MuscleLedger

TB-500 for Athletes: A Seven-Residue Fragment With No Human Study, and the Ban That Cost 34 Footballers a Season

TB-500 is a 7-amino-acid fragment of thymosin beta-4. No study has given it to a person; the one registry record says it is fictional. The full protein was tested in heart, eye and wound trials, and it is what banned 34 AFL players.

Leon H · Edited by Caroline S · Published 2026-09-27

Illustration: A lone, unbranded glass beaker containing clear liquid sits on a sterile lab bench under blue light.
Illustration

TB-500 is the second half of the most-sold research-peptide pairing in gyms, and it is marketed with the vocabulary of recovery: tendons, ligaments, muscle tears, faster return to training. What sits under that vocabulary is an unusual evidence record. No study has ever given TB-500 to a person. The one clinical-trial record that names it describes itself as fictional. The human trials people cite were of a different, much larger molecule — and that molecule is the one that cost 34 Australian footballers a season.

This page is about the performance question: what TB-500 is, what was actually tested, how sport treats it, and how laboratories find it. The chemistry and the pairing with BPC-157 are on the Wolverine stack; this page links rather than repeats. It reports research and gives no usage guidance, per our editorial standards.

One name, two molecules

Thymosin beta-4 (Tβ4) is a 43-amino-acid protein present in almost every human cell, where it holds actin — the protein of the cell's internal scaffolding — in reserve. TB-500 is Ac-LKKTETQ: seven amino acids, residues 17 to 23 of Tβ4, the stretch that binds actin, with an acetyl cap.

The two are routinely blurred. Vendor listings commonly read "TB-500 (Thymosin Beta-4)" — Peptifact's dated price survey found that wording at all seven vendors it checked, four of which also sold a separate "TB-500 Fragment". Whatever is in a given vial, the name does not say which molecule it is. The plain-language entries are Peptide Lexicon's TB-500 and thymosin beta-4 pages.

What has been tested in people — and what has not

TB-500: nothing. A ClinicalTrials.gov search for the intervention "TB-500" on 2026-09-27 returned one record, NCT07487363, a "TB-500 (Thymosin Beta 4 17-23 Fragment)" study in heart disease whose brief summary opens: "This fictional study is an example of a ClinicalTrials.gov-style record." PubMed holds 33 records mentioning TB-500 in the title or abstract; none is a human trial.

A 2024 paper from the Korea Institute of Science and Technology's doping control centre says it plainly: "The biological effects of TB-500, however, have not been documented" (Rahaman 2024, PMID 38382158).

The full protein: heart, eye and skin. The same registry search for "thymosin beta 4" returns 18 records. Read by title, they fall into four groups: acute heart attack (RegeneRx's injectable Tβ4, and Beijing Northland's recombinant NL005), dry eye and corneal wounds (RGN-259 eye drops), skin ulcers and epidermolysis bullosa, and healthy-volunteer safety studies. None tests muscle, tendon, ligament or sports injury.

The only healthy-human dosing data are for Tβ4, intravenously. Ruff et al. 2010 gave 40 healthy volunteers 42, 140, 420 or 1,260 mg of synthetic Tβ4 by drip, once and then daily for 14 days. Adverse events were "infrequent, and mild or moderate"; there was no dose-limiting toxicity. The authors' stated purpose was heart attack. Those figures are for a 43-residue protein, by vein, reaching grams over the fortnight at the top dose — not for a seven-residue fragment in milligram vials.

The muscle question

PubMed, 2026-09-27. Thymosin beta-4 with skeletal muscle, muscle injury or muscle regeneration in the title or abstract: 14 records. Restricted to humans: 2 — a review of Tβ4 in heart repair and a gene-expression study in Atlantic halibut. No record tests skeletal muscle in people. The muscle-repair story rests on cell and animal work with the full protein.

The Korean doping-lab paper adds a twist to even that. When the team tested TB-500 and its breakdown products on fibroblasts, only one metabolite, Ac-LKKTE, showed significant wound-healing activity; TB-500 itself did not. The authors suggest the wound-healing effects reported for TB-500 may come from its metabolite. That is a cell-dish finding, but it is the only direct test of TB-500's activity found for this page.

The ban that made the headlines

The best-known doping case of the peptide era is about Tβ4. On 11 January 2016 the Court of Arbitration for Sport found 34 past and present Essendon players guilty of using the banned substance Thymosin Beta-4 in the club's 2012 supplements programme and suspended them for the entire 2016 AFL season (AFL.com.au). Twelve were still on Essendon's list and five at other clubs; the two-year bans were backdated, so most ended that November.

The case turned on the full protein, not the fragment. For athletes the distinction does not matter: WADA covers both by name.

Status in sport

  • WADA 2026: S2.3, growth factors — "Thymosin-β4 and its derivatives e.g. TB-500", prohibited at all times. Every S2 substance is non-Specified, which limits how far a sanction can be reduced. Its usual partner BPC-157 sits in S0 instead; the consequences of that split are on WADA status by compound.
  • Detection. The Korean study built the first method to measure TB-500 and its metabolites together and found Ac-LKK in rat urine for up to 72 hours after dosing, with Ac-LK the main early metabolite. Because Tβ4 occurs naturally, labs also look for traces the body does not make: a French racing laboratory showed a synthesis impurity could be detected in horse plasma after a single dose of a Tβ4 product (Delcourt 2025, PMID 39314109), and reported that Tβ4 rises quickly in stored blood samples if cells are not separated — a pitfall for any test based on the natural protein. Testing context is on peptides and drug testing.
  • FDA. TB-500 was reviewed for FDA's Pharmacy Compounding Advisory Committee in July 2026; what that review searched for and found is set out on Peptifact's TB-500 side-effects page.

