A cyclic heptapeptide derived from alpha-MSH that activates melanocortin receptors in the hypothalamus and limbic system — the first compound ever approved that targets sexual desire through brain pathways rather than peripheral vascular mechanisms.
Kingsberg et al. Obstet Gynecol 2019 · Rosen et al. J Sex Med 2004. All data from peer-reviewed literature. For Research Use Only. Not the FDA-approved drug Vyleesi®.
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Found while
studying
tanning.
PT-141 wasn’t designed to target sexual desire. It emerged from research into skin pigmentation — specifically from studies of Melanotan II, a melanocortin agonist being investigated for tanning. Researchers noticed an unexpected side effect: sexual arousal. That serendipitous observation led Palatin Technologies to engineer a cleaner derivative, eventually yielding the first FDA-approved drug targeting desire through brain pathways.
1990s
Melanotan II — Tanning Research
Researchers studying melanocortin agonists for skin pigmentation notice an unexpected side effect: spontaneous sexual arousal in study participants. The compound lacked specificity and caused significant nausea.
2000
PT-141 Synthesized — Palatin Technologies
Palatin Technologies engineers a cyclic heptapeptide derived from Melanotan II by removing the C-terminal amide. This eliminates the potent tanning effect while preserving and refining the sexual response activity. PT-141 = cleaner, more selective.
2004–2008
Phase 2 Trials — Men & Women
Intranasal PT-141 showed promising Phase 2 data for erectile dysfunction in men. Blood-pressure concerns with nasal route led Palatin to pivot to subcutaneous injection and to HSDD in premenopausal women — an indication with no approved treatment at the time.
June 2019
Vyleesi® FDA Approval — RECONNECT Trials
Two identical Phase 3 RCTs (RECONNECT) demonstrated efficacy for HSDD. FDA approved Vyleesi as a 1.75 mg subcutaneous injection — the first and only FDA-approved treatment for HSDD that works through brain pathways rather than peripheral vascular mechanisms.
Every established sexual health compound before PT-141 worked peripherally — dilating blood vessels, increasing blood flow to genital tissue. PT-141 is mechanistically different: it operates centrally, in the hypothalamus and limbic system, activating the neural circuits that generate desire itself. This distinction is why it works in PDE5 inhibitor-resistant populations and why it addresses desire (not just physical response).
The FDA prescribing information notes that the exact mechanism by which Vyleesi improves HSDD is not fully characterized — an honest acknowledgment that MC4R agonism’s downstream pathway to desire is complex. What is established: MC4R knockout mice show markedly impaired sexual function, and MC4R is concentrated in hypothalamic and limbic regions governing arousal and motivation.
Mechanism Comparison
PT-141 activates melanocortin-3 and melanocortin-4 receptors in the hypothalamus and limbic system. MC4R is a Gαs-coupled GPCR — receptor binding raises intracellular cAMP, which activates downstream signaling cascades that influence dopaminergic neurotransmission and nitric oxide release. The downstream pathway from MC4R to desire involves neural circuits in the hypothalamic preoptic area, nucleus accumbens, and amygdala.
MC3R / MC4R Binding → Gαs Activation
PT-141 binds MC3R and MC4R in the hypothalamus and limbic regions. MC4R is highly expressed in the hypothalamic preoptic area and paraventricular nucleus — both established regulators of sexual behavior. Ki = 10 nM at human MC4R (competitive binding against NDP-α-MSH in HEK-293 cells). MC4R couples to Gαs protein.
cAMP Accumulation → PKA → Downstream Cascades
Gαs activation → adenylate cyclase → ↑cAMP → PKA. PT-141 induces cAMP accumulation in hMC4R-expressing HEK-293 cells (documented pharmacological assay endpoint). Parallel activation of phospholipase C → IP3/DAG → Ca2+ also documented for MC3R.
Dopamine Release → Reward Circuit Activation
MC4R activation in hypothalamic circuits enhances dopaminergic neurotransmission — the same reward circuitry underlying motivation and desire. Dopamine pathway activation in the nucleus accumbens and mesolimbic system generates the subjective experience of wanting/desire. NO (nitric oxide) release also documented as a downstream mediator.
Limbic System Activation → Sexual Arousal & Desire
Neural signal propagation through amygdala, nucleus accumbens, and cortex generates desire and arousal independent of genital stimulation or vascular events. PT-141 shows in vivo sexual arousal efficacy in both male (50 μg/kg intranasally) and female rats (100–200 μg/kg SC) by activating neurons in brain regions responsible for sexual function.
Research Endpoint Areas
Hypoactive Sexual Desire Disorder — Female Models
FDA-approved indication (Vyleesi). RECONNECT Phase 3: two identically designed 24-week RCTs. Significant improvements in desire and satisfying sexual events vs placebo. FSDS-DAO and FSFI are standard validated endpoints for in vitro and clinical research in this domain.
