# TB-500 FAQ: Identity, Mechanism, Safety, and Regulatory Questions Answered

> TB-500 FAQ: what TB-500 is, how the Ac-LKKTETQ fragment works, the tumor safety signal, whether it is FDA approved, how it compares with BPC-157, and whether it is a steroid.

Identity, mechanism, safety, dosing context, and regulatory status — each answer short, direct, and cited where it makes a quantitative claim.

## 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][5]. It is a research and veterinary-context compound with no approved therapeutic indication [5].

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

"TB" references thymosin beta. TB-500 is a research and veterinary designation for the synthetic `Ac-LKKTETQ` fragment of thymosin beta-4; it is not an official pharmacological name [5]. The "500" is a product-style numbering, not a chemical descriptor.

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

In animal and in-vitro research, thymosin beta-4 and its actin-binding region are studied for wound healing, tissue and cell migration, angiogenesis, cardiac and neurological repair, and hair-follicle activation [3][4][5]. Human efficacy of the isolated 7-mer is unproven [5].

## How does TB-500 work?

TB-500 carries the `LKKTETQ` actin-binding motif of thymosin beta-4, the body's principal G-actin-sequestering peptide [1][5]. Thymosin beta-4 binds monomeric actin 1:1 to regulate cytoskeletal dynamics, cell migration, angiogenesis, and survival signaling [1][2]; whether the isolated 7-mer reproduces these effects at research doses is not established in humans [5].

## Is TB-500 a steroid?

No. TB-500 is a short synthetic peptide fragment — seven amino acids, `Ac-LKKTETQ`, molecular weight `889.02 Da` [5]. Steroids are a different chemical class built on a fused-ring carbon skeleton. TB-500 shares neither the structure nor the hormonal mechanism of an anabolic steroid; its proposed mechanism is actin sequestration via the thymosin beta-4 motif [1].

## What is the half-life of TB-500?

No validated human pharmacokinetic half-life exists for the TB-500 heptapeptide [5]. In the intravenous full-length thymosin beta-4 Phase 1 study, half-life increased with dose (dose-proportional pharmacokinetics) [6]. Anti-doping LC-MS work characterizes TB-500 and its metabolites in equine matrices for detection, not for human pharmacokinetics [5].

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

No completed controlled human trials of the TB-500 fragment exist, so a human side-effect profile is not established [5]. The closest human safety data are for intravenous full-length thymosin beta-4, well tolerated to `1260 mg` in a Phase 1 study [6]; the principal theoretical concern is the tumor and angiogenesis signal [7], covered on the [TB-500 side effects](/side-effects) page.

## 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 [7][8]; the same pro-migratory, pro-angiogenic properties that aid repair could theoretically support tumor progression [7]. This is a theoretical safety signal from preclinical data — not a demonstrated outcome of the 7-mer in humans [5].

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

Long-term safety of the TB-500 fragment is unstudied in humans [5]. The longest controlled human exposure is 14 days of intravenous full-length thymosin beta-4 [6]; chronic dosing data come only from animals (for example 6 months intraperitoneally in `mdx` mice) [9], and the tumor-angiogenesis concern is most relevant to prolonged use [7].

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

Beyond the unproven human safety profile, preclinical results temper the narrative: in `mdx` mice, chronic thymosin beta-4 raised regenerating-fiber counts but did not improve strength, cardiac function, or fibrosis [9], and systemic thymosin beta-4 failed to limit myocardial ischemia-reperfusion injury in pigs [14]. Research-grade material purity is an added concern [5].

## Is TB-500 safe according to the research?

No research establishes the TB-500 fragment as safe in humans, because the controlled human trials are absent [5]. Available human safety data are for intravenous full-length thymosin beta-4 (well tolerated to `1260 mg`) [6]; the principal unresolved concern is the tumor and angiogenesis signal [7][8]. "Unstudied" is not "safe."

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

Animal work shows thymosin beta-4 acts as a myoblast chemoattractant and supports tissue repair [5], but a 6-month `mdx`-mouse study found more regenerating fibers without strength gains [9]. Controlled human recovery trials of the 7-mer do not exist [5].

