PT-141 (bremelanotide) is a cyclic melanocortin agonist descended from Melanotan II. This guide covers its structure, receptor profile, the rat, primate and human studies behind it, how it differs from the approved drug Vyleesi, and how to study and handle it in the lab.
PT-141, also known by its nonproprietary name bremelanotide, is a cyclic heptapeptide agonist of the melanocortin receptors. It came out of a research program on synthetic analogs of alpha-melanocyte-stimulating hormone (alpha-MSH), and it became a tool for studying how the melanocortin system shapes behavior through the brain. In 2019 bremelanotide was approved in the United States as Vyleesi for premenopausal women with acquired, generalized hypoactive sexual desire disorder [10]. The PT-141 sold by Northbridge Research Labs is not Vyleesi. It is research-grade material for laboratory investigation, not a drug product, and it is not made or released for use in people.
At the University of Arizona, investigators designed melanocortin analogs that were highly potent, long-acting and resistant to enzymes. Two reached clinical testing: melanotan I, a linear peptide studied for skin tanning, and melanotan II (MT-II), a truncated cyclic peptide studied for male erectile dysfunction. PT-141 was developed by Palatin Technologies as a newer MT-II analog [6]. The observation that set the direction came from a double-blind, placebo-controlled crossover study of MT-II in 20 men with erectile dysfunction. Without sexual stimulation, MT-II produced erections in 17 of the 20 men. Increased sexual desire was reported after 13 of 19 MT-II administrations (68%) compared with 4 of 21 placebo administrations (19%), and nausea and yawning were frequent [7]. A peptide first explored for pigmentation turned out to act on central sexual function.
PT-141 has the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, with the formula C50H68N14O10 and a molecular weight of about 1025.2 Da. A lactam bridge between the side chains of aspartic acid and lysine closes the ring. This constrains the peptide's shape and protects it from peptidases. The D-phenylalanine sits inside the His-Phe-Arg-Trp core that melanocortin peptides share. PT-141 and MT-II carry the same ring. The difference is at the C-terminus: MT-II ends in an amide, while PT-141 ends in a free carboxylic acid. Both peptides keep the N-terminal acetyl group.
That single change has a practical consequence. The average masses of the two peptides differ by about 1 Da, and deamidation also adds about 1 Da. Confirming that a sample is PT-141 and not MT-II therefore needs mass spectrometry with enough resolution and mass accuracy to separate those species, ideally alongside HPLC retention against a reference standard.
The melanocortin system consists of five G protein-coupled receptors, peptide agonists derived from the proopiomelanocortin precursor, and two endogenous antagonists, agouti and agouti-related protein, which act at three of the five receptors. Between them, these receptors regulate pigmentation, adrenal steroid production, energy homeostasis, natriuresis, erectile responses and exocrine gland secretion. Each receptor is expressed in a limited number of distinct locations, which has made it possible to study them one at a time [5].
PT-141 is an agonist at melanocortin receptors including MC3R and MC4R [1]. It is often described as MC3R/MC4R-selective, but a 2022 review of its neurobiology describes it as a nonselective agonist of several receptor subtypes, with MC4R the most relevant at clinical exposures [11]. The clinical adverse-event data point the same way. In the clinical program, focal hyperpigmentation was rare under labeled use but occurred in more than a third of subjects given repeated administrations on consecutive days [13], which fits with activity at receptors beyond MC4R. Structural biology explains why selectivity is hard to achieve. Cryo-EM structures of MC4R bound to its Gs protein and to alpha-MSH, afamelanotide, bremelanotide or a small-molecule agonist show that peptide agonists share a conserved binding mode, and that MC4R's close similarity to the other receptors has made selective ligands difficult to design [12].
In rats and nonhuman primates, PT-141 produced penile erections. When it was given systemically to rats, c-Fos immunoreactivity rose in hypothalamic neurons, a marker of neuronal activation. Neurons in the same hypothalamic region took up pseudorabies virus introduced into the corpus cavernosum, a trans-synaptic tracing method that links those brain neurons to the target tissue [1].
In female rats, PT-141 selectively increased solicitational behaviors, the appetitive part of sexual behavior. It did not change lordosis, pacing or other sexual behaviors, did not cause general motor activation, and did not alter the perception of sexual reward [3]. The design is instructive because it separates desire-like behavior from reflexive behavior, which earlier animal models had often mixed together.
Genetic evidence places MC4R in this circuitry but does not place it only in the brain. A selective non-peptide MC4R agonist increased erectile activity in wild-type mice but not in Mc4r-null mice, and copulatory behavior was reduced in mice lacking Mc4r. MC4R expression was found in the hypothalamus, brainstem, spinal cord, pelvic ganglion and penile nerve fibers, but not in cavernosal smooth muscle cells [8]. The picture is neuronal, with brain, spinal and peripheral nerve sites. It is not a purely vascular mechanism, and it is not purely central either. Animal work summarized in a 2022 review suggests that bremelanotide acts on presynaptic MC4Rs in the medial preoptic area of the hypothalamus, increasing dopamine release there [11].
The findings below come from the clinical trials of bremelanotide. They are summarized to explain the pharmacology and do not describe the research material sold here. In healthy men and in men with erectile dysfunction who had an inadequate response to sildenafil, PT-141 produced statistically significant erectile responses measured by RigiScan [4]. In a crossover study of 18 premenopausal women with female sexual arousal disorder, more women reported moderate or high sexual desire after bremelanotide than after placebo (P = 0.0114), while vaginal vasocongestion did not change significantly [2]. That dissociation between subjective and physiological measures is consistent with a central site of action.
The two phase 3 RECONNECT trials randomized 1,267 premenopausal women with hypoactive sexual desire disorder to bremelanotide or placebo for 24 weeks. In the integrated analysis, bremelanotide improved the desire domain score of the Female Sexual Function Index by 0.35 relative to placebo and reduced desire-related distress by 0.33, both statistically significant. Nausea, flushing and headache each occurred in 10% or more of participants [9]. Across the full clinical program of 3,500 subjects in 43 studies, nausea was reported in 40.0% of bremelanotide recipients compared with 1.3% on placebo, and flushing in 20.3% compared with 1.3%. Ambulatory monitoring also showed small, transient increases in blood pressure [13]. For in vivo research, these findings are a reminder to include cardiovascular and emesis-related endpoints in the study design.
PT-141 is supplied as a white lyophilized powder. It should be stored sealed at -20°C and is soluble in sterile water. Tryptophan and histidine residues are susceptible to oxidation, so solutions are best prepared fresh or stored as single-use frozen aliquots, protected from light, rather than put through repeated freeze-thaw. Let the vial reach room temperature before opening. Northbridge Research Labs has every batch tested by an independent third-party lab. The certificate for PT-141 lot PT10001 (10 mg, 99.95% purity, tested August 2026) is published on our COA page.
Note: PT-141 from Northbridge Research Labs is for laboratory research use only, not for human or veterinary use. It is not Vyleesi, the FDA-approved bremelanotide product, and it has not been manufactured, tested or labeled as a drug.
Studied compound
PT-141 (Bremelanotide)
The same material this research covers — 99%+ purity, independently tested, with the certificate for each batch published online.
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Research Use Only: The information in this article is for educational and research purposes only. All products mentioned are intended for laboratory research use only and are not approved for human or veterinary use.