TB-500 (UK): what the Thymosin Beta-4 fragment is, what the preclinical literature shows, and where UK researchers source it

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TB-500 is a synthetic 17-residue peptide fragment derived from natural Thymosin Beta-4, a 43-amino-acid actin-sequestering protein first isolated from calf thymus extracts in the late 1960s by the Allan Goldstein lab at the US National Institutes of Health. The fragment corresponds to the central actin-binding region of the parent molecule and is produced by solid-phase peptide synthesis rather than purification from tissue. In the United Kingdom it sits in the research-tier category: sold by specialist retailers under “research use only” framing, with no marketing authorisation from the Medicines and Healthcare products Regulatory Agency, no human prescribing route, and a thin human-trial record. The preclinical literature on the parent protein is sizeable. The literature on the fragment specifically is much narrower.

What TB-500 actually is

The molecule sold under the label “TB-500” is not Thymosin Beta-4. That distinction matters and is routinely glossed over in vendor copy.

Thymosin Beta-4 (TB-4) is a 43-residue polypeptide with a molecular weight of approximately 4.9 kDa. It is one of the most abundant proteins inside mammalian cells, found at high concentrations in platelets, neutrophils, and many other tissues. Its principal documented role at the molecular level is to bind and sequester G-actin monomers, which gives the cell a reserve pool of actin that can be mobilised when the cytoskeleton needs to reorganise. This actin-binding role is mediated by a short stretch of residues in the central region of the protein, sometimes called the “actin-binding domain” or LKKTET motif region.

TB-500 is a synthetic 17-amino-acid peptide whose sequence is taken from that central region. It is not a digestion product. It is not a natural metabolite. It is a designed fragment that was developed in part because the full-length TB-4 protein is expensive and laborious to manufacture by recombinant or chemical means, while a 17-residue peptide can be produced by standard Fmoc solid-phase peptide synthesis at far lower cost and at scales that suit the research-chemical market.

The two are routinely conflated in marketing copy. Many UK and overseas vendors list “TB-500” on the bottle and then describe it in the product description as “Thymosin Beta-4”, which is incorrect. Some vendors do sell full-length recombinant or synthetic TB-4, but the price tier is markedly higher and the supply is much narrower. When the literature is searched, “Thymosin Beta-4” returns several thousand publications on PubMed. “TB-500” as a standalone search term returns a far smaller, mostly veterinary or grey-literature, set. Researchers working with the 17-residue fragment should be careful about which body of evidence they are citing.

The fragment retains some, but not all, of the parent protein’s behaviour in cell-based assays. It contains the actin-binding region, so it can interact with G-actin in vitro. It does not necessarily reproduce every downstream signalling consequence of full-length TB-4, because some of those consequences depend on regions of the protein outside the 17-residue window.

What the preclinical literature shows

The animal-model evidence base is built almost entirely on Thymosin Beta-4 itself, with a smaller subset of papers using the synthetic 17-mer or related fragments. The following observations are drawn from preclinical literature only. None of them are licensed indications in any jurisdiction.

Cutaneous wound repair. A 1999 paper by Malinda and colleagues in The FASEB Journal (PMID: 10428759) reported that topical Thymosin Beta-4 accelerated dermal wound closure and increased angiogenesis in rat full-thickness wound models. Follow-up work by Philp and colleagues in 2003 (PMID: 12930770) extended the observation in murine models with similar acceleration of re-epithelialisation. These rodent findings remain the most-cited result for the molecule.

Corneal wound repair. Sosne and colleagues published a series of papers from the early 2000s onwards (representative example PMID: 11991576) on Thymosin Beta-4 accelerating corneal epithelial repair in rabbit and rat models of alkali burn. This work later became the basis for one of the only well-known human trials of the parent protein, which is discussed below.

Cardiac repair. A 2004 paper by Bock-Marquette and colleagues in Nature (PMID: 15565136) reported that systemically administered Thymosin Beta-4 protected mouse cardiomyocytes after experimental myocardial infarction and improved functional cardiac outcomes. This paper drove much of the subsequent academic interest in the molecule. Riley and colleagues at University College London later reported (PMID: 21743479) that priming with Thymosin Beta-4 mobilised an adult epicardial progenitor population in mice. The cardiac-regeneration line of work is contested: independent replication has not been clean.

