PT-141 (Bremelanotide): Research, Mechanism of Action & Overview

What Is PT-141?

PT-141 is the research designation for bremelanotide, a synthetic cyclic seven-amino-acid peptide that acts as a non-selective agonist at melanocortin receptors. Structurally it is a close analog and the principal active metabolite of Melanotan II: where Melanotan II carries a C-terminal amide, bremelanotide is the corresponding free-acid form. It incorporates non-standard residues (norleucine and D-phenylalanine) and a lactam ring that give it metabolic stability and receptor potency.

Its distinguishing feature is that it acts centrally, on melanocortin pathways in the brain, rather than on peripheral blood vessels. Bremelanotide is FDA-approved, marketed as Vyleesi (approved June 2019, a 1.75 mg subcutaneous injection for acquired, generalized hypoactive sexual desire disorder in premenopausal women). A compound sold for research use is the same molecule but is not a finished, approved drug product and carries no clinical indication.

Key Identifier

Peptide Profile

Full Name: Bremelanotide (research code PT-141)
Structure: Cyclic heptapeptide (lactam-bridged); melanocortin receptor agonist
Molecular Formula: C₅₀H₆₈N₁₄O₁₀
Molecular Weight: ~1,025.2 g/mol
CAS Number: 189691-06-3
Relationship: Free-acid analog and active metabolite of Melanotan II

Mechanism of Action

Bremelanotide's pharmacology centers on agonism at melanocortin receptors, with its functionally relevant activity localized to the central nervous system.

Melanocortin Receptor Agonism (MC4R)

Bremelanotide is a non-selective agonist across the melanocortin receptor family, with its centrally relevant target being MC4R, a receptor densely expressed in hypothalamic and limbic circuits. MC1R agonism accounts for peripheral pigmentary effects, the mechanistic link it shares with Melanotan II.

Central, Not Vascular, Initiation

Unlike vasoactive agents, bremelanotide acts upstream in the brain. Preclinical work localized its effects to central sites such as the medial preoptic area, and its downstream signaling is thought to engage central dopaminergic pathways, rather than acting primarily on peripheral vasculature.

Distinction From PDE5 Inhibitors

PDE5 inhibitors act peripherally and vascularly, enhancing genital blood flow and requiring an existing arousal signal. Bremelanotide acts on a different axis entirely: a central neuropeptide (melanocortin) pathway. The two mechanisms are complementary and non-overlapping.

MC4R and Energy Balance

MC4R is a cornerstone of central energy-homeostasis signaling; MC4R agonism is an anorexigenic (satiety) signal, and loss-of-function MC4R mutations are a leading monogenic cause of human obesity. Because bremelanotide is an MC4R agonist, MC4R-mediated effects on appetite and autonomic tone are an active area of melanocortin research, and underlie its transient blood-pressure effect.

Research Overview

Bremelanotide has an unusually complete evidence base for a research peptide, spanning preclinical mechanism, early human studies, and two Phase 3 clinical trials. The table summarizes key areas.

Research Area	Key Findings	Study Type
Sexual Function (Preclinical)	A melanocortin agonist selectively increased sexual solicitation behaviors in female rats via central sites, without altering other reflexes	In vivo (rodent behavior)
Sexual Function (Early Human)	Intranasal PT-141 produced dose-dependent erectile responses in healthy men and men with mild-to-moderate erectile dysfunction	Randomized controlled trial (human)
CNS Melanocortin Signaling	The pro-sexual action maps to hypothalamic and limbic MC4R circuits and engages central dopaminergic pathways	Preclinical mechanistic review
HSDD Phase 3 (RECONNECT)	In two identical Phase 3 trials, subcutaneous bremelanotide significantly improved sexual desire and reduced desire-related distress versus placebo	Randomized controlled trials (human)
Hemorrhagic Shock (Class Effect)	Selective MC4R agonists reversed severe hemorrhagic shock and reduced organ damage in rats; a melanocortin class effect, not bremelanotide-specific	In vivo (rat)
Central vs Vascular Action	Human data showed changes in subjective sexual response driven by a central melanocortin mechanism, distinct from vascular agents	Randomized controlled trial (human)

Research Context

Bremelanotide is the only approved on-demand melanocortin therapy, and its central (MC4R) mechanism makes it a reference tool for brain-initiated, rather than vascular, arousal research. The hemorrhagic-shock findings are a melanocortin-class result using other MC4R agonists, not bremelanotide itself. Approved-product safety notes include a transient rise in blood pressure, focal hyperpigmentation with frequent dosing, and nausea as the most common adverse effect.

Common Areas of Research Interest

Interest in PT-141 centers on central melanocortin signaling and the pathways that distinguish it from vascular agents.

Central MC4R control of sexual motivation, bremelanotide is a canonical probe for studying brain-initiated versus vascular arousal pathways
Female sexual desire neurobiology, the only approved on-demand melanocortin therapy, making it a reference tool for desire-distress research
Male erectile and sexual-response signaling, legacy intranasal PT-141 datasets remain relevant to central-pathway research
MC4R in energy balance and cardiovascular tone, appetite and satiety signaling, and the transient pressor response
Melanocortin protection in circulatory shock, an established preclinical melanocortin-class theme mediated by MC4R
Melanocortin receptor pharmacology, the cyclic lactam heptapeptide as a scaffold for receptor-subtype selectivity studies

Pharmacokinetics

Because bremelanotide is an approved drug (Vyleesi), a real human pharmacokinetic dataset exists from its prescribing information; the figures below are for the approved product.

