TB-500 Fragment (17-23): what the studies show, status and safety
Summary
The fragment LKKTETQ / fequesetide has seven amino acids and lacks the N-terminal acetyl group of Ac-LKKTETQ. It also differs from full-length TB-4, which has 43 amino acids. Aged-mouse wound results concern unacetylated LKKTETQ; a separate cell assay found no significant effect of Ac-LKKTETQ under its tested conditions. Different molecules and models do not establish clinical superiority of either fragment.
Key findings at a glance
- One small chemical cap apart from TB-500. This fragment weighs 847.0 g/mol, and the capped molecule sold as TB-500 weighs 889.0 g/mol. Each has its own registry number. The FDA states that the profile of the uncapped peptide cannot simply be carried over to TB-500 [1], [2], [3].
- The molecule and model matter. Unacetylated LKKTETQ promoted skin repair in mice aged 26 months [4]. Ac-LKKTETQ showed no significant effect in a separate 2024 cell assay [5]. These were different experiments, not a comparison establishing one fragment’s superiority.
- No verified human trial. Registry searches returned 0 studies for fequesetide and 0 for LKKTETQ [6]. The FDA found no clinical article on administering TB-500; its separate consumer reports do not provide assessable clinical evidence [3].
- The FDA advised against it, and its committee disagreed. On 15 May 2026 the agency proposed keeping TB-500 off the list of substances pharmacies may compound with. On 23 July 2026 its advisory committee voted 8 to 6, with one abstention, in favour of adding it, against the agency's advice, according to secondary reports. The vote has no legal effect [3], [7].
- No toxicology of any kind. The FDA found no studies on acute poisoning, repeated dosing, damage to genes, reproduction or immune reactions [3].
- Grey-market goods are unreliable. In Poland, 34.9 percent of 63 seized hormone-related medicines lacked their declared ingredient [8].
- Banned in sport at all times, on the plain reading of the list. Section S2.3 of the 2026 Prohibited List covers "Thymosin-ß4 and its derivatives e.g. TB-500" [9].
What it is
TB-500 Fragment (17-23) is a lab-made peptide of seven building blocks, written LKKTETQ. It copies positions 17 to 23 of thymosin β4, a protein found in almost every cell of the body [10]. The World Health Organization gave this exact molecule its own international name in 2022: fequesetide [11], [12].
The name on the label is where the trouble starts. What doping laboratories and the FDA call "TB-500" is the same chain with one addition. It carries a small chemical cap on its front end, an acetyl group, and is written Ac-LKKTETQ [13], [14].
According to the FDA, such a cap permanently changes a peptide's charge and size, and it can change how long the peptide lasts and how it binds to other molecules [3].
Three different substances therefore circulate under one name:
- This fragment, LKKTETQ, uncapped, 847.0 g/mol, CAS 476014-70-7 [1].
- TB-500, Ac-LKKTETQ, capped, 889.0 g/mol, CAS 885340-08-9; it is also sold as an acetate salt of 949.1 g/mol [2], [3]. It has its own page on TB-500.
- Thymosin β4, the complete protein of 43 building blocks, about 4.9 kilodaltons [10].
The confusion reaches into official documents. The FDA's compounding list names its entry "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500", using the uncapped sequence for the capped product [15]. A 2025 journal article calls the uncapped sequence "TB500" [16]. Which of the three a vial actually holds cannot be read from its label.
Quick facts
| Field | Value | Ref |
|---|---|---|
| International name | Fequesetide (proposed 2022, confirmed 2023) | [11], [12] |
| Other names | LKKTETQ, Tβ4 (17-23), TB4 Frag 17-23 | [1] |
| Class | Lab-made peptide of seven building blocks, a piece of a human protein | [11] |
| Sequence | Leu-Lys-Lys-Thr-Glu-Thr-Gln, free front end, no acetyl cap | [1] |
| Formula and mass | C36H66N10O13, 847.0 g/mol | [1] |
| How long it lasts | No published pharmacokinetic study of this unacetylated fragment identified | [3] |
| Status | No approved product found in the reviewed registers | [32], [33], [35], [36], [37] |
| Developer | No clinical development programme identified | [6] |
| CAS registry number | 476014-70-7 | [1] |
| PubChem CID | 10169788 | [1] |
| UNII | None; the FDA substance register has no entry | [14] |
| InChIKey | LVLWJWXFRFTMLK-JMWNXRNDSA-N | [1] |
Molecular mass of the uncapped fragment, the capped TB-500 and its acetate salt. The gap of 42 g/mol between the first two is exactly one acetyl group. Sources [1], [2], [3].
