# TB-500: Evidence, Mechanism, Dosing & Legal Status

> A clinical monograph on TB-500 — the synthetic thymosin β4 fragment (Ac-LKKTETQ) marketed for tendon, muscle and tissue repair. Strong preclinical biology, no human efficacy RCT of the fragment, and an unsettled 2026 legal status.

*Published 2026-06-30 · Updated 2026-07-01 · By Elena Soto, PharmD*

The short answer
TB-500 is the synthetic heptapeptide fragment *Ac-LKKTETQ* of thymosin β4, with a coherent *animal* evidence base for cell migration and tissue repair — but **no published human efficacy RCT of the fragment exists**, so its highest grade is **C (preclinical only)**. It is not FDA-approved, sits in a 2026 regulatory gray zone, and is prohibited in sport at all times under WADA S2.3.[1](https://peptidevox.com/#r1)[19](https://peptidevox.com/#r19)

TB-500 ("Thymosin Beta-4 fragment") is a synthetic, N-acetylated heptapeptide marketed and used as a tissue-repair agent for tendon, muscle, ligament and wound recovery. Its popularity in fitness and recovery circles is large; its proof in humans is essentially zero. This monograph separates the two, and corrects a confusion that undermines most consumer claims: **TB-500 is a fragment, not the full thymosin β4 protein.**[2](https://peptidevox.com/#r2)

*This article is informational and editorial content for research and educational purposes only. It is not medical advice, not a protocol to follow, and not a sourcing guide. TB-500 is not an FDA-approved drug; it is sold as a "research chemical not for human use" and is prohibited in sport at all times. Dosing figures are reported strictly as seen in the published literature and grey-market use for completeness — not as recommendations. Consult a licensed clinician before any health decision.*

## What is TB-500 and how does it work?

Thymosin β4 (Tβ4; gene *TMSB4X*) is a 43-amino-acid, roughly 4.9 kDa β-thymosin expressed in nearly all nucleated cells and present in platelets, plasma and tears.[7](https://peptidevox.com/#r7) TB-500 is **not** the whole protein: it is the synthetic, N-terminally acetylated heptapeptide Ac-LKKTETQ, corresponding to residues 17-23 — the segment historically designated the actin-binding "LKKTET" motif.[1](https://peptidevox.com/#r1)[2](https://peptidevox.com/#r2) This distinction is load-bearing for the whole monograph: TB-500 differs from full-length Tβ4 in chemistry, pharmacokinetics and regulatory history, and human clinical data generated with the full protein does not transfer to the fragment.[24](https://peptidevox.com/#r24) Many vendors loosely market TB-500 as a "17-amino-acid fragment," but the bona-fide synthetic doping/research agent characterized in the analytical literature is the heptapeptide.[2](https://peptidevox.com/#r2)

The core mechanism — all of it preclinical — is actin handling. Tβ4 is the major intracellular G-actin-sequestering peptide: it binds monomeric (globular) actin with roughly micromolar affinity and prevents spontaneous polymerization into filaments, maintaining a mobilizable monomer reservoir that cells draw on to remodel their cytoskeleton during migration.[1](https://peptidevox.com/#r1) Because directed cell migration of keratinocytes, fibroblasts, endothelial cells and myoblasts underlies wound closure and tissue repair, this is the proposed root mechanism for TB-500's regenerative claims. Downstream, in the landmark cardiac study, Tβ4 formed a functional complex with PINCH and integrin-linked kinase (ILK), activating the survival kinase Akt; after coronary-artery ligation in mice it improved early myocyte survival and cardiac function.[3](https://peptidevox.com/#r3)[4](https://peptidevox.com/#r4) Additional reported pathways include VEGF-mediated angiogenesis, pro-resolution macrophage polarization, MMP-mediated matrix remodeling and TGF-β modulation affecting scar quality.[7](https://peptidevox.com/#r7) As a small acetylated peptide it is not orally bioavailable and is administered parenterally; rigorous human pharmacokinetics for the fragment specifically are not established.[23](https://peptidevox.com/#r23)

## What is the evidence by indication?

The bottom line up front: there are no published human efficacy RCTs of the TB-500 fragment for any marketed use. Every claim below for the fragment is Grade C (preclinical) unless it concerns full-length Tβ4, where small human trials exist (lower-tier human) — and that molecule is not TB-500.

