PT-141 Bremelanotide UK 2026 Research Reference

For laboratory research use only. This page summarises published scientific literature on PT-141 Bremelanotide in plain English, in a neutral research style. It is not medical advice and contains no guidance on doses, administration or human use.

Last updated: April 2026 · UK research-grade reference · For laboratory research use only — not for human consumption

Table of Contents

• 1. Overview — PT-141’s distinctive position
• 2. Molecular structure
• 3. Melanocortin receptor pharmacology
• 4. MC4R in CNS sexual circuitry
• 5. Pharmacokinetics
• 6. Vyleesi — regulatory history
• 7. RECONNECT trials — the HSDD evidence base
• 8. Erectile dysfunction research
• 9. Research beyond sexual function
• 10. PT-141 vs Melanotan-II
• 14. UK research-grade sourcing standards
• References

1. Overview — PT-141’s distinctive position

For UK laboratory research, PT-141 is the reference peptide for melanocortin-system investigation — CNS melanocortin receptor pharmacology, sexual-function neurobiology, and downstream metabolic and inflammatory studies where MC3R/MC4R activation has mechanistic relevance.

2. Molecular structure

PT-141 is a cyclic heptapeptide: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. Molecular formula C₅₀H₆₈N₁₄O₁₀; molecular weight 1025.19 Da.

Structural features:

• N-terminal acetyl group for stability
• Nle (norleucine) at position 4 (corresponding to α-MSH position 4)
• Cyclic lactam bridge between Asp and Lys side chains — forms the peptide loop that constrains 3D conformation
• D-Phe at position 7 — enhances receptor affinity and metabolic stability
• Conserved His-Phe-Arg-Trp (HFRW) core motif shared with α-MSH and Melanotan-II — the pharmacophore for melanocortin receptor binding

The cyclisation and D-amino acid substitutions differentiate PT-141 from linear α-MSH: the cyclic structure increases plasma stability, reduces enzymatic degradation, and provides sufficient receptor-binding half-life for practical pharmaceutical use.

3. Melanocortin receptor pharmacology

The melanocortin receptor family comprises five subtypes (MC1R–MC5R), each with distinct tissue distribution and function:

• MC1R: melanocytes; skin and hair pigmentation
• MC2R: adrenal cortex; cortisol production (ACTH receptor)
• MC3R: hypothalamus, placenta, gut; energy homeostasis, appetite
• MC4R: hypothalamus, brainstem, spinal cord; appetite, sexual behaviour, autonomic function
• MC5R: exocrine glands; sebaceous and other secretions

PT-141 binding affinity profile (Ki in nM, approximate):

• MC4R: 0.6 nM (highest affinity)
• MC3R: 2.1 nM
• MC1R: 2.8 nM
• MC5R: 11 nM
• MC2R: >1000 nM (effectively no activity at the ACTH receptor)

The combination of high MC4R and MC3R affinity with no MC2R activity is pharmacologically important: it isolates CNS hypothalamic effects from adrenal cortisol stimulation. This is a key distinction from unselective α-MSH analogues.

Signal transduction is the standard melanocortin receptor cascade: Gαs coupling → adenylyl cyclase → cAMP → PKA → downstream effector activation. Some Gαq coupling has also been demonstrated at MC4R, contributing to IP3/Ca²⁺ signalling.

4. MC4R in CNS sexual circuitry

The mechanistic basis of PT-141’s sexual-function activity is MC4R expression in specific hypothalamic and brainstem nuclei:

• Medial preoptic area (mPOA): central integrator for male sexual behaviour; MC4R activation promotes pro-erectile and pro-copulatory signalling
• Paraventricular nucleus (PVN): oxytocinergic projections to spinal cord and limbic system; MC4R activation increases oxytocin release
• Ventral tegmental area (VTA): mesolimbic dopaminergic pathway; MC4R modulates dopamine release relevant to sexual desire/arousal
• Spinal cord sympathetic preganglionic neurons: MC4R contributes to autonomic signals driving genital response

The combined upstream activation of hypothalamic-mesolimbic and direct spinal pathways explains why PT-141 produces both subjective desire/arousal effects and objective genital responses — a profile distinct from PDE5 inhibitors which only act on the peripheral vascular component.

5. Pharmacokinetics

• Volume of distribution: ~25 L
• Protein binding: moderate
• Metabolism: peptide hydrolysis (no CYP involvement)
• Elimination: primarily renal (peptide fragments)
• Duration of effect: 6-16 hours reported in trial diaries

The ~2.7 hour half-life combined with the extended duration of reported subjective effect suggests that CNS melanocortin receptor engagement produces downstream effects that outlast plasma peptide presence — consistent with the transcriptional and neuromodulatory mechanisms of central monoaminergic signalling.

6. Vyleesi — regulatory history

Vyleesi is not approved in the UK as a prescription medicine as of 2026 — MHRA approval was not pursued given the limited European commercial opportunity.

7. RECONNECT trials — the HSDD evidence base

Primary endpoints at 24 weeks:

• Change in Female Sexual Function Index (FSFI) desire domain score: bremelanotide +0.54 vs placebo +0.27 (p < 0.001)
• Change in Female Sexual Distress Scale (FSDS-DAO) item 13 (bothered by low desire): bremelanotide −0.74 vs placebo −0.42 (p < 0.001)
• Responder analysis (FSFI desire increase ≥1.2): bremelanotide 25.2%, placebo 17.0%

8. Erectile dysfunction research

• Early Phase 2 trials showed efficacy in men with ED, including PDE5-inhibitor non-responders

9. Research beyond sexual function

MC4R activation has broader relevance beyond sexual function, and PT-141 is increasingly used as a research tool in:

• Appetite and energy homeostasis: MC4R is one of the most penetrant monogenic obesity genes (loss-of-function mutations cause severe early-onset obesity). PT-141 is a research tool for MC4R pharmacology in energy-balance studies.
• Inflammatory modulation: Melanocortin receptor activation has anti-inflammatory effects via cytokine modulation; PT-141 has been used in sepsis and autoimmune research models.
• Neuroprotection: MC4R activation in CNS has neuroprotective signalling in stroke and spinal cord injury models.
• Autonomic function: MC4R modulates sympathetic outflow; PT-141 is a research tool for studies of hypertension and cardiovascular autonomic regulation.
• Haemorrhagic shock: early research showed melanocortin agonism produces beneficial cardiovascular effects in models of severe blood loss.

