The short version of melanocortin receptor fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-01-25. Anything still debated is marked as such rather than presented as settled.
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.
Identity testing for a cyclic peptide of this size usually relies on reversed-phase high-performance liquid chromatography coupled to mass spectrometry. The mass spectrum confirms molecular weight, while the chromatographic trace indicates the proportion of related impurities. Tandem mass spectrometry can provide sequence-level information when fragmentation data are compared against a reference standard. Nuclear magnetic resonance is sometimes used to confirm the lactam bridge, although it requires more material and greater operator expertise than routine chromatographic methods.
Lyophilised peptide powder is comparatively stable when kept dry, cold and protected from light. Once dissolved, the molecule is exposed to hydrolysis, oxidation and microbial growth, and degradation accelerates at higher temperatures and in alkaline solution. Repeated freeze-thaw cycles concentrate solutes and promote aggregation. Handling guidance for research peptides commonly clusters around freezer temperatures for powder and short refrigerated use for reconstituted solutions, with pH control and sterile technique applied throughout.
Verification of a purchased sample requires documentation linking a batch to a certificate of analysis, and that document should be read for the methods used rather than the headline purity figure. A single chromatographic percentage does not establish identity. Independent laboratories can perform identity and content assays, but no such test establishes that a product is suitable for human use. Claims about efficacy rest largely on small, early studies rather than on replicated controlled trials, and that gap remains open.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Melanocortin receptor agonist |
| Molecular formula | C50H69N15O9 | Neutral form, mass near 1024.2 g/mol |
| Primary targets | MC1R, MC3R, MC4R, MC5R | Binding is non-selective across subtypes |
| Related compounds | Alpha-MSH, melanotan I, afamelanotide | Structurally or functionally related peptides |
| Common abbreviations | MT-II, MT-2 | Naming in the literature is not uniform |
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.
Research interest has centred on photoprotection and pigmentation, with a smaller body of work on appetite and sexual function. Published human data remain limited to small, frequently uncontrolled studies, and the compound has never received marketing approval from a national medicines regulator. Most laboratory work treats it as a pharmacological tool for probing melanocortin signalling in cell culture or animal models. Whether pigmentation changes observed in people translate into measurable protection against ultraviolet-induced DNA damage remains an open question.
The peer-reviewed record is dominated by small early-phase studies, case reports and pharmacovigilance summaries rather than large randomised trials. Papers typically examine tanning response, receptor selectivity or patterns of reported adverse events. Many note that participants obtained the peptide outside a clinical setting, which limits verification of composition and administered amount. Reported events vary widely, and causality is frequently unclear because the identity and purity of self-sourced material are unknown. Open questions include whether repeated melanocortin receptor stimulation produces cumulative effects, and how often label claims match actual content.
Identification in laboratories relies on reversed-phase liquid chromatography coupled with tandem mass spectrometry, with product-ion spectra compared against a certified reference standard. High-resolution mass spectrometry supplies accurate mass confirmation, and peptide mapping after enzymatic digestion separates melanotan II from closely related analogues. Quantitation of seized material is complicated by unknown counter-ions and residual trifluoroacetate left from purification. Immunoassays raised against alpha-melanocyte-stimulating hormone can cross-react, so chromatographic confirmation is normally required. Urinary detection windows are short, and reported limits of detection differ substantially between laboratories.
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.
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=== Table I === acetic anhydride N-Acetylanthranilic acid ephedrine ergometrine ergotamine isosafrole lysergic acid 3,4-methylenedioxyphenyl-2-propanone norephedrine phenylacetic acid 1-phenyl-2-propanone alpha-phenylacetoacetonitrile (APAAN) piperonal potassium permanganate pseudoephedrine safrole The salts of the substances listed in this Table whenever the existence of such salts is possible.
