This is a working overview of MC4R, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2025-12-23. Anything still debated is marked as such rather than presented as settled.
Development of the peptide passed through several delivery formats, including an intranasal version tested in early trials and an injectable version that entered later clinical study. Regulatory approval for a subcutaneous product in the United States was granted in 2019 after review of controlled trials in premenopausal women. Outside the clinic, the compound circulates in research and non-pharmaceutical markets under its code name, where identity and purity vary considerably between suppliers. Synonyms appearing across technical literature include bremelanotide, PT-141, and Palatin 141.
PT-141 is the research designation for bremelanotide, a synthetic cyclic heptapeptide developed as a melanocortin receptor agonist. The peptide contains seven amino acids with an internal lactam bridge that constrains the backbone into a stable ring. Cyclisation of this kind improves resistance to enzymatic degradation relative to linear analogues. The compound was first explored for effects on melanin production, because several melanocortin receptors influence pigmentation. Its later association with sexual desire emerged from observations made during that early work, and the molecule became the subject of a separate development programme.
Bremelanotide is a moderately large peptide with a molecular mass near 1025 daltons. In lyophilised form it appears as a white to off-white powder and is freely soluble in water and other polar solvents. The intact lactam ring is essential for receptor affinity, while linearised fragments bind far more weakly. Solutions are sensitive to extremes of pH and to prolonged exposure to light and heat, so handling typically involves buffered conditions and cold storage. Its short plasma half-life reflects rapid distribution and clearance rather than chemical breakdown inside the vial.
Development began with intranasal formulations investigated for erectile dysfunction, but blood pressure elevation limited that route and prompted a switch to subcutaneous delivery. Clinical testing then shifted toward hypoactive sexual desire disorder in premenopausal women, and a subcutaneous product received United States approval in 2019. Later trials examined other populations with mixed results, and questions about effect size, durability and patient selection remain open in the peer-reviewed literature. Research interest continues in parallel with the broader melanocortin field, where several synthetic analogues are studied together.
PT-141 is the research code for bremelanotide, a cyclic heptapeptide derived from alpha-melanocyte-stimulating hormone. The molecule belongs to the melanocortin receptor agonist family and shows highest affinity for the MC4 receptor subtype, with weaker activity at MC1, MC3 and MC5. Its structure retains the core His-Phe-Arg-Trp sequence that defines melanocortin recognition, while cyclization and terminal modifications improve metabolic stability relative to the parent hormone. Early work classified the compound as a centrally acting agent rather than a peripherally acting vasodilator, which shaped subsequent development priorities.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Cyclic heptapeptide | Synthetic melanocortin analogue |
| Molecular formula | C50H68N14O10 | Corresponds to a mass near 1025 daltons |
| Appearance | White to off-white powder | Lyophilised solid before reconstitution |
| Solubility | Soluble in water and polar solvents | Poor solubility in nonpolar media |
| Common synonyms | Bremelanotide, PT-141 | Code name and international name used interchangeably |
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.
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.
How receptor activation translates into a change in desire is not established in detail. Proposed steps include modulation of dopaminergic signalling in reward circuits and downstream effects on autonomic tone. Human data consist mainly of clinical trials measuring self-reported outcomes rather than direct measurements of brain activity or transmitter release. The transient rise in blood pressure sometimes observed after administration is likewise reported consistently but explained only partly by known melanocortin pathways.
Melanocortin receptors form a family of five G-protein-coupled proteins, labelled MC1R through MC5R, that respond to peptides derived from pro-opiomelanocortin. Alpha-melanocyte-stimulating hormone and adrenocorticotropic hormone are the best-known endogenous ligands. The receptors are distributed differently across tissues, so a single agonist can produce effects in the brain, skin, adrenal gland and vasculature. This distribution explains why one peptide can influence both pigmentation and motivated behaviour.
