# PT-141 (Bremelanotide) Research Summary — Mechanism, RECONNECT Trials, and Recent Studies

> The clinical literature on bremelanotide (PT-141): MC4R mechanism, the RECONNECT Phase 3 program, neuroimaging, safety database, and 2024-2025 work in obesity and combination ED.

**The trial record on bremelanotide, organized as evidence cards**

Mechanism, Phase 3 efficacy, long-term safety, neuroimaging, and the active 2024-2025 extension programs in obesity and combination ED.

## Mechanism: a central agonist, not a peripheral vasodilator

Bremelanotide is a non-selective melanocortin-receptor agonist with its principal therapeutic activity at MC4R, the melanocortin-4 receptor [5][16]. MC4R is expressed densely in the hypothalamic medial preoptic area (mPOA) and the paraventricular nucleus — circuits that organize the appetitive, motivational component of sexual response.

The proposed model, supported by both rodent work and human imaging, runs roughly as follows. MC4R agonism on hypothalamic dopaminergic neurons (mPOA, ventral tegmental area, nucleus accumbens) increases dopamine release in mesolimbic reward circuitry [16]. Concurrent action on amygdala and cortico-limbic networks reduces the inhibitory cognitive monitoring that, in HSDD, appears to dampen erotic processing [5]. The net effect is restored appetitive drive, not enhanced peripheral arousal mechanics.

Thurston and colleagues confirmed this in a randomized, double-blind, crossover fMRI study of 31 premenopausal women with HSDD: a single subcutaneous dose of bremelanotide increased self-reported sexual desire for up to 24 hours and modulated erotica-evoked brain activity — increasing amygdala-insula functional connectivity and reducing activity in the parietal operculum / secondary somatosensory cortex, regions associated with self-monitoring [5]. This was the first objective neuroimaging evidence that the drug acts through the central pathway its developers had hypothesized.

The preclinical behavioral foundation came from Pfaus and colleagues in 2004: in ovariectomized Long-Evans female rats, subcutaneous PT-141 at 50-200 μg/kg selectively increased solicitational behaviors (hops, darts) without affecting lordosis, pacing, or locomotion — the cleanest possible animal-model signal for an appetitive rather than consummatory effect [6].

## RECONNECT: the Phase 3 program

Approval rested on two identically-designed pivotal trials, Studies 301 and 302 (ClinicalTrials.gov NCT02333071 and NCT02338960), collectively known as RECONNECT. The integrated population of 1,202 premenopausal women with HSDD was randomized 1:1 to 1.75 mg subcutaneous bremelanotide as-needed or matching placebo over 24 weeks [1].

The co-primary endpoints were the FSFI-Desire domain (a five-point scale from the validated 19-item Female Sexual Function Index) and Item 13 of the Female Sexual Distress Scale-Desire/Arousal/Orgasm (FSDS-DAO Item 13), a single 0-4 item rating personal distress about low sexual desire. Drug produced a least-squares mean change vs placebo of +0.35 on FSFI-Desire and -0.33 on FSDS-DAO Item 13, both at P<0.0001 [1].

Prespecified subgroup analyses subsequently published by Simon and colleagues found the effect was consistent across virtually all subgroups defined by age, BMI, baseline testosterone quartile, relationship status, and HSDD duration [4]. The 2025 secondary-endpoint analysis extended the picture: FSFI arousal-domain scores improved 23-25% over baseline by week 4 (vs 5-10% on placebo) and orgasm-domain scores 16-21% (vs 0-9%), with both effects continuing to widen through week 24 [14].

## Long-term safety and the 52-week extension

RECONNECT was followed by a 52-week open-label extension. Of the approximately 856 women who completed the 24-week double-blind phase, 684 (80%) enrolled in the extension and 272 completed it — a real-world adherence pattern that Simon and colleagues characterized as consistent with treatment satisfaction despite the high baseline rate of post-dose nausea [2][18].

