# TB-500 FAQ: Mechanism, Trials, Safety, Legal Status, and Identity | TB-500

> TB-500 FAQ: what it is, how it works, whether human trials exist, the tumor and angiogenesis caution, the FDA 503A and WADA status, and why TB-500 is not a steroid — answered and cited.

Twenty-two questions on the TB-500 record: identity, mechanism, the human-trial gap, safety signals, dosing context, and regulatory status. Direct answers, sourced where quantitative.

## Identity and definitions

### What is TB-500?

TB-500 is a synthetic, N-acetylated heptapeptide (Ac-LKKTETQ) corresponding to residues 17–23 of thymosin beta-4 — the conserved actin-binding region of the protein. It is a research and veterinary-context substance, roughly 889 Da, with no approved human indication. The name denotes the fragment; most published efficacy research used the full-length protein [5].

### What does TB-500 stand for and what does TB stand for in TB-500?

The "TB" references thymosin beta-4. TB-500 is the trade and research designation for the synthetic Ac-LKKTETQ actin-binding fragment of that protein. It is a product name attached to the 7-mer, not a separate chemical class, and the number is not a dose figure.

### What is TB-500 used for in research?

In animal and in-vitro research, thymosin beta-4 and the actin-binding region in TB-500 are studied for wound healing, cell migration, angiogenesis, cardiac and neurological repair, and anti-fibrotic effects [5]. Human efficacy of the isolated 7-mer is unproven [10].

### Is TB-500 a Steroid?

No. TB-500 is a synthetic peptide — a short chain of seven amino acids carrying the actin-binding motif of thymosin beta-4 [1]. Steroids are lipid molecules built on a four-ring carbon skeleton and act through nuclear hormone receptors. TB-500 is structurally and mechanistically unrelated; it is an actin-binding peptide fragment, not a steroid.

## Mechanism and effects

### How does TB-500 work?

TB-500 carries the LKKTETQ actin-binding motif of thymosin beta-4, the body's main G-actin-sequestering peptide. Full-length thymosin beta-4 binds monomeric actin 1:1 to regulate the cytoskeleton, cell migration, angiogenesis, and anti-inflammatory and anti-fibrotic signaling [1][5]. Whether the isolated 7-mer reproduces this at research doses is not established in human trials [10].

### Does TB-500 affect the heart?

In mice, thymosin beta-4 activated PINCH–ILK–Akt survival signaling, enhanced cardiomyocyte survival, and improved function after coronary ligation [2]; scaffold-delivered thymosin beta-4 promoted cardiac repair [13]. But systemic thymosin beta-4 failed to attenuate ischemia-reperfusion injury in pigs — the results are mixed.

### Does TB-500 promote angiogenesis and is that a safety concern?

Thymosin beta-4 is pro-angiogenic, driving endothelial migration and differentiation; a thymosin-beta-4-exosome hydrogel improved vascularized wound repair [14]. Because pro-angiogenic activity can also support tumor growth, it is treated as a theoretical safety consideration alongside the repair benefit [5].

### Does TB-500 have neuroprotective effects on the brain?

In rodent stroke models, intraperitoneal thymosin beta-4 improved neurological function at 2 and 12 mg/kg but not 18 mg/kg [4], and it promoted zebrafish Mauthner-axon regeneration via actin dynamics [15]. These are preclinical findings, not human evidence.

### Does TB-500 reduce inflammation?

Thymosin beta-4 suppressed corneal NF-κB [8] and, in recent animal work, modulated inflammation in pulmonary fibrosis [12] and non-alcoholic fatty liver disease [11] models. Anti-inflammatory effects are described mechanistically in animals and in vitro, not proven for the fragment in humans.

## Evidence, safety, and timelines

### Are there any human clinical trials on TB-500?

No completed controlled trials of the TB-500 heptapeptide exist for any indication. Human data are limited to full-length thymosin beta-4 — a randomized, placebo-controlled Phase 1 intravenous safety and pharmacokinetics study, well tolerated to 1260 mg, and topical ophthalmic RCTs [6].

