Melanotan 2 (Melanotan II, MT-II) is a synthetic cyclic heptapeptide, a structural analogue of endogenous α-melanocyte-stimulating hormone (α-MSH). It was developed in the late 1980s and early 1990s at the University of Arizona as a chemically stable, superpotent ligand of the melanocortin system, convenient for studying the mechanisms of pigmentation regulation [1]. Unlike the linear natural α-MSH, in the MT-II molecule the key fragment is closed into a ring through a lactam bridge, which increases resistance to enzymatic breakdown and affinity for the receptors.
Melanotan 2 remains an experimental compound: it has no approved-medicine status in the main regulatory jurisdictions and is used primarily as a tool for basic research into melanocortin signalling pathways [3]. This article is a scientific reference and contains no usage recommendations.
What it is and its class
By chemical classification MT-II is a cyclic heptapeptide with the amino-acid sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 (CAS (Chemical Abstracts Service) registration number 121062-08-6, molecular formula C50H69N15O9, molar mass ~1024 g/mol). It reproduces the conserved "message core" of natural melanocortins, the His-Phe-Arg-Trp motif required for receptor activation.
Two key modifications distinguish it from α-MSH: replacing L-phenylalanine with D-phenylalanine and introducing norleucine (Nle) in place of methionine, together with cyclisation of the backbone. These changes lock the biologically active conformation of the peptide and protect it from proteases, which is why MT-II is described as a "superpotent" non-selective agonist of the melanocortin receptors [1].
Mechanism of action
The human melanocortin system consists of five receptors (MC1R-MC5R) coupled to a G protein and adenylate cyclase. Melanotan 2 is a non-selective agonist and activates at least MC1R, MC3R, MC4R, and MC5R.
The pigment effect is linked to MC1R on melanocytes: its activation raises intracellular cAMP and shifts melanogenesis toward eumelanin synthesis. MC3R and MC4R are mainly central and take part in regulating appetite and sexual function, while MC5R is found peripherally, particularly in exocrine glands. This broad, non-selective binding profile is why studies observed systemic effects alongside pigmentation changes [1][4]. Structural stabilisation (D-Phe, Nle, the ring) provides higher potency and a longer action than natural α-MSH.
What the research shows
The basis of the human data is a phase I pilot study (Dorr et al., 1996): healthy male volunteers received MT-II subcutaneously under a dose-escalation schedule. The authors documented dose-dependent skin darkening as well as dose-limiting reactions: nausea, flushing, and spontaneous erections [1]. This study both confirmed pigmentary activity and outlined the tolerability limit.
Observations on sexual function were studied separately by Wessells et al. (1998): in a double-blind, placebo-controlled crossover study, MT-II initiated erections in men with psychogenic erectile dysfunction, pointing to the role of central MC4R-mediated mechanisms [2]. These results spurred the development of derivative compounds aimed specifically at sexual function.
Review articles by Hadley and Dorr organise the history of melanocortin therapy, summarise the clinical observations, and describe how MT-II became a structural prototype for later molecules in the melanocortin series [3][4]. The literature also discusses dermatological safety (in particular naevi and pigmented lesions) as a direction that needs further study. This article deliberately gives no quantitative dosing figures, since they depend on the specific research protocol.
Form and handling (research-use)
Melanotan 2 is supplied as a lyophilised powder (acetate salt), usually white and readily soluble in water. The lyophilisate is stable under deep freezing; the reconstituted solution is kept refrigerated (2–8 °C), protected from light, and used within a limited period. Working with the peptide requires standard laboratory practices: a sterile environment, correct weighing, and batch documentation.
Longeva supplies Melanotan 2 as a research substance accompanied by a certificate of analysis (COA). It is a reagent for laboratory research, not a medicine or a cosmetic product. The material is intended strictly for scientific research and has no medical application.