cyclic heptapeptide comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2026-07-09. 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-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controlled human data on melanotan-2 remain sparse, and much of what circulates online derives from small studies or unpublished reports.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.
| 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 |
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.
Structurally, Melanotan-2 retains the core recognition motif of alpha-melanocyte-stimulating hormone while adding a lactam bridge that links two side chains and constrains the molecule into a ring. This modification lowers susceptibility to enzymatic degradation. The compound acts as an agonist at melanocortin receptors, particularly subtypes associated with melanin production. Because the same receptor family influences several physiological processes, researchers note that its activity is not confined to pigmentation alone. Receptor selectivity continues to be examined in published studies.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone, a naturally occurring peptide involved in pigmentation signalling. Its sequence incorporates modified residues that increase potency and extend biological activity relative to the native hormone. The compound binds receptors of the melanocortin family and is examined mainly in laboratory research. It does not occur naturally and exists only as a manufactured chemical entity produced by solid-phase synthesis.
==== Polar charged ==== Five amino acids possess a charge at neutral pH. Often these side chains appear at the surfaces on proteins to enable their solubility in water, and side chains with opposite charges form important electrostatic contacts called salt bridges that maintain structures within a single protein or between interfacing proteins. Many proteins bind metal into their structures specifically, and these interactions are commonly mediated by charged side chains such as aspartate, glutamate and histidine. Under certain conditions, each ion-forming group can be charged, forming double salts. The two negatively charged amino acids at neutral pH are aspartate (Asp, D) and glutamate (Glu, E). The anionic carboxylate groups behave as Brønsted bases in most circumstances. Enzymes in very low pH environments, like the aspartic protease pepsin in mammalian stomachs, may have catalytic aspartate or glutamate residues that act as Brønsted acids.
An analysis of clinical trials by the FDA statisticians showed the incidence of suicidal behaviour among the adults on venlafaxine to be not significantly different from fluoxetine or placebo. Venlafaxine is contraindicated in children, adolescents, and young adults. In children and adolescents with depression, venlafaxine increases the risk of suicidal thoughts or attempts.
=== Absorption === Pentamidine is completely absorbed when given intravenously or intramuscularly. When inhaled through a nebulizer, pentamidine accumulates in the bronchoalveolar fluid of the lungs at a higher concentration compared to injections. The inhaled form is minimally absorbed in the blood, but the effects of chronic inhaled administration on these levels are not known. Absorption is unreliable when given orally.
Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2 H+ + 2 ATP + 2 H2O If glycolysis were to continue indefinitely, all of the NAD+ would be used up, and glycolysis would stop. To allow glycolysis to continue, organisms must be able to oxidize NADH back to NAD+. How this is performed depends on which external electron acceptor is available.
Certain crystals alter the polarization plane of transmitted light, and when rotated between crossed polarizers, they alternate between bright and dark every 90°. The extinction angle is the angle between a specific crystal axis and the filter's polarization plane when the crystal appears dark (in extinction). For instance, this method can be employed to distinguish between perlatolic acid and imbricaric acid, which both form long, straight crystals in the GE solvent system but exhibit extinction angles of 0° and 45°, respectively, in relation to their long axis.
Sources: en.wikipedia.org
=== Selected publications === Ariely, Dan; Loewenstein, George; Prelec, Drazen (2003), "Coherent Arbitrariness: Stable demand curves without stable preferences", The Quarterly Journal of Economics, 118 (1): 73–106, doi:10.1162/00335530360535153, archived from the original on April 4, 2012 Ariely, Dan (2000), "Controlling information flow: Effects on consumers' decision making and preference", Journal of Consumer Research, 27 (2): 233–248, CiteSeerX 10.1.1.203.1798, doi:10.1086/314322 {{citation}}: Cite uses deprecated parameter |citeseerx= (help) Ariely, Dan; Wertenbroch, Klaus (2002), "Procrastination, Deadlines, and Performance: Self-Control by Precommitment" (PDF), Psychological Science, 13 (3): 219–224, doi:10.1111/1467-9280.00441, PMID 12009041, S2CID 3025329 Heyman, James; Ariely, Dan (2004), "Effort for Payment: A Tale of Two markets" (PDF), Psychological Science, 15 (11): 787–793(7), doi:10.1111/j.0956-7976.2004.00757.x, PMID 15482452, S2CID 8573184 Carmon, Ziv; Ariely, Dan (2000), "Focusing on the Forgone: Why Value can Appear so Different to Buyers and Sellers" (PDF), Journal of Consumer Research, 27 (3): 360–370, doi:10.1086/317590 Shiv, Baba; Carmon, Ziv; Ariely, Dan (2005), "Placebo Effects of Marketing Actions: Consumers May Get What They Pay For" (PDF), Journal of Marketing Research, XXII (4): 383–393, doi:10.1509/jmkr.2005.42.4.383, S2CID 14170707 Mazar, Nina; Ariely, Dan (2006), "Dishonesty in Everyday Life and Its Policy Implications" (PDF), Journal of Public Policy & Marketing, 25 (1): 117–126, doi:10.1509/jppm.25.1.117, S2CID 2813683 Lee, Leonard; Frederick, Shane; Ariely, Dan (2006), "Try it, you'll like it: The influence of expectation, consumption, and revelation on preferences for beer" (PDF), Psychological Science, 17 (12): 1054–1058, doi:10.1111/j.1467-9280.2006.01829.x, PMID 17201787, S2CID 1252769 Ariely, Dan; Gregory S. Berns (March 3, 2010). "Neuromarketing: the hope and hype of neuroimaging in business" (PDF). Nature Reviews Neuroscience. 11 (4): 284–292. doi:10.1038/nrn2795. PMC 2875927. PMID 20197790. Archived from the original (PDF) on July 11, 2013. Ariely, Dan; Michael I. Norton; Daniel Mochon (July 2012). "The IKEA effect: When labor leads to love" (PDF). Journal of Consumer Psychology. 3. 22 (3): 453–460. doi:10.1016/j.jcps.2011.08.002. Archived from the original (PDF) on May 20, 2014.
=== Hemoglobin A1c === Hemoglobin A1c is a measure of the percent of red blood cells that are glycated, or have a glucose molecule attached. This can be used as an indicator of blood glucose level over a longer period of time and is often used to diagnose prediabetes as well as diabetes. HbA1c may not accurately represent blood glucose levels and should not be used in certain medical conditions such as iron-deficiency anemia, Vitamin B12 and folate deficiency, pregnancy, hemolytic anemia, an enlarged spleen, and end-stage kidney failure.
== V == V3 loop – vaccination – vaccine – vaccinia – vaginal candidiasis – valley fever – variable region – varicella zoster virus (VZV) – vector – vertical transmission – viral burden – viral core – viral culture – viral envelope – viral load – viremia – viricide – virion – virology – virus – visceral
In 1993, 3M considered fluorocarbons as fire extinguishants to replace CFCs. This extinguishing effect has been attributed to their high heat capacity, which takes heat away from the fire. It has been suggested that an atmosphere containing a significant percentage of perfluorocarbons on a space station or similar would prevent fires altogether.
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 heptapeptide modelled on alpha-melanocyte-stimulating hormone. A lactam bridge links two side chains, forming a ring that stabilises the molecule against proteolysis. It belongs to the broader melanocortin peptide family.