Receptor for MSH (alpha, beta and gamma) and ACTH. The activity of this receptor is mediated by G proteins which activate adenylate cyclase. Mediates melanogenesis, the production of eumelanin (black/brown) and phaeomelanin (red/yellow), via regulation of cAMP signaling in melanocytes. Interacts with MGRN1, but does not undergo MGRN1-mediated ubiquitination; this interaction competes with GNAS-binding and thus inhibits agonist-induced cAMP production. Interacts with OPN3; the interaction results in a decrease in MC1R-mediated cAMP signaling and ultimately a decrease in melanin production in melanocytes. Expressed in the adrenal gland. Belongs to the G-protein coupled receptor 1 family.