TB-500

A seven-amino-acid fragment of a much better-studied protein, and the confusion between the two runs through almost everything written about it.

Summary

• TB-500 is Ac-LKKTETQ, seven amino acids, corresponding to the actin-binding region of thymosin beta-4.1

• It is not thymosin beta-4. The parent protein is 43 amino acids and has a far larger research record, which does not transfer automatically to the fragment.

• A 2024 study stated that the biological effects of TB-500 have not been documented, and concluded that reported wound-healing activity may be due to a metabolite rather than the parent compound.1

• A 2026 rat Achilles study found a significant biomechanical advantage for TB-500 at four weeks.2

• In that same study, combining TB-500 with BPC-157 conferred no additional benefit over either alone.2

• No human trial has reported results for TB-500 in any indication. One Phase 1/2 trial began recruiting in February 2026. Human orthopedic data are lacking.3

• Prohibited in sport under WADA section S2, with TB-500 named explicitly since the 2018 list.5

• Reviewed by an FDA advisory committee in July 2026 for wound healing. That is not approval.6

The Most Common Error About This Compound

Marketing for TB-500 routinely cites research on thymosin beta-4. They are different molecules. Thymosin beta-4 is a naturally occurring 43 amino acid protein with hundreds of publications and registered human trials behind it. TB-500 is a synthetic seven-amino-acid fragment with 16 indexed papers, most of which are reviews or detection-method chemistry.

ONPEPS grades them separately for that reason. Thymosin beta-4 sits at grade B. TB-500 sits at grade D. A study of the parent protein is not evidence for the fragment.

Identity

What Is TB-500?

TB-500 is a synthetic peptide with the sequence Ac-LKKTETQ. The "Ac" denotes an acetyl group on the N-terminus. It corresponds to the active site region of thymosin beta-4, specifically the actin-binding portion.1

It is not approved for human use by any global regulatory authority.

How Does It Differ From Thymosin Beta-4?

The distinction matters commercially as well as scientifically. A seller quoting trial data for thymosin beta-4 on a TB-500 product page is describing a different molecule.

Is the Injected Peptide Even the Active One?

This is the most interesting open question about TB-500, and it comes from a 2024 metabolism study.

The authors investigated how TB-500 breaks down in human serum, in enzyme systems, and in rats. They found Ac-LK to be the primary metabolite in the first six hours, and Ac-LKK detectable up to 72 hours. When they tested the parent and its metabolites for wound healing activity in fibroblasts, only the metabolite Ac-LKKTE showed significant activity compared with control.1

Their conclusion was that the previously reported wound-healing activity of TB-500 in the literature may be due to its metabolite Ac-LKKTE rather than the parent form.1

This is one laboratory and animal study and it has not been replicated. If it holds, the molecule people buy is a precursor rather than the active agent, which would matter for dose, timing and route.

Evidence Base

How Much Research Exists?

A targeted PubMed search for TB-500 returns 16 records, the count carried on the ONPEPS library index and retrieved 23 July 2026. Reading them, the categories are:

• Reviews that mention TB-500 alongside other peptides3,7

• Analytical chemistry developing doping control detection methods1,8

• A small number of animal studies2

The 2024 metabolism paper put it plainly: the biological effects of TB-500 have not been documented.1

A 2026 review of therapeutic peptides in orthopaedics reached the same position across the class, noting that although preclinical studies are promising, there is a current lack of clinical trials.7

What Human Evidence Exists?

No published results. One registered trial is under way.

NCT07487363 is a Phase 1/2 randomized, placebo-controlled, sequential dose-escalation study of TB-500 in adults aged 40 to 75 with stable atherosclerotic cardiovascular disease, evaluating safety, tolerability, pharmacokinetics and exploratory cardiovascular biomarkers. Estimated enrollment is 80. The sponsor is Hudson Biotech and the listed site is Peking University Shenzhen Hospital in China. Recruiting began 5 February 2026, primary completion is scheduled for 14 February 2027 and full completion for 17 February 2028. Primary outcomes are the incidence of treatment-emergent adverse events at 12 weeks and serious adverse events at 28 days. No results have been posted.10

Two things follow. The indication under study is cardiovascular, not tendon, muscle or injury recovery. And a safety and pharmacokinetic study of this design is not built to establish that the compound works.

A 2026 review in the American Journal of Sports Medicine assessed thymosin beta-4 and its derivative TB-500 together, concluding that both promoted angiogenesis and tissue repair in preclinical models, but that human orthopedic data are lacking and both remain banned substances in sport.3

Human trial data that does exist belongs to the parent protein. A 2007 paper described a European double-blind, placebo-controlled dose-response study of topical thymosin beta-4 in venous ulcers, designed for 72 patients across sites in Italy and Poland and treated for 84 days. That paper reports only the design and the fact that 21 patients had been enrolled in the first dose group at the time of writing. It contains no outcome data.4 The trial itself is registered as NCT00832091, sponsored by RegeneRx Biopharmaceuticals. It enrolled 72 patients, ran from July 2006 to January 2009, completed, and posted results to ClinicalTrials.gov in March 2010.114 That is a different molecule, a different route, and a different indication from how TB-500 is used.

