Melanotan II is a peptide first developed and synthesized by researchers at the University of Arizona as a possible defense against skin cancer. Melanotan II allegedly produces a natural tan which helps protect against UV exposure and subsequently would lower the risk of skin cancer.

The body's naturally occurring hormone α-MSH causes melanogenesis, a process by which the skin's pigment cells (melanocytes) produce the skin's pigment (melanin). They tested to see if administering this endogenous hormone to the body directly could be an effective method to cause sunless tanning. What they found was that while it appeared to work, natural α-MSH had too short a half life in the body to be practical as a therapeutic drug.

So they decided to find a more potent and stable alternative, one that would be more practical. What they found was Melanotan II.

Melanotan II is part of a class of peptide hormones known as Melanocortins. Melanotan II (MTII), also can have the side effect of increasing libido in Men and Women. However unlike erectile dysfunction compounds, MT-II works at a neural level on the brain to increase libido, so as a result it works both on women as well as men.