FAQ · ANSWERED FROM THE RECORD
TB-500: the questions, answered from the research
Plain, cited answers about TB-500 — what it is, how it works, what it has been studied for, what the safety signals are, and where its legal and anti-doping status stands. Each answer is grounded in a study or an authoritative source.
Identity and mechanism
What is TB-500?
TB-500 is a synthetic, N-acetylated heptapeptide (Ac-LKKTETQ) corresponding to residues 17–23 of thymosin beta-4, the body's principal G-actin sequestering peptide [1]. It is a research and veterinary-context compound with no approved human indication. Its molecular weight is roughly 889 Da, against the parent protein's ~4963 Da.
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 synthetic Ac-LKKTETQ actin-binding fragment of thymosin beta-4 [5]. The number is a supplier-style label rather than a clinical name; the fragment corresponds to residues 17–23 of the parent protein and is its actin-binding core.
What is TB-500 used for in research?
In animal and in-vitro models, thymosin beta-4 and its LKKTETQ region have been studied for wound and tissue repair, angiogenesis, cardiac and neurological recovery, hair growth, and anti-inflammatory and anti-fibrotic effects [5]. Almost all of this is preclinical evidence for the full-length protein, not the isolated TB-500 heptapeptide, and there are no human efficacy trials.
How does TB-500 work?
TB-500 carries the actin-binding LKKTETQ motif of thymosin beta-4, which sequesters monomeric G-actin 1:1 by capping both ends, regulating cytoskeletal dynamics and cell migration [1]. Whether the isolated seven-mer reproduces the full protein's downstream effects at the doses used in peptide research is unproven in controlled human trials.
What TB-500 has been studied for
Does TB-500 reduce inflammation?
Full-length thymosin beta-4 inhibited TNF-α-induced NF-κB activation and IL-8 expression in vitro [7], and suppressed corneal NF-κB [8] — a clear anti-inflammatory mechanism for the parent protein. Whether the isolated Ac-LKKTETQ fragment reproduces this in humans is unproven, and no controlled human anti-inflammatory data exist for the seven-mer.
Does TB-500 help wound healing?
Thymosin beta-4 accelerated re-epithelialization by 42% at 4 days and up to 61% at 7 days, with greater wound contraction and collagen deposition, in a rat full-thickness wound model [3]. Topical thymosin beta-4 (RGN-259) also showed corneal and dry-eye benefit in human trials [16]. These findings used the full protein, not the seven-mer.
Does TB-500 affect the heart?
In mice, thymosin beta-4 activated PINCH–ILK–Akt signaling, enhanced cardiomyocyte survival and improved cardiac function after coronary ligation [2]. However, systemic thymosin beta-4 failed to attenuate ischemia-reperfusion injury in a porcine study, and human cardiac data are limited [10]. These cardiac findings used the full protein.
Does TB-500 have neuroprotective effects on the brain?
In a rat embolic-stroke dose-response study, intraperitoneal thymosin beta-4 at 2 and 12 mg/kg improved neurological function, but 18 mg/kg did not — a non-monotonic effect with a modeled optimum near 3.75 mg/kg [4]. Neuroprotection has been shown only in animal models of the full protein, not in human trials.
Does TB-500 promote angiogenesis and is that a safety concern?
Thymosin beta-4 promotes endothelial migration and angiogenesis through VEGF, HIF-1α and Notch signaling in full-length studies [5]. Because pro-angiogenic activity can also support tumor growth, this is flagged as a safety consideration rather than a clean benefit. The data describe the parent protein, not the isolated TB-500 fragment.
Does TB-500 increase hair growth?
Thymosin beta-4 at nanomolar concentrations stimulated hair growth in rats and mice by activating hair-follicle bulge stem cells [5]. This is animal-model evidence for the full-length protein. There is no validated human hair-growth data for the TB-500 heptapeptide.
What is the difference between TB-500 and BPC-157?
TB-500 is the Ac-LKKTETQ fragment of thymosin beta-4, acting via actin sequestration [1]; BPC-157 is a distinct gastric-derived peptide with separate mechanisms. A 2026 Sports Med review lists both among unapproved peptides with animal-model promise but scarce human safety data [11]. They are different molecules with no shared target.
Efficacy and evidence
Does TB-500 work for muscle tears and recovery from exercise?
