cyclic heptapeptide 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 2026-02-18. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
Melanotan-2, also written Melanotan II, is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, and the lactam bridge between the aspartate and lysine side chains constrains the peptide into a ring. This structural change increases receptor affinity and metabolic stability relative to the native hormone. The compound was created in the 1980s as a research tool for studying pigmentation biology.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Analog of alpha-melanocyte-stimulating hormone |
| Primary receptor family | Melanocortin receptors MC1R through MC5R | Binding is not subtype-selective |
| Development period | 1980s | Synthesized during pigmentation and appetite research |
| Regulatory status | Not an approved medicine | No major regulator has authorized human use |
| Related compound | Afamelanotide | Linear analog studied for photoprotection |
Receptor binding at MC1R on melanocytes raises intracellular cyclic AMP and increases expression of tyrosinase and related enzymes. The downstream result is greater synthesis of eumelanin, the dark pigment, without ultraviolet exposure acting as the trigger. The compound is not selective, however, and also engages MC3R, MC4R and MC5R, which are expressed in the central nervous system and elsewhere. That lack of selectivity is the explanation usually offered for effects reported outside pigmentation, including appetite suppression and nausea. Selectivity remains a central theme in comparative studies of related peptides.
Human data remain limited and mostly short-term. Reports describe small trials and observational accounts rather than large controlled studies, so questions about dose-response relationships and long-term effects on melanocytes stay open. Whether repeated exposure alters naevus behaviour is not settled in the published record. Researchers also note that self-administered use outside clinical settings makes actual exposure difficult to quantify. Statements about efficacy and safety should therefore be read as preliminary rather than established.
Melanotan II is a synthetic cyclic heptapeptide that acts as an agonist at melanocortin receptors. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, the endogenous peptide involved in pigment production. The analogue carries a lactam bridge that constrains the ring and slows enzymatic breakdown relative to the native hormone. In research literature it appears under several abbreviations, and naming conventions are not fully standardized. Published descriptions usually place it within the broader melanocortin agonist family.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone, the naturally occurring peptide involved in pigmentation signalling. Its sequence is conventionally written as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, with a lactam bridge joining the aspartate side chain to the lysine side chain. The empirical formula is C50H69N15O9 and the monoisotopic mass lies near 1023.5 daltons. N-terminal acetylation and the D-configured phenylalanine both increase resistance to enzymatic breakdown compared with the parent hormone.
Pharmacologically, melanotan-2 behaves as a non-selective agonist across the melanocortin receptor family. Binding at MC1R on dermal melanocytes promotes eumelanin synthesis, which underlies the tanning response described in early human work. Activity at the centrally expressed MC4R receptor is associated with reported effects on appetite and erectile function. Because the peptide does not discriminate strongly among receptor subtypes, attributing any single observed effect to one receptor pathway is generally not possible without selective antagonists or receptor knockout models.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence incorporates a lactam bridge that constrains the peptide into a ring, which increases resistance to enzymatic breakdown relative to the natural hormone. Researchers at the University of Arizona synthesised the compound in the late 1980s and early 1990s while studying pigmentation pathways. It has never received marketing approval from any national medicines regulator. In the scientific literature it is usually described as a laboratory research reagent rather than a therapeutic product.
The peptide acts as a non-selective agonist at melanocortin receptors, showing affinity for MC1R, MC3R, MC4R and MC5R. Activation of MC1R on melanocytes drives the conversion of tyrosine into melanin and shifts production toward the darker eumelanin form. MC4R signalling in the central nervous system is linked to appetite and energy balance, which helps explain why reduced food intake appeared in early human studies. Effects on MC4R and on vascular tone also account for the erectile responses recorded as unexpected findings in those same trials.
Melanotan-2 is frequently confused with afamelanotide, a linear analogue authorised in the European Union for erythropoietic protoporphyria. The two compounds differ in chain length, ring structure and receptor selectivity, so findings for one cannot be transferred directly to the other. Published controlled human data on melanotan-2 remain sparse, and much of what circulates online derives from small studies or unpublished reports. Questions about effect size, dose-response behaviour and long-term safety therefore remain unresolved.
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.
After finding the vessel Mary Rose objects and what was left of the ship were placed in a passive storage which slowed down the process of immediate deterioration removing the vessel from its extreme environment. In 1994, an elaborate three phased conservation treatment began on Mary Rose. From 1993 to 2003 was the first phase that consisted of the wood getting sprayed with low-molecular-weight PEG to replace the water in the cellular structure of the wood. The second phase from 2003 to 2010, raised the molecular-weight of the PEG solution with the purpose to strengthen the outer surface layers. The third phase in 2016, included controlled air drying.
