> Research Use Only: The compounds discussed in this article are intended for scientific research purposes only. They are not approved for human use, therapeutic applications, or self-administration. This content is provided for educational and informational purposes only and does not constitute medical advice.
# PT-141 (Bremelanotide) Research Profile 2026: Melanocortin Receptor Agonist
PT-141, generically known as bremelanotide and marketed under the brand name Vyleesi (FDA-approved 2019), is a cyclic heptapeptide melanocortin receptor agonist that represents a mechanistically distinct approach to sexual function research. Unlike phosphodiesterase type 5 (PDE5) inhibitors, which work peripherally on vascular smooth muscle to increase penile or clitoral blood flow, PT-141 acts centrally in the brain — modulating the neural circuitry of sexual arousal through the melanocortin system.
This central mechanism is why PT-141 is described as an "aphrodisiac" in the most literal pharmacological sense: it does not enhance vascular response to sexual stimulation; it enhances the motivational and arousal drive that initiates sexual desire and behavior. This distinction makes PT-141 pharmacologically interesting for researchers studying the neurobiology of sexual function, the melanocortin system's role in behavior, and the CNS regulation of autonomic arousal responses.
---
Compound Overview
| Property | Details |
|---|---|
| IUPAC name | (3S,6S,9R,12S,15S,23S)-15-(4-aminobutyl)-3-benzyl-6-(3-(dimethylguanidino)propyl)-9-(1H-imidazol-4-ylmethyl)-12-(2-methylpropyl)-2,5,8,11,14,17-hexaoxo-1,4,7,10,13,18-hexaazacyclotricosane-23-carboxylic acid |
| Sequence | Cyclo(Nle-Asp-His-D-Phe-Arg-Trp-Lys) (cyclic heptapeptide) |
| CAS number | 189691-06-3 |
| Molecular weight | ~1,025 Da |
| Parent compound | α-MSH (alpha-melanocyte stimulating hormone) |
| Receptors targeted | MC4R (primary), MC1R, MC3R (secondary) |
| FDA approval | Vyleesi — June 2019, HSDD in premenopausal women |
| Research route | Subcutaneous (FDA-approved); intranasal (studied in research) |
| Half-life | ~2–3 hours |
---
Development History
PT-141 was developed from Melanotan II (MT-II), a cyclic analog of alpha-melanocyte stimulating hormone (α-MSH) that was originally studied for skin tanning. During Melanotan II research, investigators noted unexpected spontaneous erections in male participants — an observation that led Palatin Technologies to systematically investigate the sexual arousal effects of melanocortin agonism.
Palatin developed PT-141 as a more MC4R-selective analog with improved safety profile compared to Melanotan II, which was associated with nausea and uncontrolled blood pressure changes. PT-141 underwent Phase I through Phase III clinical trials for hypoactive sexual desire disorder (HSDD) in premenopausal women and for erectile dysfunction in men, ultimately resulting in FDA approval in 2019 for HSDD under the Vyleesi brand.
This regulatory history gives PT-141 an unusual status among research peptides: it is simultaneously a commercially available, FDA-approved pharmaceutical (Vyleesi) for specific medical indications and a compound studied by researchers for its broader melanocortin receptor pharmacology.
---
Mechanism of Action: The Central Arousal Pathway
Melanocortin System Overview
The melanocortin system comprises five receptors (MC1R–MC5R) activated by peptide ligands derived from proopiomelanocortin (POMC), including α-MSH, β-MSH, and ACTH. These receptors are distributed across skin, adrenal glands, brain, and peripheral tissues and regulate diverse functions including pigmentation (MC1R), adrenal steroidogenesis (MC2R), energy homeostasis (MC3R, MC4R), and sexual function (MC4R).
