If you have been reading about MC1R and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-02-02. Numbers and descriptions here follow the published literature rather than marketing material.
Receptor-binding studies classify melanotan II as a non-selective melanocortin agonist. It interacts with MC1R, MC3R, MC4R and MC5R, with reported affinities in the low nanomolar range and no strong subtype preference. Activation of MC1R on dermal melanocytes shifts pigment synthesis toward eumelanin, the dark polymer deposited in melanosomes and transferred to keratinocytes. Because the same peptide engages MC4R in the hypothalamus, it also appears in animal work on food intake and erectile response, which is why it is discussed in both pigment and metabolic research. Which receptor populations dominate after systemic exposure in humans is not fully established.
Published pharmacokinetic information is limited and comes mainly from small studies rather than registrational trials. Plasma half-life is usually described as short, on the order of tens of minutes, followed by rapid tissue distribution and clearance of the intact peptide. Metabolites and low concentrations of parent compound have been reported in urine, a detail relevant to anti-doping and forensic testing. Whether repeated exposure changes receptor sensitivity or clearance over time remains an open question. Values differ noticeably between analytical assays, so published numbers should be read as approximate rather than definitive.
Melanotan II is a synthetic cyclic heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, corresponding to a molecular formula of C50H69N15O9 and a monoisotopic mass near 1024 daltons. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, a peptide hormone produced by cleavage of proopiomelanocortin. A lactam bridge between the aspartate and lysine side chains closes the ring, and the C-terminal amide removes a free carboxyl group. Both modifications increase resistance to enzymatic degradation compared with the linear parent hormone. Four substitutions distinguish it from afamelanotide, the linear analogue studied under the name melanotan I.
Outside regulated medicine, melanotan II circulates through online vendors as a research chemical, often marketed for tanning. Products sold this way vary widely in purity, concentration, and labeling accuracy, and independent testing has documented discrepancies. Published reports describe both pigment effects and adverse reactions, including nausea, flushing, and darkening of existing moles. Long-term safety data are sparse, and no large controlled trial has established a risk profile. Questions about cumulative effects on melanocytes remain unresolved in the literature.
Melanotan II is a synthetic peptide analog modeled on alpha-melanocyte-stimulating hormone, a naturally occurring signaling peptide involved in pigmentation. Its structure is a cyclic heptapeptide containing two non-natural substitutions, norleucine at position four and D-phenylalanine at position seven. These modifications resist enzymatic breakdown and extend the molecule's activity relative to the native hormone. The compound binds melanocortin receptors and is studied mainly as a pharmacological tool rather than a therapeutic product. It has never received approval as a medicine in any major jurisdiction.
The compound was developed in the late 1980s and 1990s by academic researchers investigating photoprotection. The rationale held that stimulating melanin production might reduce ultraviolet damage to skin and lower skin cancer risk. Early work examined receptor binding, pigment response, and short-term tolerability in small studies. That program did not produce an approved drug, and formal development stalled after early-phase trials. Whether induced pigmentation confers meaningful photoprotection remains an open question.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C50H69N15O9 | Cyclic heptapeptide, C-terminally amidated |
| Approximate molecular mass | 1024 Da | Monoisotopic mass of the free peptide |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility class | Soluble in water and polar solvents | Also dissolves in neutral aqueous buffer |
| Common synonyms | Melanotan II, MT-II, MT-2 | Described as a melanocortin agonist in early literature |
Melanocytes are the pigment-producing cells of the skin, and they carry melanocortin-1 receptors on their surface. When the receptor is activated, cyclic adenosine monophosphate rises inside the cell and raises the activity of enzymes such as tyrosinase, which increases melanin output. Melanotan-2 binds melanocortin-1 receptors in vitro and in animal models, and this binding is generally described as the basis for the tanning effect. Other receptors account for different effects: melanocortin-4 receptors contribute to appetite and erectile signalling, while melanocortin-3 and melanocortin-5 receptors contribute to energy balance and exocrine function.
Early published reports described melanotan-2 as a tanning agent without sun protection, which means darkening is not the same as protection against ultraviolet radiation. Later studies explored the peptide in erectile dysfunction, hemorrhagic shock, and some skin conditions. No regulator in the United States or Europe has approved it for clinical use. Many products labelled melanotan-2 are sold without approval and their identity and purity are unverified. Its long-term safety in humans remains an open question.
The prevalent in political circles nationalism was fueled by the large size of Poland's minority populations and their separate agendas. According to the language criterion of the Polish census of 1931, the Poles constituted 69% of the population, Ukrainians 15%, Jews (defined as speakers of the Yiddish language) 8.5%, Belarusians 4.7%, Germans 2.2%, Lithuanians 0.25%, Russians 0.25% and Czechs 0.09%, with some geographical areas dominated by a particular minority. In time, the ethnic conflicts intensified, and the Polish state grew less tolerant of the interests of its national minorities. In interwar Poland, compulsory free general education substantially reduced illiteracy rates, but discrimination was practiced in a way that resulted in a dramatic decrease in the number of Ukrainian language schools and official restrictions on Jewish attendance at selected schools in the late 1930s. The population grew steadily, reaching 35 million in 1939. However, the overall economic situation in the interwar period was one of stagnation. There was little money for investment inside Poland, and few foreigners were interested in investing there. Total industrial production barely increased between 1913 and 1939 (within the area delimited by the 1939 borders), but because of population growth (from 26.3 million in 1919 to 34.8 million in 1939), the per capita output actually decreased by 18%.
