TB-500 (Thymosin Beta-4 Fragment)

What TB-500 is

Thymosin beta-4 is a small protein found in practically all cells. In the late 1970s, the research group led by Allan Goldstein described a whole family of messenger substances from the thymus, the gland behind the breastbone. Thymosin beta-4 was one of them; in 1981 its sequence was decoded: 43 amino acids, acetylated at the start. Only afterwards did it become clear that the molecule can do far more than accompany the immune system and that it plays a central role in wound healing and cell movement.

TB-500 is the short form of it. Analytical papers describe it as the acetylated piece Ac-LKKTETQ, that is, the region of thymosin beta-4 that binds to actin. This matters for the assessment: TB-500 and full-length thymosin beta-4 are not the same molecule. Most of the findings cited for TB-500 come from work with the full-length protein.

How it is supposed to work

The key is actin, one of the most important structural scaffolds of the cell. Thymosin beta-4 binds individual actin building blocks and keeps them ready as a reserve. This makes it easier to remodel the cytoskeleton, and every cell that is supposed to migrate needs that. Healing is to a large extent movement: repair cells, vascular cells and connective tissue cells have to reach the site of the injury.

A 2012 review summarizes the effects that were shown in the laboratory and in animals. After an injury, thymosin beta-4 is released by platelets, among others; it promotes the migration of stem and progenitor cells and the formation of new blood vessels, dampens inflammation and reduces the number of myofibroblasts, which in animal models goes along with less scar tissue. This picture is the source of its reputation as a systemic regeneration peptide that acts not in one place but wherever tissue is being repaired.

What it is used for

In the scene, the focus is mainly on tendons, ligaments and muscles, that is, tissue that is poorly supplied with blood and heals slowly. Typical users are ambitious recreational athletes with a stubborn injury, people after surgery and a longevity group that wants to preserve its capacity for repair in old age. TB-500 is often taken together with BPC-157, as the so-called Wolverine Stack: BPC-157 is regarded as local and fast, TB-500 as slower and broader.

The longevity thinking behind it is understandable. Aging is to a good extent declining repair: tissue renews itself more slowly, wounds heal more sluggishly. A molecule that triggers exactly these repair processes in animal models fits this way of thinking, and it is not about performance enhancement but about preserving the capacity to heal. Whether TB-500 delivers on this claim in humans, however, is open.

User reports mostly describe TB-500 as well tolerated. Mild reactions at the injection site and occasionally brief tiredness after the injection are mentioned. These are reports, not study data. Because TB-500 is almost always combined with BPC-157, such reports also cannot show which of the two substances triggered an observed improvement.

What the studies show

Heart muscle repair in mice, Nature 2004

The group led by Ildiko Bock-Marquette showed that thymosin beta-4 promotes the migration of heart muscle and vascular cells and activates the survival signal Akt via a complex with integrin-linked kinase. After ligation of a coronary artery in mice, the treatment improved the early survival of heart muscle cells and heart function. The paper is the most-cited basis for the heart aspect, but it is an animal experiment with the full-length protein.

Corneal defects, 9 patients, 2010

Dunn and colleagues treated 9 patients aged between 37 and 84 with chronic non-healing neurotrophic corneal defects as part of a compassionate use program with thymosin beta-4 eye drops for 28 or 49 days, with 30 days of follow-up. In 6 patients with extensive defects, the surface healed markedly; in 3 patients with punctate defects, the findings did not change. There was no control group.

Randomized trial after heart attack, 2025

Zhang and colleagues gave recombinant human thymosin beta-4 in a double-blind, placebo-controlled trial to 96 patients after an ST-elevation myocardial infarction and a catheter procedure. In the group that received the first dose within 8 hours, the infarct areas were smaller after 90 days. Calculated across all participants, the difference from placebo was not significant. The authors themselves call for further randomized trials.

