TB-500 in Sport and Horse Racing: Doping Cases, WADA Status and the Evidence

LynxLab · 24 October 2026 · 8 min read

How TB-500 moved from racing stables to the WADA list: the Hong Kong test, the Essendon case, what was really in the vials, and what the research measured.

Photo: Angelica Hasbon, Unsplash

TB-500 did not arrive through a pharmaceutical pipeline. It arrived through horse racing, and the anti-doping laboratories that police racing were the first scientists to work out what it actually was.

That history explains why tb-500 is named on the World Anti-Doping Agency's prohibited list while never having been through a human trial. This post follows the trail from the stables to the list, then looks at what the underlying tissue-repair research measured, and in which species.

WADA names TB-500 under S2.3

The 2026 WADA Prohibited List puts "Thymosin-β4 and its derivatives e.g. TB-500" in section S2.3, growth factors and growth factor modulators. The section covers substances affecting "muscle, tendon or ligament protein synthesis/degradation, vascularisation, energy utilization, regenerative capacity or fibre type switching" (WADA Prohibited List).

S2 substances are prohibited at all times, in and out of competition. Under the World Anti-Doping Code athletes are strictly liable for what is found in their samples, whatever the label on the vial said.

The US Anti-Doping Agency's advisory on the 2027 list, published on 6 October 2026, restates that TB-500 is prohibited under S2 and adds a wider change: from 1 January 2027 "peptides" in general are named as prohibited under S0, non-approved substances, whether or not a given peptide appears by name (USADA athlete advisory, October 2026).

UK Anti-Doping applies the same list to British athletes. Anyone subject to testing who is reading about tb500 uk listings should treat the substance as banned without exception.

Racing stables were where TB-500 first appeared

The earliest scientific papers on TB-500 describe it as a veterinary preparation. The Hong Kong Jockey Club's racing laboratory wrote in 2012 that "a veterinary preparation known as TB-500" had emerged, containing a synthetic, N-acetylated version of the LKKTETQ segment of thymosin beta-4, sold in 10 mg vials (Ho et al., Journal of Chromatography A, 2012).

The marketing was aimed at trainers. The US Racing Medication and Testing Consortium (RMTC) recorded claims that the product could build muscle, speed recovery, stop bleeding, increase red blood cells and reduce inflammation, at a price of 150 to 300 US dollars per 10 mg (RMTC Thymosin β4 Bulletin, 2013).

None of those claims came with a controlled study in horses. The RMTC's own reading of the literature was that the LKKTETQ sequence "may have a role in wound healing" and angiogenesis, and that the anti-inflammatory properties attributed to thymosin beta-4 belong to a different part of the protein not present in TB-500.

The Hong Kong test, 2012

Emmie Ho's team at Sha Tin built the first confirmatory method. They first worked out the metabolites of Ac-LKKTETQ by incubating it with horse liver, then isolated the parent peptide and its fragments from urine and plasma by ion-exchange solid-phase extraction and ran them through liquid chromatography-mass spectrometry.

The method confirmed Ac-LKKTETQ at 0.02 ng/mL in equine plasma and 0.01 ng/mL in equine urine. It then found the peptide and its metabolites in samples from horses that had received a single 10 mg dose of TB-500, which the authors described as the first identification of TB-500 in post-administration samples from any animal (Ho et al., 2012).

The window was short. The RMTC summarised the Hong Kong data as a metabolite unique to the synthetic peptide being detectable for 11.3 hours in plasma and 9.7 hours in urine, and concluded that out-of-competition testing, not race-day testing, was the way to catch it.

Thirteen years later the Laboratoire des Courses Hippiques outside Paris published the first estimate of natural thymosin beta-4 levels in racehorses, showed that the concentration does not depend on sex, age or breed, and demonstrated that a synthesis impurity, not present in the natural protein, could be detected in plasma after a single dose of a thymosin beta-4 product (Delcourt et al., Drug Testing and Analysis, 2025). That gives racing authorities a second route to a positive finding.

What was really in the vials

The RMTC bulletin contains the most uncomfortable fact in the TB-500 story. The Kenneth L. Maddy laboratory at the University of California, Davis analysed a number of products labelled "TB-500" and reported that many contained no thymosin beta-4 and no peptide derived from it.

Most contained no proteins, peptides or amino acids at all. One sample did contain N-acetylated LKKTETQ.

That is a 2013 finding about products sold to horse trainers, and it is not a statement about any current supplier. But it is the reason a sceptical buyer of research-grade tb-500 asks for a batch-specific HPLC and mass-spectrometry report before anything else.

