TB-500 QUESTIONS ANSWERED
TB-500: The Questions, Reconciled to the Record
Direct answers on identity, mechanism, evidence, safety and regulatory standing — each one tagged to what the studies actually tested.
What is TB-500?
TB-500 is the synthetic, N-acetylated heptapeptide Ac-LKKTETQ — residues 17–23 of the actin-binding region of thymosin beta-4 [1]. It is a research and veterinary-context compound with no approved human therapeutic indication [13]. Its molecular weight is 889.02 Da and its formula is C38H68N10O14 [1].
What does TB-500 stand for?
The "TB" refers to thymosin beta; TB-500 is a product and research designation for the Ac-LKKTETQ fragment of thymosin beta-4 [1]. The same fragment has been marketed as TB1000 in veterinary contexts. The designation refers to the heptapeptide, not the full-length protein, even though most efficacy data come from the protein.
How does TB-500 work?
Its LKKTETQ motif is the actin-binding region of thymosin beta-4, which binds monomeric G-actin 1:1 to buffer the unpolymerized actin pool and regulate cytoskeletal dynamics, cell migration and motility [1][2]. Crystallography showed the protein caps both ends of the actin monomer to prevent polymerization [1]. Whether the isolated fragment reproduces downstream repair effects in humans is unproven [10].
What is the relationship between TB-500 and Thymosin Beta-4?
TB-500 is a 7-amino-acid fragment — residues 17–23, the actin-binding motif — of the full 43-residue thymosin beta-4 protein [1][5]. Most efficacy research uses the full-length protein (~4963 Da), not the ~889 Da fragment [5]. FDA describes the two together, listing the entry as the LKKTETQ fragment of thymosin beta-4 [13].
What is the amino acid sequence of TB-500?
Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH (Ac-LKKTETQ): an N-terminally acetylated heptapeptide with molecular weight ~889 Da, corresponding to the WH2-type actin-binding region of thymosin beta-4 [1]. The seven residues are leucine, lysine, lysine, threonine, glutamate, threonine and glutamine, with an acetyl cap on the N-terminus.
What is the difference between TB-500 and full-length Thymosin Beta-4?
TB-500 is only the ~889 Da Ac-LKKTETQ actin-binding fragment; full-length Tβ4 is the ~4963 Da intact protein [1][5]. The fragment does not generate Ac-SDKP, and its human efficacy is not established in controlled trials [5][10]. The protein has reached a Phase 1 human safety study; the fragment has not [10].
What is TB-500 used for in research?
In animal and in-vitro models, thymosin beta-4 is studied for tissue repair, wound re-epithelialization, angiogenesis, cardiac and neurological recovery, and anti-fibrotic effects [5]. The isolated fragment's human efficacy is unproven [10]. Interest in TB-500 specifically stems from its carrying the protein's actin-binding motif [1].
Does TB-500 work for muscle tears and recovery?
Thymosin beta-4 acts as a myoblast chemoattractant in injury models, but in mdx mice chronic dosing increased regenerating fibers without improving muscle strength — a notable null functional result. No controlled human recovery trials of the fragment exist [10]. The recovery narrative outruns the human evidence.
Does TB-500 cause cancer or promote tumor growth?
Thymosin beta-4 is overexpressed in several cancers and is implicated in metastasis and tumor angiogenesis; the same pro-migratory, pro-angiogenic properties that aid repair could theoretically support tumor progression [5]. This is an open safety concern, not a resolved risk estimate, and it is the principal hard caveat in the literature.
Is TB-500 banned by WADA and in competitive sports?
Yes. TB-500 and thymosin beta-4 are prohibited by the World Anti-Doping Agency under peptide/growth-factor and tissue-repair categories, and are detectable by LC-MS anti-doping assays in equine and human matrices [16]. The ban applies in and out of competition for the relevant classes.
Is TB-500 FDA approved?
No. TB-500 has no FDA-approved therapeutic indication [13]. FDA placed "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" in 503A Category 2 as a bulk substance that may present significant safety risks, citing potential immunogenicity for certain routes and a lack of important safety information [13]. See the TB-500 legal status and 503A access page.
Are there any human clinical trials on TB-500?
There are no completed controlled trials of the TB-500 fragment [10]. Human data exist only for full-length Tβ4 — a randomized Phase 1 intravenous safety and pharmacokinetic study and topical ophthalmic (RGN-259) dry-eye trials [10]. An early injectable Tβ4 trial was withdrawn, so the clinical pipeline is thinner than it is sometimes portrayed.
