MC4R is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Last reviewed on 2026-02-08. Where a claim depends on a specific study, the study is described rather than over-claimed.
Activation of MC4R in the hypothalamus is thought to influence dopaminergic signaling, which in turn affects arousal and desire. This mechanism differs from that of phosphodiesterase type 5 inhibitors, which act primarily on vascular smooth muscle in the genital region. Because the pathway is central rather than peripheral, effects are not strictly dependent on local blood flow. The precise downstream cascade linking receptor binding to behavioral outcomes remains an area of ongoing investigation.
Clinical development of bremelanotide proceeded through several reformulation attempts. An early intranasal version was discontinued, and a subcutaneous auto-injector formulation later received approval for hypoactive sexual desire disorder in premenopausal women. Approval decisions have varied by country and over time, and the product has not been universally adopted. Blood pressure elevation is a documented effect, which is why some jurisdictions require monitoring after administration. The clinical evidence base continues to evolve as additional studies are published.
Bremelanotide is a cyclic heptapeptide that acts as an agonist at melanocortin receptors. It binds MC1R, MC3R, MC4R, and MC5R, with MC4R activation considered most relevant to sexual desire pathways in the central nervous system. The molecule is a synthetic analog of alpha-melanocyte-stimulating hormone, a naturally occurring peptide involved in pigmentation and energy regulation. Early research explored its use in tanning before attention shifted toward sexual dysfunction applications. Receptor binding affinity varies across these subtypes.
Bremelanotide is a synthetic cyclic heptapeptide developed as an analogue of alpha-melanocyte-stimulating hormone, a naturally occurring peptide involved in pigmentation and appetite signalling. Its structure contains seven amino acid residues joined by a lactam bridge that closes the ring between two side chains. The molecular formula is C50H68N14O10 and the nominal molecular mass is near 1025 daltons. Much of the early laboratory literature refers to the same molecule by the development code PT-141.
The compound emerged from a research programme examining melanocortin analogues for effects on skin pigmentation. During early human studies, participants reported spontaneous erections as an unexpected side effect, which redirected development toward sexual function rather than tanning. An intranasal formulation was investigated in clinical trials but did not reach market approval. A subcutaneous injectable version later completed the regulatory process, and the nasal route does not appear in approved labelling.
| Property | Value | Notes |
|---|---|---|
| Molecular class | Cyclic heptapeptide | Melanocortin receptor agonist |
| Molecular weight | Approximately 1025 Da | Calculated from the peptide sequence |
| Appearance | White to off-white powder | Common for lyophilized peptide preparations |
| Solubility | Soluble in water | Also soluble in polar organic solvents |
| Storage temperature | -20 °C or below | Used for long-term retention |
PT-141 is a synthetic cyclic heptapeptide whose development code is bremelanotide. It belongs to the class of melanocortin receptor agonists and acts by mimicking endogenous peptide hormones. The compound originated from research on melanotan II, where investigators exploring derivatives found distinct pharmacological features. Unlike the parent compound, PT-141 showed effects on pathways related to sexual desire and function in early studies, prompting its development as a separate candidate. Its molecular design aimed to separate receptor activity from pigmentary effects.
The molecular backbone consists of seven amino acid residues joined into a ring through a disulfide bridge. This cyclic conformation is critical for receptor binding. The sequence includes an acetylated N-terminus and an amidated C-terminus, modifications that improve resistance to enzymatic breakdown. One residue is in the D-configuration, a feature that further stabilizes the peptide against protease activity. Together, the ring structure and specific stereochemistry determine selectivity among melanocortin receptor subtypes.
Across literature and commercial listings, the substance appears under several names, including bremelanotide, PT-141, and various brand designations. A CAS registry number provides a unique identifier for the compound, aiding retrieval from chemical databases. Synonym lists may also contain early development codes and descriptive chemical names. When consulting sources, researchers need to confirm that the cited names refer to the same molecular structure to avoid confusion. Naming consistency matters especially when comparing analytical data across publications.
Clinical programmes in this area have relied mainly on randomised, double-blind, placebo-controlled designs in premenopausal women. Primary endpoints usually combine a validated questionnaire covering desire domains with counts of satisfying sexual events and a separate measure of distress. Reported outcomes show statistically significant but modest average improvement over placebo, with wide individual variation. Adverse events such as nausea, flushing, and headache occur frequently and can limit tolerability. Whether short-term trial gains translate into lasting change for most users is an open question.
Evidence outside the studied population is sparse. Trials have concentrated on premenopausal women with a defined diagnosis, and data for postmenopausal women, men, and people taking interacting medications remain limited. Non-prescription use of the peptide for comparable goals is widespread but is not supported by published controlled data. Observed changes in blood pressure have drawn attention to cardiovascular monitoring during use. The literature generally frames the compound as a targeted receptor agonist rather than a general libido enhancer, and basic questions about mechanism and long-term safety are unresolved.
