The melanocortins are a group of peptide hormones which include adrenocorticotropic hormone (ACTH) and the different forms of melanocyte-stimulating hormone (MSH), and are derived from proopiomelanocortin (POMC) in the pituitary gland. The melanocortins exert their effects by binding to and activating the melanocortin receptors.There are 5 melanocortin receptors (MCR) and all of them are G protein–coupled receptors. In the brain, only MC3R and MC4R are expressed and their endogenous ligand is α-MSH. Agouti-related peptide (AgRP) is the endogenous antagonist.