No new safety signals appeared. The most common treatment-related adverse events in the extension were nausea (40.4%), flushing (20.6%), and headache (12.0%) — essentially identical to the double-blind phase. Women who had received drug during the blinded phase saw an additional 1.25-1.30 point improvement in FSFI-Desire during the extension; women who crossed over from placebo gained 0.70-0.77 points [2].

The broader development-program safety database (43 completed studies, ~3,500 subjects, up to 18 months of exposure) reinforced the pattern: nausea 40.0%, flushing 20.3%, headache 11.3%, injection-site reactions 5.4%, no treatment-related deaths, and few serious adverse events [3].

## The cardiovascular signal and the dose cap

Two label-driving safety findings shape clinical use. The first is a small, transient pressor effect: approximately +3 mmHg systolic and +2 mmHg diastolic within two hours of dosing, peaking at roughly +6/+3 mmHg in clinical pharmacology studies and resolving within 8-12 hours, accompanied by a small heart-rate decrease [10]. This is the basis for the label's contraindication in uncontrolled hypertension or known cardiovascular disease and the recommendation against use in patients at high cardiovascular risk.

The second is focal hyperpigmentation: discrete darkening of skin, gums, or breasts reported in roughly 1% of bremelanotide-treated patients in Phase 3 and rising with more than eight doses per 28-day period [11]. This is mediated by MC1R activation on cutaneous melanocytes — a predictable consequence of non-selective melanocortin agonism — and may be incompletely reversible. It drives the label's maximum-eight-doses-per-month cap.

Nausea is the most common reason for discontinuation [3][12]. It begins within roughly one hour post-dose, lasts a median of about 2.4 hours, and is usually mild-to-moderate and self-limiting; antiemetics are not part of the labeled regimen.

## Pharmacokinetics in one card

Following a 1.75 mg subcutaneous dose, bremelanotide reaches a mean Cmax of 77.1 ng/mL with a median Tmax of approximately 1.0 hour and a terminal half-life of approximately 2.7 hours (range 1.9-4.0 h) [9]. Bioavailability is essentially complete (~100%) by the subcutaneous route. Protein binding is 21%, mean clearance is 6.5 L/h, and volume of distribution is 25 L. Elimination is predominantly renal (~65%) with the remainder via feces (~23%) [9].

The short half-life is the pharmacologic rationale for as-needed (not chronic daily) dosing. Onset of pharmacologic effect typically occurs within 45-60 minutes of injection — the basis for the label's recommendation to dose at least 45 minutes before anticipated activity — and self-reported desire benefit has been measurable for up to 24 hours in fMRI studies [5].

## Early development and the intranasal years

Bremelanotide did not begin as an HSDD drug. The original Diamond program in the early 2000s tested intranasal PT-141 in healthy males and men with mild-to-moderate erectile dysfunction, finding a dose-dependent, statistically significant pro-erectile response above a 7 mg threshold, with first erection typically within 30 minutes [7]. A follow-up crossover study showed that 7.5 mg intranasal PT-141 plus 25 mg oral sildenafil produced a greater erectile response than sildenafil alone in 19 men with sildenafil-responsive ED — the first demonstration that central (melanocortin) and peripheral (PDE5) mechanisms could add [8].

Development pivoted to subcutaneous administration after intranasal blood-pressure signals emerged at higher doses, and the indication shifted to HSDD on the basis of the desire-domain effects seen in early female-population studies [19]. The eventual 2019 approval rested on RECONNECT [1][19].

## What is being studied now (2024-2025)

Three active programs sit alongside the approved HSDD indication.

First, obesity. Phase 1 trials in obese premenopausal women had shown bremelanotide produced roughly 1.3-1.7 kg greater weight loss than placebo over 16 days, driven by approximately 400 kcal/day reduced caloric intake — a modest MC4R-mediated appetite effect [13]. The 2025 Phase 2 BMT-801 trial reported that low-dose bremelanotide produced appetite-suppression scores comparable to tirzepatide (71% vs 73% improvement on a validated daily appetite questionnaire) and substantially blunted the appetite/weight rebound otherwise seen on tirzepatide discontinuation [17]. This supports development of bremelanotide as both a co-administered and a maintenance therapy alongside GLP-1 / GIP agonists.

