A practical reference on cyclic peptide: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-08-22. Anything still debated is marked as such rather than presented as settled.
Activity is attributed to agonism at melanocortin receptors, particularly MC1R and MC4R. Activation of MC1R on melanocytes increases melanin synthesis, which underlies the reported tanning effect. MC4R engagement in the central nervous system is linked to appetite suppression and to effects on sexual arousal reported in early clinical studies. Those studies were small and were not designed to establish efficacy or long-term safety. Receptor selectivity among the melanocortin subtypes is not absolute, which complicates attribution of any effect to a single pathway.
Regulatory treatment varies between countries. Several national medicines agencies have classified the peptide as unapproved, and customs authorities in some jurisdictions seize shipments on that basis. A few jurisdictions channel supply through prescription-only frameworks that do not list the substance by name. Because the material circulates mainly through online vendors, composition and purity are rarely verified before sale. Surveys of unapproved peptide products have reported labels that did not match measured content in a substantial fraction of samples.
Melanotan II is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, a naturally occurring peptide involved in pigmentation signalling. Its structure substitutes a lactam bridge between side chains to increase stability relative to the native hormone. The compound is also known by the shorthand MT-II and by several non-proprietary synonyms used in research catalogues. It is not an approved therapeutic product in any major jurisdiction; material sold under this name is typically offered as a laboratory reagent rather than as a medicine.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Analogue of alpha-melanocyte-stimulating hormone |
| Common synonyms | MT-II; melanotan 2 | No internationally accepted non-proprietary name |
| Typical presentation | Lyophilised powder in a sealed vial | Often supplied alongside a separate diluent |
| Regulatory status | Unapproved therapeutic substance | Customs seizure reported in several jurisdictions |
| Reported route in use | Subcutaneous injection | Self-administered outside clinical settings |
Melanotan-2 is a synthetic peptide designed as an analog of alpha-melanocyte-stimulating hormone, a signaling molecule produced in the pituitary and skin. Its structure is a linear chain of seven amino acids that folds into a ring through an internal lactam bridge joining two side chains. The compound is sometimes written as MT-II or MEL-2 in informal and commercial contexts. It belongs to the melanocortin peptide family, a group of short signaling molecules that share a conserved core sequence recognized by melanocortin receptors.
Two structural changes distinguish the synthetic peptide from the natural hormone. A norleucine residue replaces methionine at one position, and a D-configured phenylalanine replaces the natural L-form at another. Both substitutions slow enzymatic breakdown, which extends the molecule's persistence relative to the parent hormone. The lactam bridge further constrains the backbone into a stable conformation. These features are standard design strategies in peptide chemistry and are not unique to this compound; they appear across many research peptides built for improved stability.
The compound was developed in the late 1980s and early 1990s by academic researchers investigating melanocortin signaling and pigmentation. Early work explored whether synthetic analogs could reproduce effects of the natural hormone under controlled conditions. The molecule never advanced through the full regulatory pathway required for approval as a medicine. From the mid-2000s onward it appeared in unregulated consumer markets, often distributed through informal channels. That gap between research origins and commercial availability shapes how the compound is discussed today.
Receptor studies place melanotan-2 among non-selective melanocortin agonists, binding MC1R, MC3R, MC4R and MC5R rather than a single subtype. Activation of MC1R on cutaneous melanocytes raises tyrosinase activity and shifts pigment synthesis toward eumelanin, which is darker and more photostable than pheomelanin. Central receptors, particularly MC4R, are associated with appetite suppression and with reported effects on sexual function. Because subtype selectivity is low, the same molecule engages pigment, metabolic and vascular pathways at once, and this breadth is a common explanation offered for the range of adverse events described in user reports.
No regulatory authority has approved melanotan-2 for human use, and several countries classify it as a prescription-only or controlled substance, which restricts lawful supply. Material sold online is generally labelled as a research chemical and is not required to meet pharmaceutical standards of identity or purity. Published human data consist mainly of small uncontrolled studies, case reports and adverse-event notifications, so the evidence base is descriptive rather than confirmatory. Whether repeated melanocyte stimulation alters long-term naevus behaviour remains an open question that no completed trial has resolved.
Published human data come mostly from small, short studies rather than large controlled trials. Reported outcomes include increased skin pigmentation and, in some reports, effects on appetite and libido, but sample sizes are small and follow-up is limited. Whether long-term use produces durable pigment changes or adverse effects is not established. Because products sold outside pharmacies are not standardized, the actual content of any given vial is often unknown. Independent testing of such material is uncommon.
Melanotan II is a synthetic cyclic heptapeptide analog derived from the core sequence of alpha-melanocyte-stimulating hormone. Researchers at the University of Arizona synthesized it during the 1980s while studying pigmentation and appetite signaling. The compound is not an approved medicine in any major jurisdiction and appears mainly in laboratory and research-chemical settings. Its structure incorporates a lactam bridge between side chains, which constrains the ring and slows enzymatic breakdown relative to the natural hormone.