Neurological models. Morris and colleagues reported (PMID: 20880394) Thymosin Beta-4 effects in a rat model of embolic stroke, with reduced neurological deficit scores and altered glial responses. Xiong and colleagues (PMID: 22305868) extended this to traumatic brain injury models in rats. Both lines are preclinical.

Hair follicle effects. Philp and colleagues reported (PMID: 15265688) Thymosin Beta-4 effects on the murine hair-follicle cycle, including accelerated transition into anagen and increased follicular cell migration. This paper is the academic source of the popular claim that TB-500 promotes hair growth. The work is rodent. There is no published human randomised trial of TB-500 for androgenetic alopecia or any other hair condition.

Inflammation and chemokine modulation. Several papers (representative example PMID: 17313514) report anti-inflammatory effects of Thymosin Beta-4 or its N-terminal acetylated tetrapeptide derivative N-acetyl-SDKP in rodent models of fibrosis, sepsis, and ischaemia-reperfusion injury. These findings are mechanistically distinct from the actin-binding story and remain preclinical.

Skeletal-muscle and tendon. A smaller body of work (representative example PMID: 22095033) reports rodent effects on muscle satellite-cell migration and tendon healing kinetics. The tendon line is the one most often cited by vendors when explaining why TB-500 is sold alongside BPC-157 in the so-called Wolverine stack, but the published literature is sparse compared with the cardiac or wound-healing work.

Two caveats are appropriate here. First, almost all of these papers use the parent 43-residue Thymosin Beta-4 protein, often recombinant. The 17-residue fragment marketed as TB-500 has been tested in some studies but is the minority case in the literature. Second, the bulk of high-profile cardiac work came from a small number of groups, and the field has been the subject of replication scrutiny in the past five years.

What the literature does NOT show

This section is the section that most vendor pages omit. It is the section that an editorial pillar has to contain.

No phase II or phase III human RCT for the fragment. A search of the EU Clinical Trials Register, the US ClinicalTrials.gov database, and the WHO International Clinical Trials Registry Platform returns no completed phase II or phase III randomised, placebo-controlled trial of TB-500 (the 17-residue fragment) for any indication, in any patient population, in any country.

Limited human work even on the parent protein. RegeneRx Biopharmaceuticals, the US biotech that holds patents on Thymosin Beta-4 therapeutic applications, ran a small set of early-phase studies of full-length Thymosin Beta-4 in indications such as venous stasis ulcer, diabetic foot ulcer, and dry eye disease. The dry-eye programme (RGN-259) reached phase III but did not produce a marketed product. The pressure-ulcer and epidermolysis-bullosa programmes did not progress to a commercial endpoint. None of this is TB-500 the fragment. It is TB-4 the parent protein, formulated as a regulated investigational drug, given under IRB-approved protocols. A vendor that cites the RegeneRx pipeline as evidence for retail TB-500 is making a category error.

Independent replication concerns. Several of the higher-impact cardiac and progenitor-cell papers have been the subject of editorial comment in recent years. The 2011 epicardial progenitor work by the Riley group was followed by a 2018 paper from the same lab (PMID: 30022123) that significantly walked back some of the original claims. The general lesson is that even the published animal evidence is not fully settled, and a careful researcher should not treat the 2004 Nature paper as the last word.

No reliable pharmacokinetic data in humans. Plasma half-life, distribution volume, oral bioavailability, immunogenicity profile, and long-term safety of the synthetic 17-residue fragment in humans are not characterised in peer-reviewed literature.

No long-term safety dataset. No pharmacovigilance data exist for chronic use of the fragment in humans because there is no licensed human use of the fragment. Anecdotal reports circulating on forums and in podcasts do not constitute pharmacovigilance.

UK regulatory status

TB-500 has no UK marketing authorisation. It is not licensed by the Medicines and Healthcare products Regulatory Agency as a medicine for any indication and has no Summary of Product Characteristics on the MHRA register. It is not available on private prescription in the UK because no UK manufacturer or importer holds a license to supply it for human use.

