Research
TB-500 and thymosin beta-4 are not the same molecule
Sellers cite thymosin beta-4 trials on a TB-500 product page. Thymosin beta-4 is a protein of 43 amino acids that has been through phase 1 and phase 2 human trials. TB-500 is a seven-amino-acid fragment of it, and the trial evidence does not transfer.
- The TB-500 board ranks no provider, and carries the dated regulatory position that explains why.
- Set against another compound on the same evidence standard: BPC-157 vs TB-500.
Two names, two molecules
Thymosin beta-4 is a naturally occurring protein of 43 amino acids involved in cell movement and tissue repair. It has been made recombinantly, given to people in trials, and studied for wound healing and eye disease.
TB-500 is a synthetic peptide of seven amino acids: Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH. It corresponds to a short region of thymosin beta-4, acetylated at one end. FDA lists it under exactly that description, as thymosin beta-4 fragment LKKTETQ, also known as TB-500.
One is a protein six times the length of the other. Calling the fragment by the parent protein's name is the single most consequential blur in this corner of the market. It is what lets a page of real clinical citations sit under a product that was never in any of them.
What the human trials on thymosin beta-4 actually are
A search of the published record in September 2026 returns seven randomized controlled trials under a combined search for TB-500 and thymosin beta-4. Reading the seven is the whole exercise.
One is a first-in-human phase 1 study of recombinant human thymosin beta-4 in healthy volunteers. One is a phase 2 trial in severe dry eye, reported in Cornea. One is a placebo-controlled single and multiple dose study of intravenous thymosin beta-4 in healthy volunteers. Two are European studies in venous leg ulcers.
Every one of them studies thymosin beta-4. None of them studies the seven-amino-acid fragment sold as TB-500. Searching for TB-500 by its own name returns 31 records, and several of those are unrelated papers that merely contain the character string.
The registry tells the same story. ClinicalTrials.gov lists eighteen studies naming thymosin beta-4 as an intervention and exactly one naming TB-500, a phase 1/2 cardiovascular biomarker study that began recruiting in early 2026 and has posted no results.
The one thing a regulator found on the fragment itself
FDA evaluated TB-500 for wound healing when it came before the Pharmacy Compounding Advisory Committee in July 2026. That review is the most careful public assessment of the fragment that exists.
The agency stated it found no information in the medical literature where TB-500 had been administered to patients to treat any disease or condition, wound healing included. It also found no nonclinical toxicity studies of either form of the substance.
One laboratory result is worth reading closely. FDA identified an in-vitro study reporting that TB-500 free base, at a concentration of 50 micrograms per milliliter, did not induce wound healing in fibroblast cultures with scratch-generated wounds. A metabolite of it appeared to have wound-healing properties in the same kind of test.
A compound failing the simplest laboratory model of the effect it is sold for is not proof it does nothing. It is a data point that never appears in a sales page, and it points the opposite way from the impression those pages create.
Why the nomination itself is part of the story
Regulators judge a substance partly on how well it is characterized. The TB-500 nomination gives an unusually clear picture of what that means in practice.
FDA recorded four inconsistencies in the package. The substance nominated was the free base while the certificate of analysis supplied was for the acetate salt. The identifiers on that certificate belonged to the acetate rather than the free base. The molecular formula in the nomination matched neither form. An alternate registry number in the package matched neither form either.
The agency concluded that the substance being nominated was unclear. Every one of those mismatches sits on paperwork meant to prove identity, and the paperwork could not do it.
What FDA concluded, and on what grounds
The agency proposed not adding either form of TB-500 to the list of substances that may be used in compounding under section 503A.
Its stated reasons were the lack of physicochemical characterization data, the absence of historical use in compounding, and what it called non-existing information on the use of these substances administered in humans. It added that peptides given by the proposed injection routes may pose a significant risk for immunogenicity.
Note what is not in that list. Nothing there says TB-500 is dangerous. The finding is that nobody has produced the information needed to say whether it is safe, effective, or even reliably the substance on the label.