10. PT-141 vs Melanotan-II

PT-141 is chemically derived from Melanotan-II (MT-II) — both share the cyclic heptapeptide backbone — but with key differences:

• Selectivity: PT-141 has higher MC4R/MC3R selectivity with reduced MC1R activity; MT-II has higher MC1R activity (hence MT-II’s tanning effect)
• Carboxyl terminus: PT-141 has a free C-terminal carboxyl; MT-II has a C-terminal amide
• Tanning effect: significantly reduced in PT-141 compared to MT-II, owing to reduced MC1R activity
• Clinical approval: PT-141 approved as Vyleesi (2019); MT-II never approved
• Research use: PT-141 preferred for sexual-function and MC4R research; MT-II retained for MC1R / pigmentation research

For UK laboratory research, PT-141 is the appropriate molecule for MC4R-focused studies; MT-II is the appropriate choice for MC1R-focused pigmentation biology work.

14. UK research-grade sourcing standards

PT-141 should be sourced with full documentation:

• ≥98% HPLC purity (≥99% is the emerging 2026 standard)
• Mass spectrometry identity confirmation (theoretical MW 1025.19 Da)
• Batch-specific Certificate of Analysis
• Endotoxin quantification
• Residual TFA analysis
• Cyclisation integrity confirmation (LC-MS can distinguish cyclic from linear isomers; free-carboxyl vs amide C-terminus must be confirmed)
• Lyophilised powder with cold-chain shipping

Quality-control note: PT-141’s cyclic structure is the most common site of synthesis failure. A high-quality COA should specifically address cyclisation yield and the absence of des-cyclic (linear) parent peptide. Blue colouration (suggesting copper contamination from coupling reagent residues) is occasionally observed in poorly-purified batches — an immediate visual red flag.

Limits of the evidence

Published findings come from specific study designs, often in cell systems or animals, and do not transfer automatically to other settings. A paper about a molecule is not proof that any particular batch has a given biological effect. Purity data show what is in a vial; they do not show sterility, safety or suitability for any use outside the laboratory.

Laboratory handling

• Store lyophilised powder sealed, cold (−20 °C for long-term storage), dry and protected from light.
• Let vials reach room temperature before opening to limit condensation.
• Prepare solutions with suitable laboratory solvents and calibrated equipment, and label each with lot number, concentration and date.
• Split solutions into single-use aliquots and avoid repeated freeze–thaw cycles.
• Use the peptide calculator for concentration arithmetic (mg/mL).

References

1. Kingsberg SA et al. Bremelanotide for the treatment of hypoactive sexual desire disorder: two randomized phase 3 trials (RECONNECT). Obstet Gynecol 2019;134:899–908.
2. Clayton AH et al. Bremelanotide for female sexual dysfunctions in premenopausal women: a randomized, placebo-controlled dose-finding trial. Womens Health (Lond) 2016;12:325–337.
3. Safarinejad MR. Evaluation of the safety and efficacy of bremelanotide, a melanocortin receptor agonist, in female subjects with arousal disorder. Int J Impot Res 2008;20:301–307.
4. Hadley ME. Discovery that a melanocortin regulates sexual functions in male and female humans. Peptides 2005;26:1687–1689.
5. Pfaus JG et al. Selective facilitation of sexual solicitation in the female rat by a melanocortin receptor agonist. Proc Natl Acad Sci USA 2004;101:10201–10204.
6. Molinoff PB et al. PT-141: a melanocortin agonist for the treatment of sexual dysfunction. Ann N Y Acad Sci 2003;994:96–102.
7. Shadiack AM, Sharma SD, Earle DC, Spana C, Hallam TJ. Melanocortins in the treatment of male and female sexual dysfunction. Curr Top Med Chem 2007;7:1137–1144.
8. Diamond LE et al. Double-blind, placebo-controlled evaluation of the safety, pharmacokinetic properties and pharmacodynamic effects of intranasal PT-141. J Sex Med 2005;2:620–628.
9. Tao YX. The melanocortin-4 receptor: physiology, pharmacology, and pathophysiology. Endocr Rev 2010;31:506–543.
10. Van der Ploeg LH et al. A role for the melanocortin 4 receptor in sexual function. Proc Natl Acad Sci USA 2002;99:11381–11386.

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Disclaimer: All peptides referenced are sold strictly for in vitro laboratory research use. Not for human consumption, veterinary use, food additive, cosmetic, or household purpose. Nothing in this article is medical advice. UK researchers are responsible for compliance with the Human Medicines Regulations 2012 and Misuse of Drugs Regulations 2001 where applicable.

For laboratory research use only. PT-141 Bremelanotide sold by Peptides Lab UK is supplied strictly for in vitro laboratory research. It is not for human or veterinary use, and nothing on this page is medical advice or guidance on administration. UK purchasers are responsible for complying with all applicable legislation.

Research material from Peptides Lab UK: PT-141 for laboratory research (UK dispatch, batch certificate of analysis, research use only).