## Does TB-500 affect the heart?

In mice, thymosin beta-4 activated the PINCH–ILK–Akt survival pathway, mobilized epicardial progenitors, and improved cardiac function after coronary ligation [2]. But a porcine study found systemic thymosin beta-4 did not attenuate ischemia-reperfusion injury [14], so the cardiac picture is mixed.

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

Thymosin beta-4 induces VEGF in a HIF-1α-dependent manner and drives endothelial migration, building new vessels that aid repair [10]. Because tumors also exploit angiogenesis, this pro-angiogenic activity is part of the theoretical oncologic safety signal [7].

## 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 near `3.75 mg/kg` [4]. These are rodent findings for the full-length protein, not human data for the 7-mer.

## Does TB-500 increase hair growth?

Nanomolar thymosin beta-4 stimulated hair growth in rats and mice by activating hair-follicle bulge stem-cell migration and differentiation and increasing matrix metalloproteinase-2 [5][11]. Human hair-growth data for TB-500 are not established [5].

## Does TB-500 reduce inflammation?

Full-length thymosin beta-4 suppressed corneal NF-κB as a potential anti-inflammatory mechanism [12] and shows anti-inflammatory activity at injury sites in review [5]. These are mechanistic and in-vitro/animal findings, not human anti-inflammatory efficacy.

## Does TB-500 help wound healing?

In a rat full-thickness wound model, topical or intraperitoneal thymosin beta-4 increased re-epithelialization by `42%` at 4 days and up to `61%` at 7 days versus saline, with greater contraction, collagen, and angiogenesis; as little as `10 pg` stimulated keratinocyte migration [3]. These are animal results for the full-length protein.

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

TB-500 is the `Ac-LKKTETQ` actin-binding fragment of thymosin beta-4, with an actin-sequestering mechanism [1][5]; BPC-157 is a separate gastric-pentadecapeptide-derived sequence with a different proposed mechanism. Both are unapproved research peptides — a 2026 Sports Medicine review groups them among unapproved musculoskeletal peptides with scarce human safety data [15].

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

There are no completed controlled trials of the TB-500 heptapeptide [5]. Human data exist only for full-length synthetic thymosin beta-4: a randomized placebo-controlled Phase 1 intravenous safety and pharmacokinetics study (well tolerated to `1260 mg`) [6] and topical/ophthalmic thymosin beta-4 (RGN-259) dry-eye trials [5].

## Is TB-500 FDA approved?

No. TB-500 has no FDA-approved therapeutic indication and is sold by research suppliers for laboratory use only [16]. FDA lists it as the "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" bulk substance placed in 503A Category 2 [16]. The full picture is on the [TB-500 legal status and FDA 503A category](/legal-status) page.

## 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 [15].

## Why is TB-500 used in racehorses?

TB-500 has been encountered as a veterinary or designer preparation in equine sport, which prompted the first LC-MS detection method in horse plasma and urine (limit of detection roughly 0.01-0.02 ng/mL) to control its misuse. Its use in racehorses is an anti-doping concern, not an approved indication [15].

## Is TB-500 legal?

TB-500 is not an FDA-approved drug and, as a 503A Category 2 substance, is not within FDA's enforcement-discretion policy for routine compounding [16][17]. It is sold for laboratory use only, is WADA-prohibited, and is a prescription medicine in some jurisdictions. This is general information, not legal advice — see the [TB-500 legal status and FDA 503A category](/legal-status) page.

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

Under current FDA status, no — for routine 503A compounding. TB-500 is in Category 2, so FDA has flagged it for significant safety risks and it is not afforded the enforcement discretion that lets a 503A pharmacy compound with a permitted bulk substance [16][17]. Lawful compounded access requires the ingredient to be eligible, which TB-500 is not while its Category 2 flag stands [17].

## 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 the September 29, 2023 nominated-substances update [16]. It is on the July 23-24, 2026 PCAC agenda as a substance being considered for the 503A bulks list, a scheduled discussion only, not a decision [18].

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A forest-console reading of the TB-500 record — the Ac-LKKTETQ fragment held against thymosin beta-4 study by study, every confirmed finding logged green and every full-length-protein substitution flagged, with no clinic behind the console and nothing here dispensed or sold.