Melanotan II is a synthetic cyclic lactam heptapeptide designed as a non-selective agonist of the melanocortin receptor family (MC1R through MC5R). It was originally synthesized at the University of Arizona as a structural analog of alpha-melanocyte stimulating hormone (α-MSH), with modifications intended to improve metabolic stability and receptor binding affinity. In laboratory research, Melanotan II is employed to investigate melanocortin receptor pharmacology, downstream cAMP signaling, and melanogenesis-associated pathways in in-vitro and in-vivo experimental systems. Its non-selective receptor profile makes it a versatile research tool for studying the differential roles of MC receptor subtypes across multiple cellular structure systems. Preclinical literature describes studies examining Melanotan II in the context of melanocyte biology, energy homeostasis markers, and reproductive signaling endpoints in rodent and cell culture models. Observations are model-dependent and interpreted within each study’s experimental framework. Sequence: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂ Molecular Formula: C₅₀H₆₉N₁₅O₉ Molecular Weight: 1024.19 g/mol CAS: 121062-08-6 Supplied for controlled laboratory research only. Not for human consumption.