Muscle-injury-recruited thymosin beta-4 acts as a myoblast chemoattractant, but in dystrophin-deficient mdx mice chronic thymosin beta-4 increased regenerating fibers WITHOUT improving muscle strength, cardiac function or fibrosis [5]. No human efficacy trials of TB-500 exist; the histological regeneration did not translate into a functional gain.
Are there any human clinical trials on TB-500?
No completed controlled trials of the TB-500 heptapeptide exist for any indication [6]. Human data are limited to full-length thymosin beta-4: a randomized placebo-controlled Phase 1 intravenous safety study in healthy volunteers, and topical ophthalmic thymosin beta-4 (RGN-259) dry-eye trials [16]. Efficacy of the seven-mer in humans is unproven.
How long does it take for TB-500 to work for injury healing?
No human healing-timeline data exist for TB-500. In a rat wound model, thymosin beta-4 increased re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline [3], but animal timelines do not translate to validated human protocols, and those figures describe the full-length protein rather than the seven-mer.
Can TB-500 help with tendon injuries and ligament repair?
Thymosin beta-4 has been studied across connective-tissue repair as part of its broad tissue-repair profile — decreasing myofibroblast number and supporting cell migration and angiogenesis [5]. That evidence is animal-model and used the full protein; there are no human tendon or ligament trials of the TB-500 heptapeptide.
Safety and risk
Can TB-500 cause autoimmune reactions or affect the immune system?
No controlled human safety data exist for the TB-500 fragment. Thymosin beta-4 modulates inflammatory signaling — inhibiting TNF-α-induced NF-κB activation and IL-8 expression in vitro [7] — and FDA cited potential immunogenicity for certain routes when placing the LKKTETQ fragment in Category 2 [21]. Immune-related effects of the seven-mer in humans are uncharacterized.
Does TB-500 cause cancer or promote tumor growth?
Thymosin beta-4 is overexpressed in several cancers and implicated in metastasis and tumor angiogenesis; the same pro-migratory, pro-angiogenic properties that aid repair could theoretically support tumor progression [5]. This is a noted, mechanistically grounded safety concern about the parent protein — not an established human outcome, and not a finding that TB-500 causes cancer.
What are the side effects of TB-500?
Controlled human side-effect data for the TB-500 fragment do not exist [6]. The main flagged concerns are the tumor and angiogenesis safety signal of thymosin beta-4 [5] and the unverified purity, identity and sequence of unregulated research-grade material [17]. Reported side-effect profiles for the seven-mer are anecdotal rather than trial-derived.
Is TB-500 safe for long-term use?
There are no long-term human safety data for the TB-500 fragment. A Phase 1 intravenous study of full-length thymosin beta-4 was well tolerated to 1260 mg over 14 days with no dose-limiting toxicities [6], but that is short-term data on the full protein and does not establish long-term safety of the heptapeptide [11].
Legal status and anti-doping
Is TB-500 banned by WADA and in competitive sports?
Yes. TB-500 and thymosin beta-4 fall under WADA's prohibited peptide, growth-factor and tissue-repair categories, banned in and out of competition for the relevant classes, and detectable by LC-MS anti-doping assays in equine and human matrices [13]. It has been encountered as a designer substance in racehorses, prompting dedicated detection methods.
Is TB-500 FDA approved?
No. TB-500 has no approved therapeutic indication and is not approved by the FDA for human use; it is a research-chemical and veterinary-context substance [21]. FDA placed the LKKTETQ fragment in 503A Category 2, so it is also not eligible for routine 503A compounding while that status stands [20].
Is TB-500 legal?
TB-500 is not FDA-approved, and FDA placed the LKKTETQ fragment in 503A Category 2 — bulk substances that may present significant safety risks — outside FDA's enforcement-discretion policy for 503A compounding [21][20]. It is WADA-prohibited in sport [13]. See the legal-status page; this is general regulatory information, not legal advice.
Can you get TB-500 from a compounding pharmacy?
A 503A pharmacy may compound a substance only if its bulk ingredient is eligible under the 503A framework, and ingredients FDA has flagged for significant safety risks are not eligible for routine 503A compounding while that status stands [22]. TB-500 is currently in 503A Category 2 [21], which is the practical limit on its routine 503A compounding now.
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, effective with its September 29, 2023 update, citing potential immunogenicity for certain routes and a lack of important safety information [21]. "TB-500 (free base)" and "TB-500 acetate" are individually named on the July 23–24, 2026 PCAC agenda for evaluation — a scheduled discussion, not a decision [19].