Bremelanotide: Vyleesi, drug for low sexual desire in women

What this is

Bremelanotide (sold as Vyleesi) is a peptide medication approved by the FDA in June 2019 for premenopausal women with hypoactive sexual desire disorder (HSDD) — a persistent lack of sexual desire that causes personal distress and is not explained by another medical, psychiatric, or relationship issue. Unlike Viagra and other PDE5 inhibitors, which act on blood flow in the genitals, bremelanotide acts in the brain, on circuits involved in sexual desire and arousal. The stored 7-letter sequence MCHFRWK is a one-letter approximation; the actual drug is a cyclic heptapeptide with the structure Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH — N-terminally acetylated, with a D-phenylalanine at position 4, and closed into a ring by an amide (lactam) bond, none of which is visible in the bare letters. It is given as a subcutaneous auto-injector before anticipated sexual activity, and it is the second drug ever approved in the US for HSDD in women.

History

Bremelanotide grew out of the same melanocortin chemistry program at the University of Arizona that produced Melanotan II in the 1980s and 1990s. The original goal was a synthetic α-MSH analog that could induce tanning as a skin-cancer prevention strategy — but the Melanotan II series turned out to have unexpected central effects on sexual arousal as well. Palatin Technologies licensed the chemistry and engineered bremelanotide as a more selective derivative of Melanotan II, with reduced melanocortin-1 receptor (pigmentation) activity but preserved MC3R/MC4R (sexual function) activity. Early intranasal development targeted erectile dysfunction in men through the mid-2000s; an early proof-of-concept study by Diamond and colleagues (2006) reported that a single intranasal dose of bremelanotide produced measurable subjective sexual-arousal responses in premenopausal women with sexual arousal disorder, helping motivate the pivot to a female-arousal indication. Palatin then reformulated the drug as a subcutaneous auto-injector, partnered with AMAG Pharmaceuticals, and ran the pivotal Phase 3 RECONNECT program in women with HSDD. The FDA approved Vyleesi in June 2019. Palatin reacquired full rights from AMAG in 2023, and worldwide Vyleesi rights were then sold to Cosette Pharmaceuticals in a deal closed January 2024.

What it does

Bremelanotide activates melanocortin receptors — specifically MC3R and MC4R — in the central nervous system. MC4R is the receptor most closely tied to the desire-and-arousal effect; activating it in hypothalamic and limbic regions modulates the dopamine and oxytocin pathways that the brain uses to organize sexual motivation. The clinical result, in the labeled indication, is a modest but reproducible increase in sexual desire and a reduction in HSDD-associated distress over weeks of as-needed use. Because the action is central rather than peripheral, bremelanotide does not work the way PDE5 inhibitors work: it does not directly produce an erection or directly increase genital blood flow, and the desire effect builds across multiple doses rather than appearing within a single dose the way a vasodilator does. As Pfaus and colleagues (2022) discuss in their review of the drug's neurobiology, the HSDD effect is best understood as a top-down modulation of excitation/inhibition balance in central desire circuits, not as a peripheral arousal effect.

Evidence

• Human: Two pivotal Phase 3 randomized controlled trials (the RECONNECT program, ~1,250 premenopausal women, 24 weeks) demonstrated statistically significant improvements in sexual desire scores and reduced HSDD-associated distress versus placebo, and supported FDA approval of Vyleesi in June 2019. A 52-week open-label extension provided longer-term efficacy and tolerability data. Earlier proof-of-concept work included an intranasal study in women with sexual arousal disorder (Diamond et al. 2006) and a Phase I safety study examining bremelanotide co-administered with ethanol in healthy male and female participants (Clayton et al. 2017). The trial effect sizes have been modest and have drawn published methodological re-analyses.
• Animal: Effects on female sexual behavior — including solicitation and receptivity — have been characterized in rodent models, and these preclinical findings were a key bridge between the melanocortin tanning-agent program and the eventual HSDD indication.
• In vitro / mechanistic: Bremelanotide is well-characterized as an agonist at MC3R and MC4R, with reduced MC1R activity relative to its parent compound Melanotan II — the design choice intended to preserve sexual-function effects while reducing pigmentary side effects.

Known effects

• Hypoactive sexual desire disorder in premenopausal women — FDA-approved indication (June 2019, Vyleesi).
• Female sexual dysfunction more broadly — supported by the same trial program but outside the strict labeled population (e.g., postmenopausal women are not in the approved indication and have not been studied in adequately powered trials).
• Male erectile dysfunction — historical Phase 1–2 evidence base from the intranasal PT-141 era; no approved product. A more recent program is investigating bremelanotide co-formulated with a PDE5 inhibitor in men who do not respond to PDE5i monotherapy.
• Centrally-mediated arousal modulation — supported by mechanistic and animal data, and is the underlying biology that the HSDD effect rides on.

