# TB-500 FAQ: Hair, Safety, Mechanism, Dosing and Legal Status

> TB-500 FAQ — direct, cited answers on hair-follicle activation, the tumor-angiogenesis safety signal, the actin-sequestration mechanism, the fragment-versus-protein distinction, dosing context, and the FDA 503A status.

Straight answers from the published record — what is shown, what is animal-only, what is for the parent protein, and where the human evidence stops.

## Does TB-500 increase hair growth?

In rats and mice, full-length thymosin beta-4 at nanomolar concentrations stimulated hair growth by activating hair-follicle bulge stem cells, increasing their migration and differentiation [1]. This is animal data for the parent protein, not proven for the TB-500 fragment in humans. Independent rodent studies corroborated the effect [2][3].

## How does TB-500 affect hair follicle stem cells?

Thymosin beta-4 increased the migration and differentiation of hair-follicle bulge stem cells and raised MMP-2 expression in rodent studies [1]. The bulge compartment is the follicle's regenerative reserve; the proposed action is mobilization of those cells with matrix-remodeling support [1]. The work characterized the parent protein, not the isolated 7-mer.

## 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 [6][7]. It is a research and veterinary construct of roughly 889 Da, not an endogenous human species and not an approved medicine [7].

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

TB references thymosin beta-4, the parent protein; TB-500 is a research and veterinary designation for its synthetic Ac-LKKTETQ actin-binding fragment [7]. The numeric suffix is a product/lab label, not a structural descriptor — the chemistry that matters is the Leu-Lys-Lys-Thr-Glu-Thr-Gln sequence, residues 17–23 of thymosin beta-4 [6].

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

It is studied in animal and in-vitro models of tissue repair, wound healing, angiogenesis, cardiac and neurological recovery, and hair-follicle activation; there are no approved human therapeutic indications [7][1]. Across those domains the mechanism is documented and the animal effects (mostly for the parent protein) are reproducible, while controlled human data for the fragment are absent [15].

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

Preclinical work on thymosin beta-4 shows myoblast recruitment and increased regenerating fibers, but a 6-month mdx-mouse study found no gain in muscle strength [15]. A 2026 Sports Medicine review notes animal-model promise yet scarce human safety and efficacy data for unapproved peptides in this class [15].

## 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; the same pro-migratory, pro-angiogenic properties that aid repair are a theoretical oncologic safety concern [7]. This is the main flagged safety signal for the compound, and it is one reason human safety is treated as unsettled [15].

## Is TB-500 banned by WADA and in competitive sports?

Yes. TB-500 and thymosin beta-4 fall under WADA-prohibited peptide and growth-factor categories and are banned in and out of competition for the relevant classes. The substance is detected by LC-MS anti-doping assays in equine and human matrices.

## Is TB-500 FDA approved?

No. TB-500 has no FDA-approved therapeutic indication; it is a research-chemical and veterinary-context substance, not an approved medicine [16]. FDA has also placed the LKKTETQ fragment ("also known as TB-500") in 503A Category 2, so it is not within FDA's enforcement-discretion policy for compounding [16].

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

No completed controlled trials exist for the TB-500 fragment [15]. Human data are limited to full-length thymosin beta-4 — a randomized IV Phase 1 safety study and topical ophthalmic RCTs — and one injectable acute-stroke trial was withdrawn [13][14].

## How does TB-500 work?

TB-500 carries the LKKTETQ actin-binding motif of thymosin beta-4, which binds monomeric G-actin 1:1 to buffer the unpolymerized actin pool and regulate cell migration and cytoskeletal dynamics [6]. Crystallography of a thymosin-beta-4–actin complex established the dual-end capping that underlies this sequestration [6].

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

Timelines come from animal models, not human protocols. In a rat full-thickness wound, topical or intraperitoneal thymosin beta-4 increased re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline [8]. There is no validated human timeline for the TB-500 fragment [15].

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

Thymosin beta-4 has shown connective-tissue repair effects in animal models, but human efficacy of the TB-500 fragment for tendon or ligament injury is unproven and operates outside regulatory oversight [12][15]. The animal-model promise is real; the human evidence for the 7-mer is not there.

## Does TB-500 affect the heart?

In mice, thymosin beta-4 activated PINCH-ILK-Akt survival signaling, enhanced cardiomyocyte survival and improved cardiac function after coronary ligation [9]. The results are for the full-length protein in animal models, not a demonstrated human cardiac therapy.

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

Thymosin beta-4 induced VEGF in a HIF-1-alpha-dependent manner and promotes endothelial migration [11]. This pro-angiogenic activity aids repair but is also part of the tumor-angiogenesis safety concern [7].

## 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 while 18 mg/kg did not — a non-monotonic effect — with a modeled optimal dose near 3.75 mg/kg [10]. The result is for the parent protein in an animal model.

## Does TB-500 reduce inflammation?

Reviews describe thymosin beta-4 as anti-inflammatory, limiting apoptosis and inflammation after injury [7]. These are mechanistic and animal/in-vitro findings for the parent protein, not a demonstrated anti-inflammatory effect of the TB-500 fragment in humans.

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

Human safety data for the TB-500 fragment are scarce; the main flagged concern is the tumor/angiogenesis signal [7]. A 2026 Sports Medicine review notes potential for serious harm given the absence of rigorous human data for unapproved peptides in this class [15].

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

Both are unapproved research peptides studied for tissue repair; a 2026 Sports Medicine review lists TB-500/thymosin beta-4 and BPC-157 together among unapproved peptides with favorable animal outcomes but scarce human safety data [15]. Their mechanisms differ — TB-500 acts through G-actin sequestration via the LKKTETQ motif [6].

## Does TB-500 help wound healing?

In a rat full-thickness wound model, thymosin beta-4 increased re-epithelialization, wound contraction, collagen deposition and angiogenesis; as little as 10 pg stimulated keratinocyte migration 2–3-fold [8]. These are animal-model and in-vitro results for the parent protein.

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

Long-term human safety of the TB-500 fragment is unestablished; the only multi-dose human data are a 14-day IV Phase 1 study of full-length thymosin beta-4, and the tumor-angiogenesis signal remains an open concern [13][7]. No long-term controlled human data exist for the 7-mer [15].

## Why is TB-500 used in racehorses?

TB-500 was supplied as a veterinary preparation and encountered as a designer drug in racehorses, prompting LC-MS anti-doping detection methods in equine plasma and urine. The veterinary history is part of why the substance sits in a research/veterinary register [16].

## Is TB-500 legal?

TB-500 has no FDA-approved indication, is WADA-prohibited, and is a prescription medicine in some jurisdictions; it is sold for laboratory and research use only [16]. In the U.S. compounding context it sits in 503A Category 2 today, which is not eligible for routine compounding while that status stands [16][19].

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

FDA placed TB-500 in 503A Category 2 (significant safety risks), which is not within FDA's enforcement-discretion policy, so it is not eligible for routine 503A compounding while that status stands [16][19]. It is individually listed on the July 2026 PCAC agenda for evaluation, but that is a scheduled discussion, not a change in status [18].

## 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 [16]. Category 2 substances are not covered by the enforcement-discretion policy that applies to Category 1 [16][17].

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A luminous reading of the TB-500 record — the Ac-LKKTETQ fragment lit where the studies confirm it, the full-length thymosin beta-4 substitutions and the dark human-evidence gap left plainly visible, and the FDA 503A status read first; no clinic behind the aurora and nothing here ordered, dispensed, or sold.