What is TB-500? What it does, benefits and what the evidence shows

TB-500 is a synthetic seven-amino-acid peptide (Ac-LKKTETQ) designed to copy the actin-binding region of a much larger, naturally occurring protein called thymosin beta-4. That distinction matters more than it sounds: thymosin beta-4 itself has real Phase 2–3 human trial history under names like RGN-137 and RGN-259. TB-500, the small fragment sold under that name, does not — the published research we found on it is limited to cells and animals.

What TB-500 is and how it relates to thymosin beta-4

Thymosin beta-4 (Tβ4) is a naturally occurring, 43-amino-acid protein found throughout human tissue, first characterized decades ago as the major actin-sequestering protein in cells. Its job, broadly, is binding actin monomers so cells can reorganize their internal skeleton and migrate — which is central to how skin cells and fibroblasts move toward a wound edge, and how endothelial cells migrate to form new blood vessels (PubMed, mechanistic review).

TB-500 is not that protein. It's a synthetic fragment covering just the actin-binding domain — the N-terminal acetylated amino acids 17 through 23 of the 43-amino-acid sequence (Ac-LKKTETQ) — built on the idea that this short stretch carries the biologically active part of the larger molecule. That characterization comes from analytical chemists who synthesized and identified the fragment specifically because it was suspected of being used as an unapproved doping agent, not from a therapeutic development program (Esposito et al., Drug Testing and Analysis, 2012, via PubMed). Whether a 7-amino-acid fragment reliably reproduces everything the full 43-amino-acid protein does in the body is a real scientific question. A 2026 scoping review that identified 1,772 records and included 80 studies on thymosin beta-4 and TB-500 found that most studies evaluated thymosin beta-4 rather than TB-500, that direct TB-500 evidence was limited to a single included study, and that direct musculoskeletal tissue categories such as tendon, ligament and muscle were "comparatively sparse" (scoping review, Applied Sciences, 2026). The research base for "thymosin beta-4" and the research base for "TB-500" are, in practice, two different literatures that get conflated in marketing.

What people use it for

What the research actually shows

The human trials exist — for thymosin beta-4, not for the TB-500 fragment

RegeneRx Biopharmaceuticals has run the actual human trials behind the "Tβ4" name, and they used the full 43-amino-acid protein in proprietary formulations, not the short synthetic fragment sold as TB-500:

• RGN-352, an injectable formulation aimed at heart attack and other acute injuries, has no Phase 2 results: its registered Phase 2 heart attack trial was withdrawn with no participants enrolled (ClinicalTrials.gov, NCT01311518). A separate small pilot trial — 10 total patients, 5 per group — gave heart attack patients endothelial progenitor cells pre-treated with Tβ4 or untreated cells, and reported improved heart-pumping measurements at six months and no severe procedure-related complications, but a study that size is a signal to follow up on, not proof of benefit (RegeneRx press release, 2016).
• RGN-137, a topical gel formulation, was tested in Phase 2 trials for epidermolysis bullosa, a rare and serious skin disease (both terminated early, one after enrolling 4 patients), and in Phase 2 trials for venous stasis ulcers and pressure ulcers (72 patients each) (ClinicalTrials.gov, NCT03578029).
• RGN-259, an eye-drop formulation for neurotrophic keratopathy (a corneal healing disorder), showed a promising trend in an earlier randomized, placebo-controlled Phase III trial — complete healing in 6 of 10 treated patients at four weeks versus 1 of 8 on placebo, a difference that fell just short of statistical significance (p = 0.0656) in that small trial (PMC, 2022). A later Phase 3 trial (SEER-3), reported in July 2025, missed its primary endpoint, which the sponsor attributed to a stronger-than-expected placebo response, and the drug remains unapproved as of that result (Ophthalmology Times).

None of those trials used the seven-amino-acid TB-500 fragment. They used the intact 43-amino-acid protein, manufactured and dosed under an investigational drug program. That's a materially different product from what's sold in research-labeled vials under the TB-500 name, and as of this writing, none of it has resulted in an FDA-approved drug — the eye-drop program is the furthest along and still hasn't cleared a confirmatory trial.

What's actually been studied on the TB-500 fragment itself

Separately from the thymosin beta-4 trial programs above, the short fragment marketed as TB-500 has its own — much thinner and more surprising — evidence base. A 2024 study quantified TB-500 and its breakdown products in human serum, several in-vitro enzyme systems, and urine from rats given the compound, then tested wound-healing activity of the parent molecule and its metabolites in fibroblast cultures. The result cuts against the marketing: in cultured fibroblasts, TB-500 itself did not show a significant wound-healing effect, while only one of its breakdown products, the shorter fragment Ac-LKKTE, did — leading the researchers to suggest the wound-healing activity attributed to TB-500 in earlier literature may actually belong to that metabolite rather than to TB-500 as sold (Journal of Chromatography B, 2024, via PubMed). We found no published human trial of the TB-500 fragment specifically — not a safety pilot, not a case series, nothing resembling the small human studies that exist for BPC-157 or GHK-Cu. If a claim about TB-500 in humans is circulating online, it is not, as far as we could verify, backed by a published human study of that molecule.

The broader mechanism — actin sequestration supporting cell migration and new blood vessel formation — is genuinely well studied for the parent protein, thymosin beta-4, across decades of cell and animal work (PubMed). Whether the fragment reproduces that mechanism to the same degree is the part that hasn't been directly tested and published, as far as our research turned up.

