PT-141 (Bremelanotide) is a synthetic cyclic heptapeptide analogue of α-melanocyte-stimulating hormone, engineered to selectively activate melanocortin receptors MC3R and MC4R while sparing the MC1R receptor responsible for pigmentation. Originally developed from Melanotan-II by stripping the C-terminal amide and cyclising the peptide backbone, it has been extensively characterised in central-nervous-system melanocortin signalling research and is FDA-approved (as Vyleesi) for hypoactive sexual desire disorder in premenopausal women.
PT-141 binds and activates the melanocortin-3 and melanocortin-4 receptors in the central nervous system, with greatest functional activity at MC4R — a receptor densely expressed in the hypothalamus and paraventricular nucleus. The downstream signalling pathway involves cAMP-dependent activation of pro-opiomelanocortin (POMC) neurons and indirect modulation of dopaminergic activity in the medial preoptic area, the anatomical site most associated with sexual motivation in published rodent research.
In contrast to peripherally-acting agents (e.g. PDE5 inhibitors), PT-141 acts upstream of vascular response — modulating central appetite, arousal and behavioural drive circuitry. This central mechanism is reflected in the FDA-approved indication: it is administered prior to anticipated sexual activity to influence neural state, not local blood flow.
PT-141 also has incidental activity on blood pressure regulation via MC4R-positive neurons in the brainstem, which underpins the transient pressor effect noted in clinical research.
In the RECONNECT Phase 3 trial (Kingsberg et al., Obstetrics & Gynecology, 2019), 1267 premenopausal women with hypoactive sexual desire disorder were randomised to bremelanotide 1.75 mg subcutaneous or placebo. Both desire and distress endpoints showed statistically significant improvements at 24 weeks. Headache and nausea were the most common adverse events.
Subsequent open-label extension data published in 2020 confirmed durability over 52 weeks of dosing in research subjects who continued the protocol.
Preclinical fMRI work in rodents has mapped PT-141's central activity to the medial preoptic area, periaqueductal gray and ventral tegmental area — regions historically linked to motivational and reward processing. Receptor knockout studies confirm that the behavioural response is MC4R-mediated; MC3R knockouts show partial response, MC4R knockouts show none.
Outside the libido indication, PT-141 has been studied in haemorrhagic shock models for its blood-pressure-stabilising effect via MC4R-positive brainstem neurons — a separate research line documented in published preclinical literature.