Your body already makes a hormone that tells your skin to tan. Melanotan 2 is a synthetic peptide engineered to mimic that hormone but in a version that's more potent and longer lasting than Melanotan is trending again. As a dermatologist, I strongly need to tell you It's an unapproved injectable peptide, and we're seeing: nausea and flushing darkening of existing moles Tanning Nasal Spray: Should You Skip It? Teen Boys and Young Men Are Injecting Peptides in Search of Perfection WSJ