Thymosin Beta-4 vs Products Marketed as TB-500
Thymosin beta-4 is a molecule the body makes; "TB-500" is a market name for a shorter fragment. How they differ in identity, human evidence, regulation and sport rules.
Content last updated . This page has not been medically reviewed.
Definitions
- Thymosin beta-4 is a 43-amino-acid peptide made in the body. [1]
- TB-500 is described by FDA as a synthetic, N-acetylated seven-amino-acid fragment (residues 17 to 23, LKKTETQ) of that full-length molecule. [1] A 2012 laboratory study found exactly that acetylated fragment in a product sold as TB-500. [2]
FDA also says TB-500 is "not physically and chemically well characterized," partly because its naming does not follow standard chemical nomenclature, and that it was unclear whether sources mean the free base or the acetate salt. [1] So a vial labeled TB-500 may not match what any paper tested. See research peptide naming and identity problems.
Side by side
| Thymosin beta-4 (full length) | Products marketed as TB-500 | |
|---|---|---|
| What it is | 43-amino-acid peptide the body makes [1] | Synthetic seven-amino-acid fragment, as reported by FDA [1] |
| Human trials | Yes, mainly eye drops and an intravenous safety study [3][4] | FDA found none by any route [1] |
| Animal work | Mouse heart-injury study [5] | Mouse wound study of the non-acetylated fragment, with FDA noting it may not generalize [1] |
| Approved medicine in the U.S. | Not established by the sources read | FDA says neither TB-500 form is part of an approved drug [1] |
| Anti-doping (WADA 2026) | Listed | Named as an example of a derivative [6] |
What the evidence shows
Full-length thymosin beta-4. In a phase 2 trial of 72 people with dry eye, neither main measure (discomfort, corneal staining) differed significantly from placebo, although some secondary measures did. [3] That is promising but limited, and it concerns eye drops only. An intravenous study in 40 healthy volunteers reported mild or moderate, infrequent adverse events; it tested tolerability, not benefit. [4] In mice, thymosin beta-4 improved heart function after induced heart injury; that is preclinical. [5]TB-500. FDA reported no clinical studies or human exposure data and no published case reports of TB-500 given to patients for any condition. [1] Label: Proper evidence not found. Checked: FDA's 2026 briefing document and PubMed.
Because the fragment and the whole molecule are different substances, results for one cannot be carried over to the other. A mouse or eye-drop result for thymosin beta-4 says nothing reliable about an injected product sold as TB-500.
No universal winner
These are not two options of one product. One is a natural molecule with limited, indication-specific human data; the other is a marketed fragment without human data and with open identity questions. Anyone considering either should talk with a licensed clinician. More detail: TB-500 and thymosin beta-4, thymosin beta-4, anti-doping rules, and how to evaluate peptide claims.Frequently asked questions
Is TB-500 just another name for thymosin beta-4?
No. FDA describes TB-500 as a seven-amino-acid fragment of the 43-amino-acid thymosin beta-4. [1]
Which has better evidence?
Only thymosin beta-4 has human studies, and those are mostly eye-drop trials with mixed main results. FDA found no human data for TB-500. [3][1]
Is either one allowed in sport?
WADA's 2026 list covers thymosin-beta-4 and its derivatives such as TB-500. [6]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: preclinical (cells or animals only), promising but limited, insufficient evidence, and Proper evidence not found (we looked and found nothing usable).
Regulation and sport (read 2026-10-22)
- United States. FDA reviewed TB-500 for wound healing at its July 2026 compounding advisory committee, and its staff document concluded the criteria weigh against placing it on the 503A bulks list. [7][1] The committee vote and FDA's final decision were not verified from the pages read.
- Canada. Health Canada lists TB-500 among examples of unauthorized injectable peptide drugs it has seized. [8]
- Sport. WADA's 2026 list names thymosin-beta-4 and its derivatives, for example TB-500, among prohibited growth factors and modulators; section S2 is prohibited at all times. [6]
- Other countries: not verified.
References
- U.S. Food and Drug Administration. FDA Briefing Document: TB-500-related bulk drug substances, Pharmacy Compounding Advisory Committee, July 23-24, 2026 (document dated 5/15/2026). Read 2026-10-22.
- Esposito S et al. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500. Drug Test Anal 2012. PubMed. Read 2026-10-22.
- Sosne G, Ousler GW. Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, phase II trial. Clin Ophthalmol 2015. PubMed. Read 2026-10-22.
- 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. Read 2026-10-22.
- Bock-Marquette I et al. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature 2004. PubMed. Read 2026-10-22.
- World Anti-Doping Agency. 2026 Prohibited List (in force 1 January 2026; the 2027 list was not read). Read 2026-10-22.
- U.S. Food and Drug Administration. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee (content current as of 08/06/2026). Read 2026-10-22.
- Health Canada. Think twice before injecting peptides bought online: unauthorized products can seriously harm you (public advisory, last updated 2026-04-09). Read 2026-10-22.