### Does TB-500 work for muscle tears and recovery from exercise?

A 2026 Sports Medicine review lists TB-500 and thymosin beta-4 among unapproved musculoskeletal peptides with favorable tissue-repair signals in animal models but scarce human safety data [10]. Controlled human evidence for muscle recovery is lacking.

### 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 recognized safety concern, not an established human risk for the fragment.

### How long does it take for TB-500 to work for injury healing?

Timelines come from animal models, not humans. In a rat full-thickness wound study, topical or intraperitoneal thymosin beta-4 increased re-epithelialization by 42% at four days and up to 61% at seven days versus saline [3]. No human injury-healing timeline is established for the fragment.

### Does TB-500 help wound healing?

In animal models, thymosin beta-4 accelerated wound re-epithelialization, contraction, collagen deposition, and angiogenesis [3], and recent delivery systems — a thymosin-beta-4-exosome hydrogel — improved vascularized wound repair [14]. Human wound-healing data exist for topical full-length thymosin beta-4, not the fragment.

### What are the side effects of TB-500?

There is no controlled human side-effect profile for the TB-500 fragment. A 2026 Sports Medicine review notes that unapproved musculoskeletal peptides have scarce human safety data and potential for serious harm, operating largely outside regulatory oversight [10].

### Is TB-500 safe for long-term use?

Long-term safety of the TB-500 fragment in humans is unknown — no controlled human trials exist [10]. The preclinical tumor and angiogenesis signal [5] and scarce human safety data mean long-term use cannot be characterized as safe.

### What is the difference between TB-500 and BPC-157?

They are distinct peptides studied for tissue repair: TB-500 is the Ac-LKKTETQ actin-binding fragment of thymosin beta-4, while BPC-157 is a separate gastric-derived pentadecapeptide [1]. A 2026 Sports Medicine review lists both among unapproved musculoskeletal peptides lacking rigorous human data [10].

### What is the latest research on TB-500 / thymosin beta-4?

Recent (2021–2026) thymosin beta-4 work centers on engineered delivery and tissue repair: scaffold- and exosome-delivered thymosin beta-4 for cardiac and vascularized wound repair [13][14], inhaled thymosin beta-4 against pulmonary fibrosis [12], zebrafish axon regeneration [15], and a 2026 Sports Medicine review of unapproved musculoskeletal peptides [10].

## Legal and regulatory status

### Is TB-500 FDA approved?

No. TB-500 has no FDA-approved therapeutic indication and is a research chemical and veterinary-context substance. FDA lists "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" and placed it in 503A Category 2 — bulk substances that may present significant safety risks — citing concerns including potential immunogenicity and a lack of important safety information [17].

### Is TB-500 legal?

It depends entirely on context. TB-500 is not an FDA-approved drug and is not within FDA's enforcement-discretion policy for 503A compounding because it sits in Category 2 [17]. It is sold by research suppliers for laboratory use, it is prohibited by WADA in sport, and it is a prescription medicine in some jurisdictions. See the [TB-500 legal status and 503A category](/legal-status) page for the full read.

### Can you get TB-500 from a compounding pharmacy?

Legally compounded access requires a licensed-prescriber evaluation and a valid, patient-specific prescription, filled by a 503A pharmacy or 503B outsourcing facility [20]. But a compounder may only use an eligible ingredient — and as a Category 2 substance, TB-500 is not eligible for routine 503A compounding while that status stands [17][20]. This is general information, not medical or legal advice.

### 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 — substances that may present significant safety risks — effective with its September 29, 2023 nominated-substances update [17]. Category 2 substances are not covered by FDA's enforcement-discretion policy [18]. Separately, "TB-500 (free base)" and "TB-500 acetate" are on the July 23–24, 2026 PCAC agenda as candidates being considered for the 503A bulks list — a scheduled discussion, not a decision [16].

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A phosphor-terminal reading of the TB-500 record — the Ac-LKKTETQ fragment logged green where its studies hold, every full-length thymosin beta-4 substitution flagged as a checksum mismatch, and the empty human-trial line left blinking NULL; no clinic behind the screen and nothing here dispensed or sold.