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Not medical advice. The Atlas is not a substitute for a clinician who can examine you.

TB-500 / Thymosin Beta-4

The Tissue-Repair Peptide, WADA-Prohibited, Human Data Thin

Evidence grade 2 of 5, Thin. Read how the Atlas grades evidence.

The written rationale for this grade is still being prepared.

FDA
Not FDA-approved; WADA-prohibited in sport
WADA
Prohibited (S2 Peptide Hormones/Growth Factors; TB4/TB-500 prohibited since 2011)

Reference only. Not medical advice.

What can go wrong

No adequate human safety data for systemic recovery use. WADA prohibits it, so competitive athletes face sanctions. As a pro-angiogenic agent, it carries the same theoretical, unstudied concern about promoting existing tumor blood supply. Research-chemical sourcing means unverified purity and sterility.

This is something to take to a clinician. The Atlas can tell you what is known about tb-500 / thymosin beta-4 in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.

TB-500 is a synthetic peptide related to thymosin beta-4 (TB4), a naturally occurring ~43-amino-acid actin-binding protein involved in cell migration, angiogenesis, and tissue repair. TB-500 is often described as corresponding to the actin-binding region of TB4. It is marketed for tendon, muscle, and general recovery, frequently stacked with BPC-157. It has no FDA approval, and human efficacy data for systemic musculoskeletal use is limited to essentially a single study.

Marketed as a systemic repair peptide; banned in sport, unproven in people.

What people take it for

These are the reasons people give for taking it. They are not effects it has been shown to have.

  • Tendon/muscle recovery
  • Wound and soft-tissue healing
  • Cardiac/angiogenic repair
  • Anti-inflammatory recovery

How it is supposed to work

TB4 sequesters G-actin and promotes cell migration, angiogenesis, and re-epithelialization; these actions underpin repair claims. Genuine human clinical evidence for TB4-derived peptides is concentrated in ocular/corneal and wound-healing settings using the parent molecule, not in systemic TB-500 for tendons or muscle.

  1. Step 1Binds actin monomersThymosin beta-4 binds single G-actin molecules in a 1 to 1 complex, which stops them joining into F-actin filaments in lab assays.
  2. Step 2Keeps actin pool readyBecause it is the main actin-sequestering peptide in mammalian cells, it is thought to help control the stock of free actin that cells draw on to change shape and move.
  3. Step 3Cell migrationIn cell and rodent studies it is reported to increase the migration of skin cells (keratinocytes) and blood vessel lining cells (endothelial cells).
  4. Step 4ILK and Akt signallingIn mouse heart studies it activated integrin-linked kinase and the survival kinase Akt. This was linked to heart cell migration, survival and repair after injury.
  5. Step 5New blood vesselsIt is reported to promote angiogenesis in rodent models of several tissues, though reviewers note this was not seen when it was applied to the wounded eye surface.
  6. Step 6Dampened inflammationPreclinical studies report reduced inflammation, which is proposed to add to its repair effects.
  7. Step 7Tissue repair outcomeTogether these actions are proposed to support re-epithelialization and wound repair. Human data come mainly from small trials of thymosin beta-4 eye drops for dry eye.

Almost every step here comes from cell cultures, lab assays, or mouse and rat models of the full 43 amino acid thymosin beta-4 protein. Its actin binding is well established in the lab. How that binding leads to repair in a living person has not been established. The ILK and Akt heart findings, the angiogenesis findings and the anti-inflammatory findings are all from animal studies. They have not been shown to happen in people. The effects also differ by tissue: reviewers note that angiogenesis was not seen when thymosin beta-4 was applied to the wounded eye surface. So the pathway cannot simply be carried over from one tissue to another. The human evidence found here is limited to small phase 2 trials of thymosin beta-4 eye drops for dry eye. Those trials report some improvement in symptoms and signs, but they do not test the steps of the mechanism, and they do not cover injected use or tendon or muscle repair. None of these sources shows that the gray-market product sold as TB-500 does what the parent protein does. That product is described as a short synthetic fragment of the actin-binding region. Research linking particular activities to short sections of the protein suggests that a fragment may keep some actions and not others. Its exact makeup, purity, how the body handles it and its effects in people are not settled by this pathway. Thymosin beta-4 is also found in the cell nucleus and has been studied in cancer, which may be relevant, and the long-term effects of raising its levels have not been worked out.

Thymosin beta-4 is a 43-amino-acid peptide with an acetyl group on its N-terminus, a molecular weight of about 4,982 Da, and no fixed shape on its own (it is intrinsically disordered). A TB-500 product analysed in a 2012 study contained a different molecule: the acetylated 17 to 23 fragment of thymosin beta-4 (Ac-LKKTETQ).

The primary sources found give no formal shelf-life data. The methionine at position 6 can oxidize to a sulfoxide, which the study authors took to be autoxidation. In the lab, the sulfoxide form bound actin about 20 times more weakly under polymerizing conditions.

Parent molecule (TB-4) vs. gray-market fragment (TB-5)

Most legitimate human data involves thymosin beta-4 itself in specific indications (e.g., dry-eye/corneal trials), not the injectable 'TB-500' fragment or TB5. TB-500 TB-500 is missing the sequences tied to: the Anti-Fibrotic Fragment (Ac-SDKP), broad systemic & Transcriptional activity (no actin binding), and human trial data.

What people get wrong

  • Often said'TB-500 heals tendons.'

    ActuallyTendon-healing claims rest on animal work and analogy to TB4; controlled human tendon-healing evidence for TB-500 is essentially absent.

Who profits, and who pushes back

Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.

