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 How Long Does It Take For Melanotan To Work? Viral 'Barbie drug' for tanning can cause brain swelling and even cancer, experts warn Figure 3 from The efficacy of afamelanotide and narrowband UV B phototherapy for repigmentation of vitiligo. Semantic Scholar