A synthetic analogue of alpha-melanocyte-stimulating hormone is called melanotan 2 (MT-2). Melanotan 2, which was created in the 1980s, has been found to boost lean body mass, decrease compulsive/addictive behavior, decrease compulsive behavior, and increase sexual desire. When administered throughout early childhood development, research has shown the peptide to stimulate melanocytes, resulting in increased skin pigmentation, and may assist to fight autism

  In their search for something to help reduce the incidences of skin cancer, a lab found the chains of amino acids that cause skin to tan.  Darkened skin helps protect you naturally from the UV rays and helps reduce cancer.   

At the time they were developed by oncology researchers at the University of Arizona for use as skin cancer preventatives, Melanotan I and Melanotan II presented some fairly remarkable side effects.  One of those side effects was a marked increase in all over skin pigmentation, especially on the face, arms, and legs.