Melanotan II

Synthetic melanocortin receptor agonist (MC1R-MC5R); activates MC4R for erectile function/libido; MC1R for melanogenesis; MC3R for appetite suppression

Melanotan II is a synthetic analogue of alpha-melanocyte-stimulating hormone (alpha-MSH), a neuropeptide that activates melanocortin receptors (MC1R, MC4R) involved in pigmentation, sexual arousal, and appetite regulation. By agonizing MC4R receptors in the central nervous system, melanotan II promotes erectile function and sexual arousal through a centrally mediated pathway, distinct from the peripheral vasodilatory mechanism of PDE5 inhibitors. An early randomized controlled trial demonstrated significant improvements in erectile function and sexual desire in men with organic erectile dysfunction, and subsequent reviews have characterized the melanocortin receptor class as a pharmacological target for sexual dysfunction. Melanotan II is not approved by the FDA or any major regulatory agency for any indication; it is a research compound associated with significant off-target effects, and a related compound (bremelanotide, marketed as PT-141) holds FDA approval for hypoactive sexual desire disorder in pre-menopausal women. Melanotan II vs PT-141: bremelanotide (PT-141) was developed directly from the melanotan II research program as a cleaner successor compound. PT-141 was designed to retain the MC4R-mediated sexual response effects while reducing the tanning (MC1R) and nausea side effects that characterize melanotan II. The key practical distinction is that PT-141 has completed Phase 3 trials and holds FDA approval, while melanotan II remains an unapproved research compound. Melanotan II is associated with more pronounced side effects than its successor — including facial flushing, nausea, spontaneous erections, and significant skin pigmentation from MC1R activation — which contributed to its replacement by the more selective bremelanotide in clinical development. Research doses in published studies have used subcutaneous administration in the range of 0.5–1 mg per dose; the side effect profile is dose-dependent, with nausea being the most commonly reported adverse event. Melanotan II has no approved clinical use in any jurisdiction; individuals interested in melanocortin-based sexual health compounds are better served by consulting providers offering FDA-approved PT-141 (bremelanotide), listed in the PeptideBase directory.