TB-500
Thymosin beta-4 fragment (research chemical)
Status
Not approved
Not approved anywhere; FDA listed thymosin beta-4 fragment (LKKTETQ) in 503A Category 2 until the nomination was withdrawn and it was removed in April 2026, and in July 2026 an FDA advisory committee voted 8-6 (1 abstention) to recommend adding TB-500 to the 503A bulks list against FDA staff advice, with no final FDA rule yet.
Evidence
Animal data only
FDA found no human studies of TB-500 at all; the case for it rests on animal work with the fragment and on research into full-length thymosin beta-4, a different molecule.
In sport
WADAProhibited (WADA)
TB-500 is a synthetic seven-amino-acid fragment of thymosin beta-4 (Ac-LKKTETQ), first marketed for racehorses and greyhounds and now sold as a research chemical for injury recovery. It has never been studied in people and is often confused with full-length thymosin beta-4.
Structure
7 residuesPoint at a bead, or focus the chain and use the arrow keys, to name it. Pick a chemistry to highlight it.
Sequence as text
Ac-L-K-K-T-E-T-Q-OH
What it is used for
- Wound healing, the use FDA reviewed in 2026, in animal studies only (studied)
- Neurotrophic keratopathy, using full-length thymosin beta-4 eye drops (RGN-259) rather than TB-500 (studied)
- Tendon, muscle and sports injury recovery (claimed, unproven)
How it works
Full-length thymosin beta-4 binds monomeric actin (G-actin) and is linked to cell migration, blood vessel growth and wound repair; LKKTETQ is the stretch thought to carry its actin-binding and wound-healing activity. In mice the non-acetylated LKKTETQ peptide sped skin wound closure, but FDA cautions that acetylation changes a peptide's properties, so those results cannot simply be applied to TB-500. In horses, and in lab preparations of human liver, kidney and serum, TB-500 is broken down into shorter acetylated fragments.
How strong the evidence is
Animal data only
FDA's 2026 review found no clinical studies, case reports or pharmacokinetic data for TB-500 in humans; the nomination cited only studies of full-length thymosin beta-4. Data on the fragment come from mouse wound models (Philp 2003) and horse metabolism studies used for doping control (Ho 2012). Full-length thymosin beta-4 has separate human data as RGN-259 eye drops for neurotrophic keratopathy: the small SEER-1 phase 3 trial (18 patients) trended positive, the European SEER-3 phase 3 missed its primary endpoint in 2025, and the US SEER-2 trial was still listed as recruiting at its last registry update.
Risks and side effects
- No human safety data of any kind for TB-500 (FDA 2026).
- Uncertain identity: products labelled TB-500 may contain the fragment, full-length thymosin beta-4 or other substances.
- Peptide impurities and aggregation may provoke unwanted immune reactions (immunogenicity), according to FDA.
- Prohibited in sport at all times under WADA class S2.3, which names thymosin beta-4 and its derivatives such as TB-500; doping tests can detect its metabolites.
Regulatory status
Status by country
| Jurisdiction | Status | Source |
|---|---|---|
| USUnited States | No authorised medicine | Source 1 |
| EUEuropean Union | No authorised medicine | Source 13 |
| UKUnited Kingdom | No authorised medicine | Source 14 |
| AUAustralia | No authorised medicine | Source 15 |
| CACanada | No authorised medicine | Source 16 |
Timeline
2026
- ResearchReview of 565 studies finds little human evidence for popular injectable peptides
- RegulatoryAustralian regulator seizes illegal peptides allegedly sold by a social media influencer
- RegulatoryFDA advisers vote to allow compounding of BPC-157, KPV, TB-500 and MOTS-c
- RegulatoryFDA removes BPC-157 and 11 other peptides from its compounding safety-risk list
- SafetyAustralia's TGA warns of severe reactions to unapproved injectable peptides
- SafetyHealth Canada warns against injecting peptides bought online and names seized products
Articles about TB-500
Sources
- 01FDA Briefing Document: TB-500-Related Bulk Drug Substances, Pharmacy Compounding Advisory Committee(opens the source in a new tab)
- 02Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks(opens the source in a new tab)
- 03July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee(opens the source in a new tab)
- 04Bulk-list bound? PCAC backs majority of peptides in two-day public meeting(opens the source in a new tab)
- 05PubChem Compound Summary: TB-500 (Ac-LKKTETQ) (CID 62707662)(opens the source in a new tab)
- 06UniProtKB P62328: Thymosin beta-4 (TMSB4X), human(opens the source in a new tab)
- 07World Anti-Doping Code International Standard: Prohibited List 2026(opens the source in a new tab)
- 08Doping control analysis of TB-500, a synthetic version of an active region of thymosin beta4, in equine urine and plasma by liquid chromatography-mass spectrometry(opens the source in a new tab)
- 09Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice(opens the source in a new tab)
- 100.1% RGN-259 (Thymosin beta 4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial(opens the source in a new tab)
- 11Letter to Stockholders: SEER-3 top-line results(opens the source in a new tab)
- 12Assessment of the Safety and Efficacy of 0.1% RGN-259 Ophthalmic Solution for the Treatment of NK: SEER-2 (NCT05555589)(opens the source in a new tab)
- 13Find medicine: centrally authorised medicines(opens the source in a new tab)
- 14MHRA Products: active substances beginning with T(opens the source in a new tab)
- 15Understanding your responsibilities when importing, compounding and supplying unapproved peptide products(opens the source in a new tab)
- 16Think twice before injecting peptides bought online: unauthorized products can seriously harm you(opens the source in a new tab)
Educational information, not medical advice. Talk to a licensed clinician before starting, stopping or changing any medicine.