A practical reference on prohibited substance: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-02-06 and is reviewed periodically as new material appears.
Thymosin beta-4 was isolated from calf thymus in the early 1980s and later characterised as an abundant intracellular actin-sequestering protein. Interest in short synthetic fragments grew once the actin-binding motif had been mapped to the middle of the sequence. TB-500 came out of that line of work as a truncated analogue rather than a natural isolate, and it is now sold mainly to laboratories. Published studies on the fragment have been largely in vitro or in animal models, and controlled human trials remain sparse, so claims about effects in people rest on extrapolation.
Literature and online discussion often conflate TB-500 with full-length thymosin beta-4, even though the two differ in size and are not interchangeable in analytical terms. The fragment is produced by solid-phase peptide synthesis, and the product is a defined seven-residue chain rather than a biological extract. Because the term is a trade-style label, two vendors may supply materials of the same nominal sequence but different counter-ion content, purity, or water content. Comparisons across studies are therefore difficult unless the exact sequence and purity are reported.
TB-500 is a research peptide whose sequence matches residues 17 to 23 of thymosin beta-4, a 43-residue protein present in most mammalian cells. The chain is seven amino acids long, written as LKKTETQ, and is normally supplied with an acetyl group on the N-terminus. Suppliers list it as a lyophilised powder under the code name TB-500, and the same sequence appears elsewhere in catalogues as the thymosin beta-4 actin-binding fragment. The label is commercial rather than systematic, so no single authority fixes exactly what TB-500 denotes.
TB-500 is a synthetic seven-residue peptide whose sequence, LKKTETQ, matches the N-terminal actin-binding region of thymosin beta-4. It is usually supplied in an N-terminally acetylated form, a modification that blocks the free amino terminus and can influence behavior in solution. In the research literature the same sequence appears under several names, including thymosin beta-4 fragment and shortened thymosin beta-4. Because it is a short peptide rather than the full 43-residue parent protein, its measured properties differ from those reported for thymosin beta-4 as a whole, and the two are not interchangeable in experimental design.
Thymosin beta-4 itself is a small, widely expressed protein that sequesters monomeric actin and participates in cell migration, angiogenesis, and tissue repair. Researchers have examined the shortened fragment as a possible mimic of some of these activities, reasoning that the actin-binding motif lies within the first few residues. Binding to monomeric actin has been observed in cell-free systems. Whether the fragment reproduces the broader effects of the full protein in living tissue remains an open question, and findings from animal models are frequently cited without a clear bridge to human physiology.
Discussion of TB-500 appears in several distinct literatures that rarely cite one another. Peer-reviewed studies usually describe in vitro assays or small animal experiments and are cautious about extrapolation. Veterinary and sports communities circulate anecdotal reports with limited methodological detail. Commercial listings add a third layer, often using the name interchangeably with thymosin beta-4 even though the two molecules differ in size and sequence. Regulatory status varies by country, and the compound is not a licensed medicine in most jurisdictions, so readers comparing sources should check which molecule and which purity each source actually describes.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white powder | Supplied as a lyophilised cake in sealed vials |
| Solubility class | Freely soluble in water | Polar and charged side chains dominate the sequence |
| Typical storage temperature | -20 °C or below | Dry and dark; a desiccant is often recommended |
| Identity confirmation | Mass spectrometry | Observed mass compared with the theoretical value |
| Common synonyms | Thymosin beta-4 fragment | Also written as T beta 4 fragment 17-23 |
Thymosin beta-4 is a 43-residue actin-binding protein found in most mammalian cell types, where it participates in cytoskeletal regulation and cell migration. TB-500 represents only a short fragment of that protein and does not include the remaining residues. Whether the isolated fragment reproduces the full range of activities reported for the intact protein remains an open question. Researchers commonly treat the two as related but distinct entities when comparing results.
Published work involving this sequence spans actin-binding assays, cell-migration studies, wound-healing models, and cardiovascular or musculoskeletal experiments. Much of the biological rationale derives from in vitro systems and animal models, and the number of controlled human studies is small. Reported outcomes vary across preparations, doses, and routes, which complicates comparison between studies. Reviews generally describe the evidence base as preliminary rather than settled. Mechanistic explanations are often proposed by analogy to the parent protein rather than demonstrated directly.
TB-500 is a synthetic seven-amino-acid peptide with the sequence LKKTETQ, corresponding to residues 17 through 23 of the protein thymosin beta-4. The N-terminus is typically acetylated in the described form, giving a monoisotopic mass near 888.5 Da and an average mass of about 889 Da. The designation TB-500 is a catalogue label rather than a formal chemical name, and the same sequence appears in the literature under several alternative abbreviations. It is handled as a research reagent rather than a pharmaceutical product.