Safety signals

Nausea is the dominant tolerability issue, reported in roughly 40% of participants in the pivotal trials. It is most common with the first several doses and typically attenuates with repeated use, but it is also a leading reason for discontinuation. Transient increases in blood pressure occur within hours of each dose and resolve within 8–12 hours; in an open-label ambulatory blood-pressure study, the mean daytime systolic increase was on the order of ~2 mm Hg, modest on average but the basis for cardiovascular screening and the 24-hour dose-spacing rule. Hyperpigmentation — darkening of the face, gums, or breasts — is reported in roughly 1% of users at the labeled monthly-dose limits and reflects residual MC1R activity; the rate has been substantially higher in older studies that used high-frequency consecutive daily dosing, which is the principal reason the labeled use is dose-capped per month. Other commonly reported effects include flushing, headache, and injection-site reactions. A Phase I safety study found bremelanotide was tolerated when coadministered with ethanol in healthy participants (Clayton et al. 2017), in contrast to flibanserin, the other FDA-approved HSDD drug, which has a more restrictive alcohol-interaction profile.

Regulatory status

• US: Prescription-only. FDA-approved as Vyleesi for premenopausal women with acquired, generalized HSDD (June 2019). Commercial rights are held by Cosette Pharmaceuticals (acquired from Palatin Technologies in January 2024). Not a controlled substance.
• International: Approval is limited relative to the US — Vyleesi is not broadly approved across the EU or UK, and specific-country regulatory status varies. Many jurisdictions have no approved product.
• WADA: Not specifically listed on the WADA Prohibited List and not classified as a performance-enhancing drug.
• Compounded vs. approved product: Compounded bremelanotide sold by some pharmacies and research-chemical bremelanotide sold online are not equivalent to the approved Vyleesi product in manufacturing quality, sterility assurance, or regulatory status, and the two should not be treated as interchangeable.

Myths and misconceptions

• "PT-141 is FDA-approved for men with erectile dysfunction." — It is not. Vyleesi is FDA-approved only for premenopausal women with HSDD. Earlier intranasal PT-141 development did target male ED but was not carried through to approval; no bremelanotide product is approved for any male indication.
• "PT-141 works like Viagra — by increasing blood flow." — Mechanism is fundamentally different. PT-141 acts centrally at MC4R on desire and arousal circuits; PDE5 inhibitors act peripherally via cGMP and smooth-muscle relaxation. PT-141 does not reliably produce erections on demand the way PDE5 inhibitors do.
• "Compounded bremelanotide is the same as Vyleesi." — They share a peptide sequence but differ in manufacturing quality control, sterility assurance, device presentation, and regulatory status.
• "PT-141 is a controlled substance." — It is not scheduled under the US Controlled Substances Act. It is a prescription-only medication in the US.

Related peptides

• Melanotan II — the direct chemical parent. Bremelanotide is engineered from the Melanotan II scaffold with reduced MC1R activity and preserved MC3R/MC4R activity, and the discovery that this chemistry produced central sexual-arousal effects is what motivated bremelanotide's development.
• α-MSH (alpha-melanocyte-stimulating hormone) — the endogenous melanocortin agonist that Melanotan II and bremelanotide are both synthetic analogs of.
• Flibanserin — not a peptide, but the only other FDA-approved drug for HSDD in premenopausal women, and the natural clinical comparator.
• Setmelanotide — selective MC4R agonist approved for rare monogenic obesity syndromes; contrasts with bremelanotide in receptor selectivity and indication.
• Afamelanotide — α-MSH analog that activates MC1R; approved for erythropoietic protoporphyria and used for photoprotection rather than for sexual function.

Mechanism

Bremelanotide is the cyclic heptapeptide Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH — a derivative of Melanotan II with a free C-terminal carboxylic acid in place of Melanotan II's C-terminal amide, an N-terminal acetyl-norleucine cap that confers protease resistance, and an Asp-to-Lys amide-bond (lactam) macrocycle in place of the parent disulfide ring. The D-Phe-Arg-Trp "message" sequence common to melanocortin agonists is retained. None of this chemistry is visible in the bare 7-letter sequence MCHFRWK (Pfaus and colleagues, 2022, CNS Spectrums). At the receptor level, bremelanotide is an agonist at the melanocortin-3 and melanocortin-4 receptors, with reduced MC1R activity relative to Melanotan II. MC4R engagement in the hypothalamic paraventricular nucleus and adjacent limbic regions modulates dopaminergic and oxytocinergic outputs implicated in sexual motivation (Pfaus and colleagues, 2022, CNS Spectrums; Dhillon and Keam, 2019, Drugs). Subcutaneous administration produces peak plasma concentrations at roughly one hour, with a plasma half-life of approximately 2.7 hours (Dhillon and Keam, 2019, Drugs).

Open questions

• Efficacy in men. Earlier intranasal and subcutaneous male erectile-dysfunction work was not carried forward to approval. A more recent program of bremelanotide co-formulated with a PDE5 inhibitor in PDE5i non-responders is in development but has not yet reported a definitive Phase 3 efficacy readout in the peer-reviewed literature.
• Postmenopausal HSDD. Approval is limited to premenopausal women; whether the central mechanism translates to comparable benefit in postmenopausal HSDD has not been established in adequately powered registration trials.
• Effect size and responder identification. The Phase 3 RECONNECT effect sizes were statistically significant but clinically modest, and published re-analyses have argued the clinical meaningfulness was overstated. Better predictors of who responds remain an open research question.
• MC3R vs. MC4R contributions. The relative contribution of MC3R and MC4R to the central desire effect — and the implications for next-generation, more selective melanocortin agonists — is not fully resolved.