How it works
No verified human study of this peptide was identified. The proposed mechanisms below come from cells or animals and do not establish clinical effects [3], [6].
- It may grip the cell scaffold. The stretch LKKTET is the part of thymosin β4 that holds on to actin, the protein cells build their inner scaffold from [17]. A peptide carrying it could influence how cells move.
- It may help blood vessel cells migrate. In human vein cells, the seven-building-block motif and the whole protein were about equally active. Pieces missing part of the motif did nothing [18].
- It may switch on tissue-remodelling enzymes. In one study, positions 17 to 23 carried all of the protein's ability to raise matrix metalloproteinases, enzymes that break down tissue during repair [19].
- It may calm scar-forming liver cells. In human liver cells that drive scarring, only the 17-23 piece blocked a growth signal and a key switch inside the cell called Akt [20].
- Purinergic receptors have been proposed. The authors of one study suggested these cell-surface sensors as a possible route [21].
Two findings argue against treating the fragment as a pocket version of the whole protein. A structural study showed that the protein's activity depends on the region just before the LKKTET stretch [22]. And the calming effect of thymosin β4 on inflammation is attributed to another piece entirely, Ac-SDKP, which this fragment does not contain [23].
What the trials found
No verified human trial of the unacetylated fragment was identified. The studies below used cells or animals; each result needs to be assigned to the molecule or preparation actually tested.
Skin wounds in old mice
Animal data Mice aged 26 months received small punch wounds on the back. A solution of the uncapped fragment was applied directly to the wounds [4].
By day 7, the new skin had closed more of the wound and more collagen had formed than without treatment. The authors wrote that the seven-building-block peptide promoted repair "comparable to that observed with the parent molecule". Group sizes are not given in the summary of the study.
The FDA interprets this study cautiously because it did not assess a dose-response relationship. Whether its findings extend to other wound types remains uncertain [3].
The capped molecule sold as TB-500
In vitro In 2024, researchers tested acetylated TB-500 on layers of connective-tissue cells, called fibroblasts, after making a scratch through the cells [5].
The scratch closed no better than with the plain liquid used as a control. One of TB-500's breakdown products, a shorter piece called Ac-LKKTE, did produce a small but clear effect.
The authors concluded that the wound-healing activity reported for TB-500 "may be due to its metabolite Ac-LKKTE rather than the parent form" [5]. The FDA puts it more bluntly: animal and laboratory evidence is "currently lacking" to support TB-500 promoting wound healing [3].
The mouse experiment and the cell assay tested different molecules under different conditions. Each result belongs to its own experiment. They cannot establish that the unacetylated fragment is more effective than Ac-LKKTETQ in animals or people.
Blood vessel and remodelling cells
In vitro In cell tests from 2003, the uncapped motif made human vein cells migrate and sprout. It was about as active as the whole protein [18]. Adding loose actin to the dish blocked the effect.
Animal data A 2006 study in mouse wounds and cultured cells traced the rise in tissue-remodelling enzymes to positions 17 to 23 [19]. A separate study reported that LKKTETQ improved skin wound healing in cells and in animals [21].
Scar-forming liver cells
In vitro Researchers compared two pieces of thymosin β4, at the same concentration, in human liver cells from biopsies [20]. Only the 17-23 piece blocked the rise of three scarring markers and slowed how fast the cells multiplied and moved.
The piece covering positions 1 to 15 did neither. These were cells in a dish, with no animal or human follow-up.
Eye and brain models
Animal data A gel with the LKKTETQ sequence chemically built into it helped the cornea surface regrow after an alkali burn in animals [16]. The effect belongs to the gel system, not to the loose peptide.
Animal data In mice bred to develop Alzheimer-like changes, a peptide called "TB500" and Ac-SDKP improved memory tests and calmed brain immune cells [24]. The amyloid deposits stayed unchanged, and the paper does not say whether its "TB500" was capped.
Biçer 2026
The tendon study’s TB-500 material was not chemically identified in its methods; it cannot establish an effect of either Ac-LKKTETQ or unacetylated LKKTETQ [25]. For the full-length peptide see TB-4; the TB-500 vs. TB-4 comparison explains the distinction.
