TB-500 and Thymosin Beta-4: Naming, Research and Regulatory Status

Why the name matters

"TB-500" is a market name, not a formal drug name. Thymosin beta-4 is a molecule the body makes. A product sold as TB-500 should not be assumed to be full-length thymosin beta-4, and results from one cannot be carried over to the other. This page explains what each name is known to refer to, and what is not known. For the full-length molecule, see thymosin beta-4.

Evidence labels used here: preclinical (cells or animals only), promising but limited, insufficient evidence, marketing claim and Proper evidence not found.

What each name refers to

• Thymosin beta-4 is a peptide of 43 amino acids, found in many cell types and in body fluids such as blood, tears and wound fluid. [1][2]
• TB-500, in FDA's 2026 review, is described as a synthetic, N-acetylated seven-amino-acid fragment (residues 17 to 23, LKKTETQ) of the full-length 43-amino-acid thymosin beta-4. [1] A 2012 laboratory study found exactly this acetylated fragment in a product sold as TB-500. [3]

So the two are related but different molecules. FDA also states that TB-500 is "not physically and chemically well characterized," in part because the naming does not follow established chemical nomenclature, and that it is often unclear whether sources mean a salt or the free base. [1] That is a naming-uncertainty problem: a vial labeled TB-500 may not contain what a paper tested, and a paper on thymosin beta-4 does not describe a TB-500 product.

What human research exists

Full-length thymosin beta-4 (not TB-500).

• Eye drops, dry eye. A phase 2 trial of 72 people with dry eye found that neither primary endpoint (discomfort, corneal staining) differed significantly from placebo at the main time point, although some secondary measures did. [4] A separate 9-patient phase 2 trial in severe dry eye reported significant differences on several measures; the authors called it small. [5] Two larger phase 3 dry eye trials (601 and 700 people) are registered as completed with results posted; this page does not summarize their efficacy results. [6][7] Label: promising but limited, for eye drops only.
• Nine compassionate-use patients with nonhealing corneal defects: six with geographic defects showed what the authors called dramatic healing, and three did not change. [8]
• Intravenous safety study in 40 healthy volunteers: adverse events were infrequent and mild or moderate, with no serious events. This tested tolerability, not benefit. [9]
• Heart attack. A phase 2 trial of an intravenous recombinant form in 62 people is registered as completed; no published results were found. [10]

TB-500 itself. FDA's review found no clinical studies or human exposure data using TB-500 by any route, and no report in the medical literature of TB-500 given to patients for any condition. [1] One ClinicalTrials.gov record for TB-500 exists, but its own summary calls the study "fictional" and describes itself as an example record, so it should not be treated as evidence of a real trial. [11] Label for TB-500 in people: Proper evidence not found. Checked: PubMed, ClinicalTrials.gov and FDA's 2026 briefing document.

Animal research

In a well-known 2004 mouse study, thymosin beta-4 promoted heart cell migration and survival in culture and improved heart function after induced heart injury. [12] A 2015 review says further proposed uses, such as kidney, liver, bone and ligament repair, rest on animal studies. [13] These are preclinical findings, and they concern the full-length molecule.

Regulatory and sport status (read 2026-10-22)

Laws change; this is not legal advice.

• United States. FDA lists the fragment "also known as TB-500" among substances nominated for compounding and then withdrawn, with immunogenicity concerns and no identified human exposure data (page current as of 04/22/2026). [14] For the July 2026 advisory committee, FDA reviewed TB-500 for wound healing and proposed that it not be included on the 503A bulks list. [15][16] FDA noted neither TB-500 form is a component of an approved drug. [1] The committee vote and any final decision are not verified from the FDA pages read.
• Canada. Health Canada lists TB-500 among examples of unauthorized injectable peptide drugs it has seized. [17]
• Sport. WADA's 2026 list prohibits thymosin-beta-4 and its derivatives, for example TB-500, at all times. [18]
• Other countries: not verified.

Risks

Safety in people cannot be described for TB-500, because FDA found no human exposure data. [1] Product quality is a separate concern for unapproved injectables. [17] See peptide safety and adverse events and how to evaluate peptide claims. A side-by-side view is in thymosin beta-4 vs products marketed as TB-500.