Sexual Health & Metabolic Peptides

PT-141, also known as bremelanotide, is the synthetic cyclic heptapeptide analogue of the melanocortin peptide Melanotan II (MT-II), and holds the distinction of being the only FDA-approved peptide for sexual dysfunction, specifically, hypoactive sexual desire disorder (HSDD) in premenopausal women (Vyleesi, approved 2019). Bremelanotide acts centrally as a melanocortin receptor agonist, primarily at MC4R in the medial preoptic area of the hypothalamus, a mechanism fundamentally different from the peripheral vascular action of PDE-5 inhibitors used in men (PMID 33455598).

Bremelanotide is a melanocortin receptor agonist that non-selectively activates several melanocortin receptor subtypes, of which MC4R is the most relevant at therapeutic doses (PMID 33455598). MC4R is predominantly expressed in the medial preoptic area of the hypothalamus and is important for sexual function (PMID 33455598). Animal studies suggest that activating presynaptic MC4R on neurons in the medial preoptic area increases dopamine release, an excitatory signal that raises sexual desire; this differs from PDE-5 inhibitors, which act on genital vascular smooth muscle, and from flibanserin, a serotonin mixed agonist and antagonist that is also approved for HSDD in premenopausal women (PMID 33455598)). The melanocortin system thus represents a third distinct neurobiological pathway to sexual desire modulation (PMID 25659981).

The pivotal clinical trials (the two RECONNECT phase 3 studies, 1,267 premenopausal women with HSDD randomized) showed that bremelanotide 1.75 mg given subcutaneously as needed significantly improved the co-primary endpoints of sexual desire (Female Sexual Function Index desire domain) and distress related to low desire compared with placebo (PMID 31599840). Effect sizes were statistically significant but modest in absolute terms: in the integrated analysis the desire score improved by 0.35 points and the distress score by 0.33 points more than with placebo (PMID 31599840). The modest absolute effect size reflects the complexity of female sexual desire as a multifactorial construct (psychological, relational, hormonal, and neurobiological factors all contribute) that no single agent can fully address.

Off-label use in men has been explored in small studies; for example, co-administration of low-dose intranasal PT-141 (bremelanotide) and sildenafil in men with erectile dysfunction produced a greater erectile response than sildenafil alone (PMID 15833522). Multiple small studies and clinical case series report significant erectile response to bremelanotide in men with both psychogenic and organic ED, including some PDE-5 inhibitor non-responders who respond to the central melanocortin mechanism. The combination of bremelanotide + a PDE-5 inhibitor has been used empirically for men with both central (desire) and peripheral (vascular) components of ED.