The American Diabetes Association recommends a goal of keeping hemoglobin A1C levels under 7% for most adults and 7.5% for children. The goal of insulin therapy is to mimic normal pancreatic insulin secretion: low levels of insulin are constantly present to support basic metabolism, plus the two-phase secretion of additional insulin in response to high blood sugar, then an extended phase of continued insulin secretion. This is accomplished by combining different insulin preparations that act with differing speeds and durations. The standard of care for type 1 diabetes is a bolus of rapid-acting insulin 10–15 minutes before each meal or snack, and as-needed to correct hyperglycemia. In addition, constant low levels of insulin are achieved with one or two daily doses of long-acting insulin, or by steady infusion by an insulin pump. The exact dose of insulin appropriate for each injection depends on the content of the meal/snack, and the person's sensitivity to insulin, and is therefore typically calculated by the individual with diabetes or a family member by hand or assistive device (calculator, chart, mobile app, etc.). People who cannot manage these intensive insulin regimens are sometimes prescribed alternate plans relying on mixtures of rapid- or short-acting and intermediate-acting insulin, which are administered at fixed times along with meals of pre-planned times and carbohydrate composition.
==== Female reproductive system ==== In the female, estradiol acts as a growth hormone for tissue of the reproductive organs, supporting the lining of the vagina, the cervical glands, the endometrium, and the lining of the fallopian tubes. It enhances growth of the myometrium. Estradiol appears necessary to maintain oocytes in the ovary. During the menstrual cycle, estradiol produced by the growing follicles triggers, via a positive feedback system, the hypothalamic-pituitary events that lead to the luteinizing hormone surge, inducing ovulation. In the luteal phase, estradiol, in conjunction with progesterone, prepares the endometrium for implantation. During pregnancy, estradiol increases due to placental production. The effect of estradiol, together with estrone and estriol, in pregnancy is less clear. They may promote uterine blood flow, myometrial growth, stimulate breast growth and at term, promote cervical softening and expression of myometrial oxytocin receptors. In baboons, blocking of estrogen production leads to pregnancy loss, suggesting estradiol has a role in the maintenance of pregnancy. Research is investigating the role of estrogens in the process of initiation of labor. Actions of estradiol are required before the exposure of progesterone in the luteal phase.
==== Bluetoothing ==== In early 2017, sensationalist media reports claimed that ‘nyaope’ users shared the drug-induced high through small blood transfusions, a practice supposedly called "bluetoothing" (from the Bluetooth wireless technology). The claim was untrue: the practice is not known on the street and physiologically could not achieve the claimed effect.
== History == Bungarotoxins are a group of toxins that are closely related with the neurotoxic proteins predominantly present in the venom of kraits. These toxins are directly linked to the three-finger toxin superfamily. Among them, α-bungarotoxin (α-BTX) stands out, being a peptide toxin produced by the Taiwanese banded krait, also known as the many-banded krait or the Taiwanese or Chinese krait. The venom of the many-banded krait, like the majority of the snake venoms, involves a combination of proteins that together lead to a remarkable range of neurologic consequences. The Elapid snake family is known for their potent α-neurotoxic venom, which has a postsynaptic mechanism of action. These neurotoxins primarily affect the nervous system, blocking the nerve impulse transmission, leading to paralysis and potentially death if untreated. In South and Southeast Asia, envenomation from a many-banded krait bite is a common and life-threatening medical condition when not promptly treated. Nevertheless, krait bites usually take place at night and do not show any local symptoms, so victims are not aware of the bite. This can delay medical care, which makes it the major cause of mortality associated with krait venom. The first time that the many-banded krait was described was in 1861 by the scientist Edward Blyth. It was characterized by its distinctive black-and-white banded pattern along its body, with a maximum length of 1.85 m. This very venomous species is found in central and southern China and Southeast Asia. Their venom contains various neurotoxins, including α-BTX.
Sources: en.wikipedia.org
Animals ingest amino acids in the form of protein. The protein is broken down into its constituent amino acids in the process of digestion. The amino acids are then used to synthesize new proteins and other nitrogenous biomolecules, or they are further catabolized through oxidation to provide a source of energy. The oxidation pathway starts with the removal of the amino group by a transaminase; the amino group is then fed into the urea cycle. The other product of transamidation is a keto acid that enters the citric acid cycle. Glucogenic amino acids can also be converted into glucose, through gluconeogenesis. Of the 20 standard amino acids, nine (His, Ile, Leu, Lys, Met, Phe, Thr, Trp and Val) are called essential amino acids because the human body cannot synthesize them from other compounds at the level needed for normal growth, so they must be obtained from food.
== Research == The use of a nitric oxide delivery system (glyceryl trinitrate patches) applied over the area of maximal tenderness was found to reduce pain and increase range of motion and strength. A promising therapy involves eccentric loading exercises involving lengthening muscular contractions.