Where TB-500 shows up outside human research: horse racing

One place TB-500 has drawn real regulatory attention is equine sports. Analytical chemists developed a liquid chromatography–mass spectrometry method sensitive enough to detect the fragment (as low as 0.02 ng/mL in plasma and 0.01 ng/mL in urine) to control suspected misuse of a veterinary TB-500 preparation in equine sports; the same paper confirmed the method by detecting TB-500 and its metabolites in urine and plasma from horses given a single dose of that product (Journal of Chromatography A, 2012, via PubMed). That's worth knowing because it means the fragment does have a track record of real-world administration outside a lab — just not the kind of use that generates safety data anyone would want to rely on, since the horses in that paper were dosed to validate a detection method, not to study safety.

Side effects and risks

Because there's no published human study of the TB-500 fragment, there's no human safety data to point to for it specifically — not a dose that's been shown safe, not a documented side-effect profile, nothing. What limited human safety experience exists in this space comes from the different, full-length thymosin beta-4 programs above, run under RegeneRx's investigational formulations, and that experience doesn't automatically transfer to a differently sourced synthetic fragment sold on the research market.

One theoretical concern raised in the peer-reviewed literature on thymosin beta-4 generally: because the protein supports cell migration and new blood vessel growth, a mouse study found that melanoma cells made to overproduce thymosin beta-4 formed tumors averaging 21.7 mm versus 13.3 mm for controls, produced about 47 versus 11 lung metastases, and had a 4.4-fold increase in tumor blood vessels (Cha et al., Journal of the National Cancer Institute, 2003), an angiogenesis-related concern similar to the one raised for BPC-157. That's a mouse and cell signal about the parent protein in existing tumors, not a demonstrated risk from taking the TB-500 fragment as a healthy person, and it hasn't been resolved either way for TB-500 specifically.

On the regulatory side, a 2026 scoping review states that the World Anti-Doping Agency classifies thymosin beta-4 and its derivatives, including TB-500, as prohibited substances under its current Prohibited List (scoping review, Applied Sciences, 2026). FDA previously listed the TB-500 fragment (LKKTETQ) among bulk drug substances with significant safety risks for compounding; in April 2026 it moved TB-500, along with BPC-157, to its list of nominations that were withdrawn, and its entry still notes a possible immunogenicity risk and limited safety data (FDA, page current as of April 22, 2026). That is not an approval. The picture may change further: at its July 23–24, 2026 meeting, FDA's Pharmacy Compounding Advisory Committee voted to recommend adding TB-500, along with BPC-157, KPV, MOTS-c, Epitalon and Semax, to the 503A bulks list that licensed compounding pharmacies can draw on. The vote is non-binding; the Secretary of Health and Human Services still has to approve any addition, and pharmacies can't compound it until the final rule is in place (NCPA, July 31, 2026). Even then it would be a pharmacy-compounded product, not an FDA-approved drug; it has never been approved by FDA for any human use.

On the grey-market side, our data shows TB-500 running consistently overfilled relative to label but with a clean failure record: no empty vials, no purity failures, no vial more than 20% under label among the vials we'd logged as of September 29, 2026. That's a genuinely small sample, though — a single vendor's results can shift it noticeably.

What the lab tests show

As of September 30, 2026, our database includes 22 TB-500 vials from 8 vendors, drawn from 20 lab reports dated November 2024 through February 2026. On purity, 19 of 22 vials have a purity result, 18 of those at 99% or higher and 0 under 95%, with a median purity of 99.55%. On dose against label, the median measured amount is 9.0% over label, with 2 of 22 vials landing within ±5%; 3 measured more than 20% over label and 2 more than 5% under. As of September 29, 2026, no vial in this set failed our definition (empty, under 95% pure, more than 20% under label, or more than 50% over).

That's a clean-looking record on a small sample — as of September 29, 2026, 8 vendors and about 20 reports was thin next to a compound like tirzepatide with hundreds of reports, so treat "zero failures" as a snapshot of what's been tested so far, not a guarantee about a vial you haven't tested. It's also worth noticing what these numbers don't cover: none of the 22 vials in our data on September 29, 2026 had a reported endotoxin or sterility result, so we simply don't have anything to say about that category for this compound yet, and a lab report that only covers identity, purity and quantity is silent on it too unless you specifically order it.

Here's how the ranked vendors for TB-500 look right now; the table shows current verdicts and flags any vendor whose failed-vial rate runs above 5%, and given the size of this dataset it may be short:

Buying smarter

Check a specific vendor's TB-500 history on the TB-500 results page before trusting a single report — a vendor needs at least five lab reports on file before we rank them, and more reports (especially recent ones) tell you more than a single clean result. Whatever COA a vendor shows you is a starting point, not proof on its own: see how to read a peptide COA and fake peptide COAs for what a legitimate report actually looks like and how fabricated ones get caught.

Given how consistently this compound's vials have run over label in our data, a quantity test is the most informative single check you can order on your own vial; how to get a peptide tested covers what identity, purity and quantity testing actually measures and how to order it from an independent lab. If a result comes back with a fail, stop using that batch, tell anyone who bought from the same run, take the report to the vendor, and submit it to VendorVerify so it becomes part of the public record.

It's also worth being honest with yourself about which question a lab report can and can't answer here. A purity and quantity test can tell you the vial contains a peptide matching TB-500's expected mass at a given concentration, and that's genuinely useful — it rules out an empty vial or a wildly mislabeled one. What it can't tell you is whether that peptide behaves in your body the way thymosin beta-4 does in the trials described above, because that's a different question entirely, one no lab report is designed to answer. If what drew you to this compound was the thymosin beta-4 trial data on wound healing or corneal repair, it's worth being clear-eyed that you'd be extrapolating from a different, larger molecule tested in a pharmaceutical formulation you can't buy, not confirming that the vial in front of you will do the same thing.

Database figures without a date update automatically from VendorVerify's lab results; dated figures are snapshots. This isn't medical advice; TB-500 is sold for research use only and neither it nor thymosin beta-4 has been approved by FDA for the uses discussed above.