Second, combination ED. In June 2024 the sponsor initiated a Phase 2 trial of co-formulated bremelanotide plus a PDE5 inhibitor for the roughly 30-40% of ED patients who respond inadequately to PDE5i monotherapy, with topline targeted for the first half of 2026 [19]. This is the regulatory descendant of the 2005 Diamond combination work [8].

Third, oncology. A 2024 in vitro study by Suzuki and colleagues found that bremelanotide at concentrations non-toxic to normal cells suppressed survivin expression and induced cell death in human glioblastoma cell lines; effects were blocked by melanocortin-receptor antagonists and reversed by forced survivin overexpression, identifying MC3R/MC4R as candidate oncology targets and bremelanotide as a chemosensitizer for temozolomide and osimertinib [15]. This work is preclinical and the clinical implications remain undetermined.

## References

[1] Kingsberg SA, Clayton AH, Portman D, Williams LA, Krop J, Jordan R, Lucas J, Simon JA. Bremelanotide for the Treatment of Hypoactive Sexual Desire Disorder: Two Randomized Phase 3 Trials. Obstetrics & Gynecology. 2019. — doi: 10.1097/AOG.0000000000003500 — https://pubmed.ncbi.nlm.nih.gov/31599839/
[2] Simon JA, Kingsberg SA, Portman D, Williams LA, Krop J, Jordan R, Lucas J, Clayton AH. Long-Term Safety and Efficacy of Bremelanotide for Hypoactive Sexual Desire Disorder. Obstetrics & Gynecology. 2019. — doi: 10.1097/AOG.0000000000003514 — https://pubmed.ncbi.nlm.nih.gov/31599847/
[3] Clayton AH, Kingsberg SA, Portman D, Sadiq A, Krop J, Jordan R, Lucas J, Simon JA. Safety Profile of Bremelanotide Across the Clinical Development Program. Journal of Women's Health. 2022. — doi: 10.1089/jwh.2021.0191 — https://pubmed.ncbi.nlm.nih.gov/35230116/
[4] Simon JA, Kingsberg SA, Portman D, Jordan R, Lucas J, Sadiq A, Krop J, Clayton AH. Prespecified and Integrated Subgroup Analyses from the RECONNECT Phase 3 Studies of Bremelanotide. Journal of Women's Health. 2022. — doi: 10.1089/jwh.2021.0225 — https://pubmed.ncbi.nlm.nih.gov/35230162/
[5] Thurston L, Hunjan T, Mills EG, Wall MB, Ertl N, Phylactou M, Muzi B, Patel B, Alexander EC, Suladze S, Modi M, Eng PC, Bassett PA, Abbara A, Goldmeier D, Comninos AN, Dhillo WS. Melanocortin 4 receptor agonism enhances sexual brain processing in women with hypoactive sexual desire disorder. The Journal of Clinical Investigation. 2022. — doi: 10.1172/JCI152341 — https://www.jci.org/articles/view/152341
[6] Pfaus JG, Shadiack A, Van Soest T, Tse M, Molinoff P. Selective facilitation of sexual solicitation in the female rat by a melanocortin receptor agonist. Proceedings of the National Academy of Sciences USA. 2004. — doi: 10.1073/pnas.0400491101 — https://www.pnas.org/doi/10.1073/pnas.0400491101
[7] Diamond LE, Earle DC, Rosen RC, Willett MS, Molinoff PB. Double-blind, placebo-controlled evaluation of the safety, pharmacokinetic properties and pharmacodynamic effects of intranasal PT-141, a melanocortin receptor agonist, in healthy males and patients with mild-to-moderate erectile dysfunction. International Journal of Impotence Research. 2004. — doi: 10.1038/sj.ijir.3901139 — https://www.nature.com/articles/3901139