=== Societies and administration === The International Union of Basic and Clinical Pharmacology, Federation of European Pharmacological Societies, and European Association for Clinical Pharmacology and Therapeutics are organizations representing standardization and regulation of clinical and scientific pharmacology. Systems for medical classification of drugs with pharmaceutical codes have been developed. These include the National Drug Code (NDC), administered by Food and Drug Administration; Drug Identification Number (DIN), administered by Health Canada under the Food and Drugs Act; Hong Kong Drug Registration, administered by the Pharmaceutical Service of the Department of Health (Hong Kong), and National Pharmaceutical Product Index in South Africa. Hierarchical systems have also been developed, including the Anatomical Therapeutic Chemical Classification System (AT, or ATC/DDD), administered by World Health Organization; Generic Product Identifier, a hierarchical classification number published by MediSpan and SNOMED, C axis. Ingredients of drugs have been categorized by Unique Ingredient Identifiers.
== Ion and atom sources == Sources can be adapted in many ways, but the lists below give the general uses of a number of sources. Of these, flames are the most common due to their low cost and their simplicity. Although significantly less common, inductively-coupled plasmas, especially when used with mass spectrometers, are recognized for their outstanding analytical performance and their versatility. For all atomic spectroscopy, a sample must be vaporized and atomized. For atomic mass spectrometry, a sample must also be ionized. Vaporization, atomization, and ionization are often, but not always, accomplished with a single source. Alternatively, one source may be used to vaporize a sample while another is used to atomize (and possibly ionize). An example of this is laser ablation inductively-coupled plasma atomic emission spectrometry, where a laser is used to vaporize a solid sample and an inductively-coupled plasma is used to atomize the vapor. With the exception of flames and graphite furnaces, which are most commonly used for atomic absorption spectroscopy, most sources are used for atomic emission spectroscopy. Liquid-sampling sources include flames and sparks (atom source), inductively-coupled plasma (atom and ion source), graphite furnace (atom source), microwave plasma (atom and ion source), and direct-current plasma (atom and ion source). Solid-sampling sources include lasers (atom and vapor source), glow discharge (atom and ion source), arc (atom and ion source), spark (atom and ion source), and graphite furnace (atom and vapor source).
In January 1977, four years prior to becoming president, Ronald Reagan bluntly stated, in a conversation with Richard V. Allen, his basic expectation in relation to the Cold War. "My idea of American policy toward the Soviet Union is simple, and some would say simplistic," he said. "It is this: We win and they lose." In 1980, Ronald Reagan won the 1980 presidential election, vowing to increase military spending and confront the Soviets everywhere. Both Reagan and new British Prime Minister Margaret Thatcher denounced the Soviet Union and its ideology. Reagan labeled the Soviet Union an "evil empire" and predicted that communism would be left on the "ash heap of history," while Thatcher inculpated the Soviets as "bent on world dominance." In 1982, Reagan tried to cut off Moscow's access to hard currency by impeding its proposed gas line to Western Europe. It hurt the Soviet economy, but it also caused ill will among American allies in Europe who counted on that revenue. Reagan retreated on this issue. By early 1985, Reagan's anti-communist position had developed into a stance known as the new Reagan Doctrine—which, in addition to containment, formulated an additional right to subvert existing communist governments. Besides continuing Carter's policy of supporting the Islamic opponents of the Soviet Union and the Soviet-backed PDPA government in Afghanistan, the CIA also sought to weaken the Soviet Union itself by promoting Islamism in the majority-Muslim Central Asian Soviet Union.
Subsequent follow-up recessions in 2010–2013 were confined to Belize, El Salvador, Paraguay, Jamaica, Japan, Taiwan, New Zealand and 24 out of 50 European countries (including Greece). As of October 2014, only five out of the 71 countries with available quarterly data (Cyprus, Italy, Croatia, Belize and El Salvador), were still in ongoing recessions. The many follow-up recessions hitting the European countries, are commonly referred to as being direct repercussions of the European debt crisis.
