Key points
- TB-500 is an acetylated synthetic fragment of 7 amino acids (LKKTETQ), not the full 43-amino-acid protein [1][3].
- FDA found no case in the literature of TB-500 being given to patients [2].
- In a fibroblast assay, TB-500 at 50 µg/mL “did not induce wound healing” [2].
- The full protein has small human datasets. Its phase 3 keratopathy trial (18 patients) missed its primary endpoint [3].
US status (October 2026): TB-500 is not FDA-approved and has no lawful compounding pathway. MDside providers do not prescribe it.
When someone cites thymosin beta-4 data to sell TB-500, they are citing a different molecule. FDA says so in writing, and the human evidence for the fragment is zero.
Two different molecules share one story
Thymosin beta-4 is a natural 43-amino-acid protein, present in cells and body fluids, that has been studied in tissue repair [3]. TB-500 is something else: an N-acetylated synthetic fragment of 7 amino acids (LKKTETQ, residues 17 to 23), matching the region of thymosin beta-4 responsible for actin binding [1][2]. TB-500 marketing often cites studies of the full protein as if they were its own.
FDA found no human use of TB-500
In its July 2026 briefing document FDA wrote: “FDA did not find any information in the medical literature where TB-500 was administered to patients to treat any disease or condition.” In an in-vitro fibroblast wound-healing assay, TB-500 at 50 µg/mL “did not induce wound healing,” although one metabolite (Ac-LKKTE) produced a small but significant closure. FDA identified no acute, repeat-dose or genotoxicity studies [2]. Even so, the advisory committee voted 8 to 6, with one abstention, to add it to the compounding list [5]. The vote is nonbinding.
- 7 vs 43: amino acids, TB-500 vs thymosin beta-4 [1]
- 0: documented human uses of TB-500 according to FDA [2]
- P = 0.0656: primary endpoint missed in the ocular thymosin beta-4 phase 3 [3]
The human data belong to the full protein
Full-length thymosin beta-4 does have trials, but small ones in specific uses, mainly eye drops. In a phase 3 in neurotrophic keratopathy with 18 patients, complete healing at 4 weeks was 6/10 vs 1/8, P = 0.0656. It missed the primary endpoint. Two weeks after treatment ended, the difference was significant (P = 0.0359) [3]. In a trial in healthy Chinese volunteers, intravenous recombinant protein showed no dose-limiting toxicity [4].
KPV is a similar case with no human data
KPV, a tripeptide derived from α-MSH, follows the same pattern. FDA wrote that “The nomination did not include, and FDA did not find any information on the use of these substances administered in humans” [6]. Its evidence comes from cell cultures and mouse colitis models [7]. The committee also voted 8 to 6, with one abstention, in its favor [5].
In sport. WADA’s list prohibits “Thymosin-β4 and its derivatives e.g. TB-500” under S2.3, at all times [8].
The name TB-500 can mean either molecule
Online sellers also use the name TB-500 for full-length (long-chain) thymosin β4. In a 2026 study, for example, the authors describe the commercial TB-500 they used as “synthetic thymosin beta-4” without giving its sequence [11]. This article refers to the Ac-LKKTETQ fragment defined by FDA [2]. If a patient brings a product, the certificate of analysis is where to check which molecule it claims to contain.
The supporters’ case rests on the parent protein
The protein TB-500 derives from does have positive human signals. In a small phase 2 trial in severe dry eye (9 patients), thymosin beta-4 eye drops were associated with 35.1% less discomfort and 59.1% less corneal staining than vehicle [9]. Among those who voted for TB-500, one committee member cited ongoing discrepancies in the information they receive, and another cited allowing prescriber-directed compounding in licensed pharmacies against a lower documented harm rate [10].
What this means for your clinic
A favorable committee vote is not a compounding pathway. Until FDA acts, TB-500 sold as “research use only” has no lawful compounding pathway. Track the next step on the status tracker and read whether peptides are legal for the broader framework.
References
- Ho EN, et al. Doping control analysis of TB-500, a synthetic version of an active region of thymosin β4, in equine urine and plasma by liquid chromatography-mass spectrometry. J Chromatogr A. 2012;1265:57-69. PMID 23084823. Link
- U.S. Food and Drug Administration. PCAC July 2026 briefing document: TB-500. Link
- Sosne G, et al. 0.1% RGN-259 (Thymosin ß4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial. Int J Mol Sci. 2022;24(1):554. PMID 36613994. Link
- Wang X, et al. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers. J Cell Mol Med. 2021;25(17):8222-8228. PMID 34346165. Link
- Jacobus N. FDA Panel Votes to Loosen Restrictions for Four Peptides. Pharmaceutical Executive. 24 July 2026. Link
- U.S. Food and Drug Administration. PCAC July 2026 briefing document: KPV. Link
- Dalmasso G, et al. PepT1-mediated tripeptide KPV uptake reduces intestinal inflammation. Gastroenterology. 2008;134(1):166-78. PMID 18061177. Link
- World Anti-Doping Agency. 2026 Prohibited List (S2.3), English text as published in Tractatenblad van het Koninkrijk der Nederlanden 2026, Nr. 25. Link
- Sosne G, Dunn SP, Kim C. Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea. 2015;34(5):491-6. PMID 25826322. Link
- Bascom E. FDA committee recommends looser restrictions for several peptides. Healio. 24 July 2026. Link
- Biçer O, et al. 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. PMID 42542926. Link
This is general information, not medical or legal advice. Rules vary by state and change. Confirm your own facts with counsel.