Studies in people
No data The trial registry lists 0 studies under fequesetide and 0 under LKKTETQ [6]. The one entry naming TB-500 describes itself as a fictional example and is not counted as a study here.
The FDA found no clinical article on administering TB-500, although it recorded two unassessed consumer reports involving labelled mixtures [3]. No verified human study of the unacetylated fragment was identified either [6].
What is still unknown
- Anything about people. No absorption, breakdown or safety data exist for any route [3].
- How long the uncapped peptide lasts. All breakdown data concern the capped molecule, and the FDA notes that the cap changes a peptide's lifespan [3].
- Whether the mouse result generalises. The 2003 study did not compare different amounts; it cannot establish an effect across wound types [3].
- Which molecule is active. The capped peptide failed where its breakdown product worked, which leaves the active substance open [5].
Side effects and safety
There is no established human side-effect profile for the unacetylated fragment. The FDA likewise identifies major gaps in the human safety evidence for TB-500-related preparations [3].
- No reports is not the same as no harm. The FDA's side-effect database held no report on TB-500 up to 26 March 2025. A food-safety system held two reports on a TB-500 and BPC-157 mix, without any assessment [3].
- Immune reactions. Injected peptides "may pose a significant risk for immunogenicity", the FDA writes, made worse by clumping and impurities. Reactions could range from silent antibodies to life-threatening ones [3].
- Uncontrolled quality. A public certificate of analysis the FDA reviewed did not test content, impurities, bacterial toxins or clumps [3].
- Mast cell release. In cell tests, pieces 17-23 and 16-38 made mast cells release their contents as strongly as the whole protein or more [26]. The same process drives sudden allergic reactions; what it means in people is unknown.
The FDA also lists what was never tested. No studies exist on acute poisoning, repeated dosing, damage to genes, reproduction, immune reactions or clumping, and the long-term animal safety studies that regulators normally ask for were never run either [3].
What is in the vial
Laboratories in four countries have examined products sold under these names. None found reliable contents, and none can say how much fragment versus whole protein the market holds.
- United States. A university racing laboratory reported that most products labelled TB-500 held no proteins, peptides or amino acids at all [27].
- France. A racing laboratory found that products sold as TB500 and TB1000 did not reliably match their descriptions [28].
- Germany. Among seized black-market goods from 2010 to 2013, 337 substances were analysed and 67 active ingredients identified. The whole protein thymosin β4 stood out, not the fragment [29].
- Poland. The state medicines control laboratory tested 601 performance-enhancing products seized between 2020 and 2024, TB-500 among the substance groups. Of the 63 hormone-related medicines it examined in detail, 34.9 percent lacked the declared ingredient; no separate figure for TB-500 was reported [8].
63 hormone-related medicines examined in detail, out of 601 performance-enhancing products seized in Poland from January 2020 to August 2024. These are not peptides, and no separate figure for TB-500 was reported. Source [8].
In the same group of 63, only 58.7 percent contained the declared ingredient and nothing else [8]. The FDA adds that it has found several salts and derivatives, even different active molecules, sold under one common name [3]. It calls this a safety risk, because a patient "may be dosed with a different" substance than the one ordered.
Doses used in studies
These are the doses used in the cited studies, listed for reference. They are not a recommendation.
These experiments used cells or animals. Some tested unacetylated LKKTETQ; others tested acetylated TB-500, its metabolites or material of unresolved identity. The substance column identifies those differences.
| Study | Substance | Model | Dose | Route | Schedule | Ref |
|---|---|---|---|---|---|---|
| Philp 2003, skin wounds | This fragment, uncapped | Mice aged 26 months | 0.01% solution, 50 µl per wound | On the wound | Day 0 and 48 h later, read on day 7 | [4] |
| Philp 2003, vessels | Uncapped seven-building-block motif | Human vein cells, chicken aortic rings | About 50 nM | Added to the culture | One treatment per test | [18] |
| Shah 2018 | Tβ4 (17-23) | Human liver cells, passages 4 to 6 | 10 ng/mL, with or without 50 ng/mL PDGF-BB | Added to the culture | Once, read at 24 and 48 h | [20] |
| Wyczółkowska 2007 | Pieces 17-23 and 16-38 | Mouse and human mast cells | Not given in the abstract; whole protein 0.2 to 2000 nM | Added to the culture | Once | [26] |
| Rahaman 2024 | TB-500, capped, and Ac-LKKTE | Skin cells; rats aged 6 weeks | 50 µg/mL in the dish; 50 mg/kg in rats | Culture; into the belly | Once; 8 h in the dish, urine over 72 h | [5] |
| Ho 2012 | TB-500, capped | 2 horses | One preparation containing 10 mg | Under the skin | Once, samples over several hours | [30] |
| Ou 2026 | "TB500", cap not stated, and Ac-SDKP | Nerve and brain immune cells; mice | Not given in the abstract | Not given | Not given | [24] |
No amount on this list can be scaled up to people. There is no human dose for this peptide anywhere in the published literature [3].
