It was under development as drug candidate for female sexual dysfunction and erectile dysfunction, 
Melanotan 2I acts as a non-selective agonist of the melanocortin receptors.

The melanogenesis produced by melanotan 2 is caused by activation of the MC1 receptor, whereas its sexual effects are thought to be related to its ability to activate the MC4 receptor (though the MC3 is thought to possibly also be involved).
Function

 1. It's a kind of nutritional supplement. 
 2. It can improve the aerobic metabolism of the muscle and greatly enhance muscle strength and endurance from diet alone.
 3. It can be used as nutrition enhancer.
 4. It's one of the most popular and effective nutritional supplements as well as the indispensable product for bodybuilders.
 5. It is also widely used by other athletes, such as football players, basketball players and so on.