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What is PT-141?

Research Guide · PT-141

What is PT-141?

A comprehensive examination of bremelanotide’s structure, melanocortin mechanism, and research applications in sexual function and appetite regulation

Updated September 2026 Research Use Only 11 min read

 

What is PT-141

An introduction to PT-141 (bremelanotide) as a melanocortin receptor agonist with divergent mechanisms from phosphodiesterase inhibitors.

01

Molecular Structure & Chemistry

PT-141, formally bremelanotide, is a synthetic cyclic heptapeptide (Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH). MW 1,025.18 Da; CAS 189691-06-3. Derived from MT-II, of which it is the C-terminal free-acid form. Like MT-II it is cyclised through a lactam bridge, which confers metabolic stability. Its US prescribing information describes it as a non-selective melanocortin agonist, with MC1R and MC4R binding most relevant at therapeutic doses.

02

Receptor & Mechanism

PT-141’s primary mechanism involves CNS activation of MC4R on POMC neurons within the hypothalamus and other regions governing sexual function, appetite, and arousal. MC4R activation modulates sexual response circuits through dopaminergic, serotoninergic, and oxytocinergic signalling — distinct from peripheral PDE5 inhibition (sildenafil/tadalafil).

03

Regulatory Status

FDA-approved June 2019 as Vyleesi (bremelanotide subcutaneous autoinjector) for hypoactive sexual desire disorder (HSDD) in pre-menopausal women. Developed by Palatin Technologies and AMAG Pharmaceuticals. First non-hormonal, non-PDE5 approval for female sexual dysfunction. Approval based on Phase 3 RECONNECT trials (Kingsberg et al., 2019).

 

Mechanism of Action

How PT-141 activates central melanocortin circuitry to modulate sexual arousal and physiological response.

01
MC4R Binding & Activation
Subcutaneous PT-141 crosses the BBB and engages MC4R on POMC neurons in the hypothalamic paraventricular and dorsomedial nuclei. MC4R is a Gs-coupled GPCR; agonist binding activates adenylyl cyclase, elevating cAMP and PKA signalling, phosphorylating CREB, and amplifying dopamine and oxytocin release (Clayton et al., 2022).
02
Central Arousal Circuitry
PT-141’s CNS activity potentiates the hypothalamic-limbic sexual response network. Elevated cAMP enhances dopamine release from the VTA, promoting motivation and reward-driven sexual behaviour. Oxytocin secretion from the PVN increases, facilitating sexual bonding and genital vasocongestion through both central and peripheral pathways (Kingsberg et al., 2019).
03
Sexual Response Facilitation
PT-141 operates as a pro-sexual facilitator that enhances inherent sexual responsiveness when sexual stimuli are present, rather than inducing spontaneous desire. Animal studies demonstrate increased sexual motivation and accelerated genital arousal onset only when erotic stimuli are introduced. This stimulus-dependent action distinguishes PT-141 from hormonal therapies (Pfaus & Pagano, 2020).
04
Distinction from PDE5 Inhibitors
Unlike sildenafil/tadalafil/avanafil — which enhance erectile function through peripheral PDE5 inhibition — PT-141 addresses sexual function through central neuroendocrine mechanisms. Renders PT-141 effective in patients refractory to PDE5 inhibitors, particularly those with adequate genital blood flow but impaired arousal initiation. Does not require intact endothelial nitric oxide production.

 

PT-141 vs Comparable Compounds

Comparison with related melanocortin agonists and alternative sexual dysfunction therapies.

Compound
Receptor Profile
Mechanism Context
PT-141 (Bremelanotide)
Non-selective (label potency: MC1R > MC4R > MC3R > MC5R > MC2R)
FDA-approved for female HSDD; CNS sexual arousal via hypothalamic POMC
MT-II (Melanotan-II)
MC1R ≈ MC3R ≈ MC4R (pan-agonist)
Parent compound; broader receptor profile; pigmentation effects in chronic dosing
Alpha-MSH
MC1R > MC3R > MC4R
Endogenous tridecapeptide; pigmentation, immune, appetite roles; lower CNS sexual potency
Sildenafil (Viagra)
PDE5 inhibitor
Peripheral vascular vasodilation via NO pathway; ineffective in central arousal deficits
Tadalafil (Cialis)
PDE5 inhibitor (longer-acting)
Prolonged peripheral vasodilation; 30-36 hour half-life; vascular mechanism only

Research Context: PT-141 is often described as more CNS-focused than MT-II, but its prescribing information lists it as a non-selective melanocortin agonist, and focal hyperpigmentation is a recognised adverse effect. PDE5 inhibitors fail in central arousal disorders or PDE5-refractory patients — populations where PT-141’s CNS mechanism offers research opportunity (Clayton et al., 2022).