Development and approval status
No approved product or clinical development programme for the unacetylated fragment was identified in the reviewed sources [6], [32], [33], [35], [36], [37]. The FDA’s 2026 evaluation and Australia’s Poisons Standard address the broader TB-500 family, with important distinctions between molecules [3], [31].
From a protein motif to a disputed trade name
- 1992LKKTET identified as the part of thymosin β4 that grips actinLaboratory experiments with actin, ref [17]
- 2003The uncapped fragment matches the whole protein in old miceSkin wounds, day 7, ref [4]
- 2012Ghent laboratory shows that TB-500 is the capped fragmentHigh-resolution mass spectrometry, ref [13]
- 2013Racing laboratory finds most labelled products hold no peptideRef [27]
- 2022-2023WHO names the uncapped fragment fequesetideProposed 2022, confirmed 2023, refs [11], [12]
- 2024Capped TB-500 shows no wound effect in the dishOnly a breakdown product did, ref [5]
- May 2026FDA advises keeping TB-500 off the compounding listNo human data, no toxicology, ref [3]
- June 2026New Australian Poisons Standard in forceTB-500 and thymosin β4 listed separately, ref [31]
- July 2026FDA advisory committee votes 8 to 6 for adding it, against the agency adviceOne abstention, per secondary reports; no legal effect, ref [7]
- 1992 — the actin-gripping motif LKKTET is described [17].
- 2003 — the uncapped fragment matches the whole protein on skin wounds in old mice [4].
- 2012 — analysts in Ghent establish that TB-500 is the capped fragment [13].
- 2022 to 2023 — the WHO proposes and then confirms the name fequesetide [11], [12].
- 2024 — the capped molecule fails the scratch test that its breakdown product passes [5].
- May to July 2026 — the FDA advises against compounding use, and its advisory committee votes 8 to 6 in favour of adding it, against that advice [3], [7].
| Market | Status | Note | Ref |
|---|---|---|---|
| United States | Not approved | Committee vote without legal effect | [32], [3] |
| European Union | Not approved | No marketing authorisation | [33] |
| Germany | Not approved | Anti-doping law lists derivatives | [34] |
| United Kingdom | Not approved | No product entry | [35] |
| Australia | Prescription-only | Possession without authority illegal | [31] |
| Canada | Not approved | No product entry | [36] |
| Switzerland | Not approved | No product entry | [37] |
Every register search behind this table was run on 23 September 2026, each with a control search that did return results.
The American vote. The FDA's briefing document of 15 May 2026 proposed "not adding TB-500 (free base) or TB-500 acetate" to the compounding list [3]. It named three reasons: no human data, no toxicology, and naming so inconsistent that it counts as a safety risk.
On 23 July 2026 the advisory committee voted 8 to 6, with one abstention, in favour of adding both forms [38], [7]. These counts come from secondary reports, including a law firm's analysis of 27 July 2026. No official minutes were available on 23 September 2026.
Vote on adding TB-500 to the pharmacy compounding list, against the agency's own advice. The same result applied to the free base and the acetate. Counts from secondary reports; the vote has no legal effect. Sources [3], [7].
A committee vote is advice, not approval. Adding a substance to that list requires a formal rule-making process with public comment, and until then TB-500 stays an unapproved substance [3].
Australia lists "TB-500" and "THYMOSIN BETA 4" as two separate prescription-only entries. Both also appear in an appendix of substances that must not be possessed without authority, as items 35 and 36 [31].
The uncapped fragment is not named. The Poisons Standard covers derivatives of listed substances unless they are listed elsewhere, so it would most likely be included. That is a reading of the legal text, not a decision by the regulator [31].
Anti-doping
On the plain reading of the anti-doping rules, the fragment is banned in sport at all times, in and out of competition. Section S2.3 of the 2026 Prohibited List covers "Thymosin-ß4 and its derivatives e.g. TB-500", and substances in class S2 are classified as non-specified [9].