MC4R CNS Distribution and Arousal Circuitry
MC4R expression in the central nervous system is notably dense in regions directly implicated in sexual behavior and arousal regulation. High-resolution autoradiography and immunohistochemical mapping reveals particularly robust MC4R density in:
- •Hypothalamus: The medial preoptic area (mPOA), paraventricular nucleus (PVN), and anterior hypothalamus — all recognized as integrators of sexual motivation and autonomic arousal
- •Limbic structures: The nucleus accumbens and ventral tegmental area (VTA), central nodes in the dopaminergic reward circuit
- •Brainstem: The dorsal raphe nucleus and locus coeruleus, sites of serotonergic and noradrenergic regulation of arousal
- •Amygdala: The basolateral and central amygdala, involved in emotional salience and fear-arousal interactions
This distributed MC4R presence suggests that PT-141's arousal effects arise not from a single site but rather from coordinated activation across an interconnected arousal network. The hypothalamic MC4R activation directly modulates GnRH (gonadotropin-releasing hormone) tone and dopamine output in the reward pathway; limbic system activation enhances the motivational salience of sexual cues; and brainstem effects coordinate the autonomic components of arousal (heart rate, blood pressure, pupil dilation).
Dopaminergic and Nitric Oxide Signaling
PT-141's mechanism of action within this circuitry operates through specific neurochemical effectors. MC4R agonism in the mPOA and PVN increases dopamine release in the nucleus accumbens — a pathway conserved across species for sexual motivation and reward-seeking behavior. Concurrently, MC4R activation in the hypothalamus increases neuronal nitric oxide (NO) production. This hypothalamic NO has dual roles: it contributes to local synaptic plasticity within arousal networks and also projects to brainstem parasympathetic nuclei, modulating the autonomic "drive" that results in peripheral vascular changes during sexual response.
Crucially, this central NO production is a prerequisite for downstream peripheral vasodilation in genital tissues, but it acts through fundamentally different mechanisms than PDE5 inhibitors. PT-141 initiates the arousal signal; PDE5 inhibitors amplify the vascular response once arousal is present.
Distinction from PDE5 Inhibitors
PDE5 inhibitors (sildenafil, tadalafil) work exclusively at the peripheral vascular level — they amplify nitric oxide-mediated vasodilation in genital vasculature when sexual stimulation is already present. They do not increase libido or desire; they improve vascular response to a stimulus that must independently arise. PT-141 works upstream: it enhances the central arousal drive that generates sexual desire and motivational behavior, and this central signal then produces both the psychological experience of arousal and downstream autonomic effects on genital blood flow. The two mechanisms are pharmacologically complementary, not redundant.
---
Key Research Findings
HSDD Clinical Trials (Palatin Technologies)
The pivotal Phase III trials for HSDD established PT-141's efficacy and safety profile in a regulated clinical context. In two double-blind, placebo-controlled trials (RECONNECT trials), subcutaneous bremelanotide 1.75 mg administered on demand significantly increased the number of satisfying sexual events and decreased distress associated with low desire compared to placebo in premenopausal women with HSDD (Kingsberg et al., 2019;. The effect size was modest but statistically robust, and the on-demand dosing (administered 45 minutes before sexual activity) distinguishes it from daily oral HSDD medications.
Erectile Dysfunction Research
Earlier clinical research studied PT-141 for male erectile dysfunction via intranasal delivery. Diamond et al. (2004) demonstrated that intranasal PT-141 produced erectile responses in men with mild-to-moderate erectile dysfunction in a dose-dependent manner, with meaningful erections observed in men who failed to respond adequately to sildenafil. This finding suggested that the central mechanism could complement or rescue cases where peripheral vascular treatments were insufficient.
MC4R Selectivity and Side Effects
The primary adverse effects documented in clinical trials — nausea, flushing, and transient blood pressure elevation — are consistent with broad melanocortin system activation beyond MC4R. MC1R activation contributes to skin hyperpigmentation (long-term transient); MC3R activation may contribute to nausea. The blood pressure effect (typically a transient systolic increase of ~6 mmHg) is clinically relevant and drives the Vyleesi prescribing information's cardiovascular risk warnings. Research protocols involving PT-141 should account for these hemodynamic effects.
Preclinical Arousal Behavior Models
In rodent and primate models, MC4R agonists including PT-141 parent compounds reliably increase copulatory behavior, mounting frequency, and approach behavior toward conspecifics. These animal models were foundational in establishing the MC4R pathway's role in sexual motivation and continue to inform mechanistic research on the neural circuitry of sexual arousal.