=== Epstein-Barr virus === The Epstein-Barr virus (EBV) infects about 90 to 95% of adults and can cause infectious mononucleosis. A study of more than 10 million US military members compared 801 people who developed MS to 1,566 matched controls who did not. The study found a 32-fold increased risk of MS development following EBV infection. It did not find an increased risk after infection with other viruses, including the similar cytomegalovirus. These findings strongly suggest that EBV is necessary for MS onset, although EBV alone may be insufficient to cause it. The nuclear antigen of EBV, which is the most consistent marker of EBV infection across all strains, has been identified as a direct source of autoreactivity in the human body. These antigens appear more likely to promote autoimmunity in vitamin D deficient persons. The EBV protein EBNA1 shares similarities with three human proteins, including the brain protein GlialCAM. Because of molecular mimicry, the immune system in MS mistakenly may attack these proteins. Two are part of the nervous system, while the third is a "guardian molecule" which protects the body against autoimmunity.
Sources: en.wikipedia.org
Macromolecules cannot be directly processed by cells. Macromolecules must be broken into smaller units before they can be used in cell metabolism. Different classes of enzymes are used to digest these polymers. These digestive enzymes include proteases that digest proteins into amino acids, as well as glycoside hydrolases that digest polysaccharides into simple sugars known as monosaccharides. Microbes simply secrete digestive enzymes into their surroundings, while animals only secrete these enzymes from specialized cells in their guts, including the stomach, pancreas, and salivary glands. The amino acids or sugars released by these extracellular enzymes are then pumped into cells by active transport proteins.
Fibrous papules are also termed facial angiofibromas and were formerly and incorrectly termed adenoma sebaceum (fibrous papules are unrelated to sebaceous glands). They develop in up to 8% of the general adult population and occur as 1 to 3 pink to red, dome-shaped papules in the central areas of the face, nose, and/or lips. About 75% of individuals with tuberous sclerosis present with fibrous papules in their infancy or early childhood; when associated with this rare disease, the lesions often occur as multiple papules in symmetrical, butterfly-shaped patterns over both cheeks and the nose. Fibrous papules also occur in individuals with multiple endocrine neoplasia type 1 (a study done in Japan found that 43% of individuals with this genetic disease bore facial angiofibromas) and, uncommonly, in individuals with Birt-Hogg-Dube syndrome.
The first berkelium metal sample weighing 1.7 micrograms was prepared in 1971 by the reduction of berkelium(III) fluoride with lithium vapor at 1000 °C; the fluoride was suspended on a tungsten wire above a tantalum crucible containing molten lithium. Later, metal samples weighing up to 0.5 milligrams were obtained with this method.
=== Rockefeller Mandatory Minimum Drug Laws === In 1973, New York Governor Nelson Rockefeller passed the nation's first mandatory minimum drug laws. Increasing pressure from the failed treatment programs in New York's most drug-addicted cities, Rockefeller introduced mandatory minimum drug laws. Rockefeller, according to New York District Attorney Arthur Rosenblatt, had been a champion of rehabilitation treatment methods as governor but now felt that those policies were failing, turned to the "tough on crime" ideas of Nixon, and introduced the new laws to his state. The laws called for mandatory prison sentences of 15 years to life for drug dealers. Rosenblatt testified that addict or casual users, or anyone else found in possession of even trace amounts of marijuana, cocaine, or heroin were eligible for a prison sentence and that almost immediately, there was a disproportionate rate of arrest and incarceration in urban and minority neighborhoods. Whites were using and selling drugs at similar rates to blacks, but minorities disproportionately went to prison. Rockefeller would become vice president under President Gerald Ford after the resignation of Nixon.
Sources: en.wikipedia.org
PT-141 is a laboratory code for bremelanotide, a synthetic peptide that activates melanocortin receptors. It has been developed both as an injectable pharmaceutical product and as a research chemical. The two contexts differ sharply in how identity, purity, and dosing are controlled.
It is neither a steroid nor a naturally occurring human hormone. Bremelanotide is a manufactured peptide that mimics part of the melanocortin signalling system by binding receptor proteins. Its effects come from receptor activation, not from replacing a circulating hormone.
The internal lactam bridge locks the peptide into a defined shape, which raises receptor affinity and slows enzymatic breakdown. Linear versions of the same sequence are less stable and bind more weakly. Ring geometry is therefore central to how the molecule behaves in the body.
The code designates bremelanotide, a cyclic heptapeptide melanocortin receptor agonist. It served as an internal research identifier before the compound entered formal clinical development. The code and the generic name refer to the same molecule.