The list never names LKKTETQ or fequesetide. Read as written, it would catch the fragment in two ways. One is the word "derivatives", where TB-500 is only an example. The other is a closing clause for further growth factors that affect blood vessels or regeneration [9]. This is a reading of the list, not a ruling by the World Anti-Doping Agency.
German law follows the same pattern. The annex to the Anti-Doping Act lists "Thymosin-beta-4 und seine Derivate", and derivatives are expressly included [34]. Possession becomes a criminal matter above 100 mg, the "non-small amount" set by a separate regulation [39].
Whether the uncapped fragment counts as a derivative in a given case is a legal question this page does not decide. The wider picture is at peptides banned in sport.
Compared with related peptides
| Peptide | What it is | Link to this fragment | Strongest finding in its own study |
|---|---|---|---|
| TB-500 Fragment (17-23) | Uncapped seven-building-block piece, 847.0 g/mol [1] | — | Skin wounds closed as well as with the whole protein in old mice [4] |
| TB-500 | The same seven building blocks plus an acetyl cap, 889.0 g/mol [2] | One acetyl group apart; effects not transferable [3] | TB-500 label; chemical identity unresolved [25] |
| Thymosin β4 | The complete human protein, 43 building blocks [10] | Contains this fragment at positions 17 to 23 | Closed skin wounds in old mice in the same 2003 study [4] |
| Ac-SDKP | Four building blocks from the protein's front end [23] | Not contained in this fragment | The protein's calming effect on inflammation is attributed to it [23] |
| BPC-157 | An unrelated lab-made peptide | Mixed with TB-500 in two FDA reports [3] | Studied in rats against material labelled TB-500; the comparator’s identity was unresolved [25] |
The evidence remains preclinical. The 2003 aged-mouse study and the later work by Huang and colleagues reported wound-related findings, but do not establish a human benefit [4], [21]. The FDA also cautions that the earlier mouse study lacked a dose-response assessment [3].
The rat tendon study used material labelled TB-500 without resolving its chemical identity, so it cannot be assigned to either fragment [25]. The negative Ac-LKKTETQ cell result is limited to that assay [5]. Ac-SDKP and LKKTETQ cover different parts of the parent protein; neither represents the whole molecule [23].
In sport, BPC-157 falls under section S0 as a specified substance. TB-500 is named in S2.3, which covers thymosin β4 derivatives and classifies substances as non-specified [9].
Common misconceptions
- "TB-500 Fragment (17-23) and TB-500 are the same." They differ by one acetyl group, 42 g/mol, and carry different registry numbers. The FDA says the profile of the uncapped peptide "cannot be directly extrapolated" to TB-500 [1], [2], [3].
- "The wound studies establish which fragment works better." The mouse study used unacetylated LKKTETQ, while the 2024 cell assay tested Ac-LKKTETQ and its metabolites. Those different models cannot establish comparative efficacy [4], [5].
- "The FDA approved TB-500 in July 2026." An advisory committee voted 8 to 6 against the agency's advice. That vote is not an approval and does not change the law [3], [7].
- "An international name means it is a medicine." The name fequesetide only gives the molecule an unambiguous label. It says nothing about approval, safety or effect [11].
- "It is not doping because the list does not name it." S2.3 covers thymosin β4 "and its derivatives", and TB-500 is given only as an example [9].
- "No side-effect reports means it is safe." No verified human study was identified. The available reports cannot establish a safety profile, and important toxicology data are missing [3], [6].
Frequently asked questions
Is TB-500 Fragment (17-23) the same as TB-500?
No. The fragment is the uncapped chain LKKTETQ at 847.0 g/mol, while TB-500 carries an extra acetyl group and weighs 889.0 g/mol. The two have different registry numbers. The FDA states that the profile of the uncapped peptide cannot be directly carried over to TB-500.
What is fequesetide, and how does it relate to the TB-500 fragment?
Fequesetide is the international name the World Health Organization gave to the uncapped fragment LKKTETQ, proposed in 2022 and confirmed in 2023. It gives the molecule an unambiguous label. It is not an approval and says nothing about safety or effect.
Has TB-500 Fragment (17-23) ever been tested in people?
No verified human study of fequesetide or LKKTETQ was identified. The registry entry naming TB-500 describes itself as fictional. The FDA found no clinical article on administering the TB-500 fragment, although it noted unassessed reports about products bearing that name.
