Targeting the central melanocortin system for the treatment of metabolic disorders Nature Reviews Endocrinology Melanotan (MT) II Melanocortin Receptor Agonist MedChemExpress Nasal tanners claim to work by using Melanotan II, a chemical that darkens skin pigmentation. It is illegal to sell medicinal products containing Melanotan II in the UK but since the tanners are sold Viral 'Barbie drug' for tanning can cause brain swelling and even cancer, experts warn