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.
Last reviewed on 2025-11-22. Where a claim depends on a specific study, the study is described rather than over-claimed.
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-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.
| 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 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.
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.
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-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-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.
==== Catechol O-methyltransferase (COMT) inhibitors ==== Entacapone (Comtan) – catechol O-methyltransferase (COMT) inhibitor Opicapone (BIA 9-1067; BIA-91067; Ongentys; ONO-2370) – catechol O-methyltransferase (COMT) inhibitor [341] Tolcapone (RO-407592; Tasmar) – catechol O-methyltransferase (COMT) inhibitor [342]
=== Bans === In March 2019, as a result of the previously mentioned research, the European Union banned the use of chlorothalonil dated to take effect May 20, 2020. Switzerland followed in December 2019.
House of Karađorđević: Grand Master of the Royal Order of Saint Prince Lazarus House of Karađorđević: Grand Master of the Royal Order of the Star of Karađorđe House of Karađorđević: Grand Master of the Royal Order of the White Eagle House of Karađorđević: Grand Master of the Royal Order of the Crown House of Karađorđević: Grand Master of the Royal Order of Saint Sava
Sources: en.wikipedia.org
== Others == Endogenous: Adrenomedullin Apelin Asprosin Bombesin Calcitonin Carnosine CART CLIP DSIP Enteroglucagon Formyl peptide GALP GIP GRP Integrin ligands (collagens, fibrinogen, fibronectin, laminins, ICAM-1, ICAM-2, osteopontin, VCAM-1, vitronectin) Kininogens Motilin Natriuretic peptides (ANP, BNP, CNP, urodilatin) Nesfatin-1 Neuromedin B Neuromedin N Neuromedin S Neuromedin U Obestatin Osteocalcin Resistin Secretin Thymopoietin Thymosins Thymulin Urotensin-II VGF Exogenous: Lifitegrast (LFA-1 antagonist)
=== Available forms === Finasteride (brand names Proscar, Propecia) inhibits the function of two of the isoenzymes (types 2 and 3) of 5α-reductase. It decreases circulating DHT levels by up to about 70%. Dutasteride (brand name Avodart) inhibits all three 5α-reductase isoenzymes and can decrease DHT levels by 95%. It can also reduce DHT levels in the prostate by 97 to 99% in men with prostate cancer. Epristeride (brand names Aipuliete, Chuanliu) is marketed in China for the treatment of benign prostatic hyperplasia. However, it can only decrease circulating DHT levels by about 25 to 54%. Alfatradiol (brand names Ell-Cranell Alpha, Pantostin) is a topical 5-ARI used to treat pattern hair loss in Europe.
CoQ10 is a component of the mitochondrial electron transport chain (ETC), where it plays a role in oxidative phosphorylation, a process required for the biosynthesis of adenosine triphosphate, the primary energy source of cells. CoQ10 is a lipophilic molecule that is located in all biological membranes of the human body and is a component for the synthesis of ATP and a life-sustaining cofactor for the three complexes (complex I, complex II, and complex III) of the ETC in the mitochondria. CoQ10 has a role in the transport of protons across lysosomal membranes to regulate pH in lysosome functions. The mitochondrial oxidative phosphorylation process occurs in the inner mitochondrial membrane of eukaryotic cells. This membrane is highly folded into structures called cristae, which increase the surface area available for oxidative phosphorylation. CoQ10 plays a role in this process as an essential cofactor of the ETC located in the inner mitochondrial membrane and serves the following functions:
Sources: en.wikipedia.org
== Release == Season 3 was promoted with the tagline "May God have mercy". Many of the episode titles are references to Westerns and the Bible. The premiere screened at Coachella 2026 on April 2, 2026. The season had its red carpet premiere on April 7, 2026. In the United States, the season premiered on April 12, 2026, with its finale was released on May 31. In the United Kingdom and the Republic of Ireland, each episode was released at the same time as its U.S. premiere, through Sky Atlantic's streaming service Now.
==== Antisense oligomer delivery ==== Antisense oligonucleotides (asONs) have been used in basic research and are being developed as possible medical treatments. CPP strategies have been developed to deliver antisense oligomers such as PNA and PMO into cells. Overcoming the repulsion by the cell membrane of negative-charged ONs and the degradation of asONs by enzymes, CPPs increase asONs bioavailability. Two types of neutral ON analogues, peptide nucleic acid (PNA) and phosphorodiamidate morpholino oligomers (PMO or Morpholino) are becoming dominant in this area. PNA has been conjugated with various CPPs either through disulfide linkages or through stable amide bonds. For example, antisense activity within cells that blocked expression of the galanin receptor was observed when a 21-mer PNA was coupled to the penetratin. Results on antiviral activity with PNA targeting HIV-1 have also been reported through disulfide linkage with TAT. CPP-PMO conjugates have also been successfully used to inhibit the replication of several viruses such as SARS and influenza and attachment of CPPs has improved the efficacy of splice-modifying Morpholinos in development for treatment of Duchenne muscular dystrophy
== External links == "Opioid Receptors: κ". The International Union of Basic and Clinical Pharmacology, The British Pharmacological Society, The University of Edinburgh. International Union of Basic and Clinical Pharmacology. Archived from the original on 2014-02-23. Retrieved 2007-07-23. kappa+Opioid+Receptor at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
Small-cell carcinoma is an undifferentiated neoplasm composed of primitive-appearing cells. As the name implies, the cells in small-cell carcinomas are smaller than normal cells and barely have room for any cytoplasm. Some researchers identify this as a failure in the mechanism that controls the size of the cells. At the time of diagnosis, 60–70% of people already have metastases.
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.
It is a synthetic seven-amino-acid peptide modeled on alpha-melanocyte-stimulating hormone. It carries two non-natural substitutions and a cyclic bridge that increase its stability relative to the natural hormone. It circulates as a research chemical and is not an approved medicine.