=== Historical evidence against balance of power theory === A 2021 assessment by Morten Skumsrud Andersen and William C. Wohlforth concluded that balance of power is not a universal empirical law and that it does not merit explanatory precedence in international relations research. In an attempt to disprove the balance of power theory, some realists have pointed to cases in international systems other than modern Europe where balancing failed and a hegemon arose. A collaboration between nine scholars (William Wohlforth, Richard Little, Stuart J. Kaufman, David Kang, Charles A. Jones, Victoria Tin-Bor Hui, Arthur Eckstein, Daniel Deudney, and William L. Brenner) pointed to the failure of state-like units to balance against Assyria in the first millennium BCE; the Hellenic successor states of Alexander the Great to balance against Rome; the Warring States to balance against the Qin dynasty in ancient China and five other cases. This cross-cultural research concludes:
== Early life and education == Susan Epstein (later changed to Leeman by marriage) was born on May 9, 1930, in Chicago, Illinois. Her mother was born in the United States and her father had emigrated from Russia to New York City. Her father was an academic metallurgist and her mother attended college at George Washington University at a time when few other women did. Susan also had one older brother named Henry. When Susan was six weeks old she and her family moved to Columbus, Ohio, and then to Bethlehem, Pennsylvania when she was six years old. There she grew up a part of a middle class Jewish family. She often faced discrimination in the form of antisemitism and sexism as she pursued a career in science. During her childhood Leeman attended Hebrew School and was a Girl Scout. She decided to attend Goucher College, which was an all-girls’ school at the time, from which she received a bachelor's degree in physiology in 1951. She then applied to and was accepted by Harvard Medical School, but her academic program was administered through Radcliffe College. Thus, Radcliffe College was where she received her master's degree and PhD from in 1954 and 1958 respectively. Leeman was the only woman in her class to make it through the graduate program and continue a career in science. During her time in graduate school she was introduced to the field of neuroendocrinology, within which she was able to explore her passion for how the mind connects to the body.
== External links == IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "nitrile". doi:10.1351/goldbook.N04151 IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "cyanide". doi:10.1351/goldbook.C01486
Because β-alanine dipeptides are not incorporated into proteins, they can be stored at relatively high concentrations. Occurring at 17–25 mmol/kg (dry muscle), carnosine (β-alanyl-L-histidine) is an important intramuscular buffer, constituting 10-20% of the total buffering capacity in type I and II muscle fibres. In carnosine, the pKa of the imidazolium group is 6.83, which is ideal for buffering.
Sources: en.wikipedia.org
At the third AU summit, held in Tripoli, Libya, in July 2005, Gaddafi called for greater integration, advocating a single AU passport, a common defence system, and a single currency, using the slogan: "The United States of Africa is the hope." His proposal for a Union of African States, a project originally conceived by Ghana's Kwame Nkrumah in the 1960s, was rejected at the 2001 Assembly of Heads of States and Government (AHSG) summit in Lusaka by African leaders who thought it "unrealistic" and "utopian". In June 2005, Libya joined the Common Market for Eastern and Southern Africa (COMESA). In March 2008 in Uganda, Gaddafi gave a speech once again urging Africa to reject foreign aid. In August 2008, Gaddafi was proclaimed "King of Kings" by a committee of traditional African leaders; they crowned him in February 2009, in a ceremony held in Addis Ababa, Ethiopia. That same month, Gaddafi was elected as the chairperson of the African Union, a position he retained for one year. In October 2010, Gaddafi apologized to African leaders for the historical enslavement of Africans by the Arab slave trade.
=== Amphibian === The unfertilized oocyte of a frog, or Xenopus laevis, has also been utilized as an expression system for heterologous expression. Initially used to express the acetylcholine receptor in 1982, since then it has been used for a variety of reasons. These oocytes are produced by frogs year round and thus are relatively abundant, and translation occurs with high fidelity. Of the many limitations to the oocyte system, one major one is that the produced heterologous proteins interact with the frog oocyte's proteins which changes its behavior compared to what it would be in a mammalian cell. Additionally, where mammals are diploid, these xenopus have four homologous copies of each chromosome and thus, proteins derived may have a different function. More research is needed to examine the protein production of X. laevis systems.
=== Endogenous role === DMT exists naturally in humans and other animals; it may play significant roles in mammalian physiology—potentially as a neurotransmitter, hormone, and immunomodulator—despite longstanding skepticism based on outdated or flawed evidence.
