TB-500: the trials belong to a different molecule
Many claims made for TB-500 borrow evidence from thymosin beta-4, the full 43-amino-acid protein. That protein has 1,131 indexed papers and seven trial-tagged reports. TB-500 is a seven-amino-acid piece of it, sold as if the two were interchangeable, and our September 2026 search found 26 papers and no trial-tagged reports under its names. The FDA's entry is blunter: it has found no human exposure data for the fragment.
What this comes down to
- Thymosin beta-4 returns 1,131 PubMed records and seven human trial-tagged reports in the September 2026 search. The TB-500 fragment returns 26 records and zero.
- The FDA lists the fragment by its sequence — thymosin beta-4, fragment (LKKTETQ), also known as TB-500 — and says it has not identified any human exposure data for it.
- The trials that do exist tested the full protein as eye drops for severe dry eye, as an intravenous infusion in healthy volunteers, and on venous leg ulcers. None of them is the use TB-500 is marketed for.
- One of the 387 sellers we review publishes a TB-500 line, while the identical kind of search finds sermorelin on 46 of them.
- Thymosin beta-4, the full protein7
- TB-5000
On July 23 and 24, 2026, the FDA's Pharmacy Compounding Advisory Committee considered whether BPC-157, KPV, TB-500, MOTS-c, emideltide, epitalon and Semax should be added to the 503A bulks list, the list that lets a state-licensed pharmacy compound a substance with no approved product. The FDA's own briefing document proposed that none of the seven be added[1]. Trade press reports that the committee disagreed for six of them: 8 to 6 with one abstention for BPC-157, KPV and TB-500 together, 7 to 5 for MOTS-c, and yes votes for epitalon and Semax, with emideltide voted down[2]. The vote is advisory. As of October 2026 the FDA and HHS have not added any of them to the list, so the legal position of TB-500 described here has not changed.
They are not the same thing
Thymosin beta-4 is a naturally occurring 43-amino-acid protein that sequesters actin and has been studied in wound repair for decades. TB-500 is a synthetic seven-residue fragment, LKKTETQ, taken from the actin-binding region. Marketing treats the fragment as a cheaper, more stable version of the protein. The literature treats them as different subjects: search the fragment's own names and you get 26 records, against 1,131 for the protein[3].
The search behind that zero. A PubMed search finds 0 results; the same search for thymosin beta-4 finds 7.
What the returned reports describe
Reading them one by one is the fastest way to see the gap. A phase 2 trial gave thymosin beta-4 as 0.1% eye drops to nine patients with severe dry eye, some of it associated with graft-versus-host disease, over 56 days[4]. A phase 1 study infused it intravenously into healthy volunteers to establish tolerability[5]. A first-in-human phase 1 of recombinant human thymosin beta-4 ran in healthy Chinese volunteers in 2021[6]. The rest are venous leg ulcers and a cell-therapy pilot in myocardial infarction.
That is the strongest efficacy signal in the set, and it is for a topical ophthalmic formulation of a different molecule in a condition nobody is buying TB-500 for. A tendon, a muscle tear and a dry eye are not the same experiment.
What the FDA wrote about the fragment specifically
The agency's compounding page lists it under its sequence, which is itself informative — it is identifying the fragment, not the protein[7].
“Compounded drugs containing thymosin Beta-4, Fragment (LKKTETQ) may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation as well as peptide-related impurities. FDA has not identified any human exposure data drug products containing Thymosin Beta-4, Fragment. FDA lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans.”
[7]
It sits in the table of nominations that were later withdrawn by whoever filed them, which removes the substance from the queue for the bulks list and leaves the agency's text published beside the name. The status table records where each of these peptides landed. And the phrase that recurs — peptide-related impurities, aggregation — is the same one the FDA uses for BPC-157, CJC-1295 and ipamorelin, which is a fact about how these things are made rather than about what they do.
Almost nobody we have read sells it by name
Across the 387 sellers we review, one publishes a priced line naming TB-500 or thymosin — YOURx Health, from $165 a month. Sermorelin, by comparison, is priced by 46 sellers and BPC-157 by five. Where TB-500 mostly shows up is in the gray market the sports medicine reviews describe — sold as a research chemical rather than on a prescription[8].
