Melanotan II (MT-II): the melanocortin reference agonist

Melanotan II (MT-II) is a synthetic cyclic heptapeptide analog of α-melanocyte-stimulating hormone (α-MSH). In the laboratory it plays one specific part: the broad-spectrum reference agonist for the melanocortin receptor family, the unselective baseline that more targeted analogs are measured against. If you want to say that a compound is genuinely MC4R-selective, you first need a compound that hits everything, and MT-II is that compound.

For laboratory research only. Melanotan II is supplied strictly as a reference compound for in-vitro research. It is not a licensed medicine, it has not been evaluated by the FDA, and it is not supplied for human or veterinary use, tanning, or any cosmetic purpose. This page makes no therapeutic or physiological claim and describes no dosing or administration.

The regulatory picture, up front

For most research compounds the regulatory note sits at the bottom of the page. For Melanotan II it belongs at the top, because the gap between how it is marketed to the public and what it actually is has drawn repeated regulator attention.

Regulators have warned, repeatedly, that products containing Melanotan sold for human use, usually marketed for tanning, are unlicensed, unlawful to supply for that purpose, and of unknown safety and quality when bought through those channels. The US FDA has acted against suppliers marketing them that way. Melanotan II holds no marketing authorization and has not been evaluated by the FDA for any use.

What is supplied here sits entirely outside that. It is sold as a laboratory reference compound for in-vitro research, labeled for that use, and documented with a batch certificate. If you are looking for a product for personal or cosmetic use, this is not one, and nothing on this page should be read as suggesting otherwise.

What gives it its stability

MT-II's stability is the whole reason it works as a laboratory reagent. Native α-MSH is a linear peptide that degrades readily, which makes it awkward to hold at a fixed concentration across a long assay. MT-II carries three modifications that change that:

• a norleucine (Nle) substitution
• a D-phenylalanine (D-Phe) substitution
• a lactam bridge that cyclizes the molecule

The result, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂, is far more resistant to enzymatic breakdown than the hormone it is modeled on. That resistance is what keeps it viable across long-running assay work, and it is the practical reason MT-II, rather than native α-MSH, is the reference compound labs actually reach for.

Receptor coverage across the family

MT-II is a broad, non-selective agonist across the melanocortin receptor family:

That breadth is precisely why it is useful. A non-selective agonist gives you the full-family response, the reference point you need before you can say a selective compound really is selective. The negligible MC2R activity matters too: MC2R is the adrenocortical (ACTH) receptor, so a probe that leaves it essentially untouched keeps the corticotropic axis out of the picture.

What the research actually examines

Searches for Melanotan II return a great many claims about what it "does," most of them about tanning and appearance. It is worth separating what the primary literature examines from what is claimed downstream, because the distance between the two is large.

The published work that makes MT-II useful as a reagent is in-vitro and preclinical: receptor-binding assays, cell-based signaling readouts, and structure-activity studies in defined systems. In that literature MT-II is a tool for asking mechanistic questions, not a compound with a fixed biological outcome. Reported observations cover:

• Binding and activation across MC1R, MC3R, MC4R, and MC5R
• G-protein-coupled cAMP signaling and downstream transcriptional responses
• Structure-activity relationship (SAR) work on cyclic α-MSH analogs and peptide stability
• Comparative selectivity studies against receptor-selective analogs
• Melanocyte and cell-culture assay development for melanocortin-receptor pharmacology

These are in-vitro and preclinical laboratory observations, and they vary with receptor subtype, concentration, exposure, cell model, and design. The consumer-facing marketing claims about pigmentation or appearance are a separate category from the research question this compound is actually used to probe, and this guide does not bridge that gap.

Melanotan II next to PT-141

PT-141 (bremelanotide) is a direct structural derivative of MT-II: the same scaffold, but with a free acid at the C-terminus in place of an amide. That single change tilts it toward MC4R selectivity with substantially reduced MC1R activity.

The two make an unusually clean controlled comparison. The structural gap between them is so small that a difference in response can reasonably be attributed to receptor selectivity rather than to some unrelated change in the molecule. MT-II is the broad comparator, and PT-141 is the selective test compound. Running the pair together is a common way to characterize what "MC4R-selective" actually means in a given assay.

Supply and format

Melanotan II ships in a sealed vial as a pre-mixed solution, prepared under controlled conditions and HPLC-verified, with a batch-specific Certificate of Analysis that records purity by HPLC and identity by mass spectrometry for that lot. Because it arrives as a solution rather than a lyophilized powder, there is no reconstitution step to introduce concentration variability before the material even reaches the assay. Refrigerate at 2-8°C on arrival, keep the vial sealed and out of the light, and do not freeze it. See how to store research peptides.

How Melanotan II ships in the United States

For US laboratories Melanotan II is supplied as a pre-mixed, HPLC-verified vial with its batch-specific Certificate of Analysis. Every batch is synthesized in our own UK laboratory and then verified in a US laboratory before it ships, so the material an American researcher receives has been checked on both sides of the Atlantic. Orders are dispatched cold-chain from the warehouse that serves the United States, with tracked delivery across the country next business day, priced in US dollars and payable by Visa, Mastercard or Apple Pay. Store refrigerated at 2-8°C on arrival, not frozen.

PT-141, the MC4R-selective comparator, ships the same way.

What Melanotan II is not

• It is not an approved medicine in the United States or anywhere else, holds no marketing authorization, and has not been evaluated by the FDA.
• It is not a tanning product and is not supplied for cosmetic, human, or veterinary use, whatever similarly named consumer products may claim.
• It is not a predictor of a physiological outcome. It is a non-selective reference agonist used to characterize receptor signaling in vitro.

Dosing and administration

We do not publish dosing, reconstitution-for-use, or administration guidance for Melanotan II. The material is supplied strictly for in-vitro laboratory research and is not for human or veterinary use, so quantity guidance aimed at a person would be inconsistent with what is actually supplied, and the regulator warnings above make that point sharper still for this particular compound. Experimental concentrations are specific to the receptor, model, and endpoint and belong in the primary literature. The peptide calculator handles concentration arithmetic if you are working from the vial.

Related reading

• What is PT-141? · What are research peptides? · What is a Certificate of Analysis? · How to store research peptides