# TB-500 FAQ: Sequence, Mechanism, Safety, Legal Status | TB-500

> TB-500 FAQ: what it is, the Ac-LKKTETQ sequence, how it works, the thymosin beta-4 relationship, the tumor safety signal, FDA 503A status and WADA prohibition — answered and cited.

The questions readers actually ask about TB-500, answered directly and cited to the studies — sequence, mechanism, safety signals, and where access stands.

## 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 [8]. It is supplied for research and veterinary use and has no approved human therapeutic indication [16]. As a chemical it is unambiguous; as a marketed name it borrows the parent protein's data.

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

"TB" references thymosin beta-4, the parent protein. "500" is a product and research designation — used alongside the veterinary name TB1000 — for the synthetic `Ac-LKKTETQ` fragment. It is not an official chemical name, which is why the verifiable identity is the sequence, not the label [8].

## How does TB-500 work?

TB-500 carries the LKKTETQ actin-binding motif of thymosin beta-4. Full-length Tβ4 binds monomeric (G-)actin 1:1 and caps both ends of the monomer, buffering the unpolymerized actin pool and regulating cytoskeletal dynamics, cell migration and motility [1]. Whether the isolated 7-mer reproduces these effects at research doses is not established in controlled human trials [12].

## What is the relationship between TB-500 and Thymosin Beta-4?

TB-500 is a synthetic fragment — residues 17-23, `Ac-LKKTETQ` — of thymosin beta-4, and that stretch is the conserved actin-binding region of the parent [8]. The crucial point: most published efficacy research uses full-length recombinant or synthetic Tβ4 (~4963 Da), not the ~889 Da heptapeptide [5].

## What is the amino acid sequence of TB-500 (Ac-LKKTETQ)?

TB-500 is `Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH` (`Ac-LKKTETQ`), an N-terminally acetylated heptapeptide with formula `C38H68N10O14` and a mass near 889 Da. The LKKTETQ motif is the conserved actin-binding region of the beta-thymosins [8].

## What is the difference between TB-500 and full-length Thymosin Beta-4?

Full-length Tβ4 is a 43-residue, ~4963 Da protein; TB-500 is just its 7-residue, ~889 Da actin-binding fragment [9]. A synthetic peptide containing Tβ4's actin-binding domain reproduced some wound-healing-relevant activity in mice [7], but it is not established that the fragment carries the full protein's effects in humans.

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

In animal and in-vitro studies, thymosin beta-4 — and to a lesser extent its actin-binding fragment — has been investigated for wound and corneal healing, cardiac and neurological repair, angiogenesis, hair-follicle activation and anti-fibrotic effects [5][9]. These are research findings in models, not approved human uses.

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

The recovery rationale rests on thymosin beta-4 being an exercise-released exerkine that recruits myoblasts. But a six-month mdx-mouse study found more regenerating fibers without gains in muscle strength or cardiac function, and a 2026 *Sports Medicine* review notes favorable animal-model repair signals but scarce human safety data for unapproved peptides including TB-500 [12].

## 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, so the same pro-migratory, pro-angiogenic properties that aid repair could theoretically support tumor progression [9]. This is a key open safety question; there are no long-term human safety data for the fragment [12].

## 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 are detectable by LC-MS anti-doping assays in equine and human matrices. Prohibition in sport is a regulatory status, separate from FDA's compounding category.

## Is TB-500 FDA approved?

No. TB-500 is not approved by the FDA for human use and has no approved therapeutic indication [16]. FDA lists the LKKTETQ thymosin beta-4 fragment ("also known as TB-500") as a Category 2 bulk substance for 503A compounding — not within the enforcement-discretion policy that applies to Category 1 [16][17].

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

No completed controlled trials exist for the TB-500 heptapeptide. Human data are limited to full-length synthetic Tβ4: a randomized placebo-controlled Phase 1 IV safety/PK study (well tolerated to 1260 mg) [6] and topical ophthalmic (RGN-259) trials [11]. A registered injectable acute-MI Tβ4 trial completed; an early injectable trial was withdrawn.

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

No human timeline is established. In a rat full-thickness wound model, thymosin beta-4 increased re-epithelialization by 42% at four days and up to 61% at seven days versus saline, with increased contraction and collagen [3]. Such timelines are animal-model observations, not human dosing guidance.

