Nonapeptide-1 (Melanostatine-5) acetate salt, a peptide hormone, functions as a selective and competitive antagonist of the melanocortin 1 receptor (MC1R) with a binding affinity (K i) of 40 nM. It effectively inhibits α-MSH-induced increases in intracellular cyclic AMP (cAMP) and melanosome dispersion in melanocytes, showcasing inhibitory concentrations (IC 50) of 2.5 nM and 11 nM, respectively. By inhibiting melanin synthesis, Nonapeptide-1 acetate salt finds application in research related to skin pigmentation, adrenal gland steroid production regulation, and skin cancer [1] [2] [3].