The compound binds several melanocortin receptor subtypes rather than a single target, with the strongest functional activity reported at MC4R and measurable activity at MC1R, MC3R and MC5R. MC4R populations are dense in hypothalamic nuclei that integrate energy balance, autonomic tone and reproductive behaviour, which is the anatomical basis for the proposed pro-desire effect. Because binding is not subtype-selective, pigmentary and vascular effects accompany central activity. Improving subtype selectivity is an active area of analogue design. Direct causal mapping from receptor occupancy to reported desire change in humans is not fully established.
After subcutaneous dosing, peak plasma concentrations appear within roughly one hour, and elimination is fast, with a half-life on the order of a few hours. Degradation is mainly proteolytic, and at least one circulating fragment retains receptor activity, so parent-drug levels alone do not describe total exposure. Clearance does not depend heavily on hepatic cytochrome enzymes, which lowers the likelihood of common metabolic interaction routes. Data in renal or hepatic impairment are limited. Repeated dosing does not appear to produce marked accumulation given the short half-life.
Reported pharmacodynamic effects include transient rises in blood pressure and heart rate, flushing, nausea and headache, appearing soon after dosing and resolving within hours. These responses were dose-related in early studies and shaped the label's cardiovascular cautions and blood pressure monitoring advice. Gastrointestinal upset is the most frequent reason cited for discontinuation in trials. Whether the vascular signal attenuates with repeated use is not settled. Central effects on desire are described as emerging over weeks rather than immediately, which points to a cumulative rather than acute process.
Early research on PT-141 grew out of work on melanotan II, a related cyclic peptide studied for pigmentation. Investigators observed that centrally acting melanocortin agonists also influenced sexual behaviour in animal models, and the programme shifted toward that endpoint. A nasal formulation was evaluated in clinical trials but showed inconsistent absorption, and later studies used subcutaneous administration instead. Regulatory approval in the United States followed in 2019 for a defined population of premenopausal women with acquired, generalised hypoactive sexual desire disorder. That approval was specific to that group rather than a broad indication.
Bremelanotide acts as a non-selective agonist at melanocortin receptors, with reported activity at MC1R, MC3R, MC4R and MC5R. The proposed basis for its central effects is activation of MC4R populations in the hypothalamus, a region associated with appetite and reproductive signalling. Because the peptide carries a net positive charge and polar side chains, it does not cross biological membranes freely, which is one reason oral administration is not the standard route. Effects generally appear within an hour of parenteral administration and are described as centrally mediated rather than peripheral.
Bremelanotide, developed under the code PT-141, is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone. Its structure is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, with a lactam bridge joining the aspartate and lysine side chains. The molecule has the formula C50H68N14O10 and a monoisotopic mass near 1025 daltons. It is commonly prepared as the acetate salt and appears as a white to off-white lyophilised powder in solid form. The free acid is the pharmacologically relevant species, while the counter-ion improves handling and dissolution.
In plants and most microorganisms, tyrosine is produced via prephenate, an intermediate on the shikimate pathway. Prephenate is oxidatively decarboxylated with retention of the hydroxyl group to give p-hydroxyphenylpyruvate, which is transaminated using glutamate as the nitrogen source to give tyrosine and α-ketoglutarate. Mammals synthesize tyrosine from the essential amino acid phenylalanine (Phe), which is derived from food. The conversion of Phe to Tyr is catalyzed by the enzyme phenylalanine hydroxylase, a monooxygenase. This enzyme catalyzes the reaction causing the addition of a hydroxyl group to the end of the 6-carbon aromatic ring of phenylalanine, such that it becomes tyrosine.
=== Diplomatic means === A key element of US political, military and energy economic planning occurred in 1984. The Iran–Iraq war had been going on for five years and both had sustained casualties into the hundreds of thousands. Within President Ronald Reagan's National Security Council concern was growing war could spread beyond the two belligerents. A National Security Planning Group meeting was formed, chaired by then vice president George H. W. Bush, to review US options. It was determined that the conflict would likely spread into Saudi Arabia and other Gulf states, but the US had little capability to defend the region. A prolonged war in the region would induce much higher oil prices and threaten the recovery of the world economy, which was just beginning to gain momentum. In May 1984, President Reagan was briefed on the project conclusions by William Flynn Martin who had served as the head of the NSC staff that organized the study. The conclusions were: first, oil stocks needed to be increased among members of the International Energy Agency and, if necessary, released early if the oil market was disrupted; second, the US needed to strengthen the security of friendly Arab states in the region; and third, an embargo should be placed on sales of military equipment to Iran and Iraq. The plan was approved by Reagan and affirmed by the G7 leaders headed by the UK's prime minister, Margaret Thatcher, in the 10th G7 summit, held in London in June. The plan was implemented and became the basis for US preparedness to respond to the Iraqi occupation of Kuwait in 1991.
