Reference designator · U06 · FAQ
TB-500 frequently asked questions, answered from the record
The common questions about TB-500 — definitional, mechanistic, safety, dosing, and regulatory — each answered directly and cited where the claim is quantitative.
Definitional
Common questions about what TB-500 is, what its name means, and what it has been studied for.
Mechanism and effects
How TB-500 works at the cellular level and what effects the literature reports.
Safety
The honest safety picture — what is known, what is unknown, and the tumor-angiogenesis question.
Regulatory and access
FDA approval, the 503A category, WADA status, and the racehorse association.
What is TB-500?
TB-500 is the synthetic, N-acetylated heptapeptide Ac-LKKTETQ, corresponding to residues 17–23 — the actin-binding motif — of the 43-amino-acid protein thymosin β4. It is a research and veterinary substance with no approved human indication, and it carries the parent protein's actin-binding core but not the rest of the chain [1][5].
What does TB-500 stand for and what does TB stand for in TB-500?
"TB" refers to thymosin beta. TB-500 is a research and veterinary designation for the Ac-LKKTETQ active fragment of thymosin β4 — the seven-residue actin-binding segment, residues 17–23 of the 43-amino-acid parent protein, supplied under this name in commerce and tracked under it in anti-doping science [5].
What is TB-500 used for in research?
In animal and in-vitro models, thymosin β4 and its actin-binding region have been studied for wound and corneal healing, muscle and ligament repair, cardiac and neurological recovery, angiogenesis, and hair-follicle activation [3][2][4][14]. These are research findings, largely on the full-length protein, not approved human uses.
What does TB-500 do at the cellular level?
TB-500 carries thymosin β4's actin-binding motif. The parent protein sequesters monomeric G-actin 1:1, regulating cytoskeletal dynamics and cell migration [1], and is associated with angiogenesis and anti-inflammatory, anti-scarring signaling in injury models [5]. The pro-migratory action is the engine behind its repair effects.
How does TB-500 work?
TB-500 carries thymosin β4's actin-binding motif; the parent protein sequesters monomeric G-actin 1:1, regulating cytoskeletal dynamics and cell migration [1], and is associated with angiogenesis and anti-inflammatory, anti-scarring signaling in injury models [5]. Whether the isolated fragment reproduces this in humans is not established.
Does TB-500 work for muscle tears and recovery from exercise?
Thymosin β4 acts as a myoblast chemoattractant and aided ligament healing in rats, but in dystrophin-deficient mice chronic Tβ4 increased regenerating fibers without improving muscle strength — a notable null functional result [9]. No human muscle-recovery trial of the fragment exists.
Can TB-500 help with tendon injuries and ligament repair?
Thymosin β4 enhanced healing of medial collateral ligament injury in rats — one of the few direct connective-tissue findings — but this is preclinical and uses the full-length protein [5]. There is no controlled human tendon or ligament trial of the TB-500 fragment.
Does TB-500 affect the heart?
In mice, thymosin β4 activated PINCH–ILK–Akt survival signaling and, after coronary ligation, improved early cardiomyocyte survival and cardiac function [2]. These effects are shown for full-length Tβ4 in a rodent model and are not confirmed for the seven-residue fragment in humans.
Does TB-500 have neuroprotective effects on the brain?
In rat embolic-stroke models, intraperitoneal thymosin β4 improved neurological function at 2 and 12 mg/kg but not at 18 mg/kg, with a modeled optimal dose near 3.75 mg/kg [4]. This is preclinical work on the full-length protein, not a human neuroprotection trial.
How long does it take for TB-500 to work for injury healing?
No human timeline is established. In a rat wound model, topical or intraperitoneal thymosin β4 increased re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline [3] — an animal timescale, not a human dosing schedule for the fragment.
Does TB-500 promote angiogenesis and is that a safety concern?
Thymosin β4 promotes endothelial migration and new-vessel formation [5][14]; this aids repair but is also the basis of the tumor-angiogenesis safety concern, since the same pathway can support a tumor's blood supply [7]. The benefit and the risk are the same biology read in two settings.
Does TB-500 increase hair growth?
Nanomolar thymosin β4 activated hair-follicle bulge stem cells and accelerated hair growth in rats and mice, with the effect reproduced across independent studies and reviews [12][13][14]. This is animal data for the full-length protein, not a validated human hair-loss treatment for the TB-500 fragment.
Does TB-500 reduce inflammation?
In vitro, thymosin β4 suppressed TNF-α–induced NF-κB activation and IL-8, and after injury the protein is released by platelets and macrophages to limit inflammation [5]. That is mechanistic evidence of an anti-inflammatory action, not a clinical anti-inflammatory indication for the TB-500 fragment in humans.
Does TB-500 help wound healing?