Tendon and Injury Research

What Did the 2026 Rat Study Find?

This is the most directly relevant animal study published, and it tested the exact comparison people argue about.

Thirty-two male rats underwent standardized Achilles tendon transection and repair, then were randomly assigned to four groups of eight: control, BPC-157 at 10 micrograms per kilogram per day, TB-500 at 60 micrograms per kilogram per day, and both combined. Treatment was intraperitoneal for four weeks.2

Findings:

• Maximum load to failure was higher in both treatment groups than control, reaching statistical significance in the TB-500 group

• Total Bonar scores were significantly lower in the TB-500 group, and total Movin scores significantly lower in the TB-500 and combined groups, indicating better tendon architecture and collagen alignment

• The BPC-157 group showed numerically lower scores without reaching significance on total scores

• Collagen type I expression did not differ significantly between groups, while type III expression did

Did Combining the Two Help?

No. The authors reported that combined BPC-157 and TB-500 treatment did not confer additional benefits compared to either agent alone. They suggested the absence of additive effect may reflect convergence on shared downstream pathways, while stating the hypothesis requires further experimental confirmation.2

This is a rat study with eight animals per group over four weeks, and the authors themselves describe it as exploratory. It is the only controlled head-to-head comparison of these two compounds that exists. The comparison and the stacking question are covered in more depth in the ONPEPS TB-500 versus BPC-157 article.

Sport and Drug Testing

Is TB-500 Prohibited?

Yes, and it is named specifically. TB-500 has been named as an example of a prohibited growth factor under section S2.3 since thymosin beta-4 and its derivatives were added to the WADA Prohibited List for 2018.5 It remains prohibited. For 2026, the only S2 change was the addition of pegmolesatide, and just one substance or method moved from permitted to prohibited across the entire list, in section M.1.95

Section S2 covers peptide hormones, growth factors, related substances and mimetics. Because both the parent and its derivatives are named, using the fragment rather than the protein does not sit outside the rule.

Can It Be Detected?

Yes. Detection methods have been published. A 2012 paper described doping control analysis of TB-500 in equine urine and plasma by liquid chromatography-mass spectrometry, confirming N-acetylated LKKTETQ at 0.02 ng/mL in plasma and 0.01 ng/mL in urine after a single 10 mg dose in horses.8 The 2024 metabolism work was explicitly framed around identifying metabolites and establishing detection in urine.1

The metabolite finding has a practical consequence for testing. Ac-LKK was detectable up to 72 hours in that study, described by the authors as the long-term metabolite, which makes metabolites a useful detection target.1

Regulatory Status

What Happened in July 2026?

On 23 July 2026 the FDA's Pharmacy Compounding Advisory Committee discussed TB-500 free base and TB-500 acetate, among seven peptides, for possible inclusion on the 503A Bulks List. That list governs what substances pharmacies may use in compounded preparations.6

The use the FDA evaluated for TB-500 was wound healing.6 Tendon repair, muscle injury and sports recovery were not the indications under review.

Does That Mean It Is Approved?

No. The FDA states on its own meeting page that advisory committees make non-binding recommendations, which the agency generally follows but is not legally bound to do.6

Three separate things get conflated in current marketing. Drug approval means the FDA has reviewed a specific product for safety and efficacy for a stated indication. Inclusion on the 503A Bulks List would mean pharmacies may use the substance in compounded preparations, which are not FDA-approved. An advisory committee recommendation is a vote the FDA may accept or reject.

A recommendation to permit compounding for wound healing is several steps removed from approval of an injury recovery drug, and it changes nothing about the S2 sport prohibition, which turns on approval status.

Safety

What Is Known?

There is no published human safety data for TB-500. The first trial to assess it in people began recruiting in February 2026 and is not due to report.

The 2024 laboratory study found no cytotoxicity for the parent compound or any of its metabolites in cell culture.1 That is a specific finding in a specific assay, not a clinical safety profile.

The 2026 rat study reported histological and biomechanical outcomes rather than a systematic safety assessment, and ran for four weeks.2

What Is Unknown

Everything that would normally define a safety profile. There is no established human dose, no dose-response data, no information on repeated or long-term exposure, no interaction data, and no adverse event reporting system because there is no approved product.

The angiogenesis question that attaches to this class applies here too. Promotion of new blood vessel growth is the proposed mechanism, and tumors also depend on angiogenesis. No study has examined cancer risk with TB-500 in any species over a relevant timeframe. The concern is mechanistically coherent and empirically unaddressed.

