Melanotan-II (MT-2)

Melanotan II (MT-2, also written Melanotan-II or MT-II) is a synthetic cyclic heptapeptide analog of alpha-melanocyte stimulating hormone (α-MSH), developed at the University of Arizona in the 1980s. It was designed to stimulate melanin synthesis without ultraviolet exposure. The peptide has the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, incorporating a lactam bridge that enhances metabolic stability and receptor affinity relative to native α-MSH.

Melanotan II acts as a non-selective agonist at melanocortin receptors MC1R through MC5R, which mediate diverse physiological functions including pigmentation, sexual function, appetite regulation, and inflammation. The peptide's effects on multiple receptor subtypes account for its range of biological activities observed in research settings.

Technical Data

• Synonyms: MT-2, MT-II, Melanotan 2, [Nle4-D-Phe7]-α-MSH (cyclic analog)


• CAS number: 121062-08-6


• Molecular formula: C50H69N15O9


• Molecular weight: ~1024.2 g/mol


• Sequence: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2


• Format supplied: 10mg lyophilized powder per vial, sealed under vacuum


• Assayed purity: 99.7%+ by HPLC, confirmed by mass spectrometry


• Solubility: Soluble in bacteriostatic water; sparingly soluble peptides of this class may be brought into solution with 0.1% acetic acid

Storage and Handling Best Practices

• Lyophilized vials: store at -20°C for long-term stability; short periods at 2-8°C or ambient shipping temperatures do not compromise the peptide.


• Protect from light: the tryptophan and histidine residues are photosensitive — keep vials in their original carton or an opaque container.


• After reconstitution: refrigerate at 2-8°C and use within 2-3 weeks. Avoid repeated freeze-thaw cycles, which promote aggregation and loss of potency.


• Reconstitution: add diluent slowly down the vial wall, swirl gently, and never shake — shear stress denatures cyclic peptides.


• Aliquoting: for extended study timelines, aliquot the reconstituted solution into sterile low-binding vials and freeze single-use portions at -20°C or below.

Purity Verification

Every Melanotan II lot is third-party tested and shipped with a batch-specific certificate of analysis (COA) reporting HPLC purity, mass-spectrometry identity confirmation, and appearance. The COA for the current lot is published on this page with a verification key so researchers can confirm the document against the testing laboratory's records rather than relying on a supplier-supplied PDF alone. Reviewing HPLC chromatograms and the measured molecular ion is the most reliable way to distinguish correctly synthesized MT-2 from underdosed or mislabeled material.

Melanotan II binds to melanocortin receptors, particularly MC1R on melanocytes in the skin. Activation of MC1R stimulates adenylyl cyclase through G-protein coupling, increasing intracellular cAMP levels. This activates protein kinase A and the transcription factor CREB, leading to increased expression of tyrosinase and other melanin synthesis enzymes. The result is enhanced production of eumelanin, the brown-black pigment responsible for tanning.

Beyond MC1R, Melanotan II's activity at MC3R and MC4R in the hypothalamus influences appetite and sexual function pathways. MC4R activation in particular has been associated with pro-erectile effects through central nervous system mechanisms involving oxytocin and dopamine pathways. This non-selectivity accounts for the peptide's observed effects beyond pigmentation.

Research on Melanotan II has explored both its melanogenic and sexual function effects. Early clinical studies at the University of Arizona demonstrated dose-dependent increases in skin pigmentation without UV exposure, along with side effects including nausea and facial flushing at higher doses.

Pigmentation Studies

Clinical trials showed that subcutaneous Melanotan II produced measurable increases in melanin density and skin darkening. The tanning effect was most pronounced in fair-skinned individuals and persisted for weeks after treatment cessation. Research suggested potential photoprotective benefits through increased eumelanin, though this has not been established as a therapeutic indication.

Sexual Function Research

Studies investigated Melanotan II for erectile dysfunction, leading to the development of the derivative drug bremelanotide (PT-141), which specifically targets sexual function through MC4R. Clinical research demonstrated pro-erectile effects in both psychogenic and organic erectile dysfunction populations.

Melanotan I vs Melanotan II

Melanotan I (afamelanotide) is a linear tridecapeptide with high MC1R selectivity and has regulatory approval as SCENESSE for erythropoietic protoporphyria. Melanotan II is a smaller cyclic heptapeptide that activates MC1R, MC3R, MC4R, and MC5R. In comparative research contexts, MT-1 is used where isolated melanogenesis signaling is the variable of interest, while MT-2 is used to study broad melanocortin agonism across pigmentation, appetite, and central sexual-function pathways.

Melanotan II has not been approved for therapeutic use by regulatory agencies and is supplied strictly for in-vitro and laboratory research use, not for human or veterinary use. Adverse effects reported in early clinical research include nausea, facial flushing, fatigue, and appetite suppression. Concerns exist regarding effects on existing nevi and potential melanoma risk, though causality has not been established.

Cardiovascular effects through MC3R/MC4R activation are theoretically possible. Because material from unregulated sources varies widely in purity and content, lot-specific HPLC and mass-spectrometry documentation should be reviewed before any experiment. Long-term safety data in humans is limited.