Did the TB-500 fragment speed up wound healing in studies?
In a 2003 study in mice aged 26 months, unacetylated LKKTETQ promoted skin repair by day 7. The FDA urges caution because no dose-response comparison was made. Ac-LKKTETQ showed no significant effect in a separate 2024 cell assay; the different models do not establish which fragment is superior.
Did the FDA approve TB-500 in July 2026?
No. In May 2026 the FDA advised against adding TB-500 to the list pharmacies may compound from. Its advisory committee voted 8 to 6, with one abstention, in favour of adding it, against the agency's advice, according to secondary reports. The vote is advice and changes nothing in law.
Is TB-500 Fragment (17-23) approved anywhere?
No. Register searches on 23 September 2026 in the United States, the European Union, the United Kingdom, Canada and Switzerland found no approval. Australia lists TB-500 and thymosin β4 as prescription-only and bans possession without authority, which most likely extends to the fragment.
Is the TB-500 fragment banned in sport?
The wording of section S2.3 of the 2026 Prohibited List covers thymosin β4 and its derivatives at all times, with TB-500 as one example. That supports treating the fragment as prohibited, although LKKTETQ is not named individually. Substances in S2 are classified as non-specified.
What is actually in products sold as TB-500?
Often not what the label says. A US racing laboratory found that most labelled products held no peptide at all. A Polish state laboratory found the declared ingredient missing in 34.9 percent of 63 seized hormone-related medicines, with no separate figure for TB-500. Nobody has measured how often the fragment or the whole protein is inside.
What are the known side effects of TB-500 Fragment (17-23)?
There is no established human side-effect profile. The FDA identifies possible immune reactions and gaps in toxicology for TB-500-related preparations. In cell experiments, the unacetylated fragment triggered mast-cell release, a process involved in allergic reactions; its significance in people is unknown.
Sources
- PubChem, National Library of Medicine. Compound CID 10169788, fequesetide (LKKTETQ); C36H66N10O13, 847.0 g/mol, InChIKey LVLWJWXFRFTMLK-JMWNXRNDSA-N, synonym CAS 476014-70-7. Retrieved 23 September 2026. https://pubchem.ncbi.nlm.nih.gov/compound/10169788
- PubChem, National Library of Medicine. Compound CID 62707662, Ac-LKKTETQ (TB-500); C38H68N10O14, 889.0 g/mol, InChIKey ADKDNDYYIZUVCZ-ZQNQAVPYSA-N. Retrieved 23 September 2026. https://pubchem.ncbi.nlm.nih.gov/compound/62707662
- U.S. Food and Drug Administration (2026). FDA Briefing Document, Pharmacy Compounding Advisory Committee meeting of 23-24 July 2026: evaluation of TB-500-related bulk drug substances (TB-500 free base and TB-500 acetate). Dated 15 May 2026. Proposal not to add either form to the 503A bulks list; findings on human data, toxicology, immunogenicity, product quality and nomenclature; FAERS search to 26 March 2025. https://www.fda.gov/media/193349/download
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- ClinicalTrials.gov API v2, searches run on 23 September 2026. "fequesetide" and "LKKTETQ" return 0 studies each; "TB-500", "TB500" and "thymosin beta 4 fragment" return only NCT07487363 (sponsor Hudson Biotech), whose own summary calls it "This fictional study"; the sponsor's other entries also call themselves mock or example studies, so it is not counted as a study. Control search "semaglutide" returned 786 studies. https://clinicaltrials.gov/api/v2/studies
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- World Anti-Doping Agency. The 2026 Prohibited List, section S2.3 "Growth Factors and Growth Factor Modulators" (page 8) and the S2 class header, "All prohibited substances in this class are non-Specified Substances"; S0 for comparison. Full text checked 23 September 2026. https://www.wada-ama.org/en/prohibited-list
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- World Health Organization (2022). International Nonproprietary Names for Pharmaceutical Substances, Proposed INN List 127. WHO Drug Information 36(2). Entry fequesetide: "thymosin-β4 (17-23)-peptide, non-phosphorylated", thymosin beta-4 analogue, C36H66N10O13, CAS 476014-70-7.
- World Health Organization (2023). International Nonproprietary Names for Pharmaceutical Substances, rINN List 89. WHO Drug Information 37(1). Confirms the name fequesetide.
