TB-500 vs thymosin beta-4
TB-500 is a 7-amino-acid piece of thymosin beta-4, a 43-amino-acid protein. The human trials belong to the full protein, and FDA treats the two as different substances.
- TB-500
- Preclinical2× per week, then weekly
- Thymosin Beta-4
- Human studies2× per week, then weekly
- Head-to-head trials
- None published
The short answer
Thymosin beta-4 is a protein nearly every cell makes; it binds actin and helps cells move in to repair tissue. TB-500 usually means the acetylated fragment LKKTETQ, residues 17 to 23 of it, though some products sold as TB-500 contain the full protein.
Full-length thymosin beta-4 has been tested in people as IV infusions in healthy volunteers, eye drops (RGN-259) and a wound gel. The eye drops missed their main goals in two large dry-eye trials, and none of it is approved. The fragment has never been tested in a person. FDA’s July 2026 briefing called them different substances that websites often use interchangeably.
At a glance
| Field | TB-500Thymosin beta-4 fragment (Ac-LKKTETQ) | Thymosin Beta-4Tβ4, timbetasin, RGN-259 (eye drops), RGN-137 (gel), NL005 |
|---|---|---|
| Evidence | Preclinical | Human studies |
| Class | Tissue-repair peptide | Actin-binding repair peptide |
| Approval | Not approved as a drug in the US or EU. | Not approved as a drug in the US or EU. Its eye drops (RGN-259) and a recombinant IV form are still in clinical trials. |
| Sport (WADA 2026) | Banned in sport | Banned in sport |
| Common dose | 2–2.5 mg twice weekly, then weekly | 2–2.5 mg twice weekly, then weekly |
| Frequency | 2× per week, then weekly | 2× per week, then weekly |
| Cycle | Load 5 weeks, maintain 6, then 6 off | Load 5 weeks, maintain 6, then 6 off |
| Route | Subcutaneous injection | Subcutaneous injection (community); IV, eye drops and skin gel in trials |
| Half-life | – | – |
| Typical draw | 50 units5 mg with 1 mL, 2.5 mg | 50 units5 mg with 1 mL, 2.5 mg |
| Vial sizes or form | 5, 10 mg | 5, 10 mg |
| Human studies | None found | 5 listedLargest: 700 people (2021) |
| Main cautions |
|
|
| Open TB-500 | Open Thymosin Beta-4 |
Doses shown are what labels, trials or community reports reference, not recommendations. Each compound’s page has the full detail and sources.
Key differences
Size
TB-500: 7 amino acids, 889.0 g/mol. Thymosin beta-4: 43 amino acids, 4,963.5 g/mol.
Human trials
TrialThymosin beta-4: IV safety trials (40 healthy adults, up to 1,260 mg a day for 14 days), eye-drop trials (about 1,300 people with dry eye, plus keratitis trials) and a leg-ulcer gel trial. TB-500: none.
How they’re used
CommunityUsers inject both under the skin on the same schedule, 2–2.5 mg twice a week and then weekly. That schedule comes from TB-500 guides; injection under the skin hasn’t been studied for either.
Regulatory
TB-500’s compounding nomination was withdrawn, and FDA’s advisory committee voted 8 to 6 for it in July 2026. Full-length thymosin beta-4 was never nominated. Both are banned in sport under WADA S2.3, which names “thymosin-β4 and its derivatives e.g. TB-500”.
What’s in the vial
Products under either name may contain either molecule. Only a certificate of analysis with the sequence or mass tells them apart.
Head-to-head studies
Taking them together
Open them in the stack check for sport status and one combined tracking checklist.
Questions
What is the difference between TB-500 and thymosin beta-4?
Thymosin beta-4 is a protein nearly every cell makes; it binds actin and helps cells move in to repair tissue. TB-500 usually means the acetylated fragment LKKTETQ, residues 17 to 23 of it, though some products sold as TB-500 contain the full protein.
Is TB-500 the same as thymosin beta-4?
No. TB-500 is a 7-amino-acid fragment (residues 17 to 23) of the 43-amino-acid thymosin beta-4 protein. The names are often used interchangeably online, but FDA treats them as different substances, and the human trials tested the full protein.
Can TB-500 and thymosin beta-4 be taken together?
No overlap between them is documented. No published study has tested them together.
Which has more evidence in people, TB-500 or thymosin beta-4?
TB-500 isn’t approved anywhere and rests mainly on cell and animal studies; its page lists no published human studies. Thymosin beta-4 is in clinical trials and not approved; its page lists 5 key human studies. They haven’t been compared directly in a published trial.
Are TB-500 and thymosin beta-4 banned in sport?
TB-500 and thymosin beta-4 are banned at all times. This follows the WADA 2026 Prohibited List; athletes should confirm with their anti-doping organization.
Sources
- Ruff et al., IV thymosin beta-4 in healthy volunteers, Phase 1 (Ann N Y Acad Sci 2010) PMID 20536472
- ARISE-3 dry-eye trial, posted registry results NCT03937882
- FDA briefing document: TB-500-related bulk drug substances (July 2026)
- Esposito et al., the TB-500 fragment found in TB-500 products (Drug Test Anal 2012) PMID 22962027
Each compound’s page lists its full sources: TB-500, Thymosin Beta-4.