PT-141, also known as Bremelanotide, is a synthetic peptide that is used to treat sexual dysfunction in men and women. While Viagra and Cialis, which are PDE-5 inhibitors that work to increase blood flow into the penis, PT-141 is a melanocortin, which works at the brain to increase sexual desire. The synthetic peptide blend was developed from Melanotan II, and was originally intended to darken skin pigmentation and induce tanning. However, during the initial testing, patients noted a pleasant side effect – that it caused increased sexual arousal.