TB-500 — identity, handling and published literature

A synthetic N-terminally acetylated heptapeptide corresponding to residues 17–23 of thymosin β4, supplied as lyophilised powder for laboratory research use.

Presentation and physical properties

Reconstitution arithmetic for a 5 mg vial

Concentration follows directly from the fill mass and the volume of diluent added:

concentration (mg/mL) = vial mass (mg) ÷ diluent volume (mL)

Worked for this vial at 5 mg. The third column restates the same concentration as the mass contained in one 0.01 mL graduation of a U-100 syringe barrel, which is the graduation scale most laboratories measure small volumes against. It is a property of the solution, not an instruction.

The same arithmetic for any other diluent volume, with a syringe diagram and warnings where a calculated volume exceeds the barrel or falls below two graduations, is in the reconstitution calculator, pre-selected to this vial strength. The calculator fills in vial strength only. It does not hold a target amount for any compound, and neither does this page.

Storage and stability

The lyophilised solid is the stable form. It is held sealed, desiccated and protected from light, at −20 °C or below; a supplier data sheet issued against the same CAS number states a shelf life of two years at −80 °C and one year at −20 °C for the powder, stored under nitrogen where that is available. Vials are allowed to reach room temperature before the seal is broken, so that atmospheric moisture does not condense onto cold solid and start the degradation routes described below.

Solution is markedly less stable than solid. The same data sheet states six months at −80 °C and one month at −20 °C in solvent. Repeated freeze–thaw cycling is avoided; where a solution is to be held, it is divided into single-use aliquots so that the bulk is thawed once.

The degradation chemistry follows from the sequence. The heptapeptide contains one glutamine residue, and glutamine deamidation is a recognised degradation route for peptides in both the solid state and in solution [7]. It contains two threonine residues, whose hydroxyl side chains contribute to the hygroscopic behaviour of the solid. It contains no cysteine, so disulfide scrambling is not available as a degradation route, and no methionine, so methionine oxidation is not either. Short ambient excursions in transit are ordinary for a lyophilised peptide and are not equivalent to storage at ambient temperature.

The twenty-eight day convention often quoted for a reconstituted vial that will be punctured more than once is a property of the diluent, not of the peptide. It derives from the antimicrobial preservative in bacteriostatic water, which is what limits how long a repeatedly punctured vial can be regarded as microbiologically controlled. Sterile water contains no preservative and carries no such interval. Neither figure is a statement about the chemical stability of this peptide in solution, which is set by the storage conditions above.

Full-length thymosin β4 is a much larger polypeptide and its handling follows protein rather than short-peptide practice; storage guidance for one should not be applied to the other.

Analytical identity and certificate literacy

Characterisation of this fragment by reversed-phase HPLC and electrospray mass spectrometry is described in the primary identity paper [1], which also reports a detection strategy in plasma and urine matrices on a triple-quadrupole instrument.

Expected masses, calculated from C₃₈H₆₈N₁₀O₁₄:

What area-percent purity measures. An HPLC purity figure is the area of the main peak as a proportion of total integrated peak area under one chromatographic method, at one detection wavelength. It is a statement about that separation and nothing more.

What it does not measure. It does not detect a species that co-elutes with the main peak under that method, which is why an orthogonal method or a mass-spectrometric confirmation carries information a single chromatogram cannot. It does not measure how much of the weighed material is peptide: the balance of a lyophilised peptide salt is counter-ion and bound water, and that fraction is reported separately as net peptide content, by amino acid analysis or nitrogen determination. It says nothing about endotoxin, residual solvent or elemental impurities, each of which is a separate determination.

What lot-to-certificate traceability means. A certificate is evidence about the lot it names, and it is evidence about material in hand only if that lot identifier can be matched to the material in hand. A certificate for an unrelated lot, or a certificate that cannot be tied to a specific consignment, establishes that testing was performed somewhere; it does not establish what is in a particular vial.

What the published literature investigated

Each entry below states who investigated what, in which model, and what the authors reported. Entries are grouped by the class of model used, never by condition. Where a study used full-length thymosin β4 rather than the acetylated heptapeptide, that is stated in the entry.

Analytical and identity literature

Esposito and colleagues, 2012, investigated the chemical identity of the peptide present in TB-500 material and the development of a method capable of detecting it, in an analytical chemistry setting comprising solid-phase peptide synthesis, HPLC with high-resolution mass spectrometry, and subsequent method development in plasma and urine matrices on a triple-quadrupole instrument, and reported that the peptide identified in TB-500 is the N-terminally acetylated 17–23 fragment of thymosin β4, Ac-LKKTETQ, confirmed by synthesis and HPLC–HRMS, together with an analytical strategy for its detection in plasma and urine [1].