Dose figures, reported

No human dose of TB-500 exists in the research record. The only healthy-volunteer figures are Ruff 2010's 42–1,260 mg of Tβ4 a day by vein. The amounts in circulation on vendor and forum pages, and where they come from, are compiled on Peptifact's TB-500 dosage page.

How it fits with the rest

TB-500 belongs to the healing-and-recovery claims, not to the muscle-growth ones: even its promoters sell it for repair rather than size. The evidence ledger for recovery peptides is on peptides for recovery and peptides for joints and tendons; for whether any peptide beats the basics on muscle, see peptides for muscle growth.

The honest summary

  • TB-500 is a seven-residue fragment of thymosin beta-4; vendors often sell it under the full protein's name.
  • No study has given TB-500 to a person. The one registry record calls itself fictional.
  • The full protein's 18 registered trials are in heart, eye and skin — none in muscle or sports injury. Its only healthy-volunteer data: 42–1,260 mg a day by vein, 14 days, no dose-limiting toxicity.
  • In cells, a TB-500 metabolite, not TB-500, showed wound-healing activity.
  • Prohibited at all times (WADA S2.3, non-Specified). Tβ4 use cost 34 Essendon players the 2016 season.
  • Labs can find its metabolites (72 h in rats) and synthesis impurities (horses).

Limits of this page

Registry and PubMed counts depend on query wording and were taken on one date. The detection windows come from rats and horses, not people. The Essendon ruling concerned thymosin beta-4 supplied in 2012; what exactly the players received was contested in the proceedings, and this page reports only the finding. The Korean wound-healing result is from cultured cells.

Sources and dates

  • Rahaman KA, Muresan AR, Min H, et al. Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro. J Chromatogr B 2024;1235:124033 — PMID 38382158, abstract read 2026-09-27.
  • Ruff D, Crockford D, Girardi G, Zhang Y. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Ann N Y Acad Sci 2010;1194:223–9 — PMID 20536472.
  • Delcourt V, Garcia P, Chabot B, et al. Equine doping controls of thymosin β4: a population study and strategy for misuse detection. Drug Test Anal 2025;17:1071–7 — PMID 39314109.
  • ClinicalTrials.gov API v2, read 2026-09-27: intervention "TB-500" → 1 record (NCT07487363, self-described as fictional); intervention "thymosin beta 4" → 18 records, all titles read.
  • PubMed, searched 2026-09-27: "TB-500"[tiab] OR "TB500"[tiab] → 33; thymosin beta 4 with skeletal muscle / muscle injury / muscle regeneration → 14; with humans[mh] → 2, both titles read.
  • AFL.com.au, Guilty: Court bans the Essendon 34 for 2016, afl.com.au/news/52804, read 2026-09-27.
  • World Anti-Doping Agency, 2026 Prohibited List, S2.3 — as quoted on this site's WADA status by compound.

Frequently asked questions

What is TB-500?

TB-500 is the trade name for Ac-LKKTETQ, a seven-amino-acid acetylated fragment of thymosin beta-4 taken from the part of the protein that binds actin. Thymosin beta-4 itself is a 43-amino-acid protein present in nearly every human cell. Vendors often label TB-500 as 'thymosin beta-4', which is a different, six-times-longer molecule.

Does TB-500 help muscle recovery or injuries?

No study has given TB-500 to a person, so there is no human evidence either way. The injury claims come from animal studies of the full thymosin beta-4 protein, and from its human trials in heart attack, dry eye and skin wounds — none in muscle, tendon or sports injury. A 2024 doping-lab study found the wound-healing activity seen in cells belonged to one of TB-500's breakdown products rather than to TB-500 itself.

Is TB-500 banned in sport?

Yes. WADA's 2026 Prohibited List names thymosin-β4 and its derivatives, including TB-500 by name, in S2.3, growth factors, prohibited at all times. Every S2 substance is non-Specified, which limits how far a sanction can be reduced. The Essendon case, in which 34 AFL players were banned for the 2016 season over thymosin beta-4, is the best-known sanction.

Can TB-500 be detected in a drug test?

Doping laboratories have published methods for it. The Korea Institute of Science and Technology's doping control centre identified TB-500's metabolites and found one, Ac-LKK, in rat urine for up to 72 hours after dosing. Because thymosin beta-4 occurs naturally, labs look for the synthetic fragment and its metabolites, or for synthesis impurities that the body does not make, as a French racing laboratory did in horses.

What doses of TB-500 have been studied?

None in people. The only healthy-volunteer study gave the full thymosin beta-4 protein intravenously at 42 to 1,260 mg a day for 14 days, with no dose-limiting toxicity. That is a different molecule, route and scale from TB-500 sold in milligram vials, and says nothing about a fragment that was never tested. The figures circulating on vendor and forum pages are compiled on Peptifact's TB-500 dosage page.

What is the difference between TB-500 and BPC-157?

They are unrelated molecules often sold together as the 'Wolverine stack'. TB-500 is a fragment of the human protein thymosin beta-4; BPC-157 is a 15-amino-acid sequence described as derived from a stomach protein. WADA prohibits both at all times but under different sections — TB-500 in S2.3, BPC-157 in S0 — with different sanction consequences. The pair is covered on this site's Wolverine stack page.