  TB-500 / thymosin β4 evidence by indication

    IndicationBest evidenceGrade

    Wound healing / chronic & diabetic woundsRodent excisional & diabetic-wound models (re-epithelialization, angiogenesis); human work used full-length Tβ4, not the fragmentC (fragment)
    Corneal / neurotrophic keratopathy & dry eyeFull-length Tβ4 (RGN-259) human RCTs — SEER-1 missed primary endpoint; SEER-3 failedB (Tβ4, mixed)
    Cardiac repair / post-MIMouse coronary-ligation, porcine MI & iPSC-cardiomyocyte models (full-length Tβ4)C (preclinical)
    Muscle / tendon / ligament repair, flexibilityAnimal repair signals plus actin-migration mechanism; human use anecdotal & confounded by stackingC-to-D

The corneal indication is the only one with genuine human RCT data, and it is for Tβ4, not TB-500. In the SEER-1 Phase III trial (NCT02600429; multicenter, randomized, double-masked, placebo-controlled) of 0.1% RGN-259 for stage 2-3 neurotrophic keratopathy, complete corneal epithelial healing at Day 29 was 6/10 (60%) versus 1/8 (12.5%) for placebo (p=0.0656) — the primary endpoint was not met, though a Day-43 analysis reached 5/10 versus 0/8 (p=0.0359) and symptom measures improved.[8](https://peptidevox.com/#r8) The trial was small (n=18, terminated early for rare-disease recruitment), and the subsequent SEER-3 Phase 3 trial did not meet its primary endpoint, tempering the picture.[9](https://peptidevox.com/#r9)[10](https://peptidevox.com/#r10) You can read the SEER-1 trial registration directly at [ClinicalTrials.gov](https://clinicaltrials.gov/study/NCT02600429). Net: promising but mixed for Tβ4 ophthalmic, and inapplicable to systemic-injection TB-500.

For the marketed athletic claims, the evidence thins further. Preclinically, Tβ4 and its actin-binding fragment promote re-epithelialization, keratinocyte and fibroblast migration, angiogenesis and collagen deposition in rodent wound models.[7](https://peptidevox.com/#r7)[25](https://peptidevox.com/#r25) Cardiac signals reinforced across mouse, porcine and iPSC-cardiomyocyte work via ILK/Akt.[5](https://peptidevox.com/#r5)[6](https://peptidevox.com/#r6) But there are no human trials in athletes for tendon, muscle or flexibility outcomes; human use here is anecdotal community report (Grade D) and confounded by polypharmacy such as stacking with BPC-157.[27](https://peptidevox.com/#r27)

Proven vs hyped
Proven in humans: nothing for the fragment. Hyped: muscle, tendon and cardiac "healing," which extrapolate animal findings. The only credible human trial data (corneal/dry-eye, mixed) belong to the full protein via a topical route — not the injected fragment.[8](https://peptidevox.com/#r8)

## What doses appear in the literature?

Reported strictly as information, not a protocol or recommendation. There is no validated human dosing protocol for the TB-500 fragment; the figures below circulate in grey-market and community sources and are extrapolated from animal data and practitioner observation, not from controlled human efficacy trials.[23](https://peptidevox.com/#r23) A commonly reported community "loading" phase is roughly 2-2.5 mg subcutaneous twice weekly for four to six weeks, injections spaced three to four days apart, followed by a "maintenance" phase of roughly 2-2.5 mg once weekly or stopping to re-evaluate.[23](https://peptidevox.com/#r23) A reconstitution example circulated is a 10 mg vial plus 2 mL bacteriostatic water giving 5 mg/mL, so a 2-2.5 mg dose is about 0.4-0.5 mL.[23](https://peptidevox.com/#r23) The formal human dosing context is different: Phase 1/2 safety work on full-length Tβ4 used intravenous administration at much higher absolute doses (roughly 42-1,260 mg) — a different molecule and route than community subcutaneous TB-500 use.[23](https://peptidevox.com/#r23) Community protocols favor twice-weekly over daily dosing because the longer biological persistence is attributed to tissue and actin binding rather than plasma residence, but no human PK/PD validation exists for the fragment.[23](https://peptidevox.com/#r23)