 

Key Research Applications

Primary domains in which PT-141 has demonstrated research utility.

01
Female Hypoactive Sexual Desire Disorder
The cornerstone of PT-141 research. Phase 3 RECONNECT trials demonstrated subcutaneous injection 45 minutes before anticipated sexual activity significantly improved sexual desire (FSFI-desire) and reduced distress related to low desire (FSDS-DAO) versus placebo; the number of satisfying sexual events did not differ significantly between groups (Kingsberg et al., 2019; Clayton et al., 2022).
02
Male Erectile Dysfunction Research
Although not approved for male ED, preclinical and early-phase research indicates efficacy in animal models and emerging evidence in men with ED refractory to PDE5 inhibitors. PT-141’s CNS mechanism suggests utility in ED with concurrent low desire, psychological factors, or endothelial dysfunction. A small Phase 2 study showed IIEF-EF improvements (Wessells et al., 2006).
03
Appetite Regulation & MC4R Circuits
Beyond sexual function, PT-141 and related melanocortin agonists are investigational for obesity. MC4R activation in the lateral hypothalamus and arcuate nucleus suppresses appetite. Diet-induced obesity models treated with PT-141 demonstrate reduced food intake through suppression of appetite-promoting NPY and AgRP signalling (Shearman et al., 2003).
04
Inflammation & Immune Modulation
MC3R signalling in immune cells exerts anti-inflammatory effects through suppression of pro-inflammatory cytokine production (TNF-α, IL-6, IL-8) and promotion of IL-10. PT-141 retains moderate MC3R agonism (EC50 ~200 nM vs ~50 nM for MC4R), permitting investigation of immune-modulatory applications in models of inflammation, sepsis, and endotoxaemia.
05
Comparative Pharmacology & SAR
PT-141 serves as a benchmark research tool for structure-activity relationship investigations into melanocortin receptor selectivity. Its cyclic heptapeptide scaffold permits comparative characterisation of how cyclic constraint, amino acid composition, and receptor selectivity influence sexual function, pigmentation, and immune modulation (Pfaus & Pagano, 2020).

 

Quick Reference Specifications

Essential biochemical and pharmacological parameters. Pharmacokinetic values (Half-Life, Tmax) are from human clinical trial data (Vyleesi/bremelanotide Phase 3 RECONNECT trials).

P · 01
Peptide Designation
PT-141 (Bremelanotide); USAN: bremelanotide
P · 02
Structure
Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH; cyclic heptapeptide; CAS 189691-06-3
P · 03
Molecular Weight
1,025.18 Da
P · 04
Receptor Targets
MC4R EC50 ~50 nM; MC3R EC50 ~200 nM; MC1R minimal
P · 05
Half-Life (SC)
~0.9–1.7 hours (human clinical trial data); CNS effects persist longer than serum concentration
P · 06
Tmax
0.5–1.5 hours post-subcutaneous injection (human clinical trial data)
P · 07
Approved Formulation
Vyleesi: 1.75 mg/mL SC autoinjector; FDA-approved June 2019
P · 08
Route
Subcutaneous; intranasal investigational
P · 09
Storage (Powder)
2–8°C or 15–25°C; long-term stability ~2–3 years
P · 10
Storage (Reconstituted)
2–8°C with bacteriostatic water; stable 2–4 weeks; protect from light

 

Reconstitution & Storage

Best practices for maintaining PT-141 stability and bioactivity.