Melanotan II binds several melanocortin receptor subtypes rather than a single target. MC1R on melanocytes drives melanin synthesis, while MC3R and MC4R participate in energy balance, appetite, and sexual response pathways. This lack of selectivity explains why reported effects extend beyond skin darkening. Substitutions at positions four and seven, including norleucine and D-phenylalanine, increase potency and resistance to peptidases. Understanding which receptor mediates which effect remains an active area of investigation.
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.
He described the moves as part of an idea of Porto Alegre as a marketplace and that it ought to be sold internationally as something that could be transformed into new possibilities for the accumulation of capital and mercantilism. Rafael Passos, president of the Rio Grande do Sul branch of the Institute of Architects of Brazil (IAB), is on a mission to decentralize and that the only public comment to them is how it would be done. Even debates such as these are limited as complaints from the populace of not being heard grow common. For Betânia Alfonsin, from the Conselho Diretivo do Instituto Brasileiro de Direito Urbanístico, the concession process for parks should not be analyzed in a vacuum since it forms part of the global context of the advance of private interests towards public areas, with a movement that seeks total deregulation of urbanist legislation. In January 2022, Melo promoted to send to the Chamber of Deputies a new master plan administrator who was "very liberal". While this did not occur, he tried to introduce new regulations. He has said that his government is very liberal on the economy, on entrepreneurs, and on the opening of new businesses, but has a strong eye on social issues. There are criticisms that his government has implemented large-scale projects that had been approved despite warnings from the master plan administrator and norms regarding environmental protections.
== History == 4-AcO-DMT and several other esters of psilocin were patented on January 16, 1963, by Sandoz via Albert Hofmann and Franz Troxler. The drug's chemical synthesis was improved by David E. Nichols and colleagues in 1999 and it was suggested as a more economical and accessible alternative to psilocybin for use in scientific research. 4-AcO-DMT was first detected as a designer drug in Europe in 2009. It became increasingly prevalent as a recreational drug in the 2010s and has been the most commonly used novel tryptamine. In the 2020s, 4-AcO-DMT became widely encountered in the form of mushroom edibles in the United States as an alternative to psilocybin and psilocybin-containing mushrooms.
=== Drug analysis === DSC is widely used in the pharmaceutical and polymer industries. For the polymer chemist, DSC is a handy tool for studying curing processes, which allows the fine tuning of polymer properties. The cross-linking of polymer molecules that occurs in the curing process is exothermic, resulting in a negative peak in the DSC curve that usually appears soon after the glass transition. In the pharmaceutical industry it is necessary to have well-characterized drug compounds in order to define processing parameters. For instance, if it is necessary to deliver a drug in the amorphous form, it is desirable to process the drug at temperatures below those at which crystallization can occur.
Sources: en.wikipedia.org
Now differences between the contemporary squid and octopus samples became very clear. In the octopus, broad bands of fibers passed across the plane of the tissue and were separated by equally broad bands arranged in a perpendicular direction. In the squid there were narrower but also relatively broad bundles arranged in the plane of the section, separated by thin partitions of perpendicular fibers. It seemed I had found a means to identify the mystery sample after all. I could distinguish between octopus and squid, and between them and mammals, which display a lacy network of connective tissue fibers. After 75 years, the moment of truth was at hand. Viewing section after section of the St. Augustine samples, we decided at once, and beyond any doubt, that the sample was not whale blubber. Further, the connective tissue pattern was that of broad bands in the plane of the section with equally broad bands arranged perpendicularly, a structure similar to, if not identical with, that in my octopus sample. The evidence appears unmistakable that the St. Augustine sea monster was in fact an octopus, but the implications are fantastic. Even though the sea presents us from time to time with strange and astonishing phenomena, the idea of a gigantic octopus, with arms 75 to 100 feet in length and about 18 inches in diameter at the base—a total spread of some 200 feet—is difficult to comprehend.
The exact mass of many isotopes was measured leading to the result that hydrogen has a 1% higher mass than expected by the average mass of the other elements. Aston speculated about the subatomic energy and the use of it in 1936. In 1918, Arthur Jeffrey Dempster reported on his mass spectrometer and established the basic theory and design of mass spectrometers that is still used to this day. Dempster's research over his career centered around the mass spectrometer and its applications, leading in 1935 to his discovery of the uranium isotope 235U. This isotope's ability to cause a rapidly expanding fission nuclear chain reaction allowed the development of the atom bomb and nuclear power. In 1932, Kenneth Bainbridge developed a mass spectrometer with a resolving power of 600 and a relative precision of one part in 10,000. He used this instrument to verify the equivalence of mass and energy, E = mc2.