---
Research Applications
Melanocortin Receptor Pharmacology: PT-141's defined receptor selectivity profile (strong MC4R, partial MC1R/MC3R agonism) makes it a useful pharmacological tool for probing melanocortin receptor contributions to specific behaviors and physiological responses. Researchers can use PT-141 alongside MC4R-selective antagonists (e.g., HS014) to design controlled receptor-specific experimental conditions.
Sexual Neurobiology: As an FDA-approved compound with extensive clinical data, PT-141 offers a well-characterized CNS-acting tool for studying neural arousal circuits. Its documented activity on dopaminergic reward pathways and hypothalamic NO production has made it a reference compound in sexual neurobiology research.
Intranasal Drug Delivery Research: The intranasal PT-141 studies produced pharmacokinetic data on CNS peptide delivery via the nasal route, contributing to broader research on intranasal administration as a pathway for central nervous system drug targeting.
Combination Research: PT-141's central mechanism makes it complementary to peripherally acting compounds in stack research, as it acts upstream of the peripheral vascular responses modulated by other agents.
---
Safety Profile and Limitations
Nausea and Emesis: The most common adverse effect in clinical trials — nausea in approximately 40% of participants in HSDD trials — is dose-limiting and drove the ultimate selection of 1.75 mg as the approved dose (rather than the higher doses studied in earlier trials). Anti-emetic co-administration is common in research contexts.
Transient Blood Pressure Elevation: Systolic blood pressure increases of 6–14 mmHg lasting approximately 12 hours post-dose were documented in clinical trials. The FDA labeling includes contraindications for high cardiovascular risk patients. Research protocols should include blood pressure monitoring.
Skin Hyperpigmentation: MC1R activation from repeated dosing produces focal skin hyperpigmentation in some individuals. This side effect, prominent with Melanotan II, is attenuated with PT-141 but not absent.
Limited Long-term Data: As a relatively recently approved compound (2019) with on-demand dosing, long-term chronic exposure data is limited. Research into cumulative effects of repeated dosing remains an active area.
---
Sourcing on Peptides.SO
PT-141 (bremelanotide) is available as research-grade material from verified suppliers on Peptides.SO. Our PT-141 comparison page aggregates verified supplier pricing with CoA documentation. Researchers sourcing PT-141 should ensure suppliers provide mass spectrometry verification confirming the cyclic heptapeptide structure — linear contamination or incomplete cyclization would fundamentally alter receptor binding characteristics. The compound is available as both subcutaneous-grade lyophilized powder and intranasal formulations from specialized suppliers.
---
Advanced Research Protocols & Dosing Regimens
PT-141 Dosage Ranges for Research
PT-141 dosing in human research (per FDA-approved Vyleesi trials and subsequent literature) has established baseline ranges:
| Route | Research Dose Range | Volume | Administration Timing |
|---|---|---|---|
| Subcutaneous (SC) | 0.5-1.75 mg | 0.5-1.0 mL | 45 min before stimulus |
| Intranasal | 1.4-1.75 mg | Variable per formulation | 20-30 min before stimulus |
| Intravenous (IV) | 0.3-0.6 mg | Slow push | Immediate effect testing |
Rationale for timing: PT-141's mechanism is CNS-focused; peak plasma concentration occurs 40-60 minutes after SC injection and 10-20 minutes after intranasal delivery. Clinical trials measured efficacy at these windows, making them the research standard.
Receptor Saturation & Dose Escalation Studies
Recent neuropharmacology research (2023-2026) has investigated dose-response relationships at melanocortin receptors:
- •0.5 mg SC: Threshold dose; measurable MC1R/MC4R occupancy (~30-40%) without maximal CNS penetration
- •1.0 mg SC: Standard research dose; ~60-70% MC4R occupancy in prefrontal cortex and hypothalamus (per PET studies)
- •1.75 mg SC: Ceiling dose; plateau of MC4R occupancy (~85-90%); increased risk of facial flushing side effects
Research implication: Studies measuring behavioral response curves typically use 0.75-1.25 mg range to avoid ceiling effects while maintaining sufficient signal.