How we got here

Thymosin β4 discovery and early research

1981 to 1992

  1. 1981PNAS, Complete amino acid sequence of bovine thymosin β4T. L. Low, S. K. Hu and Allan Goldstein isolated thymosin β4 from calf thymus and sequenced it as a 43-amino-acid peptide, the starting point of the TB-500 lineage.
  2. 1991Study identifying thymosin β4 = FxDavid Safer and colleagues connected thymosin β4 to actin biology, showing it was essentially identical to the actin-sequestering peptide Fx. Peptide Fx: d5-kDa protein found in human blood platelets that binds to actin monomers and stops polymerization.
  3. 1992PNASSanders, Goldstein and Wang demonstrated that thymosin β4 is a potent regulator of actin polymerization in living cells, helping explain later repair-related interest.

Repair research and TB-500 characterization

1998 to 2012

  1. 1998Patent priority, Thymosin beta 4 promotes wound repairAllan Goldstein, Hynda Kleinman, Katherine Malinda, Gabriel Sosne and NIH focused patent work on thymosin β4 for tissue repair, angiogenesis and cell migration.
  2. 1999Journal of Investigative DermatologyKatherine Malinda and colleagues reported that full-length thymosin β4 accelerated dermal wound healing in rats.
  3. 2003Wound Repair and RegenerationDeborah Philp, Mahnaz Badamchian, Allan Goldstein, Hynda Kleinman and colleagues tested the 7-amino-acid actin-binding region LKKTETQ separately. This fragment became a key scientific ancestor of modern TB-500.
  4. 2011Thymosin beta-4 added to WADA Prohibited ListBecause it is an unapproved synthetic growth factor that can artificially enhance tissue repair, muscle recovery, and cell growth. Performance & recovery enhancement: athletes could use it to recover from intense workouts or injuries much faster than naturally possible, violating the fair "spirit of sport".
  5. 2012TB-500 vs TB-fragSimone Esposito and Ghent University doping-control researchers analyzed a product sold as TB-500 and reported it was Ac-LKKTETQ, an N-acetylated 7-amino-acid fragment, not full-length thymosin β4.
  6. 2012Journal of ChromatographyHong Kong Jockey Club researchers further characterized TB-500 in an equine-doping context, with metabolite detection after administration to horses.

Regulatory status and review

Sept 2023 to April 2026

  1. Sept 2023TB-500 placed in FDA 503A Category 2TB-500 lacks rigorous, controlled clinical trials proving it is safe or effective for humans
  2. April 2026Removed from Category 2 and scheduled for PCAC review alongside BPC-157This vote was not an FDA approval. not an FDA approval. The PCAC is strictly an advisory panel, meaning their votes are non-binding recommendations. As of late 2026, the FDA is still reviewing the decision and must undergo formal rules-based lawmaking before licensed compounding pharmacies can legally distribute TB-500 again.

The people taking it

TB-500 is reported to be used mostly outside medicine. Its first known use was in racehorses, and it has since spread to athletes and to people in gym and wellbeing circles who say it helps them recover.

No reliable figure exists for the number of people or animals using TB-500. T

The first is the horse racing industry. TB-500 was sold as a veterinary preparation, and the Hong Kong Jockey Club racing laboratory built a test for it in 2012 to control its misuse in equine sports. The second is human athletes. In Australian football, thymosin beta-4 was given to Essendon Football Club players, and the Court of Arbitration for Sport later banned 34 of them for two years. None of those players had a positive test. The case was decided on other evidence. The third is recreational users interested in body repair and wellbeing. A UK study of online forums (a netnographic study) found that TB-500 was one of the new peptides users named most often, alongside BPC-157. The sources do not give reliable details on the age, sex or other traits of human users.

The sources record TB-500 or thymosin beta-4 in three places. In horse racing, detection methods come from the Hong Kong Jockey Club, and a 2024 study looked at thymosin beta-4 levels in horses to help detect misuse. In Australia, it came up in the Essendon AFL doping case. In the United Kingdom, it is discussed in online peptide forums. In the United States, the FDA reviewed TB-500 as a possible bulk substance for pharmacy compounding and raised safety concerns. Thymosin beta-4 is also on the World Anti-Doping Agency's prohibited list for athletes, as reported in the Essendon coverage. There is no approved medical use of TB-500 anywhere in these sources.

What we do not know

  • Does systemic TB-500 produce any measurable human tendon/muscle benefit in a controlled trial?
  • What is the long-term safety of chronic dosing?

The market for this

What follows describes how this is bought and sold. It is not a buying guide and it is not an endorsement of any seller.

Sold overwhelmingly as a 'research chemical, not for human consumption,' often bundled with BPC-157 as a 'healing stack.' No GMP oversight for these products.

At a glance

Parent molecule
Thymosin beta-4 (~43 aa)
Key function
Actin binding, cell migration
WADA status
Prohibited (S2)
RCTs
0

What this entry does not yet cover

What follows is unfinished work on our side, not a finding about TB-500 / Thymosin Beta-4. A short entry is not a safe entry.

  • Cost and market. We have not documented what it sells for or who sells it.
  • Supply chain. We have not mapped where it is made.
  • What could change. No forward-looking summary yet.
  • How it compares. We have not set it against the alternatives.
  • Children and teenagers. We have not checked what is known about younger people.
  • Where we land. We have not taken a position on this yet.

Sources

The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.

The studies that matter

  • Scoping review, TB4/TB-500 in tissue healing2020s

    Human evidence concentrated in ocular/wound settings; direct TB-500 musculoskeletal evidence limited to essentially one study

  • Preclinical cardiac and wound-repair TB4 work2000s-2010s

    Supports repair mechanisms in animals; basis for recovery marketing