As of September 2026, the FDA and the EMA have not approved thymosin beta-4 in any form. An eye-drop version went through human trials with mixed results, and the Phase 3 dry-eye trial meant to support approval missed its main goal. It is banned in sport. Those trials tested a developer's eye drops. Nobody can tell you from the outside what a vial sold under this name holds.
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What is thymosin beta-4?
Thymosin beta-4 is a small natural protein, found throughout the body, that helps cells move. Allan Goldstein's group first isolated and sequenced it from calf thymus tissue in the early 1980s. RegeneRx developed a lab-made version as eye drops and a skin gel, and the protein is popular in longevity and sports-recovery circles, often under the name TB-500.
Does thymosin beta-4 work?
That is unresolved after decades of research. Trials of the eye-drop version gave mixed results, and SEER-3, which the record calls the most rigorous, missed its main goal.
What we found. 3 completed randomized trials counted on the record. 4 human trials are listed below, and the record does not say which three it counts. 1 paper on the protein's sequence.
| Study | Tested in | Status | What it shows |
|---|---|---|---|
| Low et al. 1981, complete sequence of thymosin beta-4 from cattle | Animals | Published | The first complete amino-acid sequence of thymosin beta-4 |
| RGN-259 Phase 2 trial in dry eye, NCT01387347 on ClinicalTrials.gov (opens in new tab) | People | Completed | Signs and symptoms of dry eye improved compared with placebo |
| RGN-259 Phase 3 trial in neurotrophic keratopathy, an eye disease | People | Completed and published. Randomized, compared with placebo | The trial reported that it promoted healing and comfort |
| RGN-259 SEER-3 Phase 3 trial in dry eye | People | Completed | It missed its main goal for efficacy. The result was disclosed in 2024 |
| RGN-137 Phase 2 trial in epidermolysis bullosa wounds | People | Conducted | It was given to patients with these wounds. The program has not led to approval |
All four human trials tested the developer's own products, for the eye or for skin wounds.
How we count a trialIs thymosin beta-4 safe?
The record lists no safety results from the trials. It says one thing about safety: outside the eye-drop trials, the data are limited. So beyond those trials, little is known. All of that describes the developer's trial products. A vial sold under this name, or as TB-500, is a separate matter, and the vial section takes it up.
Is thymosin beta-4 legal?
- United States
- Not approved by the FDA. A lab-made version, RGN-259, completed Phase 2 and Phase 3 trials in eye disease. The Phase 3 dry-eye trial meant to support approval missed its main goal.
- European Union
- No marketing authorisation from the EMA.
- Sport
- Banned in sport. The record places TB-500, the related fragment, in WADA's prohibited growth-factor class for athletes at all times.
- Other forms
- No thymosin beta-4 or TB-500 product is approved by the FDA or the EMA for any use.
Not medical advice. Approval and sport status as of . Medical disclaimer
What is in a vial sold as thymosin beta-4?
The trials above tested a developer's eye drops and skin gel. The protein is also popular in longevity and sports-recovery circles, often under the name TB-500, and none of those trials tested a vial sold under either name. 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.
Three questions to ask the seller:
- Which lot number is this certificate for?
- Who ran the test, and are they independent of you?
- Does the report confirm identity by mass spectrometry, or purity alone?
What don't we know?
- Whether it helps dry eye. A Phase 2 trial reported gains, and SEER-3 missed its main goal.
- Whether any version will reach FDA or EMA approval. None has after decades of research.
- What its safety looks like outside the eye-drop trials. Those data are limited.
- What is in a vial sold as thymosin beta-4 or as TB-500.
The other side
A personal result is real to the person who had it. It cannot show that the vial held what the trials tested, or what time alone would have done.
What would change this record?
- A Phase 3 trial meant to support approval that succeeds, and that the FDA accepts, in one of the uses the developer is pursuing.
Three questions to ask next
- What does 'research use only' actually mean?
- How can you tell if a peptide vendor is legitimate?
- How do you read a certificate of analysis?
Ask better questions.
More questions about thymosin beta-4
Is thymosin beta-4 the same as TB-500?
- Not exactly. This record calls TB-500 a related fragment name, and says thymosin beta-4 often goes by it in sports-recovery circles. The TB-500 record says that name has no agreed chemical identity behind it.
Is thymosin beta-4 approved by the FDA?
- No. The FDA has not approved it, and it has no EMA marketing authorisation. No thymosin beta-4 or TB-500 product is approved by either for any use.
Has thymosin beta-4 been tested in people?
- Yes. A lab-made version was tested in people for dry eye, corneal injury and epidermolysis bullosa wounds. Phase 2 and Phase 3 trials were completed, and the Phase 3 dry-eye trial meant to support approval missed its main goal.
Is thymosin beta-4 banned in sport?
- Yes, on this record. Its text places TB-500, the related fragment, in WADA's prohibited growth-factor class at all times. The record's sport source is a secondary site. If you compete, check the current List.
What happened in the SEER-3 trial?
- It missed its main goal. SEER-3 was a Phase 3 trial of RGN-259 in dry eye, and the result was disclosed in 2024. The record calls it the most rigorous of the trials meant to support approval.
Record checked on . Each source shows the date it was checked.
In the same group
Often confused with TB-500. TB-500 is a seller's name for thymosin beta-4 or a piece of it, with no agreed chemical identity, and no human trial has tested a product sold under it.