Thymosin β4 accelerated re-epithelialization, contraction, collagen deposition, and angiogenesis in animal dermal and corneal wound models [3][11], and as little as 10 pg stimulated keratinocyte migration two- to three-fold [3]. The record is animal and in-vitro, on the full-length protein.
Does TB-500 cause cancer or promote tumor growth?
Thymosin β4 is overexpressed in several cancers including pancreatic and is implicated in metastasis and tumor angiogenesis [7][8]; the same pro-migratory, pro-angiogenic properties that aid repair could theoretically support tumor progression, and human safety data for the fragment are scarce [15]. This is the board's foremost flagged concern.
What are the side effects of TB-500?
No controlled human safety profile exists for the heptapeptide. Intravenous full-length Tβ4 was well tolerated to 1260 mg in a Phase 1 study [6], but the principal concern is the tumor-angiogenesis signal [7][8]; research-grade identity and purity are also a recurring issue with unregulated material.
Is TB-500 safe for long-term use?
Long-term human safety of the TB-500 fragment is unknown — no chronic controlled human trials exist [15]. The tumor-angiogenesis signal [7][8] and unregulated product quality are the main reasons community "loading then maintenance" protocols are not validated. The longest controlled exposure on record is a six-month animal study that was null on muscle strength [9].
What are the negative effects of TB-500?
Beyond the unknown human safety profile, the literature includes counter-evidence: in mdx mice, chronic Tβ4 increased regenerating fibers without improving strength or reducing fibrosis [9], and the tumor-overexpression and pro-angiogenesis findings are the most-cited theoretical harms [7][8]. A 2026 review also flags the potential for serious harm given how little human data exist [15].
What is the half-life of TB-500?
There is no validated human pharmacokinetic half-life for the TB-500 heptapeptide. In the intravenous full-length Tβ4 Phase 1 study, half-life increased with dose — pharmacokinetics were dose-proportional [6]. Anti-doping LC-MS work characterizes the compound and its metabolites for detection in equine matrices, not for human PK, so any specific fragment half-life figure is unsupported.
Are there any human clinical trials on TB-500?
There are no completed controlled trials of the TB-500 heptapeptide. Human data exist only for full-length Tβ4: a randomized placebo-controlled Phase 1 IV safety study [6] and topical ophthalmic RCTs; a completed acute-MI trial and a withdrawn injectable trial are also on record.
What is the difference between TB-500 and BPC-157?
Both appear among unapproved peptides studied for musculoskeletal repair in the 2026 Sports Med review [15]. TB-500 is the actin-binding thymosin β4 fragment, a distinct molecule with its own largely full-length-protein literature; BPC-157 is a separate pentadecapeptide. Neither is FDA-approved, and no combination trial exists.
Is TB-500 FDA approved?
No. TB-500 has no FDA-approved therapeutic indication and is not an FDA-approved drug [16][17]. The FDA evaluated the LKKTETQ thymosin β4 fragment as a bulk substance for compounding and placed it in 503A Category 2, citing significant safety concerns [16].
What is the FDA 503A status of TB-500?
The FDA placed "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" in 503A Category 2 — substances that may present significant safety risks — effective with its September 29, 2023 update, which means it is not within the enforcement-discretion policy for 503A compounding [16][17]. TB-500 is also named on the FDA's July 23–24, 2026 PCAC agenda as a candidate for the bulks list — a scheduled discussion, not a decision [18].
Is TB-500 legal?
TB-500 is not an FDA-approved drug and, as a Category 2 bulk substance, is not within the enforcement-discretion policy for routine 503A compounding [16][17]. It is supplied for research, encountered in a veterinary context, and prohibited in sport by WADA [15]. Legality depends on jurisdiction and use; this is general information, not legal advice.
Can you get TB-500 from a compounding pharmacy?
Legally compounded medication follows a licensed-prescriber evaluation (telehealth can be the front-end channel) and a patient-specific prescription, dispensed by a 503A pharmacy or 503B facility — but only if the ingredient is eligible [17]. Because TB-500 is currently a Category 2 substance, that eligibility gate is the operative constraint [16]. This is general information, not an offer to supply anything.
Is TB-500 banned by WADA and in competitive sports?
Yes. TB-500 and thymosin β4 fall under the World Anti-Doping Agency's prohibited peptide, growth-factor, and tissue-repair categories, banned in and out of competition, and are detected by LC-MS anti-doping assays in equine and human matrices [15]. For any athlete subject to anti-doping rules, it is prohibited regardless of compounding standing.
Why is TB-500 used in racehorses?
TB-500 (Ac-LKKTETQ) has been supplied as a veterinary preparation and encountered as a designer drug in racehorses, which prompted LC-MS anti-doping detection methods in equine plasma and urine [15]; it is a controlled and prohibited substance in horse sport, and that equine context is part of why it circulates under the TB-500 name rather than as an approved human medicine.