# TB-500 FAQ: Mechanism, Recovery, Safety, Dosing and Legal Status | TB-500 > TB-500 FAQ: 25 direct, cited answers on the thymosin beta-4 fragment — what it is, how it works, muscle and ligament recovery, the safety signals, dosing context, and the FDA 503A legal status. Twenty-five questions on the thymosin beta-4 fragment — each answer direct, cited, and honest about where the data are for the full-length protein. ## Identity and mechanism TB-500 questions cluster around one theme: what is actually known about the fragment versus its parent protein. Each answer below states the finding first, then the caveat. ### 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 beta-4 [5]. It is a synthetic construct supplied for research, not an endogenous molecule. ### What does TB-500 stand for and what does TB stand for in TB-500? TB references thymosin beta; the ‘500’ is a catalog number, not an acronym with an official expansion. TB-500 is a research and veterinary designation for the synthetic Ac-LKKTETQ fragment of thymosin beta-4, and the same heptapeptide also circulates under the label TB1000. ### What is TB-500 used for in research? It is studied as the actin-binding fragment of thymosin beta-4 in tissue-repair, wound-healing, muscle and ligament, cardiac, neurological, and angiogenesis models [5] — overwhelmingly using full-length thymosin beta-4, not the 7-mer. ### How does TB-500 work? It carries the LKKTETQ actin-binding motif of thymosin beta-4, which sequesters monomeric (G-) actin 1:1 to regulate cytoskeletal dynamics, cell migration, angiogenesis, and anti-inflammatory signaling in injury models [1]. Whether the isolated fragment reproduces these at research doses is unproven. ## Recovery, healing, and effects ### Does TB-500 work for muscle tears and recovery from exercise? Muscle injury induces thymosin beta-4, which acts as a chemoattractant recruiting myoblasts to injured muscle in animal models [7]. Controlled human efficacy for the TB-500 fragment is not established. ### Can TB-500 help with tendon injuries and ligament repair? Thymosin beta-4 enhanced healing of medial collateral ligament injury in a rat model [8] — one of the few direct connective-tissue repair findings underpinning the athletic-recovery rationale. It is a rodent, parent-protein result. ### How long does it take for TB-500 to work for injury healing? No human injury-healing timeline is established for the fragment. In a rat wound model, full-length thymosin beta-4 increased re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline [3] — a different molecule, tissue, and species. ### Does TB-500 affect the heart? In mice, thymosin beta-4 activated the PINCH-ILK-Akt survival pathway and improved cardiac function after coronary artery ligation [2]; a porcine ischemia-reperfusion study found no attenuation of injury, tempering the cardioprotection narrative. ### Does TB-500 have neuroprotective effects on the brain? In a rat embolic-stroke dose-response study, intraperitoneal thymosin beta-4 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] — a non-monotonic result. ### Does TB-500 promote angiogenesis and is that a safety concern? Thymosin beta-4 induces VEGF in a HIF-1α-dependent manner and promotes endothelial migration [10]. This pro-angiogenic activity aids repair but is also the basis of the tumor-angiogenesis safety signal. ### Does TB-500 increase hair growth? Hair-follicle bulge stem cells are a documented target of thymosin beta-4 in rodent models [5]. This is a parent-protein finding and is not established for the TB-500 fragment in humans. ### Does TB-500 reduce inflammation? Thymosin beta-4 suppressed corneal NF-κB and, in vitro, has been tied to reduced inflammatory signaling [12] — a mechanistic basis reported for the full-length protein, not a demonstrated clinical effect of the fragment. ## Safety and evidence ### Does TB-500 cause cancer or promote tumor growth? Thymosin beta-4 is overexpressed in several cancers and implicated in metastasis and tumor angiogenesis [13]. The same pro-migratory, pro-angiogenic properties that aid repair could theoretically support tumor progression — a key safety consideration. ### What are the side effects of TB-500? Human safety data for the fragment are scarce; the principal documented concern is the tumor and angiogenesis signal associated with thymosin beta-4 [13], alongside unverified research-grade material quality. A 2026 review notes the potential for serious harm [14]. ### Are there any human clinical trials on TB-500? There are no completed controlled clinical trials of the TB-500 fragment [13]. Human data exist only for full-length thymosin beta-4 — an intravenous Phase 1 safety and pharmacokinetics study [6] and topical ophthalmic RCTs. ### What is the difference between TB-500 and BPC-157? Both are research peptides studied for tissue repair; TB-500 is the Ac-LKKTETQ actin-binding fragment of thymosin beta-4 [5], while BPC-157 is a distinct gastric-derived pentadecapeptide. A 2026 Sports Medicine review lists both among unapproved musculoskeletal peptides [14]. ### How does TB-500 compare to other peptides for recovery and healing? A 2026 Sports Medicine review concluded that many unapproved repair peptides show favorable tissue-repair outcomes in animal models, but that rigorous human safety data are scarce and they operate largely outside regulatory oversight [14]. ## Dosing context ### How much TB-500 should be taken per week during a loading phase? Community "loading then maintenance" protocols are not derived from controlled human trials and have no published clinical validation [13]; animal studies dosed full-length thymosin beta-4 by body weight in milligram-per-kilogram ranges [4]. ### How does subcutaneous vs intramuscular injection of TB-500 compare? Rodent efficacy studies predominantly used intraperitoneal dosing [4]; subcutaneous and intramuscular are community research-use routes not validated in controlled human efficacy trials [13]. ### What is the half-life of TB-500 and how often should it be dosed? No validated human pharmacokinetic half-life exists for the TB-500 heptapeptide [13]; in the intravenous full-length thymosin beta-4 Phase 1 study, half-life increased with dose, i.e. dose-proportional pharmacokinetics [6]. ## Legal status and access ### Is TB-500 legal? TB-500 is not an FDA-approved drug, and 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 [17]. As a Category 2 substance it is not within FDA's enforcement-discretion policy for 503A compounding [18]. ### Can you get TB-500 from a compounding pharmacy? Legally compounded medications require a licensed-prescriber evaluation and a valid, patient-specific prescription, dispensed by a 503A pharmacy or sourced from a 503B outsourcing facility [18]. A Category 2 substance like TB-500 is not eligible for routine 503A compounding while that status stands [17]. ### What is the FDA 503A status of TB-500? FDA placed the "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" entry in 503A Category 2, effective with its September 29, 2023 update, citing potential immunogenicity for certain routes and a lack of important safety information [17]. TB-500 is also on the July 23–24, 2026 PCAC agenda for evaluation [16] — a scheduled discussion, not a decision. ### Is TB-500 banned by WADA and in competitive sports? Yes. TB-500 and thymosin beta-4 fall under WADA prohibited peptide, growth-factor, and tissue-repair categories, banned in and out of competition [13]; it is detected by LC-MS assays in equine and human matrices. ### Is TB-500 FDA approved? No. TB-500 has no approved therapeutic indication and is a research chemical and veterinary-context substance, not an approved medicine [17]. --- A bento board of the TB-500 record — each finding tiled and cited, every full-length-versus-fragment caveat flagged in the corner, with no clinic behind the board and nothing here dispensed or sold.