== UK appliance safety recalls == Following its 2014 acquisition of Indesit, Whirlpool identified a fire risk affecting certain vented and condensing tumble dryers sold in the United Kingdom under the Hotpoint, Indesit, Creda, Swan and Proline brands. The affected models had been manufactured between April 2004 and September 2015; lint could accumulate and come into contact with a heating element, creating a fire risk. Whirlpool told the House of Commons Business, Energy and Industrial Strategy Committee that 5.3 million affected machines had been manufactured for the UK market. Whirlpool began a modification programme in November 2015 rather than a full recall. Owners were initially advised that affected dryers could continue to be used under specified precautions, but the advice was changed in early 2017 to tell consumers not to use unmodified machines. In August 2016, a fire at Shepherds Court in Shepherd's Bush was attributed by the London Fire Brigade to an Indesit tumble dryer covered by Whirlpool's corrective-action programme. A House of Commons committee later criticised the decision not to initiate a full recall and the pace of the modification programme. In April 2019, the Office for Product Safety and Standards (OPSS) concluded that the risk of harm or injury from lint fires in dryers that had been modified was low, but required Whirlpool to improve aspects of its risk management and communication with consumers. Following further intervention by OPSS, Whirlpool agreed in July 2019 to recall remaining unmodified affected tumble dryers.
Sources: en.wikipedia.org
== Side effects and overdose == Side effects from intra-articular administration can include joint pain, swelling, lameness, and, rarely, infection of the joint. Intramuscular injection can cause dose-dependent inflammation and bleeding, since PSGAG is an analogue of the anticoagulant heparin. In dogs, this may manifest as bleeding from the nose or as bloody stools. The increased risk of bleeding has some advising not to give PSGAG to animals with bleeding disorders, though its only absolute contraindication is hypersensitivity to PSAGs when it is being given intra-articularily. Overdose on PSGAG is quite rare, as the LD50 is over 1000 mg/kg when given intravenously to dogs. Signs of overdose include exacerbated side effects such as joint pain, swelling, and lameness. When dogs received three times the normal dose intramuscularly twice a week for 13 weeks, they had increased liver and kidney weight, as well as microscopic lesions on the liver, kidneys, and lymph nodes. At 11 times the normal dose, they also had increased alanine transferase, cholesterol, and prothrombin time (i.e. coagulation via the extrinsic pathway took longer), and fewer platelets.
Source 2 was announced by Valve as the successor to Source at the Game Developers Conference in March 2015. There, Valve stated that it would be free to use for developers, with support for the Vulkan graphical API, as well as using a new in-house physics engine called Rubikon. In June 2015, Valve announced that Dota 2, originally developed with Source, would be ported over to Source 2 in an update called Dota 2 Reborn. Reborn was first released to the public as an opt-in beta update that same month before officially replacing the original client in September 2015, making it the first game to use the engine. The engine had succeeded Source by the late 2010s.
=== Gelatin === The gelatin test is used to analyze whether a microbe can hydrolyze gelatin with the enzyme gelatinase. The gelatin makes the agar solid, so if an organism can produce gelatinase and consume gelatin as an energy and carbon source, the agar will become liquid during growth.
DHT is the most important androgenic hormone and is a product of both canonical and backdoor pathways. Additionally, 11KDHT but not 11KT can be biosynthesized from the C11-oxy backdoor pathway starting from progesterone (P4). These C11-oxy androgens can contribute to the pathology of congenital adrenal hyperplasia, polycystic ovarian syndrome, and prostate cancer. The androgen backdoor route is activated during normal prenatal development and leads to early male sexual differentiation. Dihydrotestosterone synthesized by this route plays a critical role in the development of male sexual characteristics, including the differentiation and maturation of the male external genitalia, the prostate gland, and other male reproductive structures. By bypassing the conventional intermediates (A4 and T), this pathway ensures the timely and appropriate development of male sexual traits in early embryonic and fetal stages. Both canonical and backdoor pathways are essential in normal male embryonic development. A disruption in the backdoor pathway can lead to incomplete or altered male sexual differentiation. This disruption may result in abnormalities or underdevelopment of the male external genitalia, prostate gland, and other male reproductive structures. The specific consequences can vary depending on the nature and extent of the disruption and may lead to conditions such as ambiguous genitalia or other disorders of sexual development (DSD), where the individual's physical and sexual characteristics do not align clearly with typical male, i.e., undervirilization of male infants.
Sources: en.wikipedia.org
No. No major regulatory agency has granted a marketing authorisation for melanotan II as a medicine. Products sold under this name are generally presented as laboratory reagents and are not subject to the batch-release testing applied to approved drugs.
It was developed in the 1980s by researchers investigating analogues of alpha-melanocyte-stimulating hormone for pigmentation and related endpoints. Early work included small human studies during the 1990s. Development did not progress to licensing, and the compound remained a research and grey-market item.
Peptides are prone to truncation, oxidation and aggregation during synthesis and handling. Without independent testing, a buyer cannot confirm the identity or the content of a vial. Analytical surveys of unapproved peptide products have repeatedly found discrepancies between label claims and measured composition.
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.