It is not a controlled drug under the Misuse of Drugs Act 1971. It is not currently scheduled under the Psychoactive Substances Act 2016. Sale and possession of the synthetic peptide are lawful in the United Kingdom when the substance is marketed strictly for in-vitro research and not for human consumption. The line where the legal position changes is the moment a retailer, blogger, or marketer makes a therapeutic claim. Under regulation 7 of the Human Medicines Regulations 2012, a product becomes an unlicensed medicinal product if it is presented as having properties for treating or preventing disease. At that point MHRA enforcement (cease-and-desist, product seizure, prosecution) becomes available. UK retailers that sell TB-500 manage this risk by stripping all therapeutic language from their listings and labelling.

WADA prohibited-list status. TB-500 is on the World Anti-Doping Agency Prohibited List under category S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), specifically under the sub-heading “growth factors and growth-factor modulators”. It is prohibited in-competition and out-of-competition for tested athletes in any sport that operates under the WADA Code, which in the UK includes UK Sport-funded sports, UK Anti-Doping (UKAD) jurisdictions, and most Olympic and Paralympic federations. Detection methods exist. Tested athletes should treat TB-500 as a banned substance with the same care they would treat anabolic agents. Possession of a prohibited substance by an athlete subject to the Code is itself a potential anti-doping rule violation.

Non-tested athletes and members of the general public in the United Kingdom are not bound by the WADA Code, but the MHRA framing above still applies.

Where UK researchers source TB-500

A small number of UK-based retailers list TB-500 under research-use-only framing. The retailer profiles below are editorial summaries based on the PeptideClear methodology. None of these vendors are pharmacies. None of them are licensed by the MHRA to supply medicines. None of them should be treated as a route to a therapeutic product.

The four retailers covered on PeptideClear that stock TB-500 are:

Pure Peptides UK · a UK-incorporated retailer with batch certificates of analysis (CoA) attached to product pages. Tier under the PeptideClear CoA Trust Index methodology: see the retailer profile.
XL Peptides · UK-incorporated, third-party HPLC and mass-spectrometry data published per batch.
Imperial Peptides · UK-incorporated, batch CoA publication.
My Peptides · UK-incorporated, longer-running operation in the UK research-chemical space.

The single most important variable when comparing research-tier retailers is the CoA. A CoA is a third-party analytical certificate showing the peptide identity (typically by mass spectrometry) and purity (typically by reverse-phase HPLC) for the specific batch the buyer is receiving. The PeptideClear CoA Trust Index methodology assigns retailers to tiers based on whether the CoA is per-batch, third-party-issued (rather than self-issued), published openly on the product page, and clearly tied to the lot the customer is shipped. Vendors that publish only a single historical CoA, vendors that publish self-issued certificates, and vendors that publish no analytical data sit in lower tiers.

A second variable is country of incorporation. UK incorporation matters for consumer-protection purposes (Companies House registration, UK contractual recourse, UK tax) and for shipping (no customs delay, no border seizure risk for international peptide shipments). It does not change the regulatory class. A UK-incorporated retailer is still selling a research chemical, not a medicine.

PeptideClear does not sell, dispense, or ship TB-500 or any other peptide. The retailer pages linked above are editorial comparison entries. The links are affiliate links where commercial arrangements exist, declared in full on the how we are funded page.

Common stacks

The most commonly discussed combination in the research-peptide community is BPC-157 paired with TB-500, often nicknamed the Wolverine stack because of vendor marketing copy claiming the combination accelerates tissue repair beyond either alone.

The PeptideClear editorial position on the Wolverine stack is set out at /stacks/wolverine/. The summary, in short:

The two molecules have non-overlapping proposed mechanisms in the preclinical literature. BPC-157 is a 15-residue peptide derived from a human gastric-juice protein, with the bulk of its animal evidence in tendon, gut, and vascular models. TB-500 is a fragment of an actin-binding protein, with its preclinical evidence concentrated in wound repair, cardiac, and neurological models.
The notion that combining them produces additive or synergistic effects is not tested in any peer-reviewed paper. There is no published animal study, let alone human trial, of the two molecules co-administered.
The Wolverine stack is therefore a vendor and forum construct, not an evidence-based protocol.

PeptideClear publishes the Wolverine stack page as editorial commentary on the phenomenon, with no dosing instructions, no protocol, and no recommendation that any individual use it.