Research interest in thymosin beta-4 fragments centres on actin sequestration, cell migration and tissue repair models. Most published work uses cultured cells or animal wound and cardiac preparations, and findings are generally described as preliminary. No fragment of this protein has been approved as a therapeutic product by major regulators. Reviews of the field note inconsistent dosing, delivery routes and outcome measures across studies, which complicates direct comparison. The material is best understood as a laboratory reagent with an active but unresolved research literature.
TB-500 is a catalogue name applied to a synthetic peptide related to thymosin beta-4, an actin-binding protein found in most mammalian cells. Suppliers do not use the label consistently: some describe it as the full 43-residue protein, others as a short fragment from the actin-binding region, and others as a related tetrapeptide. Because the name is commercial rather than chemical, two products sold under it may not contain the same molecule. This naming ambiguity is the first point to check in any description of the material.
The most frequently cited identity is a seven-residue fragment with the sequence LKKTETQ, taken from the actin-binding domain of the parent protein. A separate molecule, N-acetyl-seryl-aspartyl-lysyl-proline, often shortened to Ac-SDKP, derives from the same protein's N-terminal region and appears in overlapping literature. Reported molecular masses therefore differ between sources, and a mass value on its own does not establish which fragment is present. Confirmation requires a defined sequence rather than a single number.
Sports authorities classify the peptide as a prohibited substance, and it appears on the World Anti-Doping Agency list under peptide hormones, growth factors, and related substances. Racing jurisdictions for horses and dogs have issued separate restrictions, and several national bodies treat it as a controlled or prescription-only item. As a research chemical it is sold without a therapeutic indication, and labels usually state that the product is not for human or veterinary use. Regulatory treatment therefore varies by country.
Detection in biological matrices generally relies on liquid chromatography coupled with tandem mass spectrometry, because the peptide lacks a convenient ultraviolet chromophore beyond the amide backbone. Immunoassays have been described, but antibodies raised against the fragment can cross-react with the full-length protein or with unrelated peptides, so findings usually require confirmation by a second technique. Sample preparation typically involves protein precipitation followed by solid-phase extraction. Reported detection windows depend on dose, route, matrix, and instrument sensitivity.
1993/2924) Social Security (Contributions) Amendment (No. 7) Regulations 1993 (S.I. 1993/2925) Dundee Healthcare National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2926) Falkirk and District Royal Infirmary National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2927) Hairmyres and Stonehouse Hospitals National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2928) Law Hospital National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2929) Perth and Kinross Healthcare National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2930) East and Midlothian National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2931) Royal Infirmary of Edinburgh National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2932) Western General Hospitals National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2933) Dumfries and Galloway Acute and Maternity Hospitals National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2934) Glasgow Community and Mental Health Services National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2935) Edinburgh Sick Children's National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2936) Fife Healthcare National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2937) Edinburgh Healthcare National Health Service Trust (Establishment) Order 1993 (S.I. 1993/2938) Petroleum Revenue Tax (Nomination Scheme for Disposals and Appropriations) (Amendment) Regulations 1993 (S.I.
== Medical uses == People diagnosed with trypanosome-caused disease should be treated with an anti-trypanosomal. Treatment is based on stage, 1 or 2, and parasite, T. b. rhodesiense or T. b. gambiense. In stage 1 disease, trypanosomes are present only in the peripheral circulation. In stage 2 disease, trypanosomes have crossed the blood-brain barrier and are present in the central nervous system. The following are considerable treatment options: Melarsoprol is a treatment used during the second stage of the disease. So far, it is the only treatment available for late-stage T. b. rhodesiense. Due to high toxicity, melarsoprol is reserved only for the most dangerous cases. Other agents associated with lower toxicity levels are used during stage 1 of the disease. The approval of the nifurtimox-eflornithine combination therapy (NECT) in 2009 for the treatment of T. b. gambiense limited the use of melarsoprol to the treatment of second-stage T. b. rhodesiense. Failure rates of 27% in certain African countries have been reported. This was caused by both drug resistance and additional mechanisms that have not yet been elucidated. Resistance is likely due to transport problems associated with the P2 transporter, an adenine-adenosine transporter. Resistance can occur with point mutations within this transporter. Resistance has been present since the 1970s. In August 2024, the World Health Organization recommended fexinidazole, developed by the Drugs for Neglected Diseases initiative and partners to replace melarsoprol as the first-line treatment for sleeping sickness caused by T.
== Overdose == Only a single case of death due to mescaline, as peyote, has been described, and was likely due to asphyxiation by vomit rather than overdose or toxicity. However, there is also a case report of death due to jumping off a cliff while on a high dose of mescaline. In terms of extrapolated human lethal dose based on animal studies, the lethal dose of mescaline relative to a typical recreational dose has been estimated to be 24-fold or around 8,400 mg. However, mescaline has reportedly been taken by humans at doses of up to 8,000 mg without apparent toxic reactions. On the other hand, there is one unverified reported case of death due to a dose of 15,000 mg intravenously, which would equate to about 150 to 200 mg/kg. The median lethal dose (LD50) of mescaline has been determined in various animal species, with the values including 212 to 315 mg/kg i.p. in mice, 132 to 410 mg/kg i.p. in rats, 328 mg/kg i.p. in guinea pigs, 54 mg/kg in dogs, and 130 mg/kg i.v. in rhesus macaques, among others. It has been said that it would be difficult to take enough mescaline to cause death in humans. No deaths due to peyote use have been reported aside from the asphyxiation case. The highest dose of peyote known to have been taken is 90 dried buttons.
