MT-2 (melanotan II, MTII) is a cyclic lactam analogue of alpha-MSH, Ac-[Nle4, Asp5, D-Phe7, Lys10]-alpha-MSH(4-10)-NH2, in which a lactam bridge links the side chains of aspartic acid 5 and lysine 10 to form a 23-membered ring. It was described in 1989 as part of a series of cyclic alpha-MSH fragment analogues designed using molecular dynamics. Melanotan II is an agonist at the neural MC3 and MC4 melanocortin receptors and has been used as a research tool for the central melanocortin system. Rodent studies have examined feeding behaviour, energy expenditure and grooming.