In vitro and rodent models

Bock-Marquette and colleagues, 2004, investigated the mechanism by which thymosin β4 acts on cardiac cells, in cardiac cell culture and in a murine myocardial infarction model, and reported that thymosin β4 formed a functional complex with PINCH and integrin-linked kinase, resulting in activation of a survival signalling pathway, and reported effects on cardiac cell migration and survival [2]. Molecule used: full-length thymosin β4, not the Ac-LKKTETQ fragment.

Biçer and colleagues, 2026, investigated histopathological and biomechanical measures after Achilles tendon transection and repair, comparing TB-500, BPC-157 and their combination, in 32 male Sprague-Dawley rats allocated to four groups of eight and assessed four weeks after operation, and reported significantly higher maximum load to failure in the TB-500 group than in the control group, significantly lower total Movin scores in the TB-500 and combination groups, and no additional effect from the combination relative to the single agents [3].

Human studies

Sosne, Dunn and Kim, 2015, investigated a thymosin β4 ophthalmic solution against vehicle, in a phase 2 randomised trial in human participants with severe dry eye, and reported differences favouring the active arm on the trial’s sign and symptom endpoints [4]. Molecule and presentation used: full-length thymosin β4, applied as an ophthalmic drop, not the Ac-LKKTETQ fragment.

Sosne and Ousler, 2015, investigated a thymosin β4 ophthalmic solution against placebo under a controlled adverse environment protocol, in a phase 2 randomised placebo-controlled trial in human participants with moderate to severe dry eye, and reported on safety and on the pre-specified ocular discomfort and staining endpoints [5]. Molecule and presentation used: full-length thymosin β4 ophthalmic formulation, not the Ac-LKKTETQ fragment.

Narrative reviews

Mendias and Awan, 2026, reviewed approved and unapproved peptides in musculoskeletal medicine, covering Tβ4 and TB-500 as separate entries, in a narrative review, and reported that rigorous human safety data for the unapproved peptides in this class are scarce, notwithstanding findings reported in animal models [6].

Evidence gaps and limitations

• No randomised controlled trial of this molecule exists. No published, peer-reviewed randomised controlled trial of the acetylated heptapeptide Ac-LKKTETQ was identified for any indication.
• The human trial literature is about a different molecule. The two randomised trials identified [4][5] used full-length thymosin β4, a 43-residue protein of roughly 4963 g/mol, formulated as an ophthalmic drop. They are evidence about that protein in that presentation. They are not evidence about the 889 g/mol fragment, and a reader who encounters them cited beneath the name “TB-500” is being shown the wrong molecule.
• Substitution of the parent protein for the fragment is widespread. Much of the material circulated as literature for TB-500 was performed with full-length thymosin β4. This is the single largest interpretive hazard on this compound.
• The fragment-specific literature is very small. What was identified amounts to one analytical identity paper [1] and one rodent tendon study [3]. There is no body of work to weigh.
• Single study, small groups, one time point. The rodent study allocated 32 animals to four groups of eight and assessed at four weeks [3]. No independent replication of it was identified.
• Effect sizes are not established for the fragment, and no exposure–response characterisation appears in the literature identified.
• No toxicology to regulatory standard was identified for the fragment, and no human pharmacokinetic characterisation of it was identified. A 2026 narrative review reported that rigorous human safety data for unapproved peptides in this class are scarce [6].
• Sponsor interest in the trial literature. The ophthalmic trials evaluate a sponsor-developed investigational formulation. Declarations of interest and funding are stated in each paper and should be read there rather than taken from any summary, including this one.
• The identification data circulating for this compound are internally inconsistent. Two different molecular formulae and masses are published against one CAS number, and one of them cannot describe the published sequence. That a discrepancy of this kind has propagated unchallenged is itself an indication of how thinly the compound is documented outside supplier catalogues.
• No primary chemical database record was verified for the fragment. The figures in the identification table are corroborated between the published sequence and a supplier data sheet; they were not confirmed against a curated primary compound record, which for the parent protein was available and is cited.

Regulatory and standards position

United Kingdom marketing authorisation. There is no UK marketing authorisation for this fragment, and none for full-length thymosin β4. Material supplied for laboratory research is not manufactured to medicinal standard and is not supplied for human or veterinary use.

Match to an authorised medicine. None. This molecule is not the active ingredient of a medicine authorised in the United Kingdom, and no comparison with any authorised medicine is drawn on this page.

