PT-141 (Bremelanotide): The Only Peptide Approved for Sexual Desire

PT-141, known scientifically as bremelanotide (CAS 189691-06-3, PubChem CID 9941379), is a synthetic cyclic heptapeptide with a molecular weight of approximately 1,025.2 Da and the molecular formula C50H68N14O10. It is a melanocortin receptor agonist – a compound that activates a family of receptors in the central nervous system involved in sexual motivation, energy balance, and pigmentation.

The compound was developed by Palatin Technologies (Cranbury, New Jersey) from Melanotan II, a non-selective melanocortin agonist originally designed for sunless tanning at the University of Arizona. During early clinical testing of Melanotan II in the 1990s, researchers observed unexpected and consistent pro-sexual effects in male subjects – spontaneous erections and increased desire that had nothing to do with tanning. Palatin Technologies isolated and refined the arousal-related activity into a cleaner molecule, creating bremelanotide as a likely metabolite of Melanotan II. The structural difference is a carboxy group where Melanotan II has an amide, which shifts the receptor selectivity profile toward MC3R and MC4R while reducing the MC1R-driven tanning and other off-target effects.

In June 2019, the FDA approved bremelanotide under the brand name Vyleesi for the treatment of acquired, generalised hypoactive sexual desire disorder (HSDD) in premenopausal women. This made it the first and, as of 2026, only FDA-approved on-demand injectable treatment for this indication and one of only a handful of peptides with full FDA marketing approval for any condition.

The bottom line: PT-141 is a centrally-acting melanocortin peptide derived from Melanotan II that received FDA approval as Vyleesi in 2019 for premenopausal HSDD, making it one of the very few peptides to achieve full regulatory approval.

PT-141 activates melanocortin receptors MC3R and MC4R in the hypothalamus and limbic system – brain regions that govern sexual motivation and arousal. This is a fundamentally different mechanism from PDE5 inhibitors like sildenafil (Viagra) and tadalafil (Cialis), which work by enhancing blood flow to erectile tissue after arousal is already present. PT-141 acts upstream of the vascular response: it increases the desire itself.

Melanocortin peptides are derived from the pro-opiomelanocortin (POMC) precursor protein and act on a family of five G protein-coupled receptors (MC1R through MC5R). MC1R controls skin pigmentation. MC3R and MC4R are expressed in hypothalamic regions implicated in feeding behaviour, energy homeostasis, and sexual function. When bremelanotide binds to MC4R, it triggers a signalling cascade that increases cyclic adenosine monophosphate (cAMP) production, activates protein kinase A (PKA), and increases dopamine release in the medial preoptic area – a brain region mapped to the “desire” rather than the “mechanics” side of sexual function.

The compound also has activity at MC1R (the pigmentation receptor), which explains the rare side effect of transient skin darkening or focal hyperpigmentation reported in some users. However, bremelanotide’s MC1R activity is substantially reduced compared to its parent compound Melanotan II, which activates MC1R far more potently and produces pronounced tanning effects. This receptor selectivity shift was the core design goal when Palatin Technologies developed bremelanotide from the Melanotan II scaffold.

The bottom line: PT-141 works by activating MC3R/MC4R receptors in the brain to increase sexual desire through dopaminergic pathways, making it mechanistically distinct from every PDE5 inhibitor on the market.

RECONNECT Phase 3 Trials (Approval Evidence)

The RECONNECT programme consisted of two identical Phase 3, randomised, double-blind, placebo-controlled, multicentre clinical trials (NCT02333071 and NCT02338960) conducted between 2015 and 2016. A combined 1,247 premenopausal women with HSDD self-administered bremelanotide 1.75 mg or placebo subcutaneously on an as-needed basis for 24 weeks using an autoinjector pen.

Both trials met their co-primary endpoints. Compared to placebo, bremelanotide produced statistically significant improvements in sexual desire (FSFI Desire Domain, P less than 0.001 integrated) and statistically significant reductions in distress related to low sexual desire (FSDS-DAO Item 13, P less than 0.001 integrated). The effect sizes of bremelanotide treatment relative to placebo were 0.29 and 0.43 for FSFI-D across the two studies, and 0.49 to 0.62 for the bremelanotide-alone treatment effect on desire.

These results were published by Kingsberg et al. in Obstetrics and Gynecology (2019) and formed the basis of FDA approval. The trials were sponsored by Palatin Technologies, with editorial support from Phase Five Communications funded by AMAG Pharmaceuticals, the original US licensee.

