Melanotan 1 is similar to naturally occurring alpha melanocyte stimulating hormone alpha-MSH (Melanotan 2). Alpha-MSH is known for its influence on melanocytes, the cells in skin and hair responsible for pigmentation. This function is mediated via strong binding to melanocortin receptor 1. Alpha-MSH is a non-selective full agonist of melanocortin receptors 1, 3, 4, and 5. Melanotan 1 differs from alpha-MSH (Melanotan 2) by a single amino acid and was actually first developed as a sunless tanning agent. Research into melanocortin receptors and their effects, scientists quickly discovered that while melanotan 1 did indeed cause pigmentation, and altered baseline metabolism. Subsequent study of melanotan 1 and other melanocortin-binding proteins helped scientists to better understand the melanocortin signaling system.