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- FDA/NCATS Global Substance Registration System. UNII QHK6Z47GTG, TB-500: "N-terminal acetylated 17-23 fragment of thymosin beta 4", CAS 885340-08-9. Searches for "fequesetide" and "LKKTETQ" returned no entry, while the control searches returned results. Retrieved 23 September 2026. https://gsrs.ncats.nih.gov
- U.S. Food and Drug Administration. Certain bulk drug substances for use in compounding that may present significant safety risks; entry "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" under bulk drug substances nominated but withdrawn. Content current as of 22 April 2026, retrieved 23 September 2026. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
- Lu P, Shan M, Peng C, Ji W, Yang T, Yang Z, Zhang Z, Wang Y (2025). Alkaline phosphatase-triggered spatiotemporal repair of corneal injury with TB500 peptide hydrogel. ACS Applied Materials & Interfaces 17(50):67503-67518. PMID 41359360. DOI 10.1021/acsami.5c14652
- Vancompernolle K, Goethals M, Huet C, Louvard D, Vandekerckhove J (1992). G- to F-actin modulation by a single amino acid substitution in the actin binding site of actobindin and thymosin beta 4. EMBO Journal 11(13):4739-4746. PMID 1464307. PMC556949
- Philp D, Huff T, Gho YS, Hannappel E, Kleinman HK (2003). The actin binding site on thymosin beta4 promotes angiogenesis. FASEB Journal 17(14):2103-2105. PMID 14500546. DOI 10.1096/fj.03-0121fje
- Philp D, Scheremeta B, Sibliss K, Zhou M, Fine EL, Nguyen M, Wahl L, Hoffman MP, Kleinman HK (2006). Thymosin beta4 promotes matrix metalloproteinase expression during wound repair. Journal of Cellular Physiology 208(1):195-200. PMID 16607611. DOI 10.1002/jcp.20650
- Shah R, Reyes-Gordillo K, Rojkind M (2018). Thymosin β4 inhibits PDGF-BB induced activation, proliferation, and migration of human hepatic stellate cells via its actin-binding domain. Expert Opinion on Biological Therapy 18(sup1):177-184. PMID 30063851. PMC6748868. DOI 10.1080/14712598.2018.1478961
- Huang CM, Wang CC, Barnes S, Elmets CA (2006). In vivo detection of secreted proteins from wounded skin using capillary ultrafiltration probes and mass spectrometric proteomics. Proteomics 6(21):5805-5814. PMID 17001601. DOI 10.1002/pmic.200600163
- Simenel C, Van Troys M, Vandekerckhove J, Ampe C, Delepierre M (2000). Structural requirements for thymosin beta4 in its contact with actin. European Journal of Biochemistry 267(12):3530-3538. PMID 10848969
- Sosne G, Qiu P, Goldstein AL, Wheater M (2010). Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB Journal 24(7):2144-2151. PMID 20179146. DOI 10.1096/fj.09-142307
- Ou H, Chen R, Zhou L, Zhang Y, Zhao S, Yang Z (2026). Thymosin β4-derived peptides alleviate neuroinflammation and neurite atrophy in both in vitro models and in vivo 5×FAD mice. International Immunopharmacology 170:116097. PMID 41443105. DOI 10.1016/j.intimp.2025.116097
- Biçer O, Adanir O, Güleryüz Y, Balci EC, Dinçel YM, Yenigün MY, Aydin C, Bayrak BY (2026). Effects of BPC-157 and TB-500 on Achilles tendon healing in rats. Joint Diseases and Related Surgery 37(3):822-837. PMID 42542926. DOI 10.52312/jdrs.2026.2951
- Wyczółkowska J, Walczak-Drzewiecka A, Wagner W, Dastych J (2007). Thymosin beta4 and thymosin beta4-derived peptides induce mast cell exocytosis. Peptides 28(4):752-759. PMID 17289217
- Racing Medication and Testing Consortium (2013). Thymosin β4 bulletin, version 2.0; findings of the Kenneth L. Maddy Laboratory, University of California-Davis, on products labelled TB-500. https://rmtcnet.com/wp-content/uploads/2013-07-TB-500-Bulletin-v-2.0-Final.pdf
- Delcourt V, Garcia P, Chabot B, Barnabé A, Bouscarel M, Loup B, Popot MA, Bailly-Chouriberry L (2023). TB500/TB1000 and SGF1000: a scientific approach for a better understanding of misbranded and adulterated drugs. Drug Testing and Analysis 15(4):458-464. PMID 36482504. DOI 10.1002/dta.3421
