D tier · weak
TB-500 itself has no human trials at all; the phase 2 data people cite belong to full-length thymosin beta-4, a different 43-residue molecule, and TB-500 is WADA-prohibited and unapproved everywhere.
tb-500
TB-500 is a seven-residue acetylated fragment corresponding to the actin-binding region of thymosin beta-4, originally popularised in veterinary and equine settings. Human clinical data exist for the full-length parent protein but not for this fragment, so its effects in people are unestablished.
// we supply this one
available as a research reagent
≥ 99% HPLC · lyophilised powder · batch certificate published. Grade D above is our own and is not adjusted because we stock it.
the explanation
TB-500 is a small piece cut out of a larger natural healing protein called thymosin beta-4. The human studies that get quoted for it were actually done on the full protein, not this fragment, so TB-500's own track record in people is effectively blank.
regulatory status
not approved for human use anywhere
Explicitly named by WADA under class S2.3 (prohibited growth factors) since the 2018 Prohibited List; nominated for the FDA 503A compounding bulks list with aggregation and peptide-impurity immunogenicity concerns before withdrawal; full-length Tβ4 reached phase 2 but no product has been approved. At the Pharmacy Compounding Advisory Committee meeting of 23 July 2026 the panel voted 8 to 6 with one abstention to recommend adding TB-500 to the section 503A bulks list, against FDA staff advice. A recommendation is non-binding, confers no approval and is not a finding of efficacy; implementation would require notice-and-comment rulemaking. FDA has not published meeting minutes and these tallies are trade-press reporting from the room.
how it works · proposed mechanism
The fragment is defined by a single structural motif rather than a characterised signalling pathway.
Binds monomeric actin
The LKKTETQ motif is the region of thymosin beta-4 that sequesters G-actin and buffers the polymerisation pool. This is the one mechanistic property the fragment is designed to reproduce.
Cell migration and angiogenesis
Parent-molecule studies show promotion of endothelial and keratinocyte migration and new vessel formation in wound models. These effects are attributed to the intact protein, not specifically to the isolated heptapeptide.
Anti-inflammatory signalling
Full-length Tβ4 downregulates NF-kB-driven inflammatory cytokines in animal injury models. Whether the fragment reproduces this is untested.
Fragment is not the parent
Thymosin beta-4 is a 43-residue intrinsically disordered protein with several activities mapped outside the actin-binding region. Extrapolating the parent's trial results to a 7-residue fragment is not scientifically supported.
what’s reported
evidence shape
5 sourcesThe composition of the cited literature by study type. This describes the shape of the evidence, not its quality — and it does not by itself set the grade.
⚠ the catch
Essentially every efficacy claim made for TB-500 is borrowed from research on full-length thymosin beta-4, a structurally and functionally different molecule. The fragment itself has no published human efficacy trial, no human pharmacokinetics, and no evidence that it retains the parent's activity.
key published findings
- Randomised, double-masked, placebo-controlled phase 2 trial of thymosin beta-4 ophthalmic solution for dry eye (Clinical Ophthalmology, 2015, n=72) reduced discomfort scores by 27% versus placebo (P=0.0244) and improved central and superior corneal staining (P=0.0075 and P=0.0210) - conducted with full-length Tβ4, not TB-500.
- Review of phase 2 dermal wound programmes (Annals of the New York Academy of Sciences, 2012) reported that full-length Tβ4 accelerated healing by nearly a month in pressure and stasis ulcer patients who healed.
- Review of Tβ4 dermal healing (Vitamins & Hormones, 2016) found accelerated healing in diabetic and aged animal models and described phase 2 treatment as safe and well tolerated, again for the parent protein.
- WADA added thymosin beta-4 and its derivatives, explicitly naming TB-500, as examples of prohibited growth factors under S2.3 in the 2018 Prohibited List.
- FDA's compounding review flagged thymosin beta-4/TB-500 for immunogenicity risk arising from aggregation and peptide-related impurities.
limitations of the evidence
- No human study has ever administered the TB-500 fragment under controlled conditions.
- Human efficacy data are systematically misattributed from full-length thymosin beta-4 to the fragment across popular sources.
- No published human pharmacokinetics, half-life or bioavailability figures exist for the fragment.
- Eight ClinicalTrials.gov records naming research peptides — including BPC-157, TB-500, MOTS-c, GHK-Cu and melanotan II — share one sponsor, Hudson Biotech, and one site. A July 2026 investigation established that all eight are fabricated: at least two declare themselves fictional or mock in their own text, and two reproduce an Eli Lilly protocol design and compound code that Eli Lilly states it never authorised. The records were still listed as recruiting after the investigation was published. A registry entry is a form submission, not peer review, and this index does not treat one as evidence.
identity
| full name | N-acetyl thymosin beta-4 (17-23) actin-binding fragment |
| category | Healing & Repair |
| modality | peptide |
| formula | C38H68N10O14 |
| molar mass | 889.02 g/mol |
| cas | 885340-08-9 |
| sequence | Ac-LKKTETQ |
laboratory handling
| storage | Lyophilised powder is typically held at -20 °C protected from light; reconstituted research solutions are handled refrigerated at 2-8 °C for short-term use or aliquoted and frozen to limit freeze-thaw degradation. |
| solubility | Soluble in sterile or bacteriostatic water and in saline for laboratory preparation. |
| co-studied with | Most often co-studied and co-marketed with BPC-157 in regenerative contexts, though no controlled human study of the pairing exists. |
Handling information describes laboratory practice for a research reagent. It is not a preparation guide for use in humans.
the receipts
7 citedUS Anti-Doping Agency · 2017 · official
US Food and Drug Administration · 2026 · official
Clinical Ophthalmology · 2015 · peer-reviewed
Annals of the New York Academy of Sciences · 2012 · review
Vitamins and Hormones · 2016 · review
Dr Noc (Morgan McSweeney PhD) · 2026 · investigation
Regulatory Affairs Professionals Society · 2026 · trade press
others in Healing & Repair