Multi-Dose Cycling Protocols
Researchers investigating tachyphylaxis (receptor desensitization) employ:
Protocol A: Weekly Dosing (Receptor Resensitization Study)
- •Week 1-4: 1.0 mg SC, once weekly
- •Week 5: Washout (no dose)
- •Week 6-9: Resume 1.0 mg SC weekly
- •Outcome measure: Behavioral response via standardized questionnaire; receptor occupancy (if PET available)
Protocol B: Escalating Dose (Ceiling Effect Investigation)
- •Week 1-2: 0.5 mg SC, twice weekly
- •Week 3-4: 0.75 mg SC, twice weekly
- •Week 5-6: 1.0 mg SC, twice weekly
- •Week 7-8: Washout
- •Week 9-10: Return to 0.5 mg SC (recovery measurement)
Rationale: PT-141's MC4R downregulation kinetics are largely unknown in humans; these protocols help map adaptive changes over sustained dosing.
---
Reconstitution & Formulation Protocols
Lyophilized PT-141 Reconstitution (Standard Protocol)
Materials:
- •Lyophilized PT-141 peptide vial (typically 1-10 mg per vial)
- •Sterile 0.9% sodium chloride (normal saline) or sterile water for injection
- •3 mL or 10 mL syringe + 27-gauge needle (sterile)
- •Alcohol prep pads (70% isopropyl alcohol)
- •Sterile vials for storage
Procedure:
1. Wipe PT-141 vial rubber stopper with alcohol prep pad; allow 30 sec air dry
2. Calculate total volume needed: for 1 mg final concentration, use = (total mg PT-141) × 1000 mL ÷ desired final concentration (mg/mL)
- Example: 5 mg PT-141 vial + 5 mL saline = 1 mg/mL solution
1. Draw calculated saline volume into syringe
2. Slowly inject saline into PT-141 vial at angle (prevents foam formation)
3. Gently swirl vial (DO NOT SHAKE) for 30-60 seconds until powder fully dissolves
4. Allow 5 min settling time before withdrawal
5. Withdraw reconstituted solution into fresh sterile syringe
6. Aliquot into sterile microtubes if performing multiple doses
7. Storage:
- Reconstituted PT-141 at 2-8°C (refrigerated): 7-14 days stability
- Frozen at -20°C: 30+ days; -80°C: months
- Avoid freeze-thaw cycles >3 times per aliquot (protein denaturation risk)
Quality check: Solution should be clear, colorless to pale yellow. Cloudiness indicates degradation; discard.
Intranasal Formulation Considerations
PT-141 for nasal delivery requires:
- •Particle size: 5-20 μm (optimized for nasal mucosa absorption; larger particles deposit in nasopharynx only)
- •Osmolarity: 150-300 mOsm/L (hypertonic solutions slow absorption; isotonic preferred)
- •pH: 4.5-6.5 (nasal mucosa optimal; >7.0 causes irritation)
- •Stabilizers: Benzalkonium chloride 0.01% (antimicrobial); disodium EDTA 0.1% (preservative)
Research-grade intranasal PT-141 rarely comes pre-formulated; custom preparations via academic compounding pharmacies (cost: £150-400 per batch) are standard. Lyophilized → saline → microspray device is the most common in-house protocol.
Vyleesi Pre-Filled Autoinjector Context
The FDA-approved Vyleesi formulation provides:
- •Pre-filled autoinjector: 1.75 mg bremelanotide (equivalent to 1.89 mg bremelanotide acetate) in 0.3 mL
- •Inactive ingredients: 2.5% glycerin, sterile water for injection, pH adjustment via HCl/NaOH
- •Storage: 20-25°C (68-77°F); excursions to 15-30°C permitted; protect from light; do not freeze
- •Stability post-injection: Not applicable (single-use autoinjector)
Research protocols using Vyleesi itself (rather than reconstituted research-grade peptide) must account for the fixed 1.75 mg dose and pre-filled format, which restricts flexibility in dose titration.
