Question 1

Is thymosin beta-4 the same thing as TB-500?

Accepted Answer

No. Thymosin beta-4 is a 43-amino-acid protein human cells make; UniProt lists the mature chain as residues 2 to 44 of the TMSB4X product, with an acetyl group on the first serine. TB-500 is far shorter. When a doping-control laboratory took a commercial TB-500 formulation apart in 2012 and characterised what was in it, what they identified and then resynthesised was the N-terminal acetylated 17-23 fragment of human thymosin beta-4: seven residues, Ac-LKKTETQ. The FDA uses the same wording on its compounding list, where the entry reads 'Thymosin beta-4, fragment (LKKTETQ), also known as TB-500'. Seven residues out of forty-three is a different molecule, and the burden is on anyone selling one to show that data from the other carries over.

Question 2

Why do so many TB-500 pages cite thymosin beta-4 research?

Accepted Answer

Because there is almost no TB-500 research to cite. A PubMed search for the exact string TB-500 returned 16 records when we ran it, and most of those are analytical-chemistry papers about detecting the compound in urine or plasma for doping control, not studies of what it does to a person. The same search for thymosin beta-4 returned 1,031. So a page selling the fragment reaches for the full-protein literature, and the reader ends up looking at a citation about a molecule they are not buying. Two narrative reviews published in 2026, one in the American Journal of Sports Medicine and one in Sports Medicine, both list thymosin beta-4 and TB-500 as separate entries rather than folding them together.

Question 3

Has thymosin beta-4 actually been tested in people?

Accepted Answer

Yes. RegeneRx Biopharmaceuticals ran randomised, double-blind, placebo-controlled Phase 2 studies of a thymosin beta-4 gel in pressure ulcers and in venous stasis ulcers, 72 participants in each, both completed. A third Phase 2 in epidermolysis bullosa, with the FDA Office of Orphan Product Development named as the funding source, stopped early with 30 participants enrolled. On the eye side, ReGenTree took a thymosin beta-4 eye drop through three late-stage dry-eye studies, ARISE-1, ARISE-2 and ARISE-3, the largest randomising 700 people. Chinese sponsor Beijing Northland Biotech has completed two Phase 1 studies in healthy volunteers and two Phase 2 studies in acute myocardial infarction with a recombinant thymosin beta-4 injection. That is a real clinical programme, not a forum rumour.

Question 4

What did the wound studies find?

Accepted Answer

Not what the marketing implies. In the pressure-ulcer study the registry posts wound closure at day 84 as a secondary outcome: 3 of 18 participants on placebo, and 8 of 54 across the three peptide groups. In the venous stasis study it was 4 of 17 on placebo and 12 of 55 across the peptide groups. Read those as fractions and the placebo arms did at least as well. The primary outcome in both studies was safety and tolerability rather than efficacy, so neither was designed to settle the efficacy question, but nobody reading those counts would call them a positive signal. The epidermolysis bullosa study, which stopped for lack of patient availability and expiry of the study drug, posted 5 of 8 on placebo and 8 of 22 on the peptide.

Question 5

What happened with the eye-drop trials?

Accepted Answer

ARISE-2 is the one with numbers you can check. It randomised 601 participants, 299 to the active drop and 302 to placebo, and posted its results. On the ocular-discomfort co-primary, the mean change from baseline at day 29 was 0.07 on the active drop and minus 0.04 on placebo, with 95 percent confidence intervals that overlap heavily. The corneal-staining co-primary, reported in a smaller analysis set of 111 and 107 participants, came out at 0.07 against minus 0.01. Higher is worse on both of those scales, so neither endpoint favoured the drop. ARISE-3, the 700-participant Phase 3 that finished in October 2021, has still posted no results to the registry. A Phase 3 in neurotrophic keratopathy was listed as recruiting when we checked.

Question 6

What does thymosin beta-4 do inside a cell?

Accepted Answer

It sequesters actin. UniProt records its function as binding actin monomers, the G-actin pool, and thereby inhibiting actin polymerisation, which puts it in the middle of how a cell organises its skeleton and how it moves. That is a well-characterised molecular job, and it is the reason laboratories keep testing the protein in wound, cornea and cardiac models. It is also a long way from a measured outcome in a person. The first four residues of the mature protein, AcSDKP, are themselves a separately studied bioregulatory peptide, so the molecule is not one tidy unit even in its own biology.

Question 7

So where does the enthusiasm come from?

Accepted Answer

Preclinical models, mostly. The 2026 American Journal of Sports Medicine review summarised the position for orthopaedic clinicians in one line: thymosin beta-4 and its derivative TB-500 promoted angiogenesis and tissue repair in preclinical models, human orthopaedic data are lacking, and both are banned substances in sport. The 2026 Sports Medicine review reached a similar place across the whole gray-market peptide category, noting that many of these compounds show favourable tissue-repair and metabolic outcomes in animal models, that rigorous human safety data are scarce, and that social media amplifies the placebo effect. Animal results are a reason to run a human trial. They do not substitute for one.

Question 8

Is thymosin beta-4 approved anywhere?

Accepted Answer

We could not find an approved thymosin beta-4 medicine in any market. It is not approved by the FDA. It does carry a nonproprietary drug name, timbetasin, and a UNII identifier code, but those are naming and indexing handles rather than any statement about whether it works. The FDA compounding list that was current in April 2026 names the TB-500 fragment, not the full protein, and states that the agency has not identified any human exposure data for products containing that fragment. Registered trials in China and the United States are still trials, not products on a pharmacy shelf.

Question 9

Is it banned in sport?

Accepted Answer

Yes, by name. The WADA 2026 Prohibited List includes thymosin beta-4 and its derivatives, giving TB-500 as the worked example, under section S2.3 for growth factors and growth factor modulators. Everything in the S2 class is prohibited at all times, in and out of competition, and is a non-Specified Substance, which is the category carrying the heavier default sanction. Naming the parent protein and its derivatives together in one line is deliberate: an athlete cannot argue that the vial said TB-500 rather than thymosin beta-4.

Question 10

What are the risks?

Accepted Answer

The safety picture is thinner than the trial count suggests, and it is thinnest exactly where people are buying. The completed studies were topical: a gel on a wound, a drop in the eye. In ARISE-2, three of 299 participants on the active drop and two of 302 on placebo had a serious adverse event, and 19 of 299 against 21 of 302 had other adverse events at the registry reporting threshold, so nothing jumped out over 28 days of eye drops. None of that tells you anything about an injectable product used systemically over months, which is what the online market offers. RegeneRx registered an intravenous Phase 1 and an injectable Phase 2 and withdrew both before enrolling anyone, one of them over contract-manufacturing problems. Gray-market vials add the usual problems on top: unverified purity, endotoxin risk, and a label that may not match the contents. Anyone weighing this up should talk to a clinician who knows their history.

Question 11

What would change the verdict?

Accepted Answer

A completed, adequately powered human study whose primary endpoint the peptide actually met, in a population and by a route that resembles how people are using it. The closest thing to that on the board is ARISE-3, which enrolled 700 people, finished in 2021, and has never posted results. Until those numbers are public and independently readable, the honest position is that thymosin beta-4 has been through several randomised placebo-controlled human trials and has not shown a benefit in the ones whose results we could read.

Thymosin Beta-4

Which form actually works?

Eye drops (investigational, RGN-259)

Topical gel (investigational, wound studies)

Injectable research vials sold online

Third-Party Testing & Certificate of Analysis (COA)

Sources

Related peptides

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