Thymosin Beta-4 (full-length)

What Thymosin Beta-4 is

Thymosin Beta-4 was isolated from the thymus, the gland behind the breastbone in which immune cells mature. In 1981, the group led by Allan Goldstein decoded its sequence: 43 amino acids, acetylated at the start. It was initially thought to be a thymic hormone. Today it is known that almost all cells produce it and that its main task lies elsewhere, in the remodeling of the cytoskeleton.

This page is about the full-length protein. TB-500 is something different: a synthetic piece of seven amino acids that mimics the actin-binding region. An analytical paper from 2024 states that the biological effects of TB-500 itself have not been documented. The human data that are often cited for TB-500 in the scene come almost entirely from studies with full-length Thymosin Beta-4. The two substances carry the same idea, but not the same body of evidence.

How it is supposed to work

The core is actin, one of the most important scaffolding proteins of the cell. Thymosin Beta-4 binds individual actin building blocks and keeps them in reserve. This facilitates the rapid remodeling of the cytoskeleton that every migrating cell needs. Healing is to a large extent movement: vascular cells, connective tissue cells and progenitor cells have to reach the site of the injury.

A review from 2012 summarizes what has been shown in the laboratory and in animals. After an injury, blood platelets, macrophages and many other cells release Thymosin Beta-4. It then promotes the migration of stem and progenitor cells and the formation of new blood vessels, dampens inflammation and cell death, and lowers the number of myofibroblasts, the cells that form scars. The best-known single paper appeared in Nature in 2004: after a heart attack in mice, Thymosin Beta-4 improved the early survival of heart muscle cells and pump function.

What it is used for

In medicine, Thymosin Beta-4 has progressed furthest as eye drops, for dry eye and for corneal defects that do not heal because of impaired nerve supply. In addition, work is under way on skin wounds and, especially in China, on a recombinantly produced form for the heart and skin.

In the biohacking scene, the focus is different: tendons, ligaments and muscles, faster regeneration after injuries, and the longevity idea of preserving repair capacity in old age. The full-length protein is offered there less often than TB-500, usually with the argument that it is closer to the studies. That is true as far as the molecule is concerned. The areas of use in the studies are different, however, and it was injected, as is customary in the scene, only in the heart study, as an infusion under clinical supervision.

What the studies show

Dry eye, 72 participants, 2015

Sosne and Ousler randomly assigned 72 people with moderate to severe dry eye to Thymosin Beta-4 drops or placebo, double-masked, for 28 days. Both primary endpoints, symptoms and staining of the inferior cornea, did not differ significantly at the end. In secondary endpoints they did: in a chamber with dry air, symptoms on day 28 were 27 percent below placebo, and the cornea was less damaged in two further regions. No adverse events occurred.

Non-healing corneal defects, phase 3

In neurotrophic keratopathy, the cornea does not heal because its nerve supply is impaired. In a randomized, double-masked study with patients in stages 2 and 3, 6 of 10 defects had completely healed after 4 weeks under Thymosin Beta-4, versus 1 of 8 under placebo. This narrowly missed the statistical threshold. On day 43, two weeks after the end of treatment, the difference was significant, and no defect recurred under the active substance. The forerunner was a compassionate-use series from 2010 in which 6 of 9 patients with extensive defects healed markedly.

Heart attack, 96 patients, 2025

Zhang and colleagues gave recombinant human Thymosin Beta-4, double-blind and placebo-controlled, to 96 patients after an ST-elevation myocardial infarction and catheter intervention. 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 was not significant. Beforehand, a phase 1 study had tested the infusion in 54 healthy volunteers as a single dose and in 30 more over 10 days: mild to moderate side effects, none serious.

Where the data stop

The studies are small, and none has clearly won its primary endpoint. In dry eye the primary endpoints were missed, in keratopathy with 10 versus 8 patients it initially remained a trend, and in heart attack the effect appeared only in a subgroup. On skin ulcers, a review reports 2 phase 2 studies in which healing was almost a month faster in the patients who healed at all. The 2021 scalp study with 71 patients compared the gel with an antifungal over 4 weeks, but is not described as randomized in the abstract.

For what the scene uses the protein for, there are no controlled data in humans: not for tendons, ligaments, muscles, hair or longevity. The studies were conducted on the eye, on the skin and on the heart, under clinical supervision and with tested product. Long-term data are lacking; the longest controlled use lasted a few weeks.

Status, approval and legal

Thymosin Beta-4 is not approved as a medicine in the EU. The eye drops have been in clinical development for years; no approval was found in our research. On the gray market the protein is sold as a research peptide, which is why usage and dosage information is omitted here. In sport, the situation is clear: the 2026 Prohibited List of the World Anti-Doping Agency lists Thymosin Beta-4 and its derivatives under S2.3, explicitly with the example TB-500. The ban applies at all times, in competition and in training.

Safety

For the tested forms, short-term tolerability is reasonably well documented. The eye drops caused no relevant side effects in the studies, the infusion in healthy people only mild to moderate ones. There are no data on self-injection. A 2026 review of unregulated injectable peptides names contamination, incorrect dosing, unwanted new blood vessel formation and open cancer questions as risks. The last point has a concrete background: in a 2003 mouse model, melanoma cells that produced increased amounts of Thymosin Beta-4 formed a mean of 46.7 lung metastases, control cells 10.9. That is overproduction in tumor cells and not a statement about an injection in humans. Anyone with a known or suspected tumor disease should nevertheless not use a substance that promotes cell migration and blood vessel formation without consulting a physician. Pregnancy and breastfeeding have not been studied.

Sources

• Low TL et al., PNAS 1981 — sequence of Thymosin Beta-4, 43 amino acids
• Goldstein AL et al., Expert Opinion on Biological Therapy 2012 — review of Thymosin Beta-4
• Bock-Marquette I et al., Nature 2004 — heart repair in mice
• Sosne G, Ousler GW, Clinical Ophthalmology 2015 — dry eye, phase 2, 72 participants
• Sosne G et al., International Journal of Molecular Sciences 2022 — neurotrophic keratopathy, phase 3
• Zhang Y et al., Cardiovascular Research 2025 — randomized study in 96 patients after heart attack
• Wang X et al., Journal of Cellular and Molecular Medicine 2021 — phase 1 in healthy volunteers
• Treadwell T et al., Annals of the New York Academy of Sciences 2012 — skin healing in animals and in 2 phase 2 studies
• Cha HJ et al., Journal of the National Cancer Institute 2003 — Thymosin Beta-4, metastases and blood vessel formation in a mouse model
• WADA Prohibited List 2026, officially published in the Austrian Federal Law Gazette III No. 219/2025