Melanotan II (MT-2) is a synthetic cyclic lactam heptapeptide analogue of alpha-melanocyte-stimulating hormone, derived from the His-Phe-Arg-Trp core with D-phenylalanine substitution and cyclisation for metabolic stability. It is a non-selective agonist at MC1R, MC3R, MC4R, and MC5R, with a molecular weight near 1024 daltons and a short plasma half-life of roughly one to two hours in early pharmacology reports.
Mechanistically, MC1R activation in melanocytes shifts melanin synthesis toward eumelanin, producing pigmentation. MC3R and MC4R activation in the hypothalamus explains reported appetite suppression and arousal effects; the MC4R-selective successor bremelanotide (Vyleesi) was approved in 2019 for hypoactive sexual desire disorder. MC5R activity in exocrine tissue is a plausible contributor to reported skin oiliness. Nausea, flushing, and transient blood-pressure changes are the most consistently reported acute effects.
The published record consists of small exploratory pharmacology studies, sexual-function studies that motivated a selective successor, dermatology case reports describing darkening and eruptive nevi that confound melanoma screening, isolated adverse-event case reports, and product-quality analyses showing grey-market material frequently diverges from label claim. There are no controlled efficacy or safety trials of MT-2, no photoprotection endpoint data, and no established human dose-response safety dataset.
Regulatory status: MT-2 is an unapproved drug in the United States and an unlicensed medicinal product in the European Union, United Kingdom, and Australia, with published consumer warnings from MHRA and TGA. The MC1R-selective analogue afamelanotide (SCENESSE) is approved narrowly for erythropoietic protoporphyria; neither that nor the Vyleesi approval extends to Melanotan II.
Related: Melanotan 2 reconstitution calculator, half-life estimator, dosage comparator, Peptide Reconstitution Guide, peptide purity explained, How to read a COA, regulation desk, A–Z directory, glossary.