Related ONPEPS Coverage

• TB-500 versus BPC-157: Mechanisms and the Wolverine stack

• Dosing patterns, cycle length and observed protocols

• Thymosin Beta-4, the parent protein, graded separately

• BPC-157 library entry

What Would Change This Page

Replication of the metabolite finding would be the single most useful result, because it determines whether TB-500 is the active molecule or a precursor to one.

Beyond that: any controlled human trial, a human pharmacokinetic study, longer animal studies with systematic safety endpoints, and the FDA's decision on the July 2026 advisory recommendation.

References

1. Rahaman KA, Muresan AR, Min H, Son J, Han HS, Kang MJ, Kwon OS. 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 Analyt Technol Biomed Life Sci. 2024;1235:124033. Free article. pubmed.ncbi.nlm.nih.gov/38382158

2. Biçer O, Adanir O, Güleryüz Y, Balci EC, Dinçel YM, Yenigün MY, Aydin C, Yaprak Bayrak B. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study. Jt Dis Relat Surg. 2026;37(3):822-837. Free article. pubmed.ncbi.nlm.nih.gov/42542926

3. Mayfield CK, Bolia IK, Feingold CL, Lin EH, Liu JN, Hatch GFR, Gamradt SC, Weber AE. Injectable Peptide Therapy: A Primer for Orthopaedic and Sports Medicine Physicians. Am J Sports Med. 2026;54(1):223-229. Paywalled. pubmed.ncbi.nlm.nih.gov/41476424

4. Guarnera G, De Rosa A, Camerini R. Thymosin beta-4 and venous ulcers: clinical remarks on a European prospective, randomized study on safety, tolerability, and enhancement on healing. Ann N Y Acad Sci. 2007;1112:407-412. Paywalled. Concerns thymosin beta-4, not TB-500. pubmed.ncbi.nlm.nih.gov/17495250

5. United States Anti-Doping Agency. 2018 Prohibited List: Summary of Major Changes. Archived advisory, marked by USADA as not updated and for historical reference. Records that thymosin-beta 4 and its derivatives, for example TB-500, were added as examples of prohibited growth factors. Accessed 12 August 2026. usada.org

6. US Food and Drug Administration. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee. Agenda and evaluated uses. Docket FDA-2025-N-6895. fda.gov

7. Rahman OF, Lee SJ, Seeds WA. Therapeutic Peptides in Orthopaedics: Applications, Challenges, and Future Directions. J Am Acad Orthop Surg Glob Res Rev. 2026;10(1):e25.00236. Open access. pubmed.ncbi.nlm.nih.gov/41490200

8. Ho EN, Kwok WH, Lau MY, Wong AS, Wan TS, Lam KK, Schiff PJ, Stewart BD. Doping control analysis of TB-500, a synthetic version of an active region of thymosin beta-4, in equine urine and plasma by liquid chromatography-mass spectrometry. J Chromatogr A. 2012;1265:57-69. Paywalled. pubmed.ncbi.nlm.nih.gov/23084823

9. United States Anti-Doping Agency. Athlete Advisory: What's New on the 2026 WADA Prohibited List? Accessed 12 August 2026. Records that for 2026 only one substance or method changed from permitted to prohibited, in section M.1, and that the sole S2 addition was pegmolesatide. usada.org

10. ClinicalTrials.gov. NCT07487363. A Phase 1/2, Randomized, Double-Blind, Placebo-Controlled, Sequential Dose-Escalation Study of TB-500 (Thymosin Beta 4 17-23 Fragment) in Adults With Stable Atherosclerotic Cardiovascular Disease to Evaluate Safety, Tolerability, Pharmacokinetics, and Exploratory Cardiovascular Biomarkers. Sponsor Hudson Biotech. Recruiting; record retrieved 12 August 2026. clinicaltrials.gov/study/NCT07487363

11. ClinicalTrials.gov. NCT00832091. A Randomized, Double-Blind, Placebo-Controlled, Dose-Response Study of the Safety and Efficacy of Thymosin Beta 4 in the Treatment of Patients With Venous Stasis Ulcers. Sponsor RegeneRx Biopharmaceuticals. Phase 2, 72 participants enrolled, July 2006 to January 2009, completed. Results first posted 24 March 2010. Record retrieved 12 August 2026. clinicaltrials.gov/study/NCT00832091

Not Medical Advice

TB-500 is not approved for human use in any jurisdiction, no human dose has been established, and it is prohibited in sport under WADA section S2. Consult a qualified healthcare provider before acting on anything here.

Literature and regulatory sources verified 12 August 2026. As of 12 August 2026, the FDA had published no outcome for the July 2026 advisory recommendation, and its meeting page was marked current as of 6 August 2026. Re-verify against docket FDA-2025-N-6895 before relying on any regulatory statement here.