Key takeaways
- TB-500 is a 7-amino-acid fragment of thymosin beta-4, not the protein itself.
- The FDA found no identified human exposure data for drug products containing the fragment.
- Studies of full-length thymosin beta-4, or of ophthalmic RGN-259, are not evidence for TB-500.
- 21 vendors sell it at $23.96 to $254.95, a 10.6x spread, on 4 published lab records.
The name is doing something
Most peptides are named after what they are. TB-500 is named after what it came from, and that gap is where the trouble starts.
TB-500 is a fragment.
Specifically, a synthetic acetylated peptide corresponding to residues 17 through 23 of thymosin beta-4. Seven amino acids, written out as N-acetylated LKKTETQ.
Thymosin beta-4 is the full protein it was cut from, and residues 17 through 23 are a short stretch from the middle of it.
So when you see "TB" in the name, you're seeing a reference to a bigger molecule that TB-500 is not. Our profile calls it an unapproved seven-amino-acid fragment often confused with full-length thymosin beta-4, and the word confused is carrying real weight.
Why a fragment isn't a smaller dose of the protein
It's tempting to assume a fragment behaves like a smaller dose of the whole thing. Peptides don't work that way.
A short sequence and the protein it was taken from can differ in how they fold, how long they survive in the body, what they bind to, and whether they reach the tissue anyone cares about. Cutting a protein down produces a new molecule, not a concentrate of the old one.
Sometimes an active fragment does retain the useful behaviour. That's a finding you have to establish, not an assumption you get for free.
For TB-500, our profile is explicit: proposed repair mechanisms are not established in humans for this fragment.
The evidence problem, stated precisely
Two separate things are true, and keeping them apart is the whole skill here.
Thymosin beta-4 has been studied in people. Including ophthalmic formulations such as RGN-259, which is a real clinical programme on a real molecule.
TB-500 has not. Our profile records that the FDA found no identified human exposure data for drug products containing the TB-500 fragment.1
Read that second sentence twice. Not thin data, not mixed data. No identified human exposure data.
So when marketing points at thymosin beta-4 research, or at RGN-259, it's swapping molecules mid-argument. Sometimes it swaps the formulation and the route of administration too, since an eye drop and an injection are not interchangeable evidence.
| What's cited | What it actually studied |
|---|---|
| "Thymosin beta-4 promotes tissue repair" | The full 43-residue protein |
| "RGN-259 human trials" | An ophthalmic formulation of the full protein |
| Cell-migration and wound-repair literature | Largely the full protein, not the fragment |
We rate TB-500 very low evidence with an early signal, in the bottom tier of our research directory alongside BPC-157, GHK-Cu, and MOTS-c.
This is evidence laundering, and it's subtle enough that most people repeating it aren't doing it on purpose. It's also the reason TB-500 looks better sourced than it is.
What it's actually studied for
The research focus is cell migration and wound repair, which is genuine biology and worth saying plainly rather than dismissing.
Thymosin beta-4 is involved in actin regulation, and actin dynamics matter for how cells move into damaged tissue. That's why the area attracted interest at all.
What's missing is the step from that biology to an outcome in a person, using this molecule. Mechanism earns more research; it doesn't yet earn your trust. We work through that distinction in why evidence maturity beats online momentum.
For how TB-500 sits against the compound it's most often stacked with, see BPC-157 vs TB-500.
The market: 21 sellers, 4 lab records
TB-500 is listed by 21 vendors in our price market at $23.96 to $254.95 per package, as of the 25 July 2026 check.
That's a 10.6x spread, one of the widest we track, though not the widest. AOD-9604 runs 23x and Thymosin Alpha-1 about 15x.
Some of that range is package size. A gap that wide across 21 sellers on an unapproved compound also reflects that there's no approved product to anchor a price against, so nothing constrains what anyone asks.
Against those 21 sellers, our testing ledger holds four published lab records.3
| Across 4 records | Result |
|---|---|
| Identity confirmed | Every record |
| Purity range | 99.33% to 99.90% |
| Vials over labelled dose | 4 of 4 |
| Median variance | +13.2% |
| Range | +3.4% to +16.1% |
Clean material, every vial over its label, consistent with the pattern across our whole ledger.
Four samples cannot describe what 21 storefronts ship. And when a seller does show you a certificate, check the values against any other you've seen: identical lab numbers appear under multiple vendor names in our ledger, which is covered in how to evaluate a peptide vendor.
Where TB-500 sits
It isn't the molecule most of its evidence is about. That single fact reorganises everything else on this page.
No human exposure data has been identified for the fragment, which is about as clear a statement of an evidence gap as a regulator makes.
It's widely sold and barely documented, 21 sellers against four published records.
Advertising it as an established recovery treatment is the kind of unsupported health claim regulators police.2
None of that proves the compound does nothing. It means nobody has established that it does anything in people, and the research usually offered to suggest otherwise was run on something else.
Profile with graded outcomes and sources: TB-500. New to the topic? Start at what peptides actually are.
Frequently asked questions
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is the full-length protein. TB-500 is a synthetic acetylated fragment corresponding to residues 17 through 23 of it, so seven amino acids taken from the middle of a much longer chain. They are different molecules, and evidence about one does not transfer to the other.
Is TB-500 FDA approved?
No. It is not approved for any use and is sold labelled for research only. Our profile records that the FDA found no identified human exposure data for drug products containing the TB-500 fragment, which is a stronger statement than saying the data is limited.
What about the RGN-259 studies?
RGN-259 is an ophthalmic formulation studied in humans, and it is based on full-length thymosin beta-4 rather than the TB-500 fragment. Citing it as evidence for injectable TB-500 changes the molecule, the formulation, and the route of administration all at once.
Does TB-500 help with injury recovery?
There is no adequate human evidence establishing that. Proposed repair mechanisms are not established in humans for this fragment, and the research most often cited studied a different molecule. That is a statement about the state of the evidence rather than a claim that the compound does nothing.
Read next
Educational information only. This article does not recommend a treatment, supplier, dose, or medical decision. See how we evaluate evidence.