The Effect Size Debate

The approval has drawn independent scrutiny. Spielmans, Parry, and Rosenbaum-Ashe published a reanalysis in the Journal of Sex Research (2021, PMID 33678061) documenting that 72.7% of the secondary outcomes pre-registered on ClinicalTrials.gov were absent from the primary RECONNECT publication. Several unreported outcomes favoured placebo on sensitivity analyses. The authors of the primary publication, all with Palatin Technologies financial relationships, have not published the missing outcomes elsewhere. A second independent critique in the same journal (2024) questioned the clinical meaningfulness of the small-to-moderate Cohen’s d values of approximately 0.27 to 0.39 for the treatment difference relative to placebo.

A 52-week open-label extension (Simon et al., Obstetrics and Gynecology, 2019) did not identify additional safety signals. Outcomes related to sexual desire improvement appeared to be sustained over the longer treatment period. Discontinuation rates were notable: 40% of bremelanotide-treated patients left the 24-week double-blind period prematurely compared to 13-25% of placebo patients, largely due to nausea.

Male Erectile Dysfunction Evidence (Off-Label)

PT-141 has never been approved for any male indication, and no company has filed for FDA approval in men. The male evidence base consists of Phase 1-2 studies using the earlier intranasal formulation and more recent observational data.

The most significant male study is the Safarinejad 2008 trial published in the Journal of Urology: a randomised controlled trial of 342 men with sildenafil-failure erectile dysfunction given intranasal PT-141 (10 mg) or placebo on demand over approximately 4 to 8 weeks. About 33.5% of men on bremelanotide achieved a positive clinical response (improved erections sufficient for intercourse) compared to only 8.5% on placebo (P = 0.03). These men had previously failed to achieve satisfactory results with Viagra, making the response rate clinically notable as a “salvage” therapy for PDE5 inhibitor non-responders.

Earlier Phase 1 work (Diamond et al. 2004, International Journal of Impotence Research) tested intranasal PT-141 in 32 healthy males and showed statistically significant erectile response at doses above 7 mg, with onset in approximately 30 minutes. A separate study (Diamond et al. 2005, Urology) demonstrated that co-administration of low-dose intranasal PT-141 with sildenafil produced an enhanced erectile response compared to sildenafil alone in men with ED.

However, intranasal bremelanotide development for men was halted in 2008 after some subjects experienced dose-related blood pressure increases. The switch to subcutaneous injection substantially reduced the blood pressure signal, but Palatin Technologies chose to pursue the female HSDD indication rather than restart the male ED programme.

Study	Population	Design	Key Finding	Evidence Tier
RECONNECT (Kingsberg 2019)	1,247 premenopausal women, HSDD	Two Phase 3 RCTs, double-blind, 24 weeks	Both co-primary endpoints met (P < 0.001)	Phase 3 human RCT (approval-grade)
Simon 2019 (extension)	RECONNECT participants	52-week open-label extension	No new safety signals, sustained efficacy	Open-label extension
Safarinejad 2008	342 men, sildenafil-failure ED	RCT, double-blind, intranasal 10 mg	33.5% vs 8.5% response (P = 0.03)	Phase 2 human RCT
Diamond 2005	32 men, ED	Placebo-controlled, PT-141 + sildenafil	Enhanced erectile response vs sildenafil alone	Phase 2 human (combination)
Spielmans 2021 (reanalysis)	RECONNECT data	Independent outcome reporting audit	72.7% secondary outcomes unreported	Independent critical reanalysis

The bottom line: PT-141 has Phase 3 approval-grade evidence for female HSDD and Phase 2 evidence for male ED (including PDE5 inhibitor non-responders), but independent reanalyses have raised questions about selective outcome reporting in the pivotal trials.

Independent Brain Imaging Confirmation (Thurston 2022)

The most significant independent mechanistic evidence comes from outside the Palatin-funded research ecosystem entirely. In October 2022, Thurston et al. at Imperial College London’s Section of Endocrinology and Investigative Medicine published an fMRI study in the Journal of Clinical Investigation (JCI 2022;132(19):e152341) examining bremelanotide’s effects on brain activity in women with diagnosed HSDD. This was a double-blinded, placebo-controlled, crossover study in 31 women who each received both bremelanotide 1.75 mg and placebo on separate study visits while undergoing functional brain imaging during visual erotic stimuli.

The study found that MC4R agonism enhanced sexual brain processing in measurable, specific ways: bremelanotide improved functional connectivity between the amygdala and insula during sexual stimulation, enhanced cerebellar and supplementary motor area activity, and deactivated the secondary somatosensory cortex. The BOLD (blood-oxygen-level-dependent) signal change in limbic structures averaged 0.74% under bremelanotide versus 0.48% under placebo. Critically, self-reported sexual desire increased significantly (P less than or equal to 0.01) and persisted for up to 24 hours after administration – providing neuroimaging evidence that the mechanism operates on a timescale consistent with the on-demand clinical use pattern.