- Krug O, Thomas A, Walpurgis K, Piper T, Sigmund G, Schänzer W, Laussmann T, Thevis M (2014). Identification of black market products and potential doping agents in Germany 2010-2013. European Journal of Clinical Pharmacology 70(11):1303-1311. PMID 25168622. DOI 10.1007/s00228-014-1743-5
- Ho EN, Kwok WH, Lau MY, Wong AS, Wan TS, Lam KK, Schiff PJ, Stewart BD (2012). Doping control analysis of TB-500, a synthetic version of an active region of thymosin β4, in equine urine and plasma by liquid chromatography-mass spectrometry. Journal of Chromatography A 1265:57-69. PMID 23084823. DOI 10.1016/j.chroma.2012.09.043
- Therapeutic Goods (Poisons Standard—June 2026) Instrument 2026, authorised version F2026L00633, registered 28 May 2026, in force 1 June 2026. Schedule 4 entries "# TB-500." and "# THYMOSIN BETA 4 (THYMOSIN β4)."; Appendix D clause 5, items 35 and 36; derivative rule in section 7. https://www.legislation.gov.au/F2026L00633/asmade/2026-05-28/text/original/pdf
- openFDA, drug/drugsfda.json and drug/label.json. No match for "fequesetide", "TB-500" or "LKKTETQ"; control searches for semaglutide returned results. Run 23 September 2026. https://api.fda.gov/drug/
- European Medicines Agency. Dataset of European public assessment reports (medicines_output_european_public_assessment_reports_en.xlsx); no entry for fequesetide, thymosin, TB-500, LKKTETQ or timbetasin; control semaglutide present. Retrieved 23 September 2026.
- Annex to section 2 subsection 3 of the German Anti-Doping Act (AntiDopG), BGBl. 2023 I No. 67, pages 1-5. Part II.3: "Thymosin-beta-4 und seine Derivate — Zum Beispiel: TB-500"; closing sentence includes derivatives. Retrieved 23 September 2026. https://www.gesetze-im-internet.de/antidopg/
- Electronic medicines compendium (emc), United Kingdom. Searches for fequesetide, thymosin and TB-500 returned no results; control semaglutide returned entries. Run 23 September 2026. https://www.medicines.org.uk/emc/search
- Health Canada. Drug Product Database API, active ingredient endpoint; 0 records for fequesetide, thymosin and TB-500; control semaglutide 51 records. Run 23 September 2026. https://health-products.canada.ca/api/drug/activeingredient/
- Swissmedic. Extended list of medicinal products (Erweiterte Arzneimittelliste HAM); no entry for fequesetid, thymosin, TB-500, LKKTETQ or timbetasin; control semaglutid 17 entries. Retrieved 23 September 2026.
- U.S. Food and Drug Administration. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee; agenda with TB-500 free base and TB-500 acetate for wound healing, docket FDA-2025-N-6895. Retrieved 23 September 2026. https://www.fda.gov/advisory-committees/advisory-committee-calendar/july-23-24-2026-meeting-pharmacy-compounding-advisory-committee-07232026
- Annex to the German Doping Agents Quantity Regulation (DmMV), BGBl. 2023 I No. 67, pages 5-10. "Thymosin-beta-4 und seine Derivate — Zum Beispiel: TB-500": 100 mg. https://www.gesetze-im-internet.de/dmmv_2023/anlage.html
Cite this page
The original register checks were completed on 23 September 2026. The identity and evidence review was updated on 30 September 2026. Any FDA decision following the July 2026 advisory vote would require a further status review.
myPeptides Research & Editing. (2026). TB-500 Fragment (17-23): what the studies show, status and safety. Version 1.1, 30 September 2026. myPeptides Peptide Register. Retrieved from https://mypep.app/peptides/tb-500-fragment-17-23
How pages in this register are compiled and graded is described under methodology; the full register is at peptides.
| Version | Date | Change |
|---|---|---|
| 1.1 | 2026-09-30 | Identity and evidence audit; distinguish full-length TB-4 and unresolved study material. |
| 1.0 | 2026-09-24 | Initial publication |
Last verified: 30 September 2026. Original register searches: 23 September 2026. Next review: on publication of official minutes of the July 2026 committee meeting, on any FDA rule-making on TB-500, on any study of the fragment in people, or on a change in the anti-doping or Poisons Standard entries.