PT-141

Overview

PT-141 (international nonproprietary name bremelanotide; brand name Vyleesi) is a synthetic cyclic peptide that acts as a melanocortin receptor agonist. Unlike most peptides documented on this site, bremelanotide is an FDA-approved prescription medicine. It was approved by the U.S. Food and Drug Administration on June 21, 2019, for the treatment of acquired, generalized hypoactive sexual desire disorder (HSDD) in premenopausal women: low sexual desire that causes marked distress or interpersonal difficulty and is not better explained by another condition, medication, or relationship factor.

PT-141 was originally derived from research on melanotan II, an earlier melanocortin agonist studied for skin tanning that also produced unexpected sexual-arousal effects. Bremelanotide was developed as a more defined molecule and pursued specifically for sexual function. The two are pharmacologically related but very different in regulatory standing: bremelanotide is an approved medicine for HSDD, whereas Melanotan II is an unapproved research chemical. PT-141 is part of the broader Sexual & reproductive health topic area, which also includes signaling peptides such as Kisspeptin.

Chemistry and structure

Bremelanotide is a cyclic heptapeptide lactam analog of alpha-melanocyte-stimulating hormone (alpha-MSH), the natural ligand for melanocortin receptors. Its structure is commonly written as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH: an N-acetylated chain in which a lactam bridge between aspartate and lysine side chains forms a constrained ring. This cyclization and the use of non-natural residues (norleucine; a D-phenylalanine) increase metabolic stability and receptor affinity compared with native alpha-MSH.

Bremelanotide is chemically distinct from PDE5 inhibitors such as sildenafil; it is a peptide that acts on receptors in the central nervous system rather than a small molecule that relaxes vascular smooth muscle.

Mechanism of action

Bremelanotide is a non-selective melanocortin receptor (MCR) agonist. According to its prescribing information, it activates several melanocortin receptor subtypes, and at therapeutic exposures the most relevant are MC1R and MC4R. The precise mechanism by which it improves sexual desire is not fully established, but MC4R, which is expressed widely in the central nervous system, is thought to modulate neural pathways involved in sexual desire and arousal. Activation of MC1R on skin melanocytes increases melanin production, which underlies the pigmentation effects seen with melanocortin agonists.

A key conceptual point is that bremelanotide works centrally, on brain signaling, rather than as a peripheral vasodilator. This separates it mechanistically from erectile-dysfunction drugs that increase genital blood flow. It is taken as needed ahead of anticipated sexual activity rather than on a fixed daily schedule.

Clinical evidence

FDA approval was based principally on two large, identical Phase 3, randomized, double-blind, placebo-controlled trials known as the RECONNECT studies (Studies 301 and 302), together with an open-label safety extension.

Kingsberg et al., Obstetrics & Gynecology 2019 (RECONNECT, Studies 301/302). Approximately 1,267 premenopausal women with acquired, generalized HSDD were randomized 1:1 to bremelanotide 1.75 mg subcutaneously as needed or placebo for 24 weeks. The co-primary endpoints were change from baseline in the Female Sexual Function Index–desire domain and in a Female Sexual Distress Scale item measuring distress about low desire. Both trials showed statistically significant improvements in sexual desire and in desire-related distress versus placebo. The treatment effect, while statistically robust, was modest in absolute terms, and tolerability-related adverse events (especially nausea) were common.

Simon et al., Obstetrics & Gynecology 2019 (open-label extension). Women who completed the 24-week double-blind phase could continue into an open-label extension of up to 52 weeks. The most common drug-related adverse events were nausea (about 40%), flushing (about 21%), and headache (about 12%). Blood pressure showed small, transient increases (roughly 3 mmHg systolic and 2 mmHg diastolic) within the first couple of hours after a dose, resolving over several hours.

The approved evidence is specific to premenopausal women with acquired, generalized HSDD. Bremelanotide is not approved or established for HSDD in postmenopausal women, in men, for erectile dysfunction, or for general "libido enhancement," even though it is sometimes discussed for those purposes outside the approved indication.

Safety and risks

The following reflects the U.S. prescribing information and the published trial data.

Contraindications (per FDA label):

• Uncontrolled hypertension or known cardiovascular disease. Because bremelanotide transiently raises blood pressure, it should not be used by people with these conditions.

Warnings and precautions:

• Transient increases in blood pressure and reductions in heart rate. Each dose causes a short-lived rise in blood pressure (typically peaking within a few hours and resolving thereafter), with a compensatory decrease in heart rate. The label advises against use in those with cardiovascular risk and limits use to roughly one dose per 24 hours and no more than eight doses per month.
• Focal hyperpigmentation (skin darkening). Because the drug activates MC1R, it can cause darkening of the skin, gums, or face, including the breasts. This was reported more with frequent dosing and may not always reverse after stopping.
• Nausea. Very common (about 40%), most pronounced with the first injection; a minority of participants required anti-nausea medication or discontinued for this reason.
• Naltrexone interaction. Bremelanotide can slow gastric emptying and significantly reduce the absorption of oral naltrexone, potentially lowering its effectiveness; co-use with oral naltrexone-containing products is not recommended.
• Use in pregnancy is not recommended.

Common adverse reactions in trials included nausea, flushing, injection-site reactions, and headache. A single case of acute hepatitis was reported in the program; expert review considered a causal link to bremelanotide unlikely, and the event resolved after discontinuation.

Regulatory status

United States (FDA — approved):

• June 21, 2019: The FDA approved Vyleesi (bremelanotide) for the treatment of acquired, generalized HSDD in premenopausal women. It is a prescription-only, as-needed subcutaneous injection. The label explicitly states it is not indicated for HSDD in postmenopausal women or in men, and not for general improvement of sexual performance.

European Union (EMA — not approved):

• There is no EMA central marketing authorisation and no European Public Assessment Report (EPAR) for bremelanotide or Vyleesi. A search of the EMA medicines database returns no authorised or withdrawn central application for this product. As a result, bremelanotide is not an EU-authorised medicine and is not generally available as a licensed product across the EU.

How it compares

Bremelanotide is notable as the approved melanocortin agonist for sexual desire, which sets it apart from related but unapproved peptides:

• Melanotan II is a closely related, non-selective melanocortin agonist that is not approved for any use. It is sold and used unofficially for skin tanning and is also discussed for erectile/arousal effects. Bremelanotide grew out of melanocortin research that included melanotan II, but only bremelanotide underwent the controlled trials and regulatory review that produced an approved indication.
• Kisspeptin acts on an entirely different system, upstream of the reproductive hormone (HPG) axis, and is investigational, not an approved therapy for sexual desire.

So while several peptides touch on sexual and reproductive function, bremelanotide is currently the one with a formal regulatory approval, and only for a narrowly defined indication. For broader context, see the Sexual & reproductive health overview.

Common misconceptions

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This article is provided for educational purposes only and is not medical advice. Bremelanotide (Vyleesi) is a prescription medication that should be used only under the supervision of a qualified healthcare professional, who can assess contraindications such as cardiovascular disease. Nothing here should be interpreted as encouragement to obtain or use PT-141 outside of an approved, supervised clinical context.