TB-500 is a synthetic seven amino acid peptide, Ac-LKKTETQ. It copies one region of thymosin beta-4.
Sellers use both names interchangeably, although they describe different molecules. Because of that, the confusion runs through most of what gets written about TB-500.
So this page separates three things. What TB 500 is, what the research shows, and what nobody has established. Because the third list is longer than the first two, it deserves its own section.
What TB-500 actually is
Thymosin beta-4 is a protein of 43 amino acids, and most human cells contain it. TB 500 reproduces seven of those acids, the part that binds actin.
That is a fragment, not the protein. Yet the distinction matters later, because the human trial data belongs to the whole protein.
| Property | What is known |
|---|---|
| Structure | Synthetic heptapeptide, Ac-LKKTETQ, seven amino acids |
| What it reproduces | The central actin-binding sequence of thymosin beta-4 |
| Human pharmacokinetics | None published, so the human half-life is unknown |
| Human trials of TB-500 itself | None |
| Approval status | Unapproved in the US, the EU and the UK |
How TB-500 works
Actin is the protein that cells use to build their internal scaffolding, and it exists in two forms. Single units float free, while long filaments give a cell its shape.
Thymosin beta-4 binds those single units and keeps them available. Because of that, a cell can reshape itself quickly when it has to move, and cells have to move to close a wound.
That is the basis of the interest in TB-500. Short sequences containing LKKTETQ have also promoted blood vessel growth in laboratory work, and that is where the vascular claims come from.
BPC-157 works from a different origin entirely, and the two get stacked in conversation because shops sell them together. Our comparison of BPC-157 and TB-500 covers that properly.
What the research shows
| Area | Evidence level for TB-500 | What that means |
|---|---|---|
| Tendon and ligament repair | Animal and cell models | Plausible, because the mechanism fits, but nobody has shown it in people |
| Skin and wound closure | Animal models, plus human data for the full protein | The human data belongs to a different molecule |
| Cardiac tissue | Preclinical models | Early stage work, mostly in rodents |
| Eye and corneal disease | Human trials of the protein, not of TB-500 | See the next section, because the results were mixed |
| Muscle growth or strength | Nothing published | No endpoint, in any species, supports this use |
The parent protein’s human trials
This is the part people skip, and it usually gets skipped in both directions. Thymosin beta-4 reached human trials as an eye drop, under the name RGN-259, for a corneal condition.
One published trial reported faster healing of corneal defects than placebo, with no significant adverse effects in that study. Then a European phase 3 trial in the same condition missed its primary endpoint.
Both results are real. Together they mean something specific. At the highest level of evidence available for any member of this family, delivered straight to the affected tissue, the results were mixed.
Therefore a claim that a seven amino acid fragment rebuilds a tendon deserves real caution. The stronger version of the molecule did not clear its own trial.
What nobody knows about TB-500
- The human half-life. No published figure exists, so our half-life chart lists TB-500 as not established.
- Whether it reaches tissue intact. A small peptide meets the same enzymes as any other, and no human data describes what survives.
- Any dose response. Without pharmacokinetics, there is no basis for an amount, an interval or a duration.
- Long-term safety. No safety database, no adverse event rates, and no interaction data.
- Purity in the market. No approved manufacturing standard exists for this molecule.
Regulatory and anti-doping status
No regulator has approved TB-500 for human use. The FDA also lists the thymosin beta-4 fragment, by its sequence LKKTETQ, among compounding substances that may present significant safety risks.
In particular, the agency cites immunogenicity for certain routes, plus difficulty characterising peptide impurities.
Sport treats it as prohibited. WADA names “Thymosin-β4 and its derivatives e.g. TB-500” in the S2 class, which covers peptide hormones and growth factors, and that class applies at all times.
People often describe TB-500 as an S0 substance. However, the list places it in S2, and that detail matters if you ever have to defend a test result.
Reading a TB 500 label
Sellers blur the two names. However, three checks separate a specification from a slogan.
- The sequence or the mass. A heptapeptide specification should show LKKTETQ, or a mass matching seven amino acids.
- Batch matching. The certificate of analysis should carry a batch number that matches the vial.
- Purity method. Look for a percentage plus the method, usually liquid chromatography.
If a certificate reports the mass of the full 43 amino acid protein while the label says TB500, it describes a different product. That single check catches most of what goes wrong in this niche.
Handling is the part you can control. Keep the powder dry and out of light.
Then refrigerate a mixed vial, and never freeze one. Our guides on reconstitution and how long a mixed vial lasts cover both.
FAQ
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is a 43 amino acid protein, and TB-500 is a seven amino acid fragment of it. Sellers use the names interchangeably, yet the human trial data belongs to the protein.
Has TB-500 been tested in humans?
Not the fragment itself. Nobody has run a human trial of TB500, and nobody has published its pharmacokinetics.
What is the half-life of TB-500?
Unknown, because no human figure exists. Any number you see quoted for it is an estimate rather than a measurement.
Does TB-500mg heal tendons?
Animal and cell models suggest it could, and no human trial has tested that. The tendon evidence comes from rodents.
Is TB-500 legal?
It is unapproved everywhere, and the FDA lists it among compounding substances that may present significant safety risks. Whether a shop may sell it is a separate question, and that answer varies by country.
Is TB-500 banned in sport?
Yes. WADA names thymosin beta-4 and its derivatives, including TB, in the S2 class covering peptide hormones and growth factors, and it applies at all times.
Can I stack TB-500 with BPC-157?
This page will not answer that. Nobody has studied the combination in humans, and animal work cannot supply a dose.
What should I check before buying a TB500 product?
That the specification describes a heptapeptide rather than the full protein, that the certificate matches the batch on the vial, and that purity comes with the method used to measure it.
The bottom line
TB-500 is a plausible molecule with a thin human record. The mechanism is real, the animal work is broad, and the human evidence belongs to a larger protein that failed a phase 3 endpoint.
Because of that, treat any confident claim about TB-500 as a question. First ask which species it came from. Then ask whether the paper studied the protein or the fragment.
Last reviewed: October 2026 by Julian Hart.
This page is educational and is not medical advice. TB-500 is unapproved for human use, and anything involving dosing or a health condition belongs with a qualified clinician.
Sources
- McGuire FP, et al. Thymosin beta-4 and TB-500 in tissue healing, regeneration and musculoskeletal research: a scoping review. 2026.
- Maar K, et al. Thymosin beta-4 in organ regeneration and repair. 2021.
- Xing Y, et al. Progress on the function and application of thymosin beta-4. 2021.
- Sosne G, et al. 0.1% RGN-259 (thymosin beta-4) ophthalmic solution in neurotrophic keratopathy. 2022.
- Ophthalmology Times. HLB Therapeutics misses primary endpoint in phase 3 SEER-3 trial of RGN-259.
- FDA. Certain bulk drug substances for use in compounding that may present significant safety risks, listing the thymosin beta-4 fragment (LKKTETQ).
- WADA. The Prohibited List, S2 peptide hormones, naming thymosin-β4 and its derivatives including TB-500.
- Goldstein AL, et al. Biological activities of thymosin beta-4 defined by active sites in short peptide sequences.