2C-EF is metabolized by monoamine oxidase (MAO) enzymes, including monoamine oxidase A (MAO-A) and/or monoamine oxidase B (MAO-B). Monoamine oxidase inhibitors (MAOIs) such as phenelzine, tranylcypromine, moclobemide, and selegiline may potentiate the effects of 2C-EF. This may result in overdose and serious toxicity.
Sources: en.wikipedia.org
Early experiments resembling activity-based profiling were conducted in the 1970s, when small molecules were used to study the mechanism of action of the serine-modifying antibiotic penicillin. The modern era of ABPP began in the 1990s with the development of ABPs compatible with proteomic workflows, and the first applications of ABPP were reported during this decade in studies of proteases. In 1999, the Cravatt lab formally introduced the term "activity-based protein profiling," establishing a framework for systematic functional proteomics. Subsequent work by Ben Cravatt at The Scripps Research Institute, Matthew Bogyo at Stanford University, and Herman S. Overkleeft at Leiden University helped define the field through the design of probes targeting serine hydrolases, cysteine proteases, oxidoreductases, human cytochrome P450s and other enzyme families. Since its inception, ABPP has expanded rapidly, with bibliometric analyses documenting exponential growth in publications and widespread adoption across North America, Europe, and Asia. Advances in mass spectrometry and protein separation technologies further accelerated the integration of ABPP into proteomic research, enabling the characterization of enzyme activity on a global scale and establishing ABPP as a cornerstone of functional proteomics.
The phenolic ring that is indispensable for binding to estrogen receptor The ring of isoflavones mimicking a ring of estrogens at the receptors binding site Low molecular weight similar to estrogens (MW=272) Distance between two hydroxyl groups at the isoflavones nucleus similar to that occurring in estradiol Optimal hydroxylation pattern In addition to interaction with ERs, phytoestrogens may also modulate the concentration of endogenous estrogens by binding or inactivating some enzymes, and may affect the bioavailability of sex hormones by depressing or stimulating the synthesis of sex hormone-binding globulin (SHBG). Emerging evidence shows that some phytoestrogens bind to and transactivate peroxisome proliferator-activated receptors (PPARs). In vitro studies show an activation of PPARs at concentrations above 1 μM, which is higher than the activation level of ERs. At the concentration below 1 μM, activation of ERs may play a dominant role. At higher concentrations (>1 μM), both ERs and PPARs are activated. Studies have shown that both ERs and PPARs influence each other and therefore induce differential effects in a dose-dependent way. The final biological effects of genistein are determined by the balance among these pleiotrophic actions.
Auto-oxidation reaction is also observed with common ethers, such as diethyl ether, diisopropyl ether, tetrahydrofuran, and 1,4-dioxane. An illustrative product is diethyl ether peroxide. Such compounds can result in a serious explosion when distilled. To minimize this problem, commercial samples of THF are often inhibited with butylated hydroxytoluene (BHT). Distillation of THF to dryness is avoided because the explosive peroxides concentrate in the residue. Although ether hydroperoxide often form adventitiously (i.e. autoxidation), they can be prepared in high yield by the acid-catalyzed addition of hydrogen peroxide to vinyl ethers: C2H5OCH=CH2 + H2O2 → C2H5OCH(OOH)CH3 Many industrial peroxides are produced using hydrogen peroxide. Reactions with aldehydes and ketones yield a series of compounds depending on conditions. Specific reactions include addition of hydrogen peroxide across the C=O double bond: R2C=O + H2O2 → R2C(OH)OOH In some cases, these hydroperoxides convert to give cyclic diperoxides:
Sources: en.wikipedia.org
PT-141 is the research code for bremelanotide, a cyclic peptide developed as a melanocortin receptor agonist. The code has appeared in literature and catalog listings since early development. Bremelanotide is the international nonproprietary name.
PDE5 inhibitors act on peripheral vascular tissue to increase blood flow. Bremelanotide acts centrally on melanocortin receptors and is associated with dopaminergic pathways. The two approaches therefore target different parts of the arousal response.
It is a synthetic peptide analog rather than a hormone produced by the body. Alpha-melanocyte-stimulating hormone is the natural peptide it resembles. The two share structural features but are distinct molecules.
It is a synthetic cyclic peptide that acts as an agonist at melanocortin receptors. It is not a hormone replacement therapy and not a vasodilator in the usual clinical sense, although it does affect vascular tone. Chemically it belongs to the melanocortin analogue family.