Real-World Male Use: The Refill Rate Signal

A data point that no Phase 3 trial captures but that speaks to real-world clinical utility: Goldstein et al. presented refill rate data from a sexual medicine clinic at the 2024 ISSWSH/ISSM meeting covering 18 months of prescribing (January 2022 through June 2023). Among 219 male patients, 30 premenopausal women, and 29 postmenopausal women prescribed bremelanotide, the refill rates diverged sharply: 73% for men, 52% for postmenopausal women, and 47% for premenopausal women. This is observational, single-centre data with inherent selection bias, but the pattern suggests that the off-label male population – for which no company has pursued FDA approval – may derive the most consistent real-world benefit. The investigators noted that increasing refill rates “imply that bremelanotide, a centrally acting agent, can be used on demand to successfully treat a variety of sexual dysfunctions.”

Bremelanotide’s journey from laboratory curiosity to FDA-approved product spans more than two decades and involves multiple corporate transitions. Palatin Technologies originally licensed the sexual dysfunction applications of Melanotan II from Competitive Technologies, the technology transfer company representing the University of Arizona. Palatin ceased development of Melanotan II itself in 2000 and synthesised bremelanotide as a structurally modified version. A contract dispute between Competitive Technologies and Palatin over bremelanotide ownership was settled in 2008, with Palatin retaining bremelanotide rights, returning Melanotan II rights to Competitive Technologies, and paying US$800,000.

After the intranasal blood pressure setback in 2008, Palatin reformulated bremelanotide as a subcutaneous injection, conducted the RECONNECT programme, and secured FDA approval in 2019. The commercial journey that followed is instructive for understanding how the peptide industry works at the pharmaceutical level.

The AMAG Chapter: A $1 Billion Estimate Meets Reality

In January 2017, Palatin granted exclusive North American development and commercialisation rights to AMAG Pharmaceuticals (Waltham, Massachusetts). AMAG estimated that bremelanotide had $1 billion in revenue potential; GlobalData projected $810 million in sales by 2024. AMAG’s management believed that even 1% penetration of the approximately 5.8 million affected premenopausal women could translate to $35 million per year. The company launched Vyleesi nationally in September 2019, generating coverage from more than 300 news outlets.

Those projections proved dramatically overoptimistic. Less than a year after launch, in July 2020, AMAG and Palatin mutually terminated the license agreement. AMAG paid Palatin $12 million at closing and a further $4.3 million in March 2021 to exit. The commercial failure was driven by the same tolerability barrier that clinical trials had already documented: roughly four in ten patients experienced nausea, suppressing uptake in a cosmetically discretionary indication where patients have an immediate alternative (doing nothing). Vyleesi also carried a subcutaneous injection barrier that daily-oral competitor Addyi (flibanserin) did not, though Addyi had its own problems – Bausch Health (formerly Valeant) had paid $1 billion for Addyi in 2015 before selling it back to Sprout Pharmaceuticals in a 6% royalty deal.

The Palatin Solo Period and Cosette Acquisition

Palatin regained full control of Vyleesi and commercialised it directly. By fiscal year 2023, net product revenue reached $12.5 million, with Palatin CEO Carl Spana noting that quarterly revenue of $4.9 million “continues to exceed Vyleesi quarterly operating expenses” – a modest claim that reflects the drug’s niche commercial reality. In December 2023, Palatin sold Vyleesi to Cosette Pharmaceuticals (Bridgewater, New Jersey) for $12 million upfront plus up to $159 million in contingent sales-based milestones. Cosette received five Orange Book-listed patents with protection extending to 2041. Crucially, at the time of acquisition, Vyleesi had experienced eight consecutive quarters of double-digit prescription growth under Palatin’s ownership – slow but consistent adoption that a dedicated women’s health company may be better positioned to scale.

Bremelanotide is also licensed internationally: Fosun Pharma holds rights in China and Kwangdong Pharmaceuticals in South Korea, though neither market has generated significant revenue to date.

Palatin Technologies continues as an independent biopharmaceutical company developing other melanocortin receptor modulators, including PL9643 (an MCr agonist for dry eye disease, which has completed Phase 3 enrolment) and oral PL8177 for inflammatory bowel diseases (Phase 2).

PT-141 occupies a unique regulatory position: it is the active ingredient in an FDA-approved product, which creates specific constraints on compounding that do not apply to unapproved peptides.