Sources: en.wikipedia.org
Critical response to Ellipse was generally positive. At Metacritic, which assigns a normalized rating out of 100 to reviews from mainstream critics, the album received an average score of 68, based on 12 reviews. It also earned her a further two Grammy Nominations on 2 December for Best Pop Instrumental Performance for "The Fire" and Best Engineered Non-Classical Album. On 31 January 2010, it was announced that Heap had won the latter award.
==== Mastocytosis ==== Mastocytosis involves both excessive accumulation and activation of mast cells and is considered a primary type of mast cell activation disorder (MCAD). Mastocytosis is a rare clonal mast cell disorder involving rapid, uncontrolled cell growth and the presence of too many mast cells (mastocytes). The most commonly affected organs in mastocytosis are bone marrow, skin, liver, spleen, and lymph nodes. Symptoms of mastocytosis depend upon the organs involved. In 2016, the World Health Organization (WHO) classified mastocytosis as cutaneous (CM, skin only), systemic (SM, involving at least one additional organ) or mast cell sarcoma (MCS, involving rapidly spreading solid tumors). In 2022, WHO divided SM into subcategories which include the less advanced forms of bone marrow mastocytosis (BMM), indolent systemic mastocytosis (ISM), smoldering systemic mastocytosis (SSM), and the more advanced forms of aggressive systemic mastocytosis (ASM), systemic mastocytosis with an associated hematologic neoplasm (SM-AHN), and mast cell leukemia (MCL). Although not always present, mutations in KIT appear to result in uncontrolled growth of MCs. The KITD816V mutation is present in over 90% of mastocytosis patients. It is located in exon 17 in the intracellular tyrosine kinase 2 (TK2) domain. This mutation, as well as expression of either CD2 or CD25 (confirmed by immunostaining or flow cytometry), are characteristic of primary clonal/monoclonal mast cell activation syndrome (CMCAS/MMAS).
=== Early pre-commercial research === In 1761, Ebenezer Kinnersley demonstrated heating a wire to incandescence. However such wires tended to melt or oxidize very rapidly (burn) in the presence of air. Limelight became a popular form of stage lighting in the early 19th century, by heating a piece of calcium oxide to incandescence with an oxyhydrogen torch. In 1802, Humphry Davy used what he described as "a battery of immense size", consisting of 2,000 cells housed in the basement of the Royal Institution of Great Britain, to create an incandescent light by passing the current through a thin strip of platinum, chosen because the metal had an extremely high melting point. It was not bright enough nor did it last long enough to be practical, but it was the precedent behind the efforts of scores of experimenters over the next 75 years. Davy also demonstrated the electric arc, by passing high current between two pieces of charcoal. For the next 40 years, much research was given to turning the carbon arc lamp into a practical means of lighting. The carbon arc itself was dim and violet in color, emitting most of its energy in the ultraviolet, but the positive electrode was heated to just below the melting point of carbon and glowed very brightly with incandescence very close to that of sunlight. Arc lamps burned up their carbon rods very rapidly, expelled dangerous carbon monoxide, and tended to produce outputs in the tens of kilowatts. Therefore, they were only practical for lighting large areas, so researchers continued to search for a way to make lamps suitable for home use.
The Strecker amino acid synthesis, also known simply as the Strecker synthesis, is a method for the synthesis of amino acids by the reaction of an aldehyde with cyanide in the presence of ammonia. The condensation reaction yields an α-aminonitrile, which is subsequently hydrolyzed to give the desired amino acid. The method is used for the commercial production of racemic methionine from methional.
Sources: en.wikipedia.org
No. Thymosin beta-4 is a 43-residue protein, while TB-500 matches only residues 17 to 23 of that chain. The two are related but differ in size, and a method that identifies one does not automatically identify the other.
It corresponds to the actin-binding region of thymosin beta-4. Commercial synthesis reproduces that seven-residue stretch, usually with an acetyl group on the N-terminus.
It is not authorised as a medicine in the United States or the European Union and is distributed as a research chemical. Labels consequently carry research-use-only statements rather than clinical indications.
No. Thymosin beta-4 is a 43-residue protein, while TB-500 refers to a seven-residue fragment corresponding to its N-terminal region. The two names are often used loosely in commercial and community writing, which obscures the difference in size, sequence, and likely behavior.