemically and pharmacologically different — the linear one is relatively selective for skin pigment, while the cyclic one hits every melanocortin receptor and so has much broader effects [3]. ## MT2 MT2 is simply a common shorthand for Melanotan 2 — you will also see MT-2, MT-II, and MTII. They all refer to the same molecule, whose formal chemical name is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 and whose CAS registry number is 121062-08-6. Chemists describe it as a cyclic, truncated, modified piece of the natural alpha-MSH hormone, redesigned for superpotent and enzyme-resistant activity [3]. Its molecular weight is about 1024 daltons. ## Melanotan II Melanotan II is the original, full spelling (with Roman numerals) used in the scientific literature, while Melanotan 2 is the everyday spelling. They are the same compound. The 'II' distinguishes it from Melanotan I, the linear analog developed alongside it. In the foundational research, both were patented and tested in humans — Melanotan I aimed at tanning, Melanotan II tested for male erectile dysfunction after its pro-erectile effect was noticed during a tanning study [1][3]. ## What is Melanotan 2 used for in research? In the published research, Melanotan 2 has been studied for four overlapping things. The original goal was tanning and photoprotection — darkening skin without UV exposure to potentially lower skin-cancer risk [1]. The most robust modern animal work is on appetite and body weight, where it reliably cuts eating and fat in rodents [5][7]. It has been studied for sexual function, producing erections in men in a small controlled trial [2]. And it is used as a research tool to probe the melanocortin system's role in energy balance, glucose handling, and behavior [10][11]. None of these uses is an approved human treatment. For the cell-level detail of how all of this happens, see the [melanotan 2 mechanism of action](/mechanism-of-action) page; for the full study list, see the [Melanotan 2 research](/research) page and its [Melanotan 2 references](/references). --- A dark-mode reading of the Melanotan 2 record that leads with the appetite and metabolic studies — the robust rodent fat-loss data set in plain type, the tiny old human trials and the documented melanoma, kidney, and priapism harms kept in full view, and the community reports pinned to one side as anecdote; no clinic behind the name despite the 'Rx', and nothing here dosed, sourced, prescribed, or sold.