Jurisdiction	Status	Detail
United States (FDA)	Approved	Vyleesi approved June 21, 2019 for premenopausal HSDD. Category 2 status carried forward April 15, 2026 for compounding. “Essentially a copy” restriction applies under 503A.
United Kingdom (MHRA)	Not Licensed	Vyleesi has not received marketing authorisation from the MHRA. No application filed.
Australia (TGA)	Not Approved	Not listed on the Australian Register of Therapeutic Goods (ARTG).
WADA	Prohibited	Prohibited under S2 (peptide hormones and mimetics). Athletes prescribed Vyleesi for HSDD would require a Therapeutic Use Exemption (TUE).

The Compounding Question

Because Vyleesi is a commercially available FDA-approved product, Section 503A of the Federal Food, Drug, and Cosmetic Act restricts compounding pharmacies from regularly producing drug products that are “essentially a copy” of a commercially available drug. This does not mean compounded bremelanotide is entirely unavailable – a prescriber can document a patient-specific clinical need (such as a dose or concentration not commercially available) that justifies compounding. However, the barrier is higher than for unapproved peptides like BPC-157 or TB-500, which do not have approved commercial equivalents. For a detailed explanation of how the FDA category system works, see our dedicated guide.

In practice, compounded bremelanotide remains widely available through 503A pharmacies under physician prescription, particularly for male off-label use where the commercially available product is approved only for premenopausal women. The regulatory and legal nuances of this practice vary. For country-specific guidance, see our pages on US, UK, and Australian peptide legality.

The bottom line: PT-141 is FDA-approved (as Vyleesi) for premenopausal HSDD only – not for men, not for postmenopausal women – and compounding is subject to “essentially a copy” restrictions because a commercial product exists.

PDE5 inhibitors (sildenafil, tadalafil, vardenafil) amplify the vascular response after arousal is already present. They prevent the breakdown of cyclic GMP in penile tissue, maintaining blood flow to sustain an erection. They do not increase desire. PT-141, by contrast, works on the neural circuitry that generates arousal in the first place – the “wanting” system rather than the “performing” system.

This distinction matters clinically. PDE5 inhibitors are ineffective when the problem is absent desire rather than impaired blood flow. PT-141 addresses the desire component directly, which is why the Safarinejad study specifically recruited men who had already failed sildenafil therapy and still saw a 33.5% response rate. The Diamond 2005 combination study further suggested that the two mechanisms can work synergistically, though this also stacks cardiovascular risk.

For women, the comparison point is flibanserin (Addyi), the only other FDA-approved HSDD treatment. Addyi is a daily oral medication that modulates serotonin and dopamine receptors and was approved in 2015. Its sales have been disappointing, and it cannot be taken with alcohol. PT-141, by contrast, is used on-demand and has no alcohol interaction, though its high nausea rate remains a significant tolerability barrier.

Nausea is the dominant side effect of bremelanotide, affecting approximately 40% of women in the Phase 3 trials. It is typically mild to moderate, peaks with the first one to two doses, and diminishes with repeated use. Other common adverse events include flushing (approximately 20%), injection site reactions (13.2%), and headache (11%).

The Vyleesi label carries specific contraindications. Bremelanotide is contraindicated in patients with uncontrolled hypertension or known cardiovascular disease because it causes transient increases in blood pressure. This cardiovascular concern was the reason the earlier intranasal formulation was abandoned for men – higher doses delivered intranasally produced more pronounced blood pressure elevations than the subcutaneous route.

Focal hyperpigmentation (darkening of skin areas, particularly the face, gums, and breasts) has been reported in a small number of users, consistent with residual MC1R activity. This effect is generally reversible upon discontinuation.

Pharmacokinetic data from the FDA label: subcutaneous bioavailability is approximately 100%, protein binding is 21%, the elimination half-life is 2.7 hours, and excretion is primarily renal (64.8% urine, 22.8% faeces). The label restricts use to a maximum of one dose per 24-hour period and no more than eight doses per month.

The bottom line: Nausea (40%), flushing (20%), and injection site reactions (13%) are the most common side effects, and the compound is contraindicated in patients with uncontrolled hypertension or cardiovascular disease.

PT-141 belongs to the melanocortin peptide family. Its parent compound, Melanotan II, is a non-selective melanocortin agonist that activates MC1R through MC5R and produces pronounced tanning, appetite suppression, and sexual effects but has never progressed past Phase 1 clinical trials and is not approved in any country. Afamelanotide (Scenesse), sometimes called Melanotan I, is a linear 13-amino-acid selective MC1R agonist developed by Clinuvel Pharmaceuticals and FDA-approved in October 2019 for erythropoietic protoporphyria (EPP), a rare genetic photosensitivity disorder. All three compounds trace their origins to the same University of Arizona melanocortin research programme led by Victor Hruby and the late Mac Hadley.

For information on verifying the identity and purity of any research peptide, see our guide on how to read a certificate of analysis.