Melanotan II (MT-II) is a synthetic, superpotent, cyclic heptapeptide lactam analog of α-melanocyte-stimulating hormone (α-MSH) (sequence: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂; CAS 121062-08-6; PubChem CID 92432) developed at the University of Arizona in the 1990s as a non-selective agonist of melanocortin receptors (primarily MC1R, MC3R, MC4R, and MC5R). It potently induces eumelanin production and skin pigmentation independent of UV exposure, suppresses appetite and increases energy expenditure through central MC4R activation, markedly enhances sexual arousal and erectile function via hypothalamic and spinal melanocortin pathways, and exhibits additional cardiovascular, anti-inflammatory, and neuroprotective properties. Research has explored its therapeutic potential as a sunless tanning agent and photoprotective drug for UV-sensitive skin disorders, as a treatment for erectile dysfunction (showing superior efficacy to sildenafil in some trials), as an anti-obesity agent, and for neuroprotection in ischemia and neurodegenerative models;