PT-141, commonly known as PT141 or Bremelanotide, is a synthetic heptapeptide analogue of the naturally occuring alpha-Melanocyte stimulating hormone (?-MSH) that is currently being studied for its numerous theoretical therapeutic applications. Alpha-MSH has potent influence over lipid metabolism, appetite, and sexual libido. PT-141 Bremelanotide, a metabolite of its predecessor Melanotan II, has the amino acid sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH and a molecular weight of 1025.2 Dalton. In initial testing, Melanotan II did induce melanogenesis, but additionally caused sexual arousal and spontaneous erections as unexpected side effects in nine out of the ten original male volunteer test subjects. Alpha-MSH activates certain melanocortin receptors in the process of exerting its effects. Resultantly, PT-141 has been shown in studies to exhibit libido-enhancing effects by activating melanocortin receptors. PT 141 has been researched extensively for its possible treatment of male sexual dysfunction (erectile dysfunction or impotence), female sexual dysfunction (sexual arousal disorder), hemorrhagic shock and reperfusion injury.