Erectile Dysfunction — Including PDE5-Resistant
Phase 1 and 2 data demonstrated erectogenic effects in men including those with inadequate response to sildenafil. 62% improvement vs 21% placebo in PDE5-resistant population (Safarinejad & Hosseini 2008). IIEF and nocturnal penile tumescence are standard endpoints.
Melanocortin Receptor Pharmacology — CNS Biology
PT-141 is the primary research tool for MC4R pharmacology studies. cAMP HTRF assay in MC4R-expressing HEK-293 cells. Receptor binding competition assays against NDP-α-MSH. MC4R knockout phenotype comparison. Behavioral paradigms in rodent models.
SSRI-Induced Sexual Dysfunction Models
PT-141 is studied in models of SSRI-induced sexual dysfunction — a common adverse effect of antidepressants that operates through serotonergic suppression of MC4R signaling. Research into melanocortin system modulation as a reversal mechanism for iatrogenic sexual dysfunction.
Two identically designed, randomized, double-blind, placebo-controlled Phase 3 trials — the basis for FDA approval of Vyleesi® in 2019. The most rigorous clinical evidence base of any peptide in our research catalogue.
2 trials
Identical Phase 3 RCTs
RECONNECT 1 and RECONNECT 2 — 24-week core periods, 52-week extension. Randomized, double-blind, placebo-controlled. Same design, replicated results.
Kingsberg SA et al., Obstet Gynecol 2019;134(5):924–933
67%
Reported Improved Erections (Men)
Phase 1/2 study of PT-141 in men with erectile dysfunction: 67% reported improved erections vs 33% placebo (p <0.01). Sustained improvement over 8-week period.
Rosen RC et al., J Sex Med 2004
62%
Improvement in PDE5-Resistant ED
In 180 men with sildenafil-resistant erectile dysfunction: 62% improvement in PT-141 group vs 21% placebo (p <0.001). Confirms mechanism independent of PDE5 pathway.
Safarinejad & Hosseini, Urology 2008
2019
FDA Approval Year
Vyleesi® — first CNS-targeted sexual desire drug approved in the US
1st
Of its Kind
Only FDA-approved peptide targeting sexual desire through brain pathways, not vascular mechanisms
Molecular and analytical data from peer-reviewed literature and Eon Peptides batch records.
Long-term
-20°C
Lyophilized sealed. Stable 24 months. Avoid frost-free freezers.
In solution
4°C
Stable 7–14 days. Single-use aliquots. Do not refreeze.
Solvent
Sterile H2O
Reconstitute in sterile water or PBS pH 7.0–7.4. 0.5–1 mg/mL stock.
Avoid
Oxidants
Protect from light. Cyclic peptide backbone is sensitive to oxidative degradation.
For Research Use Only — Not for Human Consumption. Not Vyleesi® or any approved drug. Supplied exclusively for in vitro laboratory research by qualified researchers.
| Common Name | PT-141 / Bremelanotide |
| Brand Name | Vyleesi® (bremelanotide injection) — FDA-approved drug. Not Eon Peptides’ product. |
| Sequence | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH |
| CAS Number | 189691-06-3 |
| Molecular Formula | C50H68N14O10 |
| Molecular Weight | 1,025.16 Da |
| Structure | Cyclic heptapeptide · lactam ring · N-terminal acetylated norleucine · D-Phe pharmacophore |
| Primary Targets | MC3R, MC4R (melanocortin receptors) — hypothalamus and limbic system |
| Receptor Affinity | MC4R Ki = 10 nM (HEK-293 competitive binding vs NDP-α-MSH) |
| Signaling | MC4R → Gαs → ↑cAMP → PKA → dopamine → arousal circuits |
| PK Peak (Tmax) | ~1 hr post-subcutaneous administration (Vyleesi prescribing info) |
| Plasma t½ | 2.7 hr (range 1.9–4.0 hr) |
| Bioavailability | ~100% subcutaneous (Vyleesi prescribing info) |
| Form | Lyophilized powder · sealed glass vial |
| Purity | ≥99% HPLC · Mass Spec verified · 6-panel COA · Freedom Diagnostic |
| Endotoxin | <0.05 EU/mL · LAL-tested · Freedom Diagnostic |
| Regulatory | RUONot Vyleesi® — In Vitro Research Use Only |
Independent peer-reviewed studies. Not Eon Peptides claims. For Research Use Only.
Bremelanotide for the Treatment of Hypoactive Sexual Desire Disorder — RECONNECT Phase 3
Kingsberg SA, Clayton AH, Portman D, et al.