How long does it take for TB-500 to work?
No human healing-timeline data exist for the fragment [10]. In a rat wound model, full-length Tβ4 raised re-epithelialization 42% by day four and up to 61% by day seven — an animal timeline, not a human one [7]. Any human timeframe presented for the 7-mer is unsupported by the literature.
Can TB-500 help with tendon and ligament injuries?
Thymosin beta-4 enhanced medial collateral ligament healing in a rat model — one of the few direct connective-tissue findings underpinning athletic interest — but this has not been confirmed in controlled human studies [5][10]. It was the full-length protein, not the fragment, that produced the ligament result.
Does TB-500 affect the heart?
In rodents, thymosin beta-4 activated PINCH–ILK–Akt survival signaling and improved cardiac function after coronary ligation [6]. However, systemic Tβ4 failed to reduce ischemia-reperfusion injury in a porcine study, so cardiac results are mixed. These are full-length-protein findings, not fragment outcomes.
Does TB-500 promote angiogenesis?
Thymosin beta-4 promotes endothelial migration and new-vessel formation, a repair mechanism [5]. The same pro-angiogenic activity is part of the tumor safety concern, since angiogenesis also supports tumor growth. The mechanism is genuinely double-edged, which is why it appears in both the benefits and the safety reading.
Does TB-500 have neuroprotective effects?
In a rat embolic-stroke dose-response study, thymosin beta-4 improved neurological function at 2 and 12 mg/kg but not at 18 mg/kg — a non-monotonic result [8]. These are rodent findings for the full-length protein; no human neuro trials of the fragment exist [10]. Higher dosing did not improve the outcome.
Does TB-500 increase hair growth?
Nanomolar thymosin beta-4 stimulated hair-follicle bulge stem cells and accelerated hair growth in rats and mice [5]. These are animal results for the full-length protein, not demonstrated human effects of the TB-500 fragment.
Does TB-500 reduce inflammation?
Thymosin beta-4 suppressed TNF-α-induced NF-κB activation and IL-8 in vitro and was recently linked to pro-resolving inflammation pathways [12]. These are mechanistic and animal findings, not human anti-inflammatory claims for the fragment.
What are the side effects of TB-500?
No controlled human safety data exist for the fragment [10]. The principal theoretical concern is the tumor/angiogenesis signal [5]; research-grade material purity and identity (fragment versus full-length) are additional unknowns. The human safety profile of the 7-mer is, in short, uncharacterized.
What is the difference between TB-500 and BPC-157?
They are distinct research peptides studied for tissue repair via different mechanisms — TB-500 via the thymosin beta-4 actin-binding motif [1]. Both are unapproved for human use and were flagged in a 2026 review for scarce human safety data [11]. No controlled human trial has tested them together.
Does TB-500 help wound healing?
Full-length thymosin beta-4 accelerated re-epithelialization, contraction and collagen deposition in animal wound models, and a synthetic actin-binding-domain peptide reproduced some of this [7][3]. Human efficacy of the fragment remains unproven [10]. The wound data are strong in animals and absent in humans for the 7-mer.
Is TB-500 legal?
TB-500 is not an FDA-approved drug, and FDA placed it in 503A Category 2 — a flag meaning it is not within FDA's enforcement-discretion policy for routine 503A compounding [13]. It is prohibited in sport by WADA [16]. This is the present-tense regulatory standing as general information, not legal advice; the TB-500 legal status and 503A access page lays it out in full.
Can you get TB-500 from a compounding pharmacy?
Not through routine 503A compounding while its current FDA status stands. TB-500's Category 2 placement means FDA identified it as a significant-safety-risk substance not afforded enforcement discretion, and a compounder may use a bulk ingredient only if it is eligible under the 503A/503B rules [13][15]. Lawful compounded access in general begins with a licensed-prescriber evaluation and a valid prescription, but the ingredient-eligibility caveat applies regardless [15].
What is the FDA 503A status of TB-500?
FDA placed "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" in 503A Category 2 — bulk substances that may present significant safety risks — effective with its September 29, 2023 nominated-substances update [13]. Category 2 substances are not covered by FDA's enforcement-discretion policy for compounding [13]. TB-500 is also named on the July 23–24, 2026 PCAC agenda as a substance being considered for the bulks list — a scheduled discussion, not a decision [14].