Melanotan 2

Chemical identity

Melanotan II is a cyclic lactam analogue of α-melanocyte-stimulating hormone, truncated to seven residues from the native thirteen and constrained by a bridge between the Asp and Lys side chains. It differs from PT-141 by a single functional group: MT-2 carries a C-terminal primary amide, PT-141 a free acid.

That 18-dalton difference produces meaningfully different receptor profiles, and it also means the two compounds are trivially confused on a label and non-trivially distinguished without mass spectrometry. Verify the observed mass on any batch.

The compound is a non-selective agonist across the melanocortin family. Where selective analogues exist for specific receptor subtypes, MT-2 is the blunt instrument of the group.

Mechanism in research models

MC1R activation on melanocytes raises cAMP, upregulates microphthalmia-associated transcription factor and increases tyrosinase expression — the rate-limiting step in eumelanin synthesis. This is the pathway behind the pigmentation effects that gave the compound its name.

MC4R and MC3R activity in the central nervous system accounts for the appetite and behavioural effects reported in animal work, and MC5R activity affects exocrine gland function. A single compound engaging four receptor subtypes across several tissue systems is difficult to use for clean mechanistic work — which is precisely why selective analogues were developed.

The α-MSH scaffold was originally developed at the University of Arizona as a probe for melanocortin pharmacology. Its research value today is largely as a reference agonist in receptor assays rather than as a tool for in-vivo studies.

What the literature establishes

The pigmentation pharmacology is well documented and mechanistically clear. The receptor binding data are solid and reproducible across laboratories.

The safety literature is where investigators should pay attention, and it is unusually well populated for an unapproved compound — largely through case reports arising from unsupervised human use. Documented findings include eruptive and changing melanocytic naevi, one report of melanoma developing in a treated individual, rhabdomyolysis, and posterior reversible encephalopathy syndrome. There is a plausible mechanistic basis for the naevus findings given MC1R's role in melanocyte proliferation.

This literature exists because people used the compound outside any research setting. It should be read as a description of what the molecule does in a mammalian system, and it argues for handling MT-2 with the same care as any potent uncharacterised agent.

Handling, reconstitution and storage

Lyophilised material is typically held at −20 °C and protected from light; confirm the validated condition on the lot documentation. The cyclic structure confers reasonable stability relative to linear peptides of similar length.

Reconstitute gently with bacteriostatic or sterile water down the vial wall. The tryptophan residue is photolabile — keep solutions in amber vials or foil-wrapped.

Aliquot and freeze immediately. Discard any solution that develops colour, haze or particulates.

Analytical documentation

Require RP-HPLC purity and an observed mass. Given the 18-Da separation from PT-141 and the frequency with which the two are mislabelled in the supply chain, the mass spectrum is the identity check that matters here.

Ask for confirmation of D-Phe configuration where the intended use is quantitative receptor work. As with PT-141, the L-diastereomer is a plausible synthesis impurity and is not resolved by mass.

References and authoritative sources

Chemical identity, regulatory status and anti-doping classification should be confirmed against primary sources rather than against this page. The records below are the ones to check first.

1. PubChem compound record (US National Library of Medicine)
2. PubMed indexed literature
3. ClinicalTrials.gov registered studies

These are database and regulatory sources. Citations to specific primary papers are being added to this page as part of ongoing scientific review; until they appear, treat the mechanism and literature sections above as a summary to verify rather than a citation of record.