Two identically designed, randomized, double-blind, placebo-controlled Phase 3 trials (RECONNECT 1 and RECONNECT 2) evaluating bremelanotide 1.75 mg SC for HSDD in premenopausal women. 24-week core periods. Primary endpoints: Female Sexual Function Index (FSFI) desire domain and Female Sexual Distress Scale-Desire/Arousal/Orgasm (FSDS-DAO). Both trials demonstrated statistically significant improvements in sexual desire and distress vs placebo. The basis for FDA approval of Vyleesi® in June 2019. Obstet Gynecol 2019;134(5):924–933. PMID: 31599840.
Evaluation of the Safety, Pharmacokinetics and Pharmacodynamic Effects of PT-141 in Men with Erectile Dysfunction
Rosen RC, Diamond LE, Earle DC, et al.
Phase 1/2 evaluation of intranasal PT-141 in men with erectile dysfunction. 67% of PT-141 recipients reported improved erections vs 33% placebo (p <0.01). Sustained improvement throughout 8-week treatment. Also demonstrated sexual arousal enhancement independent of PDE5 pathway. First published human evidence of PT-141’s erectogenic efficacy. The study also characterized intranasal PK and BP effects that led to the subsequent shift to subcutaneous administration. J Sex Med 2004. PMID: 15787219.
The Melanocortin System and Sexual Function — PT-141 Pharmacological Characterization
Molinoff PB, Shadiack AM, Earle D, et al.
Detailed pharmacological characterization of PT-141’s melanocortin receptor binding and functional activity. Documents MC3R and MC4R binding affinities, cAMP induction in receptor-expressing cell lines, and behavioral sexual arousal effects in animal models. Reviews the role of the melanocortin system in sexual function, establishes that MC4R knockout impairs sexual function in both sexes, and provides the mechanistic rationale for PT-141 as a CNS-targeted sexual dysfunction research model. Ann NY Acad Sci 2003;994:96–102. PMID: 12851301.
PT-141 vs Placebo in Sildenafil-Resistant Erectile Dysfunction — Crossover RCT
Safarinejad MR, Hosseini SY.
180 men with sildenafil-resistant erectile dysfunction in a randomized crossover design. PT-141 vs placebo in men who had failed to respond to maximum-dose PDE5 inhibitors. PT-141 group: 62% improvement in IIEF erectile function domain. Placebo: 21% (p <0.001). The critical study confirming that PT-141’s CNS mechanism is genuinely independent of the PDE5/vascular pathway — and that it can succeed where PDE5 inhibitors have failed. PMID: 18439624.
Vyleesi® (Bremelanotide Injection) Full Prescribing Information
AMAG Pharmaceuticals / FDA.
FDA prescribing information for Vyleesi® (bremelanotide injection 1.75 mg/0.3 mL subcutaneous). Complete molecular characterization: C50H68N14O10, MW 1025.16 Da, CAS 189691-06-3. Full PK data: Tmax ~1 hr, t1/2 2.7 hr, subcutaneous bioavailability ~100%, excretion 64.8% urine/22.8% feces. Complete Phase 3 RECONNECT trial efficacy and safety data. Contraindications, warnings (BP/HR monitoring), adverse reactions (nausea most common), drug interactions. Authoritative regulatory reference. NDA 210557.
PT-141 (Bremelanotide): Complete Research Guide — Melanocortin Receptor Agonist
Eon Peptides Research Team.
2026 comprehensive research review covering PT-141’s MC3R/MC4R pharmacology, CNS mechanism, discovery origin from Melanotan II, clinical trial evidence base (RECONNECT, Rosen 2004, Safarinejad 2008), and research applications. Reviews central vs peripheral mechanism distinction in detail. Covers receptor pharmacology assay methodologies, binding kinetics, cAMP reporter assays, and behavioral endpoints. Positions PT-141 as the reference research tool compound for melanocortin system sexual function research. March 2026.
Independent peer-reviewed research — not Eon Peptides claims. PT-141 (research-grade) is not Vyleesi®. Supplied for in vitro research use only. Not for human consumption.
Kingsberg SA, Clayton AH, Portman D, et al.
Bremelanotide for the treatment of hypoactive sexual desire disorder: two randomized phase 3 trials
Rosen RC, Diamond LE, Earle DC, et al.
Evaluation of the safety, pharmacokinetics and pharmacodynamic effects of subcutaneously administered PT-141 in men with erectile dysfunction
Molinoff PB, Shadiack AM, Earle D, et al.
PT-141: a melanocortin agonist for the treatment of sexual dysfunction
Safarinejad MR, Hosseini SY.
Intranasal bremelanotide: an association between central melanocortin receptor activity and penile erection
AMAG Pharmaceuticals / FDA.
Vyleesi® (bremelanotide injection) Full Prescribing Information
Eon Peptides Research Team.
PT-141 (Bremelanotide): Complete Research Guide — Melanocortin Receptor Agonist