FAQ

Is TB-500 the same as Thymosin Beta-4? No. Thymosin Beta-4 is a 43-residue protein found naturally in mammalian cells. TB-500 is a synthetic 17-residue peptide fragment that contains the central actin-binding region of the parent protein. The two molecules are routinely conflated in vendor copy but they are not the same chemical entity and the preclinical literature on the parent protein is much larger than the literature on the fragment.

Is TB-500 legal in the United Kingdom? The substance itself is not a controlled drug under the Misuse of Drugs Act 1971 and is not scheduled under the Psychoactive Substances Act 2016. UK retailers may sell it under “research use only” framing without therapeutic claims. It has no MHRA marketing authorisation, no UK prescribing route, and becomes an unlicensed medicinal product the moment a therapeutic claim is attached. WADA-tested athletes are prohibited from using it in or out of competition.

Are there published human trials of TB-500? No phase II or phase III randomised placebo-controlled trial of the 17-residue TB-500 fragment has been published or registered for any indication. Some early-phase work has been conducted on the full-length parent protein Thymosin Beta-4 by RegeneRx Biopharmaceuticals (corneal and dermal indications), but no programme has produced a marketed product, and the parent-protein work does not generalise to the fragment.

What does the preclinical literature suggest? Animal-model evidence reports effects in cutaneous and corneal wound repair, cardiac protection after experimental infarct, models of stroke and traumatic brain injury, and rodent hair-follicle cycling. Almost all of this work uses the full-length Thymosin Beta-4 protein, often from a small number of research groups, with limited independent replication of the higher-impact findings.

Why is TB-500 on the WADA Prohibited List? WADA classifies it under section S2 of the Prohibited List (peptide hormones, growth factors and related substances) on the basis that it falls within the broad class of growth-factor and tissue-repair modulators. The classification applies in and out of competition for tested athletes. Detection methodologies for the peptide exist.

Why do UK retailers sell it as “research use only”? The framing is a regulatory firewall. UK Human Medicines Regulations 2012 (regulation 7) define a medicinal product partly by its presentation. A peptide marketed without therapeutic claims and intended for in-vitro laboratory use is not a medicinal product under that definition. The moment a retailer or commentator makes a claim that the substance treats, prevents, or cures a condition, the substance becomes an unlicensed medicinal product, which gives the MHRA grounds for enforcement.

Outstanding research questions

The body of work on TB-500 specifically (as distinct from full-length Thymosin Beta-4) leaves a number of open questions that an honest editorial pillar should name.

First: does the 17-residue fragment reproduce the downstream effects of the parent protein, or only the proximal actin-binding step? The literature has not directly tested fragment versus full-length in matched models for most of the high-profile indications. A vendor claim that “TB-500 does X” because “Thymosin Beta-4 does X” assumes a mechanistic equivalence that has not been rigorously demonstrated.

Second: what is the human pharmacokinetic profile of the fragment? Without phase I human data, basic parameters such as plasma half-life, distribution volume, immunogenicity, and route-of-administration bioavailability are unknown. Any extrapolation from rodent pharmacokinetics is speculative.

Third: what is the long-term safety profile? Even the parent protein has limited long-term safety data in humans. The fragment has effectively none.

Fourth: how reproducible is the cardiac-regeneration line of work, after the 2018 reanalysis from the same UCL group that produced the original epicardial-progenitor result? This is the question that matters most for the molecule’s long-term scientific standing.

Fifth: what is the manufacturing quality variability in the UK research-tier market? CoA publication varies by retailer. Independent third-party testing of marketed batches, conducted at scale and published openly, would be the single most useful thing a UK editorial source could add to the field. PeptideClear’s methodology page sets out the current CoA Trust Index, which is the closest published proxy available.

The honest summary, as of mid-2026: TB-500 is a real molecule, a real fragment of a real protein, with a real (if narrow) preclinical evidence base on the parent and a thinner one on the fragment itself. It is not a licensed medicine in any jurisdiction. It is prohibited for tested athletes under WADA. UK retailers sell it for laboratory research. None of the above is a recommendation that any individual use it.

Author: Oliver Mackman, editor, PeptideClear. Published 19 May 2026.

PeptideClear is an editorial comparison hub. We are not a pharmacy, not a clinic, and not a research-peptide retailer. Nothing on this page is medical advice. Research peptides referenced on this site are not licensed medicines in the United Kingdom and have no MHRA marketing authorisation. See our editorial policy and how we are funded pages for our disclosure and methodology.