MT-2 (Melanotan II)

MT-2 (Melanotan II) is a cyclic heptapeptide and synthetic analogue of alpha-melanocyte-stimulating hormone (α-MSH), originally developed at the University of Arizona in the 1980s and 1990s as a potential drug for melanoma prevention through enhanced tanning without UV exposure. It differs from endogenous α-MSH by incorporating norleucine at position 4 and D-phenylalanine at position 7, modifications that dramatically increase potency and metabolic stability. Early human trials in the mid-1990s confirmed that subcutaneous injection produced skin darkening and, unexpectedly, provoked spontaneous penile erections — a side-effect profile that redirected the compound's research trajectory. The erection-inducing properties were studied in small double-blind crossover trials through the late 1990s and early 2000s, with generally positive findings for both psychogenic and organic erectile dysfunction. However, development of MT-2 itself was ultimately abandoned in favour of more selective analogues, most notably bremelanotide (PT-141 / Vyleesi), which is a ring-opened metabolite of MT-2 and the only melanocortin-based drug to reach FDA approval (for hypoactive sexual desire disorder in premenopausal women, 2019). MT-2 itself has never been submitted for regulatory approval and holds no marketing authorisation in any jurisdiction. It is prohibited in competitive sport under WADA's S2 (Peptide Hormones, Growth Factors, Related Substances) class. Material sold online is typically labelled "for research use only," and its quality is unregulated. Published case reports describe serious adverse events including dysplastic nevi eruption, melanoma arising from pre-existing moles, priapism requiring surgical intervention, rhabdomyolysis, and renal infarction. This entry summarises the available evidence and community-reported practice for reference only; it is not medical advice and does not endorse human use.