TB-500 pages almost always open with thymosin beta-4's biology and close with a dosing table. The biology is real. The molecule sold as TB-500 is not the molecule the biology was measured on, and that distinction is the whole page.
What it is
Thymosin beta-4 (Tβ4) is a 43-amino-acid protein present in most human cells, best known for binding actin and for a role in cell migration and wound repair. TB-500 is a synthetic fragment: the seven residues LKKTETQ, the segment of Tβ4 that binds actin. FDA's own listing uses exactly that description: "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500."
A fragment can share a binding motif with its parent protein and still behave differently in the body: different half-life, different distribution, different immune recognition, different off-target effects. Whether TB-500 does what Tβ4 does in any human tissue has not been tested.
The human evidence
For the fragment: none. FDA states it "has not identified any human exposure data" on drug products containing the thymosin beta-4 fragment. Our PubMed search for TB-500 in humans on September 4, 2026 found no interventional study.
For full-length thymosin beta-4, three controlled studies, all developer-sponsored and none leading to an approved product:
| Year | Design | Result | PubMed |
|---|---|---|---|
| 2010 | Randomised, placebo-controlled; four cohorts of 10 healthy adults; single then 14 daily intravenous doses | Adverse events infrequent, mild or moderate; no serious adverse events. A safety and pharmacokinetic study only. | 20536472 |
| 2015 | Phase 2 randomised, placebo-controlled; severe dry eye; eye drops (RGN-259) | Statistically significant differences in some sign and symptom scores at several time points; the treated group had 12 eyes at the day-56 analysis reported. | 25826322 |
| 2021 | Phase 1 randomised, double-blind, placebo-controlled; 54 healthy adults; recombinant Tβ4 intravenous | No dose-limiting toxicity or serious adverse events; kinetics dose-proportional. | 34346165 |
Two things follow. First, even the parent molecule has no efficacy trial in the uses TB-500 is marketed for: tendon, muscle, ligament, hair. Second, none of these studies bears on the safety of the fragment, which has a different sequence, different manufacturing impurities, and, per FDA, a different immunogenicity question.
Regulatory status
FDA placed the thymosin beta-4 fragment in Category 2 of the 503A nominations on September 29, 2023, citing risk of immunogenicity from aggregation and peptide-related impurities and the absence of human exposure data. The Category 2 page (content current as of April 22, 2026) now lists it as nominated but withdrawn, with the concerns retained.
The Pharmacy Compounding Advisory Committee discussed TB-500 free base and acetate on July 23, 2026 with wound healing as the use FDA evaluated. No vote tally was on FDA's page when we checked, and we do not report press accounts as fact. The 503A process has three steps; the committee is the second.
Full-length thymosin beta-4 is a separate case: it has been through registered, placebo-controlled clinical trials as a drug candidate. That history belongs to Tβ4, not to TB-500.
Safety signals
No human data for the fragment means no human safety signal either way, which is the regulator's concern rather than reassurance. Injectable products sold as TB-500 are research-use-only chemicals with no sterility, potency or identity requirement; the compounding site's page on salt forms and research use only explains what that label does and does not promise.
Grade: D + X
D because no controlled human study of the fragment exists; the Tβ4 studies are shown for context and excluded from the grade. X because FDA has published a specific safety concern. See the grading scale and the guide on how to read a peptide study, which uses the Tβ4 versus TB-500 substitution as its first worked example.
Questions people ask
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is a 43-amino-acid protein made in the body. TB-500 is a synthetic seven-amino-acid piece of it (the LKKTETQ actin-binding segment). Human trials of full-length thymosin beta-4 as an eye drop or an intravenous infusion say nothing direct about the fragment's safety or effect, and FDA states it has identified no human exposure data for the fragment.
Has thymosin beta-4 itself passed human trials?
It has been through placebo-controlled phase 1 safety studies (PubMed 20536472 in 40 healthy adults; PubMed 34346165 in 54) and a phase 2 dry-eye trial with an eye-drop formulation (PubMed 25826322). None led to an approved product, and none used the fragment sold as TB-500.
What did the July 2026 advisory committee decide about TB-500?
FDA's meeting page (content current as of August 6, 2026) lists TB-500 free base and acetate on the July 23 agenda with wound healing as the evaluated use. The page did not carry a vote tally when we checked. A committee recommendation, if made, does not place a substance on the 503A bulks list; a final rule does.
Sources
- FDA: Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks (content current as of April 22, 2026) Accessed September 4, 2026.
- FDA: July 23-24, 2026 Meeting of the Pharmacy Compounding Advisory Committee Accessed September 4, 2026.
- Ruff D et al. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Ann N Y Acad Sci 2010. PubMed 20536472 Accessed September 4, 2026.
- Sosne G et al. Thymosin beta4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea 2015. PubMed 25826322 Accessed September 4, 2026.
- Wang X et al. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin beta4. J Cell Mol Med 2021. PubMed 34346165 Accessed September 4, 2026.
Canonical URL: https://formblendspeptides.com/peptides/tb-500. Written by the FormBlends editorial team. This page is educational and is not medical advice; see the medical disclaimer.