Melanotan-II is a synthetic cyclic heptapeptide analogue of α-melanocyte-stimulating hormone (α-MSH), developed at the University of Arizona in the 1980s as a photoprotection research compound. Unlike the endogenous α-MSH, the cyclic backbone confers metabolic stability and extends the half-life sufficient for once-daily research dosing. MT-II is broadly active across MC1R, MC3R, MC4R and MC5R — the broad receptor profile underlies both its melanogenic (pigmentation) research applications and the body of MC3R/MC4R-mediated effects on appetite, behaviour and sexual function.
Melanotan-II activates all four functional melanocortin receptors. MC1R activation drives the eumelanin/pheomelanin switch in melanocytes — the principal pathway behind its long-standing photoprotection research role. MC3R and MC4R activation in the hypothalamus engages the same satiety and sexual-motivation circuitry that distinguishes the related PT-141 compound; MC5R activation has been studied in lacrimal and sebaceous gland models.
The C-terminal amide group (absent in PT-141) and intact cyclic backbone account for MT-II's substantially longer half-life and broader receptor activity compared with endogenous α-MSH, which is rapidly degraded.
Photoprotection research conducted at the University of Arizona established that MT-II-induced eumelanin synthesis provides quantifiable UV-A and UV-B absorption across treated skin in preclinical models — the original research rationale.
Originally synthesised at the University of Arizona by Dr Victor Hruby and colleagues with the explicit research objective of identifying a photoprotection compound. Subsequent preclinical research has documented dose-dependent skin darkening (eumelanin synthesis) and measurable UV-absorption changes in treated tissue. No regulated medicinal product currently exists in this class.
Distinct from the more selective PT-141 (which omits the C-terminal amide), MT-II's broad receptor profile makes it the standard research probe for non-selective melanocortin biology.
Beyond the dermal research, MT-II's central MC4R activity has been characterised in appetite-suppression and sexual-motivation preclinical models. The same circuitry underpins the PT-141 indication; MT-II is studied where broader receptor coverage is the research aim.
Adverse-event findings consistent across the literature include transient nausea, facial flushing, spontaneous penile erection in male research subjects, and pigment darkening of pre-existing nevi — the latter is the reason photoprotection development stalled.