How do the two records compare?
One name has been through completed randomized trials and the other has not. Neither is an approved medicine in the US or the EU, and both records say banned in sport. A completed randomized trial is a finished study that assigns people by chance to the compound or to a comparison. The Table counts only those.
| TB-500 | Thymosin beta-4 (TB4) | |
|---|---|---|
| What it is | A seller's name for thymosin beta-4 or a piece of it, with no agreed chemical identity | A small natural protein, found throughout the body, that helps cells move |
| Human evidence | Grade D: no randomized trial | Grade B: some trials |
| Completed randomized trials | 0 | 3 |
| Approved? | Not approved in the US or the EU | Not approved in the US or the EU |
| Sport | Banned in sport | Banned in sport |
| Checked on | 22 Sep 2026 | 22 Sep 2026 |
- A seller's name for thymosin beta-4 or a piece of it, with no agreed chemical identity
- Grade D: no randomized trial
- 0
- Not approved in the US or the EU
- Banned in sport
- 22 Sep 2026
- A small natural protein, found throughout the body, that helps cells move
- Grade B: some trials
- 3
- Not approved in the US or the EU
- Banned in sport
- 22 Sep 2026
Every cell but the first is a field from the records. The trials section says why the counts differ.
What does each name stand for?
Thymosin beta-4 is a small natural protein found throughout the body, and it helps cells move. TB-500 is a seller's name, used loosely for lab-made thymosin beta-4 or for a smaller piece of it.
Here the two records put it differently, and we print both. The TB-500 record says no agreed chemical identity stands behind the name. By that record, a vial labeled TB-500 may hold the whole protein or a fragment, and nothing in the name says which. The thymosin beta-4 record calls TB-500 "the related fragment", and says the protein is popular in longevity and sports-recovery circles, often under that name.
Other names add to the mix-up. Thymosin beta-4 is also written Tb4. The TB-500 record lists "TB4 fragment" and "Thymosin beta-4 fragment" as other names for TB-500. Allan Goldstein's group first isolated and sequenced the protein from calf thymus tissue in the early 1980s. Neither record gives a date for the TB-500 name or says which seller coined it.
What was tested in people, and under which name?
Every human trial on both records tested a developer's lab-made thymosin beta-4, under that developer's program names. The name TB-500 appears on no trial on either record.
The thymosin beta-4 record lists four human trials:
- RGN-259 eye drops in dry eye, a Phase 2 trial (NCT01387347 on ClinicalTrials.gov (opens in new tab)). It reported improved signs and symptoms compared with placebo.
- RGN-259 in neurotrophic keratopathy, an eye disease, a randomized Phase 3 trial compared with placebo. It reported healing and comfort.
- RGN-259 in dry eye again, the Phase 3 SEER-3 trial. It missed its main goal, disclosed in 2024.
- RGN-137 in epidermolysis bullosa wounds, a Phase 2 trial. The record says the program has not led to approval.
That record counts 3 completed randomized trials and does not say which three. The TB-500 record lists two of the same programs and counts 0. Its reason is the fifth test of the counting rule: a trial counts only when it tested the same compound the record describes. Those trials tested pharmaceutical-grade thymosin beta-4, and nothing sold as TB-500 was in any of them.
Is either one approved, and for what?
No. Neither thymosin beta-4 nor anything sold as TB-500 is an approved medicine in the US or the EU. Both records state that as a status: no FDA approval and no EMA marketing authorisation, for any use, under either name.
On these records, the closest either name has come is the developer's eye-drop program. Phase 2 and Phase 3 trials were completed, and SEER-3, the Phase 3 dry-eye trial meant to support approval, missed its main goal. The thymosin beta-4 record calls the result its biggest gap: whether the protein helps is unresolved after decades of research. Our records check the FDA and the EMA only, so no other regulator is covered here.
What is banned in sport?
Both records say banned in sport, and they do not back it the same way. The TB-500 record links WADA's 2026 Prohibited List and says the List names TB-500, banned at all times.
The thymosin beta-4 record also carries the status. Every sport sentence in its text is about TB-500, which it places in WADA's prohibited growth-factor class for athletes at all times. Its only sport source is a secondary site, so the status for the protein itself has no WADA document behind it. Neither record's text gives the class code. If you compete, read the current List for both names before you trust either row.
What can nobody tell you about your vial?
Nobody can tell you from the outside what a vial labeled TB-500 holds. The name has no agreed chemical identity, so even an honest label leaves open whether the vial holds the whole protein or a piece of it. Products sold under the name are unregulated and unverified in what they hold, and no human trial has tested one.
A vial sold as thymosin beta-4 was not in the trials either, because they tested a developer's eye drops and skin gel. A "research use only" label guarantees nothing about purity. A certificate of analysis counts only if it names your lot number, a lab with no stake in the result, and the method used. Purity and identity are separate tests. For this name the identity test matters: a purity figure says how much of the vial is one substance, and only an identity test says which. The checklist scores a seller on 20 criteria.
The other side
A personal result is real to the person who had it. It cannot show which molecule was in the vial, or what the body would have mended on its own.
What would change this answer?
- A published, completed human trial, large enough to give an answer, of a chemically verified, standard peptide identical to what is sold as TB-500, with a submission to a regulator. That is the TB-500 record's own test.
- A Phase 3 trial that succeeds and that the FDA accepts, in one of the developer's uses. That would change the approval picture for thymosin beta-4. It would not test a vial sold as TB-500.
- An agreed, published chemical identity for TB-500. Until one exists, "the same as" has no testable answer.
Three questions to ask next
Every source below sits on one of the two records, checked 22 Sep 2026.
Regulators
- [1] 2026 Prohibited List (opens in new tab). WADA. From the TB-500 record
Trial registries
- [2] Thymosin Beta 4 Ophthalmic Solution for Dry Eye Study, NCT01387347 (opens in new tab). ClinicalTrials.gov. On both records
Journals and papers
- [3] Complete amino acid sequence of bovine thymosin beta 4 (opens in new tab). From the thymosin beta-4 record Paywalled
- [4] 0.1% RGN-259 Ophthalmic Solution Phase III Trial (opens in new tab). From the thymosin beta-4 record
- [5] Thymosin β4 significantly improves signs and symptoms of severe dry eye (opens in new tab). From the thymosin beta-4 record Paywalled
Secondary Leads. Weaker than a primary document.
- [6] TB-500 status, risks and bans in sport (opens in new tab). From the TB-500 record Secondary
- [7] HLB Therapeutics misses primary endpoint in phase 3 SEER-3 trial (opens in new tab). From the thymosin beta-4 record Secondary
- [8] WADA S2 Prohibited List (Growth Factors) (opens in new tab). From the thymosin beta-4 record Secondary