[8] Diamond LE, Earle DC, Garcia WD, Spana C. Co-administration of low doses of intranasal PT-141, a melanocortin receptor agonist, and sildenafil to men with erectile dysfunction results in an enhanced erectile response. Urology. 2005. — doi: 10.1016/j.urology.2004.10.060 — https://pubmed.ncbi.nlm.nih.gov/15833522/
[9] Bremelanotide injection US Prescribing Information. US FDA Approved Label, NDA 210557. 2019. — https://www.accessdata.fda.gov/drugsatfda_docs/label/2019/210557s000lbl.pdf
[10] Bremelanotide Prescribing Information: Section 5 Warnings and Precautions. US FDA Approved Label, NDA 210557. 2019. — https://www.accessdata.fda.gov/drugsatfda_docs/label/2019/210557s000lbl.pdf
[11] Bremelanotide Prescribing Information: Section 5.2 Focal Hyperpigmentation. US FDA Approved Label, NDA 210557. 2019. — https://www.accessdata.fda.gov/drugsatfda_docs/label/2019/210557s000lbl.pdf
[12] Edinoff AN, Sanders NM, Lewis KB, Apgar TL, Cornett EM, Kaye AM, Kaye AD. Bremelanotide for Treatment of Female Hypoactive Sexual Desire. Neurology International. 2022. — doi: 10.3390/neurolint14010006 — https://www.mdpi.com/2035-8377/14/1/6
[13] Spana C, Jordan R, Fischkoff S. Effect of bremelanotide on body weight of obese women: Data from two phase 1 randomized controlled trials. Diabetes, Obesity and Metabolism. 2022. — doi: 10.1111/dom.14672 — https://pubmed.ncbi.nlm.nih.gov/35170192/
[14] RECONNECT investigators. Positive Effects of Bremelanotide on Female Sexual Arousal and Orgasm in Premenopausal Women with HSDD: FSFI Data from the RECONNECT Trials. The Journal of Sexual Medicine (Supplement). 2025. — doi: 10.1093/jsxmed/qdaf068.108 — https://academic.oup.com/jsm/article/22/Supplement_1/qdaf068.108/8119524
[15] Suzuki S, Kitanaka C, Okada M. Melanocortin Receptor Agonist Bremelanotide Induces Cell Death and Growth Inhibition in Glioblastoma Cells via Suppression of Survivin Expression. Anticancer Research. 2024. — doi: 10.21873/anticanres.17214 — https://pubmed.ncbi.nlm.nih.gov/39197897/
[16] Pfaus JG, Sadiq A, Spana C, Clayton AH. The neurobiology of bremelanotide for the treatment of hypoactive sexual desire disorder in premenopausal women. CNS Spectrums. 2022. — doi: 10.1017/S109285292000219X — https://pubmed.ncbi.nlm.nih.gov/33455598/
[17] Positive Appetite Suppression Results From Phase 2 Obesity Study of MC4R Agonist Bremelanotide and Tirzepatide (BMT-801). Sponsor press release. 2025. — https://palatin.com/press_releases/palatin-reports-positive-appetite-suppression-results-from-phase-2-obesity-study-of-mc4r-agonist-bremelanotide-and-tirzepatide/
[18] Simon JA, Kingsberg SA, Portman D, et al. Long-Term Safety and Efficacy of Bremelanotide for Hypoactive Sexual Desire Disorder (open-label extension enrollment data). Obstetrics & Gynecology. 2019. — doi: 10.1097/AOG.0000000000003514 — https://pubmed.ncbi.nlm.nih.gov/31599847/
[19] Dhillon S, Keam SJ. Bremelanotide: First Approval. Drugs. 2019. (Regulatory history review; also covers initiation of the Phase 2 co-administered bremelanotide + PDE5i ED trial, June 2024.) — doi: 10.1007/s40265-019-01187-w — https://link.springer.com/article/10.1007/s40265-019-01187-w

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