If a company does offer it to you, the questions are the same ones we would ask about any compounded peptide: which pharmacy, which grade of material, and what happens if you react to it.
Questions people actually ask
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is a 43-amino-acid protein; TB-500 is a synthetic seven-amino-acid fragment of it. The FDA lists the fragment separately and by its sequence. Evidence for one is not evidence for the other.
Has TB-500 been tested in a clinical trial?
Our September 2026 PubMed search found no trial-tagged reports under the fragment's names, against seven for the full protein. That search does not establish that no study exists.
What did the thymosin beta-4 trials find?
The strongest was a phase 2 trial of 0.1% eye drops in nine patients with severe dry eye, which reported improvement in signs and symptoms. Others tested intravenous infusion in healthy volunteers for tolerability, and topical treatment of venous leg ulcers. None studied injury recovery in athletes.
Is TB-500 legal to buy?
It is not a controlled substance, but it is also not an approved drug and it is not on the FDA's 503A bulks list, so a pharmacy compounding it is operating outside the three routes the statute names for bulk substances. Most of what is sold online is labeled for research use.
Sources
Primary sources and the claims they support.
- 1.FDA Briefing Document, Pharmacy Compounding Advisory Committee meeting, July 23-24, 2026. U.S. Food and Drug Administration, 2026. Source · Document dated July 2026The committee was asked whether BPC-157, KPV, TB-500 and MOTS-c (July 23) and emideltide, epitalon and Semax (July 24) should be added to the 503A bulks list. For each one, in both the free-base and acetate forms, the FDA's own proposal was that it NOT be included. The document says the FDA will not issue a final determination until the committee's input has been considered.
- 2.FDA Panel Backs 6 Peptides for Compounding. AJMC (trade press report of the committee vote), 2026. SourceTrade press, not an FDA document: the committee voted 8-6 with 1 abstention to recommend BPC-157, KPV and TB-500, 7-5 with 2 abstentions for MOTS-c, also recommended epitalon and Semax, and voted emideltide down 7-6 with 1 abstention.
- 3.PubMed, queried through the E-utilities API. National Library of Medicine, 2026. SourceOn September 11, 2026, the TB-500 fragment names returned 26 records and 0 randomized trials with the human indexing tag; thymosin beta-4 returned 1,131 records and 7 such trials through the identical filter.
- 4.Thymosin beta 4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea, 2015. PMID 25826322 · doi:10.1097/ICO.0000000000000379A multicenter, randomized, double-masked, placebo-controlled 56-day phase 2 trial at two US sites treated nine patients with severe dry eye using thymosin beta-4 eye drops at 0.1% or vehicle.
- 5.A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Annals of the New York Academy of Sciences, 2010. PMID 20536472 · doi:10.1111/j.1749-6632.2010.05474.xIntravenous thymosin beta-4 has been given to healthy volunteers in a randomized placebo-controlled single and multiple dose study.
- 6.A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin beta4 in healthy Chinese volunteers. Journal of Cellular and Molecular Medicine, 2021. PMID 34346165 · doi:10.1111/jcmm.16693Recombinant human thymosin beta-4 reached a first-in-human phase 1 study in healthy volunteers in 2021, which is the stage the full protein had reached by then.
- 7.Substances in Compounding that May Present Significant Safety Risks. U.S. Food and Drug Administration, 2026. Source · Document dated April 2026The FDA's page, face-dated April 22, 2026, lists "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" in its table of withdrawn nominations and states that it has not identified any human exposure data for drug products containing the fragment.
- 8.Injectable Peptides in Sports Medicine: A Structured Narrative Review of Evidence, Safety, and Antidoping Implications. JBJS Reviews, 2026. PMID 42160466 · doi:10.2106/JBJS.RVW.26.00027Thymosin derivatives are grouped with the other regenerative peptides as investigational, with uncertain safety profiles, product quality concerns and widespread antidoping restrictions.
Key figures