Controlled drug status. Not scheduled under the Misuse of Drugs Act 1971 or the Misuse of Drugs Regulations 2001.

Anti-doping. The World Anti-Doping Agency Prohibited List names “Thymosin-β4 and its derivatives, e.g. TB-500” within section S2, among growth factors and growth factor modulators. Substances in section S2 are prohibited at all times, both in and out of competition, and are non-specified substances.

United States bulk-substance status. The status of this substance on the FDA’s interim list of bulk drug substances for use in compounding under section 503A has changed more than once, and it could not be confirmed against a current primary FDA source at the review date below. It is therefore not stated here rather than stated approximately. That status governs compounding in the United States in any event and has no bearing on supply in the United Kingdom.

Export restriction. None applies to this item.

Laboratory handling and safety

Classification. No harmonised classification under GB CLP was identified for this substance. In the absence of a harmonised entry, handle it in accordance with the safety data sheet supplied with the material and with your laboratory’s general practice for uncharacterised lyophilised peptides. Absence of a classification is absence of an assessment, not evidence of low hazard.

Personal protective equipment. Gloves, eye protection and a laboratory coat. The dry solid is light and readily dispersed, so open vials with the mouth directed away from you and avoid actions that generate airborne powder. Weigh and transfer solid in a ventilated enclosure where one is available.

Spill. For solid, avoid raising dust: cover, collect mechanically, then wipe the area with a damp absorbent and decontaminate the surface. For solution, absorb with inert material and collect. Place all collected material and contaminated absorbent into the laboratory chemical waste stream.

Disposal. Dispose of unused material, solutions and contaminated consumables through your chemical waste arrangements in accordance with local requirements. Do not discharge to drain.

Related compounds and consumables

• Library entries in the same category: BPC-157, GHK-Cu
• Diluents: bacteriostatic water, sterile water
• Tool: reconstitution calculator, pre-selected to this vial strength
• Comparison articles covering this compound: none currently published

Availability

Listing: TB-500 5mg. Price: £22.99. Stock state and the basket control are resolved from the product record when this page is rendered. Where the product is not published, this block renders as “Not currently listed” and emits no link.

References and provenance

Article titles are given where the published title is a neutral description of the work, and omitted where the published title is phrased as a statement of effect. A PubMed identifier is given in every case, so every reference resolves to its original whether or not its title is reproduced here.

1. Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. “Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential.” Drug Test Anal. 2012;4(9):733–8. Model: analytical chemistry — solid-phase synthesis, HPLC with high-resolution mass spectrometry, method development in plasma and urine. PMID 22962027. DOI 10.1002/dta.1402.
2. Bock-Marquette I, Saxena A, White MD, Dimaio JM, Srivastava D. Nature. 2004;432(7016):466–72. Model: cardiac cell culture and murine myocardial infarction. Molecule: full-length thymosin β4. Title omitted, see PMID. PMID 15565145.
3. Biçer O, Adanir O, Güleryüz Y, Balci EC, Dinçel YM, Yenigün MY, Aydin C, Bayrak BY. Jt Dis Relat Surg. 2026;37(3):822–837. Model: 32 male Sprague-Dawley rats in four groups of eight, assessed four weeks after Achilles tendon transection and repair. PMID 42542926.
4. Sosne G, Dunn SP, Kim C. Cornea. 2015;34(5):491–6. Model: phase 2 randomised trial in human participants. Molecule: full-length thymosin β4, ophthalmic solution. Title omitted, see PMID. PMID 25826322.
5. Sosne G, Ousler GW. Clin Ophthalmol. 2015;9:877–84. Model: phase 2 randomised placebo-controlled trial in human participants, controlled adverse environment protocol. Molecule: full-length thymosin β4, ophthalmic solution. PMID 26056426.
6. Mendias CL, Awan TM. Sports Med. 2026 Apr 12 [Epub ahead of print]. Model: narrative review. PMID 41966639.
7. Li B, et al. J Pharm Sci. 2005;94(8):1723–35. Model: peptide stability chemistry; cited here for deamidation as a recognised degradation route. PMID 15986465.

Identification data derive from the published sequence in reference 1 and from a commercial product data sheet issued against CAS 885340-08-9; masses in the identification and analytical sections are calculated from the molecular formula. Comparative data for full-length thymosin β4 derive from PubChem CID 45382195. Regulatory statements derive from the WADA Prohibited List and from UK legislation as cited.

Last reviewed 8 August 2026 · First publication of this entry.