TB-500 vs Thymosin Beta-4: What the Human Evidence Shows
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TB-500 vs Thymosin Beta-4: What the Human Evidence Shows

Fragment vs full protein · Eye and wound trials · FDA review, July 2026

Published · By Ethen Amezquita

Short answer: TB-500 and thymosin beta-4 are not the same thing. Thymosin beta-4 (Tβ4) is a 43-amino-acid protein that has been tested in a few small human trials, mostly as eye drops and skin gels. TB-500, as FDA describes it, is a 7-amino-acid acetylated fragment (Ac-LKKTETQ). In its July 2026 review, FDA said it found no clinical studies or human exposure data for TB-500 by any route. So the human evidence people cite for "TB-500" is almost always evidence for a different molecule, given a different way.

TB-500 is usually sold as a recovery peptide and is often stacked with BPC-157. Search results tend to treat "TB-500" and "thymosin beta-4" as one thing, and borrow the research on one to support the other. This article separates them, walks through the human trials that exist, and summarizes what FDA concluded when it reviewed TB-500 for compounding in July 2026.

What TB-500 actually is

Thymosin beta-4 is a naturally occurring protein. A trial report on venous ulcers describes the drug used there as "a synthetic copy of the naturally occurring 43 amino-acid peptide" (Guarnera 2010). TB-500 is something else. FDA's 2026 briefing document describes TB-500 (free base) as "a peptide containing seven amino acids with an acetyl group at the N-terminal Leucine (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH)." That stretch, LKKTETQ, is the part of Tβ4 thought to bind actin. FDA's list of compounding safety risks names it as "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500."

So a study of full-length Tβ4 is not a study of TB-500. A seven-amino-acid fragment can behave very differently from the whole protein in how it is absorbed, how long it lasts and what it does.

FDA also flagged a naming problem: nominations and products often do not say whether they mean TB-500 free base or TB-500 acetate, which are different active ingredients. Neither has an official nonproprietary name (INN or USAN).

Human trials of full-length thymosin beta-4

These are the human studies of Tβ4 we could verify on PubMed. All used the full protein. None used TB-500.

Eye drops for dry eye

  • Severe dry eye, phase 2 (Sosne 2015, Cornea): 9 patients used 0.1% Tβ4 drops (RGN-259) or a vehicle six times a day for 28 days. At day 56, the treated group had 35.1% less eye discomfort and 59.1% less corneal staining than control, with statistical significance. The trial was very small.
  • Moderate to severe dry eye, phase 2 (Sosne and Ousler 2015): 72 subjects were randomized to 0.1% Tβ4 or placebo for 28 days. Neither primary endpoint (eye discomfort and inferior corneal staining at day 29) differed between groups. Some secondary measures improved. No adverse events were seen.

Eye drops for neurotrophic keratopathy

  • Phase 3 (Sosne 2022): 18 patients with non-healing corneal defects. Complete healing at 4 weeks occurred in 6 of 10 on Tβ4 and 1 of 8 on placebo (p = 0.0656, which the authors called a "strong efficacy trend", not a clear win). Some later time points reached significance. Two authors were employed by the company developing the drug.

Skin gel for venous ulcers

  • Phase 2 (Guarnera 2010): 73 patients at eight European sites, topical Tβ4 at several strengths vs placebo. Safety was "acceptable and comparable to placebo." The authors wrote that a 0.03% dose "may have the potential" to speed healing. That is a hypothesis, not a demonstrated effect.

IV safety in healthy volunteers

  • Phase 1 (Wang 2021): 54 healthy Chinese volunteers received single IV doses of recombinant human Tβ4 (0.05 to 25 µg/kg), and 30 more received daily doses for 10 days. Side effects were mild to moderate, with no dose-limiting toxicity. This was a first step toward heart-attack trials, not a test of healing.

Put together: full-length Tβ4 has small, mixed results as an eye drop, an early signal as a skin gel, and a clean phase 1 safety run by IV. No Tβ4 product is FDA-approved, and none of these trials tested muscle or tendon recovery, which is what most people buy TB-500 for.

What FDA said about TB-500 in July 2026

FDA's Pharmacy Compounding Advisory Committee reviewed TB-500 on July 23, 2026, for the use the nominator proposed: wound healing. The original nomination had been withdrawn, and FDA evaluated the substance on its own initiative. The briefing document is direct:

  • No human data: FDA "did not identify data, such as clinical studies, on the use of TB-500 in humans," and found no human pharmacokinetic studies by any route.
  • Safety unknown: with no clinical studies or human exposure data, "potential safety risks associated with the use of TB-500 in humans are unknown." Its adverse event database search through March 2025 returned no reports, which FDA notes is not the same as safe.
  • Lab result: FDA cited an in-vitro study in which TB-500 at 50 µg/mL did not induce wound healing in fibroblast scratch assays, though one of its breakdown products appeared to have wound-healing properties in vitro.
  • Quality and immune risk: FDA said neither form is well characterized, public certificates of analysis lacked tests for impurities, aggregates and endotoxin, and injected peptides carry a risk of immune reactions.
  • Conclusion: the balance of criteria "weighs against" placing TB-500 free base or acetate on the 503A bulks list.