=== Discrete pathophysiology and CTS === Hereditary neuropathy with susceptibility to pressure palsies is a genetic condition that appears to increase the probability of developing CTS. Heterozygous mutations in the gene SH3TC2, associated with Charcot-Marie-Tooth, may confer susceptibility to neuropathy, including CTS. Association between common benign tumors such as lipomas, ganglion, and vascular malformation should be handled with care. Such tumors are very common and are more likely to compress the median nerve. Similarly, the association between transthyretin amyloidosis-associated polyneuropathy and carpal tunnel syndrome is under investigation. Prior carpal tunnel release is often noted in individuals who later present with transthyretin amyloid-associated cardiomyopathy. There is consideration that bilateral carpal tunnel syndrome could be a reason to consider amyloidosis, timely diagnosis of which could improve heart health. Amyloidosis is rare, even among people with carpal tunnel syndrome (0.55% incidence within 10 years of carpal tunnel release). In the absence of other factors associated with a notable probability of amyloidosis, it is not clear that biopsy at the time of carpal tunnel release has a suitable balance between potential harms and potential benefits. Other specific pathophysiologies that can cause CTS via pressure include:
Sources: en.wikipedia.org
== Toxicity == Azacitidine causes anemia (low red blood cell counts), neutropenia (low white blood cell counts), and thrombocytopenia (low platelet counts), and patients should have frequent monitoring of their complete blood counts, at least prior to each dosing cycle. The dose may have to be adjusted based on nadir counts and hematologic response. It can also be hepatotoxic in patients with severe liver impairment, and patients with extensive liver tumors due to metastatic disease have developed progressive hepatic coma and death during azacitidine treatment, especially when their albumin levels are less than 30 g/L. It is contraindicated in patients with advanced malignant hepatic tumors. Kidney toxicity, ranging from elevated serum creatinine to kidney failure and death, have been reported in patients treated with intravenous azacitidine in combination with other chemotherapeutic agents for conditions other than myelodysplastic syndrome. Renal tubular acidosis developed in five patients with chronic myelogenous leukemia (an unapproved use) treated with azacitidine and etoposide, and patients with renal impairment may be at increased risk for renal toxicity. Azacitidine and its metabolites are primarily excreted by the kidneys, so patients with chronic kidney disease should be closely monitored for other side effects, since their levels of azacitidine may progressively increase. Based on animal studies and its mechanism of action, azacitidine can cause severe fetal damage.
Enolase next converts 2-phosphoglycerate to phosphoenolpyruvate. This reaction is an elimination reaction involving an E1cB mechanism. Cofactors: 2 Mg2+, one "conformational" ion to coordinate with the carboxylate group of the substrate, and one "catalytic" ion that participates in the dehydration.
== Procedure == To perform microcrystallization, a small piece of lichen is extracted using acetone or other solvents, filtered, and evaporated to yield a residue. The residue is transferred to a microscope slide, and a drop of microcrystallization reagent is added before capping with a cover glass. Commonly used reagents include GAW (H2O/glycerol/ethanol 1:1:1, v/v/v) and GE (acetic acid/glycerol 1:3). Slides using GE or GAW are gently heated and then allowed to cool, promoting the crystallization process. Once formed, crystals are best observed under polarized light with a 200–1,000-fold magnification. This method requires basic laboratory equipment, including a microscope equipped for polarized light, test tubes, pipettes, a micro spirit-lamp or micro Bunsen burner, spatula or scalpel, and microscope slides and cover glasses. Lichen substances can be identified based on the distinctive shape and color of their crystals.
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide and a non-selective melanocortin receptor agonist. Structurally it is modelled on alpha-melanocyte-stimulating hormone, a peptide that occurs naturally in the body.
Activation of MC1R increases pigment synthesis independently of ultraviolet exposure, which is the mechanism usually cited for darkening without sun exposure. Ultraviolet light still influences skin response through separate biological pathways.
Because the peptide binds several melanocortin receptor subtypes, its effects are not confined to pigmentation. This complicates interpretation of both intended and unintended outcomes reported in studies.
Mass spectrometry combined with liquid chromatography provides both molecular weight confirmation and a measure of related impurities. Tandem mass spectrometry adds sequence information. A purity percentage reported without a mass measurement does not confirm what the material is.