What is Melanotan II?

Melanotan II (MT-II) is a synthetic cyclic heptapeptide analogue of α-melanocyte-stimulating hormone (α-MSH). In laboratory research it functions as the broad-spectrum reference agonist for the melanocortin receptor family — the unselective baseline against which more targeted analogues are measured.

Research use only. Melanotan II is supplied strictly as a reference compound for in-vitro laboratory research. It is not a licensed medicine, it is not supplied for human or veterinary use, tanning, or any cosmetic purpose, and this page makes no therapeutic or physiological claim. It does not describe dosing or administration.

The UK regulatory position, stated plainly

This matters more for Melanotan II than for most compounds, so it belongs near the top rather than in a footnote.

The MHRA has repeatedly warned that products containing Melanotan sold for human use — typically marketed for tanning — are unlicensed, unlawful to supply for that purpose, and of unknown safety and quality when obtained through those channels. It has acted to close suppliers marketing them that way. Melanotan II holds no UK marketing authorisation.

Material supplied here sits outside that entirely. It is sold as a laboratory reference compound for in-vitro research, labelled for that use, and documented accordingly. If you are looking for a product for personal or cosmetic use, this is not one. See are peptides legal in the UK? for how the research-use framing works and where its limits are.

Structure

MT-II's stability is the reason it is usable as a laboratory reagent at all. Native α-MSH is a linear peptide and degrades readily; MT-II carries three modifications that change that:

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

The result — Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂ — is markedly more resistant to enzymatic degradation than the hormone it is modelled on, which is what makes it viable across long-running assay work.

Receptor coverage

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

| Receptor | MT-II activity | | --- | --- | | MC1R | Agonist | | MC2R | Negligible | | MC3R | Agonist | | MC4R | Agonist | | MC5R | Agonist |

That breadth is exactly why it is useful. A non-selective agonist gives you the full-family response, which is the reference point you need in order to say that a selective compound is in fact selective.

What researchers study

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

Reported observations vary with receptor subtype, concentration, exposure, cell model and design. These are in-vitro and preclinical laboratory observations only.

Melanotan II vs PT-141

PT-141 (bremelanotide) is a direct structural derivative of MT-II — identical scaffold, with a free acid at the C-terminus instead of an amide. That one change shifts it toward MC4R selectivity with substantially reduced MC1R activity.

The pair is unusually clean as a controlled comparison, because the structural difference between them is so small that a difference in response can reasonably be attributed to receptor selectivity. MT-II is the broad comparator; PT-141 is the selective test compound.

Handling and verification

Melanotan II ships in a sealed vial with a batch-specific Certificate of Analysis. Refrigerate at 2–8°C on arrival, keep the vial sealed and away from light, and do not freeze it. See how to store research peptides.

Browse Melanotan II and PT-141.