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 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 II A Sun Kissed Look, and a Confident You.