TB-500 FAQ: Safety, Comparisons, and Status
The full question set, answered directly and cited where quantitative. The fragment-versus-protein caveat applies to every efficacy answer.
Identity and use
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 [1]. It is studied as a research and veterinary peptide. Most published efficacy data use the full-length protein, not the fragment, so the two are kept distinct throughout this site.
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 fragment of thymosin beta-4. The number is a product designation, not a chemical descriptor — the chemistry is captured by the sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln and formula C38H68N10O14.
What is TB-500 used for in research?
In animal and in-vitro studies the parent peptide thymosin beta-4 and its actin-binding region are investigated for wound and tissue repair, cell migration, angiogenesis, cardiac and neurological recovery, and anti-fibrotic effects [5]. Human efficacy of the isolated fragment is unproven [6].
Mechanism and effects
How does TB-500 work?
TB-500 carries the actin-binding LKKTETQ motif of thymosin beta-4, which sequesters monomeric (G-) actin 1:1 to regulate cytoskeletal dynamics, cell migration, and motility [1]. Whether the isolated 7-mer reproduces the full protein's downstream effects at researched doses is not established in controlled human trials.
Does TB-500 work for muscle tears and recovery from exercise?
Preclinical signals exist — myoblast chemotaxis and regenerating fibers in mdx mice — but a six-month mdx study found more regenerating fibers without gains in strength or cardiac function. A 2026 Sports Medicine review lists TB-500 among unapproved musculoskeletal peptides with scarce rigorous human safety data [11].
How long does it take for TB-500 to work for injury healing?
Timelines come only from animal models. In a rat full-thickness wound study, full-length thymosin beta-4 increased re-epithelialization by about 42% at four days and up to 61% at seven days versus saline [3]. No validated human healing-timeline data exist for the fragment.
Can TB-500 help with tendon injuries and ligament repair?
Thymosin beta-4 enhanced healing of medial collateral ligament injury in a rat model, and a 2026 Sports Medicine review lists TB-500 among unapproved peptides studied for musculoskeletal injury [11]. Evidence is preclinical and review-level, not from controlled human trials.
Does TB-500 affect the heart?
In mice, thymosin beta-4 activated PINCH–ILK–Akt survival signaling, enhanced early cardiomyocyte survival, and improved cardiac function after coronary ligation [2]; scaffold-released thymosin beta-4 promoted cardiac repair [12]. A porcine study found systemic thymosin beta-4 did not attenuate ischemia-reperfusion injury, and no fragment cardiac trials exist.
Does TB-500 promote angiogenesis and is that a safety concern?
Thymosin beta-4 promotes endothelial migration and angiogenesis [5], shown again in a scaffold-delivery cardiac study [12]. Because pro-angiogenic activity can also support tumor vascularization, it is noted as a theoretical safety consideration rather than an established human outcome.
Does TB-500 have neuroprotective effects on the brain?
In rat embolic stroke, intraperitoneal thymosin beta-4 improved neurological function at 2 and 12 mg/kg, with a modeled optimum near 3.75 mg/kg and no benefit at 18 mg/kg [4]. A 2024 zebrafish study showed thymosin beta-4 promoted axon regeneration via actin dynamics [14]. These are animal findings.
Does TB-500 reduce inflammation?
Thymosin beta-4 has been reported to suppress NF-kB and IL-8 signaling and to modulate inflammation in recent fibrosis models — inhaled thymosin beta-4 in bleomycin pulmonary fibrosis [13] and a 2025 NAFLD inflammation study [15]. The anti-inflammatory effects are described preclinically, not as approved human outcomes.
Safety, comparisons, and pharmacokinetics
What are the side effects of TB-500?
There is no controlled human side-effect profile for the TB-500 fragment. Full-length thymosin beta-4 was well tolerated intravenously in a 14-day Phase 1 study [6], but a 2026 review stresses that rigorous human safety data for unapproved peptides are scarce with potential for serious harm [11]; a tumor and angiogenesis signal is a separately noted concern.
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 stated safety concern, not an established human outcome — but it is the central reason caution is warranted.
Is TB-500 safe for long-term use?
No long-term human safety data exist for the TB-500 fragment. Full-length thymosin beta-4 was tolerated over 14 days intravenously in Phase 1 [6], but chronic human safety is unstudied, and a tumor/angiogenesis concern plus scarce human data argue against assuming long-term safety [11].
What is the difference between TB-500 and BPC-157?
They are distinct peptides. TB-500 is the Ac-LKKTETQ fragment of thymosin beta-4, an actin-binding sequence [1], while BPC-157 is a separate gastric-derived peptide. A 2026 Sports Medicine review lists both among unapproved peptides studied for musculoskeletal injury without rigorous human safety data [11].
How long does TB-500 stay in your system?
No validated human pharmacokinetic half-life exists for the TB-500 fragment. In the IV full-length thymosin beta-4 Phase 1 study, half-life increased with dose, with dose-proportional pharmacokinetics [6] — but that describes the protein. Anti-doping LC-MS work characterizes TB-500 and its metabolites mainly in equine matrices, for detection rather than human pharmacokinetics.
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. It is detected by LC-MS anti-doping assays in equine and human matrices, and was encountered as a designer drug in racehorses.
Regulatory and access
Is TB-500 FDA approved?
No. TB-500 has no FDA-approved therapeutic indication and is not an approved medicine [17]. 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 the September 29, 2023 update [17].
Is TB-500 legal?
TB-500 is not an FDA-approved drug [17]. FDA's page, current through April 22, 2026, shows TB-500 in the 'Bulk drug substances nominated but withdrawn' table and no longer in Category 2, but does not make clear what a 503A pharmacy may do with it [18]. It is prohibited in sport by WADA and is a prescription medicine in some jurisdictions, so legal status varies by jurisdiction and use.
Can you get TB-500 from a compounding pharmacy?
A compounder may use a bulk substance only if it is eligible under the 503A/503B rules — a USP/NF monograph, a component of an approved drug, or on FDA's bulks list [18]. FDA records the TB-500 nomination as withdrawn and continues to publish its safety concerns, leaving the 503A question unanswered [18]; for the July 2026 PCAC meeting, FDA staff proposed that TB-500 not be included on the 503A Bulks List, and as of September 2026 FDA had published no record of the committee's votes [19].
What is the FDA 503A status of TB-500?
FDA lists 'Thymosin beta-4, fragment (LKKTETQ), also known as TB-500' in 503A Category 2, effective with the September 29, 2023 update, citing potential immunogenicity for certain routes and a lack of important safety information [17]. Category 2 substances are not covered by FDA's enforcement-discretion policy for 503A compounding [18].