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

Quick summary

TB-500 is a name used for a synthetic fragment related to thymosin beta-4, a protein-like peptide the body makes. No approved medicine for the uses TB-500 is marketed for was found in the sources read. Human evidence for TB-500 itself: Proper evidence not found (we checked PubMed for trials of TB-500 and FDA's compounding page). Evidence labels used here: preclinical (cells/animals only), promising but limited, insufficient evidence and marketing claim.

TB-500

Laboratory analysis of a TB-500 product identified the fragment Ac-LKKTETQ, the acetylated 17-23 segment of human thymosin beta-4. [1] The same paper describes TB-500 as suspected of use as a doping agent in sport. [1] FDA's compounding page lists the thymosin beta-4 fragment (LKKTETQ), also known as TB-500, and says it has not identified any human exposure data for drug products containing it, so it lacks information on whether it would cause harm in humans. It also notes immunogenicity risk because of possible aggregation and impurities. [2]

Regulatory status. United States: FDA lists the fragment among bulk substances it reviewed for compounding concerns (the nomination was later withdrawn by the nominators; page current as of April 22, 2026). [2] Compounded drugs are not FDA-approved. [3] Sport: the World Anti-Doping Agency's 2026 list prohibits thymosin-beta-4 and its derivatives, for example TB-500, at all times. [4] Other countries: not verified. Laws change; this is not legal advice.

Thymosin-Related Research

Full-length thymosin beta-4 has been studied as a medicine candidate, which is different from TB-500 products sold online.

• Eye drops. In a phase 2 trial of nine patients with severe dry eye, an eye-drop form (RGN-259) gave statistically significant improvements versus vehicle control; the authors called the trial small. [5] In nine compassionate-use patients with nonhealing corneal defects, six with geographic defects showed what the authors called dramatic healing, while three others showed no change. [6] Label: promising but limited, and for eye drops only.
• Injection in healthy volunteers. A placebo-controlled study of intravenous synthetic thymosin beta-4 in 40 healthy volunteers reported infrequent mild or moderate adverse events and no serious events. [7] That was a safety study, not a test of benefit.
• Review. A 2015 review says thymosin beta-4 has been used in several clinical trials involving tissue repair, and that further possible uses, such as kidney and liver disease or repair of bone and ligament, rest on animal studies. [8]

None of these studies tested TB-500, and none supports use of products sold online. A 2026 review of injectable peptides in sports medicine calls thymosin derivatives investigational with uncertain safety and product-quality concerns. [9]

Preclinical Mechanisms

Thymosin beta-4 is described as a G-actin sequestering peptide. In a well-known mouse study, it promoted heart cell migration and survival in culture and, after induced heart attack in mice, improved heart function. [10] These are preclinical (cells/animals only) findings. They should not be read as results in people. The same review stresses that its broader proposed uses come from animal studies. [8]

Risks and cautions

Because FDA has no human exposure data on the fragment, no safety profile can be described. Product quality and contamination are concerns for unapproved injectables ([11]); see peptide safety and adverse events. Talk with a licensed clinician; see how to evaluate peptide claims and BPC-157 for another investigational peptide.