FDA's separate page on compounding safety risks lists the TB-500 fragment among substances that were in category 2 before their nominations were withdrawn, noting FDA "has not identified any human exposure data." Press coverage of the meeting that we could verify did not report a vote count for TB-500, and FDA had not posted minutes on its meeting page as of October 22, 2026. See our explainer on the 2026 decisions.

Is TB-500 banned in sport?

Yes. The WADA 2026 Prohibited List, under S2.3 (growth factors and growth factor modulators), names "Thymosin-ß4 and its derivatives e.g. TB-500." It is banned at all times.

Why people still stack it with BPC-157

Most of the case for TB-500 comes from cell and animal work on full-length Tβ4, plus anecdotes. The one human study that used a combination, a knee-injection chart review, gave some patients BPC-157 plus "thymosin beta-4" with no control group, and three of four combination patients reported improvement (see our BPC-157 evidence review). FDA's adverse event review for BPC-157 also included a report of skin darkening with a BPC-157 plus TB-500 product that recurred on restarting. For how the two compare, see BPC-157 vs TB-500 and our blends guide.

What we do not know

  • Whether TB-500 does anything in people.
  • How much injected TB-500 reaches the blood in humans and how fast it is broken down.
  • Whether results for full-length Tβ4 eye drops or gels say anything about injected fragments. There is no reason to assume they do.
  • What is in a given vial. FDA noted that public COAs lacked key tests; our COA guide explains what to look for.

Keeping records

We do not give doses, and no human trial has established one for TB-500. If you use it under a clinician's care, write down the product, the vial, the reconstitution date, each injection and any reactions. Dose Track can hold all of that in one place, including stacks with BPC-157 logged as separate compounds, so changes in how you feel can be lined up against what you actually took. For mixed-vial storage, see how long reconstituted peptides last.

Frequently asked questions

Is TB-500 the same as thymosin beta-4?+
No. Thymosin beta-4 is a 43-amino-acid protein. FDA describes TB-500 as a 7-amino-acid acetylated fragment, Ac-LKKTETQ. Studies of full-length thymosin beta-4 are not studies of TB-500.
Has TB-500 been tested in humans?+
FDA said in its July 2026 briefing document that it did not identify any clinical studies or human exposure data for TB-500 by any route of administration.
What human trials exist for thymosin beta-4?+
Small trials of 0.1% eye drops for dry eye (9 and 72 patients) and neurotrophic keratopathy (18 patients), a 73-patient phase 2 trial of a topical gel for venous ulcers, and a phase 1 IV safety study of recombinant thymosin beta-4 in 84 healthy volunteers. Results were mixed, and none tested muscle or tendon injuries.
Is TB-500 FDA approved?+
No. FDA's briefing states that TB-500 free base and acetate are not components of any FDA-approved drug and have no USP monograph. FDA's review concluded the criteria weigh against adding TB-500 to the 503A bulks list.
Is TB-500 banned by WADA?+
Yes. The 2026 WADA Prohibited List names thymosin beta-4 and its derivatives, such as TB-500, under S2.3. It is prohibited at all times.

Related reading

Questions about the app? See the help center or join the Dose Track community.

Sources

Every number in this article comes from one of these sources, checked on October 22, 2026. This article is for education. It is not medical or legal advice, and nothing here is a dose recommendation.

  1. U.S. Food and Drug Administration. FDA Briefing Document: TB-500-related bulk drug substances (TB-500 free base and TB-500 acetate). Pharmacy Compounding Advisory Committee, July 23-24, 2026. fda.gov/media/193349/download
  2. U.S. Food and Drug Administration. Certain bulk drug substances for use in compounding that may present significant safety risks (content current as of April 22, 2026). fda.gov
  3. Sosne G, Dunn SP, Kim C. Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea. 2015;34(5):491-496. PMID 25826322. pubmed.ncbi.nlm.nih.gov/25826322
  4. Sosne G, Ousler GW. Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, phase II clinical trial conducted using the controlled adverse environment (CAE) model. Clin Ophthalmol. 2015;9:877-884. PMID 26056426. pubmed.ncbi.nlm.nih.gov/26056426
  5. Sosne G, et al. 0.1% RGN-259 (thymosin ß4) ophthalmic solution promotes healing and improves comfort in neurotrophic keratopathy patients in a randomized, placebo-controlled, double-masked phase III clinical trial. Int J Mol Sci. 2022;24(1):554. PMID 36613994. pubmed.ncbi.nlm.nih.gov/36613994
  6. Guarnera G, DeRosa A, Camerini R. The effect of thymosin treatment of venous ulcers. Ann N Y Acad Sci. 2010;1194:207-212. PMID 20536470. pubmed.ncbi.nlm.nih.gov/20536470
  7. Wang X, et al. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers. J Cell Mol Med. 2021;25(17):8222-8228. PMID 34346165. pubmed.ncbi.nlm.nih.gov/34346165
  8. World Anti-Doping Agency. 2026 Prohibited List, section S2.3. wada-ama.org/en/prohibited-list