~2.7 h

Terminal Half-Life

~1.0 h

Median Tmax

~100%

SC Bioavailability

1,025

Molecular Weight (Da)

Administered subcutaneously, bremelanotide shows near-complete bioavailability, a median time to peak plasma concentration of about one hour, and a terminal half-life of roughly 2.7 hours. As a seven-amino-acid peptide it is cleared primarily by hydrolysis of amide bonds rather than by cytochrome-P450 metabolism, with plasma protein binding around 21%.

Approved-product safety notes, which apply to the finished drug and not as dosing guidance for a research compound, include a transient increase in blood pressure with a compensatory heart-rate decrease, focal hyperpigmentation that is more likely with frequent dosing and in darker skin, and nausea as the most common adverse effect; the product is not recommended with uncontrolled hypertension or known cardiovascular disease.

Comparison to Similar Compounds

PT-141 is best understood against its parent peptide and the mechanistically distinct class of vascular agents.

Feature	PT-141 / Bremelanotide	Melanotan II	PDE5 Inhibitor
Origin	Cyclic heptapeptide; free-acid analog of MT-II	Synthetic cyclic alpha-MSH analog	Small-molecule enzyme inhibitor
Mechanism	Central melanocortin (MC4R) agonism	Non-selective melanocortin agonism	Peripheral: blocks cGMP breakdown
Primary Research Focus	Sexual desire/arousal via CNS; MC4R biology	Melanogenesis; appetite; sexual behavior	Erectile hemodynamics; pulmonary hypertension
Receptor / Target	MC1R, MC3R, MC4R (MC5R weak)	MC1R, MC3R, MC4R, MC5R	PDE5 enzyme (no melanocortin activity)
Approval Status	FDA-approved (Vyleesi, 2019)	Not approved anywhere	FDA-approved (multiple products)

Frequently Asked Questions

Is PT-141 the same molecule as bremelanotide?

Yes. "PT-141" is the research and development designation; "bremelanotide" is the international nonproprietary name for the same cyclic heptapeptide.

Is bremelanotide FDA-approved?

Yes. It is approved as Vyleesi, since June 2019, for acquired, generalized hypoactive sexual desire disorder in premenopausal women, as a 1.75 mg on-demand subcutaneous injection. A compound sold for research use is the same molecule but is not a finished approved drug product and carries no clinical indication or dosing guidance.

How is its mechanism different from Viagra-type drugs?

PDE5 inhibitors act peripherally on genital blood flow. Bremelanotide acts centrally, on brain melanocortin (MC4R) pathways, an entirely different axis.

What is its relationship to Melanotan II?

Bremelanotide is a close structural analog and the principal active metabolite of Melanotan II. Melanotan II carries a C-terminal amide, while bremelanotide is the corresponding free-acid form. Melanotan II itself is not medically approved.

What does the MC4R system have to do with appetite?

MC4R is central to energy-homeostasis and satiety signaling, and MC4R loss-of-function is a common monogenic cause of obesity. Bremelanotide's MC4R agonism links it to appetite research and explains its transient cardiovascular (pressor) effect.

What safety findings are associated with it?

From the approved-drug record: a transient rise in blood pressure with a reflex heart-rate decrease, focal hyperpigmentation (more with frequent dosing and darker skin), and nausea as the most common adverse effect; it is not recommended with uncontrolled hypertension or cardiovascular disease.

Sources & References

Kingsberg SA, Clayton AH, Portman D, et al. "Bremelanotide for the Treatment of Hypoactive Sexual Desire Disorder: Two Randomized Phase 3 Trials." Obstet Gynecol. 2019;134(5):899-908. PubMed
Simon JA, Kingsberg SA, Portman D, et al. "Prespecified and Integrated Subgroup Analyses from the RECONNECT Phase 3 Studies of Bremelanotide." J Womens Health (Larchmt). 2022;31(3):391-400. PubMed
Clayton AH, Kingsberg SA, Portman D, et al. "Safety Profile of Bremelanotide Across the Clinical Development Program." J Womens Health (Larchmt). 2022;31(2):171-182. PubMed
Molinoff PB, Shadiack AM, Earle D, et al. "PT-141: a melanocortin agonist for the treatment of sexual dysfunction." Ann N Y Acad Sci. 2003;994:96-102. PubMed
Diamond LE, Earle DC, Rosen RC, 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(1):51-9. PubMed
Diamond LE, Earle DC, Heiman JR, et al. "An effect on the subjective sexual response in premenopausal women with sexual arousal disorder by bremelanotide (PT-141), a melanocortin receptor agonist." J Sex Med. 2006;3(4):628-638. PubMed
Pfaus JG, Shadiack A, Van Soest T, et al. "Selective facilitation of sexual solicitation in the female rat by a melanocortin receptor agonist." Proc Natl Acad Sci U S A. 2004;101(27):10201-4. PubMed
Giuliani D, Mioni C, Bazzani C, et al. "Selective melanocortin MC4 receptor agonists reverse haemorrhagic shock and prevent multiple organ damage." Br J Pharmacol. 2007;150(5):595-603. PubMed

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This product is intended for research and laboratory use only. It is not intended for human consumption.

Disclaimer: This content is provided for educational and informational purposes only. It is not intended as medical advice, nor does it constitute a recommendation for the treatment, cure, or prevention of any disease or condition. PT-141 is sold for research purposes only and is not intended for human consumption. Although bremelanotide is approved as a prescription drug (Vyleesi), the research-use material offered here is not a finished, approved drug product. Always consult a qualified healthcare professional before making decisions about your health. Somata Peptides does not claim that any products treat, cure, or prevent any disease.

PT-141: Melanocortin Agonist