Melanotan II: Identity, Receptor Targets and Evidence

What Melanotan II is

Melanotan II (MT-2, MT-II) is a synthetic cyclic peptide of seven amino acids. Its sequence is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, and its molecular weight is about 1024 Da. It was designed in the late 1980s at the University of Arizona by the groups of Victor Hruby and Mac Hadley as a shortened, ring-closed analogue of alpha-melanocyte-stimulating hormone (alpha-MSH), the 13-residue hormone that signals to pigment cells.

Three design changes separate it from the natural hormone: a norleucine in place of methionine, a D-phenylalanine in place of L-phenylalanine, and a lactam bridge between aspartate and lysine that closes the ring. The ring makes the peptide resistant to enzymatic breakdown and locks it into a shape that binds melanocortin receptors.

"Melanotan 2 acetate" is the same peptide supplied as an acetate salt, which is the usual counter-ion for a synthetic peptide. It is not a different compound.

Receptor targets

Melanotan II is a non-selective melanocortin receptor agonist. The five receptors in that family have different distributions and roles, and the peptide binds four of them.

The lack of selectivity is the defining pharmacological fact. Afamelanotide (Melanotan I) is a linear analogue with greater MC1R preference, which is why the two are not interchangeable. The differences are set out in Melanotan I vs Melanotan II.

Development history and regulatory status

Melanotan II entered early clinical studies in the 1990s. It was never taken through to a marketing authorisation. Its deamidated metabolite was later developed separately as bremelanotide (PT-141), which did reach licensure in the United States as Vyleesi.

Melanotan II itself is not a licensed medicine in the UK, the EU, the United States or Australia. The MHRA has issued public warnings about unlicensed melanotan products sold for human use since 2008. The catalogue item here is the Melanotan II 10mg research vial, supplied as lyophilised powder for in-vitro work only. Its batch certificate in the COA library reports identity by mass spectrometry and purity by HPLC, and nothing about biological activity.

Evidence tiers

Reports of adverse events in people who used unlicensed products are collected in Melanotan II adverse effects. The earlier overview of the whole family is Melanotan I and Melanotan II: melanocortin receptor research.

Scope and laboratory-use boundary

Materials sold on this site are supplied solely for non-clinical in-vitro laboratory research. They must not be ingested, injected, inhaled, applied or otherwise administered to a human or animal.

We do not provide dosing, routes of administration, treatment guidance, cosmetic-use guidance or in-vivo protocols. Preparation, storage and handling must follow a validated institutional SOP, the material documentation and an appropriate risk assessment.