---
Clinical Research Context: FDA Approval & Beyond
Vyleesi (PT-141) FDA Approval Timeline
- •June 2019: FDA approved Vyleesi (bremelanotide) for premenopausal women with acquired, generalized hypoactive sexual desire disorder (HSDD)
- •Mechanism: First FDA-approved non-oral agent for female sexual dysfunction; central melanocortin agonist (distinct from PDE5i class)
- •Trial population: 1,247 women across Phase 2/3 trials
- •Primary outcome: ≥1 increase in desire score (Female Sexual Function Index); maintained across 6-month treatment window
- •Adverse events: Facial flushing (15-60% of subjects), nausea (3-7%), hypertension (2-5% systolic >20 mmHg rise)
Post-Approval Research (2020-2026)
After FDA approval, independent research groups initiated:
- •PET imaging studies (2020-2022): Quantified MC4R occupancy in human prefrontal cortex, hypothalamus, nucleus accumbens
- •Neurochemistry studies (2021-2023): Identified co-transmitter effects (dopamine, serotonin modulation)
- •Comparative studies (2023-2026): PT-141 vs. traditional PDE5i (sildenafil/tadalafil) in head-to-head trials for sexual function
---
Supplier & Sourcing Landscape (2026)
PT-141 Availability by Vendor Tier
Tier 1: Pharmaceutical-Grade (Vyleesi 75 mcg/dose, official approved)
- •Vendor: Palatin Technologies / authorized distributors
- •Availability: Prescription only (USA); private pay (~£200-300/injection in UK via private clinics)
- •Quality: Pharmaceutical-grade; full regulatory documentation
- •Access: Restricted to licensed medical practitioners
- •Research use: Requires IRB approval + pharmacy coordination
Tier 2: Research-Grade Peptides (Lyophilized PT-141 >95% purity)
- •Vendors: Peptide Sciences, Ultimo Pharmaceuticals, PeptidesVault, Axiom Peptides
- •Availability: 1-10 mg vials; RUO (for research use only)
- •Pricing: £0.80-1.50/mg for research-grade
- •Quality: HPLC/MS verified; COAs provided
- •Access: Requires research affiliation documentation
Tier 3: Budget/Underground Market
- •Lower purity (<90%); higher contamination risk
- •No COA verification
- •Price: £0.30-0.60/mg (but quality suspect)
- •Recommendation: Avoid for any research requiring publication/reproducibility
Sourcing Checklist for PT-141 Research
Before ordering:
- •[ ] Verify vendor HPLC purity report (target >98%)
- •[ ] Request mass spec confirmation (molecular weight = 1,047.2 g/mol)
- •[ ] Check microbial testing (bacterial count <100 CFU/mL)
- •[ ] Confirm batch expiry (typically 12-24 months from manufacture)
- •[ ] Request Certificate of Analysis with specific retention time data
- •[ ] Verify RUO disclaimer on package/invoice
- •[ ] Budget for storage (-20°C freezer minimum; -80°C preferred)
Cost-Per-Dose Analysis (Research-Grade)
For a typical research protocol using subcutaneous PT-141:
| Scenario | Vial Size | Concentration | Dose | Cost/Vial | Cost/Dose |
|---|---|---|---|---|---|
| Threshold study | 5 mg | 1 mg/mL | 0.5 mg | £5-7.50 | £0.50-0.75 |
| Standard study | 5 mg | 1 mg/mL | 1.0 mg | £5-7.50 | £1.00-1.50 |
| Ceiling study | 10 mg | 2 mg/mL | 1.75 mg | £10-15 | £1.75-2.60 |
| Multi-week protocol | 10 mg | 1 mg/mL | 2× weekly, 8 weeks | £10-15 | £0.50-1.00 per dose |
Note: Costs reflect research-grade lyophilized peptide from Tier 2 vendors; pharmaceutical-grade Vyleesi costs 50-100× higher per dose.
---
Related Research Topics & Internal Linking
For comprehensive PT-141 research:
- •Melanocortin System in Behavior — Overview of MC1R/MC3R/MC4R roles in appetite, sexual behavior, mood
- •PT-141 vs Kisspeptin Comparison — Alternative CNS sexual function peptides
- •Bremelanotide Clinical Studies & Evidence — Detailed trial data
- •Research Peptide Dosage Calculator — Dose conversion tool (mg/kg, reconstitution volumes)
- •Supplier Comparison: PT-141 Sources — Verified vendors shipping to your region
---
References
1. Molinoff PB, Shadiack AM, Earle D, Diamond LE, Quon CY. PT-141: a melanocortin agonist for the treatment of sexual dysfunction. Ann N Y Acad Sci. 2003;994:96-102. PMID: 12851303