=== General references === Daxer, Albert; Misof, Klaus; Grabner, Barbara; Ettl, Armin; Fratzl, Peter (1998). "Collagen fibrils in the human corneal stroma: Structure and aging". Investigative Ophthalmology & Visual Science. 39 (3): 644–8. PMID 9501878. Daxer, Albert; Fratzl, Peter (1997). "Collagen fibril orientation in the human corneal stroma and its implication in keratoconus". Investigative Ophthalmology & Visual Science. 38 (1): 121–9. PMID 9008637. Fratzl, Peter; Daxer, Albert (1993). "Structural transformation of collagen fibrils in corneal stroma during drying. An x-ray scattering study". Biophysical Journal. 64 (4): 1210–4. Bibcode:1993BpJ....64.1210F. doi:10.1016/S0006-3495(93)81487-5. PMC 1262438. PMID 8494978.
== Gene == The COL2A1 gene is located on the long (q) arm of chromosome 12 between positions 13.11 and 13.2, from base pair 46,653,017 to base pair 46,684,527. The expression of COL2A1 is regulated by SOX-9 and retrotransposon gag-like-3 gene RTL3 in chondrocytes. There are two transcripts identified for this gene.
Sources: en.wikipedia.org
== Release == An error on the Steam store page for the Valve Index listed a release date of 15 June 2019 initially. The headset eventually released on 28 June 2019, priced at US$999 for the full kit containing the headset itself, Knuckles controllers and tracking sensors. The Valve Index sold an estimated 149,000 sets in 2019. 103,000 were in the fourth quarter following the announcement of Valve's flagship VR game, Half-Life: Alyx, which was made free to Index owners, so that they could get the best possible experience with the title, whilst also giving access to limited time exclusive content in-game. The sudden demand caused the unit to be sold out in all 31 countries except Japan in January 2020. While Valve had anticipated supply for many of those that had ordered the Index in time for the March 2020 release of Half-Life: Alyx, the COVID-19 pandemic slowed production, which left Valve with a reduced number of units available on the release date. As of January 2025, 13.2% of the VR units connected to Steam are Valve Index sets.
At the time of Exubera's discontinuation, several other companies were pursuing inhaled insulin including Alkermes working with Eli Lilly and Company, MannKind Corporation, and Aradigm working with Novo Nordisk. By March 2008, except for MannKind's Afrezza product, all of these products had been discontinued because investors all decided to withdraw funding. On March 16, 2009, MannKind submitted a new drug application for their inhalable insulin. In 2011, the FDA denied approval of Afrezza; because the design of the delivery device had changed, it requested additional clinical trials to ensure that people would use it the same way as the earlier versions. After conducting further studies, Mannkind submitted a new application, and in June 2014, the FDA approved Afrezza for both type 1 and type 2 adult diabetics, with a label restriction for patients having asthma, active lung cancer, or COPD. In 2014, Mannkind and Sanofi agreed that Sanofi would take over manufacturing and marketing of Afrezza, but Sanofi said it was dropping the effort in January 2016 due to poor sales of US$7.5 million in 2015; the companies formally terminated the agreement in November 2016. At the time that Sanofi announced it was dropping the product Mannkind said it would continue alone, and it had taken over manufacturing and relaunched the drug by July 2016.
==== DXP-dependent biosynthesis ==== The DXP-dependent biosynthetic route requires several steps and a convergence of two branches, one producing 3-hydroxy-1-aminoacetone phosphate from erythrose 4-phosphate, while the other (single enzyme) producing deoxyxylulose 5-phosphate (DXP) from glyceraldehyde 3-phosphate (GAP) and pyruvate. The condensation product of 3-hydroxy-1-aminoacetone phosphate and deoxyxylulose 5-phosphate is pyridoxine 5'-phosphate. The condensation is catalyzed by PNP synthase, encoded by pdxJ, which creates PNP (pyridoxine 5' phosphate). The final enzyme is PNP oxidase (pdxH), which catalyzes the oxidation of the 4' hydroxyl group to an aldehyde using dioxigen, resulting in hydrogen peroxide. The first branch is catalyzed in E. coli by enzymes encoded by epd, pdxB, serC and pdxA. These share mechanistical similarities and homology with the three enzymes in serine biosynthesis (serA (homologue of pdxB), serC, serB — however, epd is a homologue of gap), which points towards a shared evolutionary origin of the two pathways. In several species there are two homologues of the E. coli serC gene, generally one in a ser operon (serC), and the other in a pdx operon, in which case it is called pdxF.
Sources: en.wikipedia.org
No regulator in a major market has approved it for human use. It appears in research settings and in products marketed outside pharmacy channels. Legal status for personal possession varies by country.
Afamelanotide is a linear analog that has received approval in some jurisdictions for a specific photoprotection indication. Melanotan II is cyclic and less selective across melanocortin receptors. The two are related but are not interchangeable in regulatory or clinical terms.
A compound that activates several receptor subtypes may produce effects beyond pigmentation. Selectivity influences which tissues respond and shapes the side-effect profile described in reports. Designing subtype-selective analogs is a stated goal of melanocortin research.
No. It is a laboratory-made peptide, while the natural hormone is alpha-melanocyte-stimulating hormone, a longer peptide produced by the pituitary gland and by skin cells. Melanotan-2 mimics only a short active region of that hormone and contains non-natural residues such as D-phenylalanine.