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 Man warns against 'dangerous' tanning injections after turning so dark he 'looked like Madge from Benidorm' and now has the freckled skin of a 60 year old How Long Does It Take For Melanotan To Work? Melanotan Erectile Dysfunction: What the Research Actually Shows