How to check a citation on a TB-500 page
The test takes about a minute and it works on any product page in this category.
Open the study being cited and read what was administered. If the paper says thymosin beta-4, recombinant human thymosin beta-4, or a proprietary formulation of it, the study is not about the vial being sold. If the paper says TB-500, check whether the subjects were people, rats, horses or cells in a dish.
The same test catches the reverse error. A doping-control paper detecting TB-500 in urine proves the fragment can be measured, not that it does anything.
How this compound is graded here
TB-500 sits in the lowest of the three evidence tiers used on this site: no controlled human evidence. That tier describes the published record for the substance being sold, not the parent protein it is derived from.
Thymosin beta-4 would be graded differently, because trials in people exist for it. No product on the consumer market is thymosin beta-4, so the distinction has no shopping consequence today beyond making the citations on a TB-500 page easier to read correctly.
TB-500 also appears on the World Anti-Doping Agency's prohibited list, which is relevant to anyone subject to testing in sport.
Key takeaways
- Thymosin beta-4 has 43 amino acids; TB-500 is a seven-amino-acid fragment of it, and FDA names it that way.
- All seven randomized controlled trials returned by a combined September 2026 search studied thymosin beta-4, not TB-500.
- ClinicalTrials.gov lists eighteen studies for thymosin beta-4 and one for TB-500, with no results posted.
- FDA found no medical literature where TB-500 was administered to patients for any condition.
- An in-vitro study FDA identified reported that TB-500 did not induce wound healing in scratched fibroblast cultures.
- The TB-500 nomination named the free base while its certificate of analysis described the acetate salt.
Frequently asked questions
Is TB-500 just thymosin beta-4?
No. Thymosin beta-4 is a protein of 43 amino acids. TB-500 is a synthetic seven-amino-acid fragment of it, acetylated at one end, and FDA identifies it in exactly those terms. The two have different chemical identifiers and different evidence behind them. Human trials exist for thymosin beta-4. They do not exist for the fragment.
Then why do TB-500 sellers cite clinical trials?
Because trials on the parent protein are real and easy to find. A search that combines both names returns seven randomized controlled trials, and every one of them studied thymosin beta-4 rather than the fragment. Citing them under a TB-500 heading is not fabrication. It is a substitution, and it is only visible if you open the papers and read what was administered.
Has TB-500 ever been given to people in a study?
FDA stated in July 2026 that it found no information in the medical literature where TB-500 had been administered to patients to treat any condition. One phase 1/2 study naming TB-500 began recruiting in early 2026 and has posted no results. That is the whole human record as of September 2026.
Why does the free base versus acetate distinction matter?
Because they are different substances with different identifiers, and the paperwork that is supposed to establish which one is in a vial routinely names one while the vial contains the other. FDA recorded exactly that mismatch in the TB-500 nomination and concluded it could not tell which substance was being nominated. If a regulator with the full package could not resolve it, a certificate of analysis on a seller's website will not resolve it either.
Does TB-500 work for injuries?
No published human study answers that. The closest laboratory evidence points away from it: FDA identified an in-vitro study in which TB-500 did not induce wound healing in scratched fibroblast cultures. Nonclinical work supporting the wound-healing claim was not found in the agency's review, and neither were toxicity studies.
Sources
Each document below is named as it names itself, with the date printed on that document rather than the day it was read.
- FDA Briefing Document for TB-500-Related Bulk Drug Substances, Pharmacy Compounding Advisory Committee — U.S. Food and Drug Administration, May 2026
- Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks — U.S. Food and Drug Administration, April 2026
- Thymosin beta-4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial — Cornea, May 2015
- A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin beta-4 in healthy Chinese volunteers — Journal of Cellular and Molecular Medicine, September 2021
- Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500 — Drug Testing and Analysis, September 2012
- Registered study census for TB-500 and thymosin beta-4, run with a positive control through the same query — ClinicalTrials.gov, National Library of Medicine, September 2026