== Cast == Johnathon Schaech as Justin Wise Sarah Lancaster as Elli Wise Taegen Burns as Maddie Wise A Martinez as Connor McGrath Avianna Mynhier as Maxine 'Maxx' Covington Greg Perrow as Deputy R.P. Ericsson Tom Proctor as Jeremiah Wade Lev Cameron as Blade Wade Odessa Feaster as Mayor Brady Grayson Russell as Dwayne Dixon Burgess Jenkins as Ryan Lucas
Sources: en.wikipedia.org
McCoy warned that, if China's numerous breaches on Taiwan become "a crippling embargo of Taiwan", the US would lose Taiwan, risking a break of "America's island chain in the Pacific littoral, pushing it back to a 'second island chain' in the mid-Pacific", regardless of the US's decisions on Taiwan. He further cited growing anti-American sentiment in the Philippines, the opposition toward AUKUS (trilateral security partnership between Australia, the United Kingdom, and the United States) from certain members of the Labor Party as a threat to Australia's sovereignty, and the Republican Party populism in the US under Trump (or his successor-in-line JD Vance) potentially curtailing the US's ability to maintain its alliance with the Asia-Pacific countries. In January 2025, almost two weeks before Biden ended his term, Hoover Institution senior fellow Niall Ferguson wrote that the US has had "a second cold war" with China for at least six years and that the war further intensified under the Biden administration. Ferguson drew comparisons between Trump and then-US president Ronald Reagan, like assassination attempts on them, but further suggested that Trump use the Reagan administration's past approach in foreign policy.
Emboldened by the footage, Aditya gets reinstated by the police by proving his physical and mental stability. He then traces Ajay's true biological origins to Hari. Attempting to evade Aditya, Hari organises the murders of numerous police officers. Undeterred, Aditya traces Hari's location to an old office building of Mumbai Media that media tycoon Pramod Gupta owns, who is one of Hari's associates. With the help of the police, Aditya launches a raid on the complex. He kills Hari's goons and captures Gupta but fails to capture Hari, who retreats to the site of his earlier massacre and lures Aditya by holding the families of the murdered police officers hostage at gunpoint. Aditya fights with Hari and wins. Hari attempts to shoot Aditya, but he throws a knife at Hari's neck then stabs him repeatedly to death. As Aditya walks out of the police station, a young boy dressed in a police uniform looks at him and salutes with a smile. Aditya returns the smile and salute.
== Signs and symptoms == In one of the few reported cases, the subject presented with muscle weakness and fatigue, muscle twitching, excessive sweating and salivation, small joint pain, itching and weight loss. The subject also developed confusional episodes with spatial and temporal disorientation, visual and auditory hallucinations, complex behavior during sleep and progressive nocturnal insomnia associated with diurnal drowsiness. There was also severe constipation, urinary incontinence, and excessive lacrimation. When left alone, the subject would slowly lapse into a stuporous state with dreamlike episodes characterized by complex and quasi-purposeful gestures and movements (enacted dreams). Marked hyperhidrosis and excessive salivation were evident. Neurological examination disclosed diffuse muscle twitching and spontaneous and reflex myoclonus, slight muscle atrophy in the limbs, absence of tendon reflexes in the lower limbs and diffuse erythema especially on the trunk with scratching lesions of the skin. Compulsive behaviours, stereotypies and reduplicative paramnesias can be part of the CNS spectrum.
== References == Albert Szent-Györgyi et al.: The role of chemistry in the evolution of molecular medicine. Szeged, 2004, pp. 694–695. A Magyar Tudományos Akadémia tagjai 1825–2002 II [Members of the Hungarian Academy of Sciences 1825-2002]. Budapest, 2003, pp. 676–677.
=== Europe === The prevalence of congenital corneal opacities (CCO) is estimated to be 3 in 100,000 newborns. This number increases to 6 in 100,000 if congenital glaucoma patients are included. A study of live births in Spain reported that corneal opacities accounted for 3.11% of congenital eye malformations (Bermejo et al, 1998). About 4% of keratoplasties done in the pediatric population in Denmark are due to congenital anomalies (Hovlykke et al, 2014).
Sources: en.wikipedia.org
No. It is a synthetic analogue carrying four amino acid changes, a lactam ring and an amidated C-terminus. The natural hormone is a linear thirteen-amino-acid peptide processed from proopiomelanocortin.
Afamelanotide is the linear analogue [Nle4-D-Phe7]-alpha-MSH, sometimes called melanotan I, while melanotan II is cyclic and carries three further substitutions. The two are distinct molecules and are not interchangeable in analytical testing.
Binding to the four melanocortin receptor subtypes is well documented in vitro. The relative contribution of each subtype to whole-body effects in humans is far less certain.
It is a synthetic cyclic peptide designed as an analog of alpha-melanocyte-stimulating hormone. It acts on melanocortin receptors and is best known from research into pigmentation. It is not an approved pharmaceutical product.