MT-2 (Melanotan II): Cyclic Structure, Non-Selectivity and the Research Record

Evidence at a glance

Limited human data, unapproved

Melanotan II showed clear effects in small early human studies, then development was abandoned. Read the two columns below together, because this is the compound where that matters most.

Why researchers are interested

It is a potent, broad melanocortin agonist. That is exactly why it produces pigmentation without UV exposure, and also why its effects are hard to confine to one system. The same lack of receptor selectivity drives both the findings and the harms.

What the research found

• Tanning without UV exposureStimulates melanogenesis directly through melanocortin-1 receptors, independent of sun exposure
• Erectile responseInitiated erections in men with psychogenic erectile dysfunction (Wessells)
• Receptor activity mappedCore sequence and receptor selectivity characterised (Oosterom, 1999, and Tomassi)

Reported in the literature

• Nausea, facial flushing and spontaneous erections were common in the early human studies.
• Darkening, enlargement and proliferation of existing moles is widely described.
• The dermatology literature carries case reports of melanoma diagnosed in people using unregulated melanotan.
• Case reports also describe rhabdomyolysis and posterior reversible encephalopathy after unregulated use.
• No regulator has approved it. Development was discontinued rather than completed.

Findings are summarised from the sources listed under References on this page, and from approved product labelling where a compound has one. These are outcomes observed in published studies, not effects claimed for any person, and nothing here is a recommendation for human use.

← All research guides

MT-2 (melanotan II) is a synthetic cyclic analogue of α-melanocyte-stimulating hormone, studied as a broadly non-selective melanocortin-receptor agonist. Its value as a research tool comes from two properties: a constrained ring that makes it far more stable than the native hormone, and a lack of receptor selectivity that made it the scaffold later work was built on. This guide covers identity, structure, receptor pharmacology and the published record. It is written for researchers and is not medical guidance.

What MT-2 is

• Names MT-2, melanotan II, MT-II
• CAS 121062-08-6 (PubChem CID 92432)
• Molecular formula C₅₀H₆₉N₁₅O₉
• Molar mass 1024.2 g/mol
• Sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂

Verified against PubChem on 2 October 2026.

Research-use note: MT-2 is a research chemical supplied strictly for laboratory research. It is not an approved drug, cosmetic, or supplement and is not for human or animal consumption. Nothing below describes or endorses use in people.

Why the ring matters

MT-2 is a cyclic lactam heptapeptide. The lactam bridge — a covalent link between side chains that closes part of the sequence into a ring — holds the peptide in a fixed conformation.

That has two consequences a researcher cares about. It resists enzymatic degradation, giving MT-2 far greater laboratory stability than native α-MSH, which is short-lived. And it locks the pharmacophore into the shape the receptor recognises, which is why cyclisation improved potency rather than merely durability.

This is the general lesson of the melanocortin literature: conformational constraint is how a fragile endogenous hormone becomes a usable research compound. The same logic produced PT-141, which is a metabolite of MT-2, and the KPV tripeptide, which takes the opposite approach by stripping the molecule down to its C-terminal fragment.

Non-selectivity is the defining property

There are five melanocortin receptors, MC1R through MC5R, and they sit in different tissues serving different functions — MC1R in skin and pigmentation, MC4R in the central nervous system and energy balance, the others elsewhere.

MT-2 is broadly non-selective across all five. In an experiment that is a limitation rather than a feature: an observed effect cannot be attributed to a single receptor subtype without further work to separate them.

Which is precisely why it matters. Receptor selectivity is the central question in melanocortin structure–activity work, and MT-2’s lack of it made it the standard scaffold — the starting structure researchers modify in order to produce selective analogues and then measure what changed.

What the published record contains

The literature spans receptor pharmacology, analog design and human studies conducted largely in the 1990s and 2000s.

• Oosterom et al. (J Biol Chem, 1999) — examined how the conformation of the core sequence in melanocortin peptides directs selectivity for the MC3 and MC4 receptors. This is the structure–activity work the scaffold argument rests on.
• Tomassi et al. (J Med Chem, 2022) — used melanotan II as a scaffold to generate functionally selective human melanocortin-receptor agonists, which is the modern continuation of that line.
• Wessells et al. — reported controlled studies of the compound in men, first as a double-blind placebo-controlled crossover trial (J Urol, 1998) and later in a review of melanocortin-receptor agonists and sexual motivation (Int J Impot Res, 2000).

These findings belong to the published research record and do not represent approved or validated uses of the research compound supplied here. MT-2 itself has never been approved by any regulatory authority for any indication.

Form, reconstitution and storage

Supplied as a lyophilized powder. Standard laboratory practice is to reconstitute with bacteriostatic water, swirl rather than shake until dissolved, and store the reconstituted solution refrigerated at 2–8 °C. The sealed vial is kept frozen and protected from light, and repeated freeze-thaw cycles are avoided. See how to reconstitute peptides.

(General lab-handling notes, not usage instructions.)

For research use only

All products and information referenced here are intended strictly for laboratory and scientific research use only. They are not for human or animal consumption and are not drugs, foods, supplements, cosmetics, or medical devices. MT-2 has not been approved by any regulatory authority for medical use. Nothing here should be interpreted as medical advice, and no outcome in a person is described, implied or promised. Products are supplied against a stated purity specification.

Explore MT-2 and related research peptides

• MT-2 (Melanotan II) — specifications and stated purity
• PT-141 — the metabolite of MT-2
• KPV — the C-terminal tripeptide of α-MSH
• Full research catalog

Common questions about MT-2

What is the difference between Melanotan I and Melanotan II?

Melanotan I (afamelanotide) is a linear α-MSH analog that is more selective for the MC1 receptor. Melanotan II is a smaller cyclic analog that acts across the melanocortin receptors broadly.

Is MT-2 approved?

No. MT-2 is not approved by any medicines regulator and is supplied for laboratory research only.

How is MT-2 related to PT-141?

PT-141 is a metabolite of MT-2 with a free-acid end in place of MT-2's amide, and its research focuses on the MC4 receptor.

References

1. Oosterom J, et al. Conformation of the core sequence in melanocortin peptides directs selectivity for the melanocortin MC3 and MC4 receptors. J Biol Chem. 1999. PubMed
2. Tomassi S, et al. Melanotan-II as a scaffold for functionally selective human melanocortin receptor agonists. J Med Chem. 2022. PubMed
3. Wessells H, et al. Synthetic melanotropic peptide initiates erections in men with psychogenic erectile dysfunction: double-blind, placebo controlled crossover study. J Urol. 1998. PubMed
4. Wessells H, et al. Melanocortin receptor agonists, penile erection, and sexual motivation. Int J Impot Res. 2000. PubMed
5. Compound identity verified against the PubChem database, retrieved 2 October 2026. PubChem