## Can TB-500 help with tendon injuries and ligament repair?

Connective-tissue evidence is limited. Thymosin beta-4 enhanced healing of a medial collateral ligament injury in rats, and muscle-injury-induced Tβ4 acts as a myoblast chemoattractant [9]. These are animal findings; there are no controlled human tendon or ligament trials of the fragment [12].

## Does TB-500 affect the heart?

In mice, thymosin beta-4 formed a complex with PINCH and integrin-linked kinase, activated Akt, promoted cardiac cell migration and, after coronary ligation, enhanced early myocyte survival and improved cardiac function [2]. Counter-evidence exists — systemic Tβ4 did not attenuate myocardial ischemia-reperfusion injury in pigs — and these are animal models.

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

Thymosin beta-4 promotes endothelial migration and new-vessel formation, and recent delivery-system studies report improved vascularized wound repair [14]. Because pro-angiogenic activity can also support tumor growth, angiogenesis is both a proposed repair mechanism and a safety consideration [9].

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

In rats with embolic middle cerebral artery occlusion, intraperitoneal thymosin beta-4 improved neurological function at 2 and 12 mg/kg (a modeled optimal near 3.75 mg/kg), but 18 mg/kg gave no significant benefit, illustrating non-monotonic dosing [4]. These are rodent stroke models, not human evidence.

## 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 and increasing their migration, differentiation and MMP-2 expression [9]. This is the parent protein in animal models; the fragment has not been validated for hair growth in humans.

## Does TB-500 reduce inflammation?

Thymosin beta-4 has been reported to suppress NF-κB and IL-8 signaling and to act through pro-resolving (inflammation-resolution) pathways in recent work [13]. These are mechanistic and animal/in-vitro findings, not demonstrated anti-inflammatory effects of the TB-500 fragment in humans.

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

There is no controlled human safety profile for the TB-500 fragment. Intravenous full-length Tβ4 was well tolerated to 1260 mg in a Phase 1 study [6], but the main flagged concerns are the tumor/angiogenesis signal [9] and the unverified identity and purity of research-grade material. A 2026 *Sports Medicine* review highlights scarce human safety data and potential for serious harm [12].

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

Both are research peptides studied for tissue repair, but they are chemically distinct: TB-500 is the `Ac-LKKTETQ` fragment of thymosin beta-4 acting on the actin cytoskeleton [1], whereas BPC-157 is a separate gastric-derived pentadecapeptide with a different proposed mechanism. Neither is FDA-approved for human use [16].

## Does TB-500 help wound healing?

In a rat full-thickness wound model, thymosin beta-4 increased re-epithelialization by up to 61% at seven days, raised wound contraction and collagen, and as little as 10 pg stimulated keratinocyte migration [3]. Topical Tβ4 (RGN-259) also showed corneal-healing benefits in human trials [11]. These data are largely for full-length Tβ4.

## Is TB-500 a steroid?

No. TB-500 is a synthetic seven-amino-acid peptide (`Ac-LKKTETQ`), not a steroid hormone. Steroids are ring-structured lipids acting through nuclear receptors; TB-500 carries an actin-binding peptide motif and works on the cytoskeleton [1]. It is grouped with anabolic agents only by anti-doping context, not by chemistry.

## Is TB-500 legal?

It depends on jurisdiction and intended use. TB-500 is not an FDA-approved drug and FDA lists the LKKTETQ thymosin beta-4 fragment as a Category 2 bulk substance for 503A compounding [16]. It is prohibited in sport by WADA and is classified as a prescription medicine in some jurisdictions. It is supplied for research and veterinary use, not as an approved medicine. This is general information, not legal advice.

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

FDA placed the LKKTETQ thymosin beta-4 fragment ("also known as TB-500") in 503A Category 2 — bulk substances that may present significant safety risks — so it is not within the enforcement-discretion policy for routine 503A compounding while that status stands [16][17]. "TB-500" is on the July 2026 PCAC agenda as a substance under evaluation, which is a scheduled discussion, not a listing decision [18]. This is regulatory background, not access guidance or an offer to supply anything.

## 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 — significant-safety-risk bulk substances not afforded enforcement discretion — effective with its September 29, 2023 nominated-substances update [16]. TB-500 has no approved therapeutic indication [16]. It appears on the July 23-24, 2026 PCAC agenda for discussion, which is evaluation in progress, not a decision [17][18].

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A developer-console reading of the TB-500 record — the actin-binding fragment logged against its studies, with the full-length thymosin beta-4 caveat flagged in every diff, no clinic behind the terminal and nothing here prescribed or sold.