## How safe is TB-500?

Human safety data are anecdotal because there are no controlled human safety trials of the fragment. The most commonly reported effects are injection-site reactions, transient lethargy or fatigue, and a head-rush or flushing sensation; in formal Tβ4 ophthalmic RCTs adverse events were mild and mostly ocular.[8](https://peptidevox.com/#r8)[26](https://peptidevox.com/#r26) The central safety concern is mechanistic. Tβ4 is a documented driver of tumor angiogenesis and metastasis in preclinical models: in a pivotal JNCI study, overexpression produced roughly a 2.3-fold increase in melanoma cell migration and a 4.4-fold increase in tumor blood-vessel number, and raised metastatic lung nodules to 46.7 versus 10.9 for controls (P<.001).[11](https://peptidevox.com/#r11) Tβ4 is overexpressed in colon, renal, lung, osteosarcoma and hepatoblastoma tissue and promotes EMT and metastasis via ILK/IQGAP1/Rac1 signaling.[12](https://peptidevox.com/#r12)[13](https://peptidevox.com/#r13) The same migration and angiogenesis biology that underlies TB-500's repair claims raises a plausible, mechanism-based concern that exogenous administration could accelerate occult or established tumors — unproven in humans but a serious precautionary flag, and the literature is mixed, with some tumor-suppressive contexts.[14](https://peptidevox.com/#r14) Fibrosis and immunogenicity are additional theoretical flags, and the FDA cited immunogenicity and manufacturing-impurity concerns (endotoxin, truncated peptides, diastereomers) when placing the class in Category 2.[18](https://peptidevox.com/#r18) Precautionary exclusion populations include active or prior malignancy, pregnancy and lactation, and pediatric use.

## What is the FDA and WADA status in 2026?

TB-500 / thymosin β4 is not FDA-approved for any human indication and is not a lawful dietary-supplement ingredient.[20](https://peptidevox.com/#r20) The regulatory timeline is precise: in September 2023 the FDA placed thymosin β4 / TB-500 — among 19 peptides — into 503A Category 2, barring compounding pharmacies from using it.[15](https://peptidevox.com/#r15)[18](https://peptidevox.com/#r18) In April 2026 the FDA removed TB-500 from Category 2 and announced a Pharmacy Compounding Advisory Committee meeting on July 23-24, 2026 to evaluate whether seven peptides — including BPC-157, KPV and TB-500 — should be added to the 503A bulk-substances list, which would, for the first time since 2023, permit patient-specific compounding if approved.[16](https://peptidevox.com/#r16)[17](https://peptidevox.com/#r17) As of mid-2026 the outcome is pending; the current status is "not Category-2-barred, but not affirmatively listed or permitted either." Outside any compounding pathway, TB-500 is sold as a research chemical not for human use, typically without established quality controls.[20](https://peptidevox.com/#r20)

For athletes the picture is unambiguous. TB-500 is prohibited at all times under WADA S2.3 (Growth Factors and Growth Factor Modulators), explicitly named as "Thymosin-β4 and its derivatives, e.g. TB-500"; it is also captured by S0 and is a non-Specified Substance, the strictest sanction tier.[19](https://peptidevox.com/#r19) It was added as an explicit S2.3 example in the 2018 list; sanctions run two to four years, and a real case produced a four-year ban for combined BPC-157 and TB-500 use.[21](https://peptidevox.com/#r21)[20](https://peptidevox.com/#r20) The U.S. Department of Defense has adopted the WADA categories, making it prohibited for testable military personnel, and it is a regulated or prescription medicine in jurisdictions such as Australia and New Zealand.[22](https://peptidevox.com/#r22)

**Bottom line.** TB-500 is a mechanistically interesting, preclinically supported tissue-repair fragment with essentially zero human efficacy evidence for the indications it is marketed for — graded C overall, drifting to D where claims rest on athlete anecdote. Three caveats dominate: it is the heptapeptide fragment, not full-length Tβ4; no human RCT of the fragment exists for muscle, tendon, cardiac or wound repair; and a mechanism-based tumor/angiogenesis safety concern is unresolved. Regulatory facts here are current as of June 2026; the July 23-24, 2026 PCAC outcome was pending at the time of writing and should be re-verified after that date.

---
Source: https://peptidevox.com/peptide-encyclopedia/tb-500
Index: https://peptidevox.com/llms.txt · Full text: https://peptidevox.com/llms-full.txt