In the same period, the Ghent University doping laboratory bought TB-500 as sold and, using high-resolution mass spectrometry, confirmed the content as the acetylated 17 to 23 fragment of human thymosin beta-4 (Esposito et al., Drug Testing and Analysis, 2012). WADA then funded a Ghent project to map how humans would metabolise it, synthesise reference standards of the three main metabolites, and distribute them to other accredited laboratories (WADA research project 13D34PV).

The Essendon case and the move into human sport

The largest doping case involving thymosin beta-4 was not about TB-500 as such, but it set the tone for how sport treats the whole family. In February 2013 the Australian Crime Commission reported widespread peptide use in Australian sport. The Australian anti-doping agency charged 34 past and present Essendon Football Club players with using thymosin beta-4 during the club's 2012 supplements programme.

The AFL's tribunal cleared the players in March 2015. WADA appealed, and on 11 January 2016 the Court of Arbitration for Sport upheld the appeal and imposed two-year bans backdated to 31 March 2015, ruling out most of the players for the 2016 season (The Guardian, 12 January 2016). There was no positive test; the case was built on injection records, text messages and witness evidence, which WADA described as a precedent for "non-analytical" cases (WADA statement, January 2016).

Racing followed within months. In April 2016 Racing Victoria charged Stawell trainer Paul Jones after stewards found four vials of a thymosin beta-4 fragment product at his property; he admitted administering it to the horse General Sateen in mid-2015, and the state's chief steward called it "the first real direct case we have had to do with peptides" (Sydney Morning Herald, April 2016).

What the tissue-repair research measured

Strip away the marketing and the peer-reviewed record on the LKKTETQ fragment is short and specific.

Philp and colleagues at the US National Institutes of Health showed in 2003 that the seven-residue actin-binding motif matched whole thymosin beta-4 in human endothelial cell migration and chick aortic-arch sprouting at about 50 nM, and that peptides lacking any part of the motif were inactive (Philp et al., FASEB Journal, 2003).
The same paper reported better epidermal closure and collagen content at day 7 in 26-month-old mice given the non-acetylated fragment topically.
In 2024 a Korean doping-control group tested acetylated TB-500 itself at 50 µg/mL in a fibroblast scratch assay and saw no significant closure, while the metabolite Ac-LKKTE did show an effect (Rahaman et al., Journal of Chromatography B, 2024).

Cells, chick embryos, aged mice, rats and racehorses. The FDA reviewed the literature for its July 2026 compounding committee and "did not identify data, such as clinical studies, on the use of TB-500 in humans" (FDA briefing document, 2026). The gap between what the fragment and the full protein have each shown is the subject of our companion post, TB-500 versus thymosin beta-4.

The FDA also found the opposite of a safety record: no adverse-event reports at all, which it treated as absence of data rather than evidence of safety. Anyone sourcing tb-500 for research should read the agency's document for the current state of knowledge, not any supplier's description.

UK status and what changes in January 2027

In the UK, TB-500 is not a licensed medicine, and tb-500 uk listings are for laboratory research only. The FDA's survey of other regulators listed no approved TB-500 product in the United Kingdom, the EU, Canada or Australia.

In the US the picture moved in 2026. FDA staff recommended against adding TB-500 to the list of substances compounding pharmacies may use, but on 23 July 2026 the advisory committee voted narrowly to allow it, alongside several other peptides; the agency is not bound by the vote and had not finalised a decision at the time of writing (BBC News, 23 July 2026).

For athletes nothing softens. WADA published the 2027 list on 21 September 2026, in force from 1 January 2027, and TB-500 stays under S2 while unnamed peptides fall under the new S0 wording.

LynxLab stocks tb-500 5mg for research use at £23.99 a vial, tested to 99% purity with the batch certificate of analysis on the product page.

Frequently asked questions

Is TB-500 banned by WADA?

Yes. The WADA Prohibited List names "Thymosin-β4 and its derivatives e.g. TB-500" under S2.3, growth factors and growth factor modulators, prohibited at all times. UK Anti-Doping applies the same list to British athletes.

Can TB-500 be detected in a drug test?

Yes. The Hong Kong Jockey Club confirmed Ac-LKKTETQ at 0.01 ng/mL in horse urine in 2012, and WADA funded synthesis of reference standards for the human metabolites so that accredited laboratories can screen for them.

Why is TB-500 associated with horse racing?

Because it was first sold as a veterinary product for racehorses, and racing laboratories in Hong Kong, the US and France did the early analytical work. Racing Victoria's 2016 charge against trainer Paul Jones was described by the state's chief steward as its first direct peptide case.

Is it legal to buy TB-500 in the UK?

It is not a controlled drug, but it is not a licensed medicine either. Researchers can buy tb-500 for laboratory use; athletes under anti-doping rules cannot use it at any time.

Sources

Research use only

TB-500 from LynxLab

5mg vials from £23.99. ≥99% purity, lab report on the page. Same-day dispatch, UK stock.

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