Where the data stop

The central gap concerns the product itself. A 2024 analytical paper notes that the biological effects of TB-500 have not been documented so far; what was studied was its breakdown in serum and in rats and wound healing in cell culture. The human data all come from full-length thymosin beta-4, in a different form, a different application and often locally, for example as eye drops. Whether the short fragment, injected, does the same has not been tested.

The largest studies with full-length thymosin beta-4 were two placebo-controlled phase 3 trials with eye drops (RGN-259) for dry eye, with around 600 and 700 participants (ARISE-2, ARISE-3). According to the results posted in the trial registry, the primary endpoints were almost level with placebo. A clinical benefit is therefore not established even for the full-length protein.

The remaining clinical data on the full-length protein are small. On skin ulcers, a review reports 2 phase 2 trials in which healing, among the patients who healed at all, was almost a month faster, a finding from a subgroup. The corneal data are an uncontrolled case series, and the heart attack trial did not win its overall comparison. For tendons, ligaments, hair or longevity there are no controlled data in humans. Long-term safety data are missing entirely.

Status, approval and legal

TB-500 is not approved as a medicine in Germany or the EU and is traded as a research peptide. Dosage information is therefore omitted. It is not approved in the US either; the FDA found no data on use in humans and placed TB-500 in Category 2 for compounding pharmacies because of safety concerns. On July 23–24, 2026, an FDA expert panel discussed whether TB-500 should be permitted for compounded medicines in the US. The FDA’s own reviewers advised against it; the panel nonetheless voted in favor by majority (votes 8:6, 1 abstention). An FDA decision is pending; a formal procedure is unlikely to begin before 2027. In sport the situation is clear: the World Anti-Doping Agency’s 2026 prohibited list explicitly lists thymosin beta-4 and its derivatives under S2.3, with TB-500 as an example. The ban applies at all times, in competition as well as in training. In Germany, TB-500 is also listed in the annex to the Anti-Doping Act.

Safety

There is no systematically collected safety profile for TB-500. User reports mention mild reactions at the injection site and brief tiredness; serious problems are rarely reported, but reports do not replace monitoring. A 2026 review of unregulated injectable peptides names as risks contamination from manufacturing, incorrect dosing, unwanted new blood vessel formation and open questions about cancer development. The last point is theoretical, but it follows directly from the mechanism: a substance that promotes cell migration and blood vessel formation does not belong anywhere near a known or suspected tumor. Pregnancy and breastfeeding have not been studied. Anyone considering TB-500 should discuss it with a physician and pay attention to origin and purity.

Sources

• Bock-Marquette I et al., Nature 2004 — thymosin beta-4 and heart repair in mice
• Goldstein AL et al., Expert Opinion on Biological Therapy 2012 — review of thymosin beta-4
• Low TL et al., PNAS 1981 — sequence of thymosin beta-4, 43 amino acids
• Treadwell T et al., Annals of the New York Academy of Sciences 2012 — skin healing in animal models and in 2 phase 2 trials
• Dunn SP et al., Annals of the New York Academy of Sciences 2010 — corneal defects, 9 patients
• Zhang Y et al., Cardiovascular Research 2025 — randomized trial in 96 patients after heart attack
• Rahaman KA et al., Journal of Chromatography B 2024 — TB-500 as Ac-LKKTETQ, breakdown and cell experiments
• Moiz A et al., Missouri Medicine 2026 — risks of unregulated injectable peptides
• WADA prohibited list 2026, officially published in the Austrian Federal Law Gazette III No. 219/2025
• German Anti-Doping Act, annex (thymosin beta-4 and its derivatives, e.g. TB-500)
• FDA – substances with possible safety risks in pharmacy compounding (as of April 2026)
• McDermott Will & Schulte – FDA expert panel (PCAC) on peptides, July 23–24, 2026
• ClinicalTrials.gov NCT02974907 – ARISE-2, RGN-259 for dry eye (results)
• ClinicalTrials.gov NCT03937882 – ARISE-3, RGN-259 for dry eye (results)