What is Melanotan II?

Melanotan II is a cyclic lactam analogue of α-MSH that acts as a non-selective agonist across melanocortin receptor subtypes. It is supplied here as a lyophilised powder for in-vitro laboratory research only.

Last editorial review: 2026-09-18 · Part of the Melanotan II research hub

Definition and structure

Melanotan II is a synthetic heptapeptide analogue of α-melanocyte-stimulating hormone in which the sequence is cyclised through a lactam bridge. Cyclisation constrains the molecule’s conformation, which both increases potency at melanocortin receptors and makes the peptide far more resistant to enzymatic degradation than the linear native hormone.

It derives from the earlier linear analogue melanotan I (afamelanotide); the cyclic structure is the principal chemical difference between the two, and it is also the reason their receptor selectivity profiles differ.

Receptor profile

The melanocortin receptor family comprises five subtypes, MC1R to MC5R, with distinct tissue distributions: MC1R is associated in the literature with pigmentation biology, MC3R and MC4R with central regulation of energy balance, MC2R with adrenal function and MC5R with exocrine tissue.

Melanotan II is non-selective, activating several subtypes rather than one. That lack of selectivity is central to its research use: it is a probe of melanocortin signalling in general, and any experiment using it must account for the possibility of parallel activity at more than one subtype.

Research context

Published work with melanotan II concentrates on melanocortin receptor pharmacology, pigmentation pathway models, and the structure-activity relationships of cyclic peptide analogues. It is also used as a reference agonist when subtype-selective analogues are being characterised.

Melanotan II is not an approved medicine in the United Kingdom. Material supplied here is laboratory research material, and the literature should not be read as evidence of safety or benefit in any human context.

How it is supplied for research

Biovanta Research supplies melanotan II as a 10mg lyophilised vial with an independent certificate of analysis published for the batch.

Material is supplied strictly for in-vitro laboratory research by qualified persons. It is not a medicine and is not for human or veterinary use.

Why non-selectivity matters in experimental design

Because melanotan II activates more than one melanocortin receptor subtype, an observed effect in a tissue or cell model cannot be attributed to a single receptor on the basis of the agonist alone. Study designs in the published literature therefore pair it with subtype-selective antagonists, with cell lines expressing a single recombinant receptor, or with receptor-knockout comparisons, so that the contribution of each subtype can be separated. Reporting which of those controls were used is as important as reporting the agonist itself, since a result generated in a mixed-receptor background supports a much weaker conclusion than one generated in an isolated system.

Concentration is the second design variable that determines how a result should be read. At higher concentrations a non-selective agonist recruits lower-affinity subtypes that contribute little at lower concentrations, so a concentration-response series across a defined range is more informative than a single-point measurement, and the range used should always be stated alongside the result.

Comparison with related melanocortin analogues

Melanotan II is most often compared with the native hormone α-MSH and with the linear analogue afamelanotide (melanotan I). The native hormone is the reference ligand against which analogue potency is expressed, but it is rapidly degraded, which limits its usefulness in longer in-vitro protocols. Afamelanotide is linear and has a different selectivity profile, and unlike melanotan II it has been developed and licensed as a medicine for a specific narrow indication in some jurisdictions. That regulatory distinction is frequently blurred online, and it is worth stating plainly: the licensed status of one analogue confers nothing on another.

For structure-activity work, the cyclic constraint in melanotan II is the point of interest. Comparing a cyclic and a linear analogue in the same assay illustrates how conformational restriction affects both receptor affinity and metabolic stability, which is one of the main reasons the compound continues to appear in melanocortin literature as a reference agonist.

Analytical verification of supplied material

Identity and purity should be read from the batch-specific certificate of analysis rather than assumed from the product name. A useful certificate reports the analytical methods used, typically high-performance liquid chromatography for purity and mass spectrometry for identity confirmation, names the laboratory that performed the work, and carries a batch number that matches the number printed on the vial. Cyclic peptides can carry closely related impurities such as linear or partially cyclised species, so the stated purity figure and the method behind it both matter when interpreting a result.

Any specific numerical value that matters for an experiment, including exact purity, residual solvent content or moisture, should be taken from that certificate for the specific lot in hand and not from a general description of the product.

Handling, reconstitution and stability considerations

Lyophilised peptide is the more stable form and is normally kept frozen and protected from light until it is needed. Once reconstituted, stability is finite and depends on the diluent, concentration, temperature and the number of freeze-thaw cycles the solution has been through, so laboratories generally aliquot a reconstituted vial rather than repeatedly thawing a single container. Recording the diluent, the final concentration and the date of reconstitution alongside each result is what allows a finding to be traced back to a defined material state.

Regulatory and safety framing

Melanotan II holds no marketing authorisation in the United Kingdom, the United States or elsewhere, and it is supplied strictly as laboratory research material. Regulators and published case literature have reported adverse observations associated with unlicensed use of this class of compound, including dermatological changes and reports involving pigmented lesions. Those reports are noted here as factual context for why the compound is not a medicine; they are not guidance of any kind, and nothing on this page should be read as describing use in people or animals.

A laboratory’s own obligations rest on its risk assessment, its supplier’s batch documentation and the research-use-only terms of purchase. The existence of published literature on a compound does not alter that position.

Finding the primary literature

For receptor-level detail, searching PubMed for the compound name together with a specific receptor subtype, for example MC1R or MC4R, returns more useful results than the compound name alone, because it surfaces papers that isolate a single receptor arm rather than general commentary. Searching for the terms cyclic α-MSH analogue and structure-activity relationship alongside the subtype name is a productive way to locate the characterisation work that underpins how this peptide is described, and reading those primary papers is the only reliable way to obtain specific potency figures, which should never be quoted second-hand.

Strength of the current evidence

Melanocortin receptor pharmacology and the structure-activity basis of cyclic α-MSH analogues are well established in peer-reviewed literature. Melanotan II itself is unlicensed and is supplied for research only.

References

1. Indexed melanotan II publications (PubMed search listing)
2. Melanocortin receptor pharmacology literature (PubMed search listing)

Back to the Melanotan II research hub · Melanotan II research material · Certificates of analysis

Research use only. Everything on this page describes published laboratory and preclinical research into a compound supplied strictly for in-vitro research by qualified persons. It is not medical advice, it does not describe human or veterinary use, and no dosing guidance is given.