01
Reconstitution Protocol
Reconstitute lyophilised PT-141 with bacteriostatic water (0.9% NaCl with 0.9% benzyl alcohol). Use sterile 1–3 mL syringe and sterile needle. Inject solvent slowly; allow powder to dissolve gently. Avoid shaking or aggressive agitation. Complete dissolution typically requires 2–5 minutes of gentle swirling.
02
Storage & Stability
Reconstituted PT-141 stored at 2–8°C maintains bioactivity 2–4 weeks (some protocols extend to 6 weeks). Protect from light using amber vials or aluminium foil. Freeze-thaw cycles cause irreversible peptide aggregation and loss of activity. Lyophilised vials retain stability 2–3 years at 2–8°C.
03
Visual Inspection
Reconstituted solutions should be clear, colourless to slightly yellow. Cloudiness, particulates, discolouration, or crystalline precipitation indicates degradation; discard immediately. Sterile 0.22 µm filters may be used cautiously, noting potential peptide adsorption onto membranes.
04
Handling Best Practices
Maintain consistent 2–8°C; minimise air exposure with sealed sterile syringes; avoid shaking; use fresh sterile needles per withdrawal; never expose to direct sunlight or heat; equilibrate solutions to room temperature gradually before use; document reconstitution date; aliquot small volumes for extended programmes; discard solutions older than 4 weeks.

Key Published Research

The studies behind bremelanotide’s approval.

2003
From MT-II to PT-141
PT-141 was developed from melanotan II as a melanocortin agonist for sexual dysfunction, initially as an intranasal formulation.1
2004
Early studies in men
Intranasal PT-141 produced dose-related erectile responses in healthy men and men with mild-to-moderate erectile dysfunction.2
2016
Phase 2b in women
A randomised dose-finding trial in premenopausal women with female sexual dysfunction reported improvements in desire and arousal measures versus placebo.3
2019
RECONNECT phase 3
Two phase 3 trials in premenopausal women with hypoactive sexual desire disorder showed significant improvements in sexual desire (FSFI-desire) and reductions in distress (FSDS-DAO) versus placebo. The number of satisfying sexual events did not differ significantly. Nausea occurred in 40.0% of participants versus 1.3% on placebo, flushing in 20.3% and headache in 11.3%.4

Regulatory & Research Status

Where bremelanotide stands in 2026.

US
Approved (2019)
Vyleesi is FDA-approved for acquired, generalised hypoactive sexual desire disorder in premenopausal women. It is not approved in the UK or EU.
LABEL
Receptor profile
The US prescribing information describes bremelanotide as a non-selective melanocortin agonist with potency in the order MC1R, MC4R, MC3R, MC5R, MC2R; at therapeutic doses MC1R and MC4R binding are most relevant. Focal hyperpigmentation and transient increases in blood pressure are listed effects.
2025
Obesity research
In Palatin’s eight-week phase 2 BMT-801 study, co-administering bremelanotide with tirzepatide met its primary endpoint, with 4.4% weight reduction for the combination, renewing interest in MC4R agonism for obesity.

Evidence Quality & Limitations

Bremelanotide is one of the few peptides in these guides with an approved indication, but its effects in the pivotal trials were modest and centred on desire and distress scores rather than behavioural outcomes. Male sexual-function data come from earlier, smaller studies. Because it activates MC1R as well as MC4R, pigmentation effects should be expected in models using repeated dosing.

References

  1. Molinoff PB, et al. PT-141: a melanocortin agonist for the treatment of sexual dysfunction. Ann N Y Acad Sci. 2003;994:96–102. PubMed
  2. Diamond LE, et al. 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. Int J Impot Res. 2004;16:51–9. PubMed
  3. Clayton AH, et al. Bremelanotide for female sexual dysfunctions in premenopausal women: a randomized, placebo-controlled dose-finding trial. Womens Health. 2016;12:325–37. PubMed
  4. Kingsberg SA, et al. Bremelanotide for the treatment of hypoactive sexual desire disorder: two randomized phase 3 trials. Obstet Gynecol. 2019;134:899–908. PubMed
⚠ Research Use Only. The compounds discussed in this guide are intended strictly for in-vitro laboratory research. They are not intended for human consumption, therapeutic use, or veterinary application. Researchers must comply with all applicable local regulations.
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