TB-500 questions, answered from the record.

Definition and identity

What is TB-500?

TB-500 is the synthetic, N-acetylated heptapeptide Ac-LKKTETQ corresponding to residues 17–23 of thymosin beta-4 — the actin-binding motif ^[1]. It is a research and veterinary-context chemical with no approved human indication ^[11].

What does TB-500 stand for?

TB refers to thymosin beta-4 (Tβ4); TB-500 is a product and research designation for the synthetic Ac-LKKTETQ fragment of that protein. The number is a label, not a dose or concentration.

What is TB-500 used for in research?

In animal and in-vitro studies, thymosin beta-4 and its actin-binding region are investigated for wound and tissue repair, cell migration, angiogenesis, cardiac and neurological repair, and anti-fibrotic effects ^[5].

How does TB-500 work?

The LKKTETQ motif is thymosin beta-4's actin-binding region; the parent protein binds monomeric (G-) actin 1:1, regulating cytoskeletal dynamics, cell migration, angiogenesis, and survival signaling ^[1][2]. Whether the isolated 7-mer reproduces these at research doses is not established in humans.

Is TB-500 a steroid?

No. TB-500 is a peptide fragment — seven amino acids, Ac-LKKTETQ — not a steroid ^[1]. Steroids share a four-ring lipid scaffold and act on nuclear hormone receptors; TB-500 is a short peptide carrying an actin-binding motif and works, if at all, through entirely different cytoskeletal and signaling biology.

Mechanism and effects

Does TB-500 reduce inflammation?

Full-length thymosin beta-4 inhibited TNF-α–induced NF-κB activation and IL-8 expression in vitro ^[13] and activates pro-resolving pathways ^[14] — the mechanistic basis for an anti-inflammatory effect; whether the isolated heptapeptide reproduces this in humans is unproven.

Can TB-500 cause autoimmune reactions or affect the immune system?

Thymosin beta-4 is reported to modulate inflammatory and pro-resolving pathways rather than provoke autoimmunity ^[14], but there are no controlled human safety data for the TB-500 fragment to confirm immune effects either way.

Does TB-500 work for muscle recovery?

Muscle-injury-induced Tβ4 acts as a myoblast chemoattractant in rodents, but a six-month mdx-mouse study found more regenerating fibers without gains in strength or cardiac function ^[5]. No controlled human exercise-recovery data exist for the fragment.

Does TB-500 help wound healing?

Full-length thymosin beta-4 accelerated re-epithelialization, contraction, collagen deposition, and angiogenesis in animal wound models and topical ophthalmic trials ^[3][5]; human data for the fragment are absent.

How long does TB-500 take to work?

No validated human timeline exists. In a rat wound model, full-length Tβ4 raised re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline ^[3], but animal kinetics do not translate to a human schedule.

Can TB-500 help tendon and ligament repair?

Thymosin beta-4 has been studied in connective-tissue repair within its broad migration-and-angiogenesis profile ^[5], but there is no controlled human tendon or ligament data for the fragment.

Does TB-500 affect the heart?

In mice, thymosin beta-4 activated PINCH–ILK–Akt survival signaling and improved cardiac function after coronary ligation ^[2]; systemic Tβ4 failed to attenuate ischemia-reperfusion injury in a porcine study, and human cardiac data are limited to a completed registered acute-MI trial ^[10].

Does TB-500 have neuroprotective effects?

In a rat embolic-stroke dose-response study, intraperitoneal Tβ4 improved neurological function at 2 and 12 mg/kg but not at 18 mg/kg, with a modeled optimum near 3.75 mg/kg ^[4]. An injectable human stroke trial was withdrawn ^[11].

What is the half-life of TB-500?

No validated human pharmacokinetic half-life exists for the heptapeptide. In the IV full-length Tβ4 Phase 1 study, half-life increased with dose ^[6]; anti-doping LC-MS work characterizes TB-500 for detection, not human PK.

Safety and comparison

What are the side effects of TB-500?

Human safety data for the fragment are scarce. Full-length Tβ4 was well tolerated to 1260 mg IV in a Phase 1 study ^[6]; the principal theoretical concern is the pro-angiogenic and pro-migratory tumor signal ^[5], and research-grade purity is a recurring issue.

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 and pro-angiogenic properties that aid repair could theoretically support tumor progression ^[5]. This is an unresolved safety concern.

Is TB-500 safe for long-term use?

There are no long-term human safety data for the TB-500 fragment. The longest controlled exposure is a 14-day IV Phase 1 study of full-length Tβ4 ^[6]; the tumor and angiogenesis signal makes chronic use an open question ^[5][12].

Are there human clinical trials on TB-500?

There are no completed controlled trials of the TB-500 heptapeptide. Human data exist only for full-length thymosin beta-4: a randomized Phase 1 IV safety study ^[6] and topical ophthalmic trials ^[7]; a registered injectable acute-MI trial completed ^[10] and an early injectable stroke trial was withdrawn ^[11].

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

They are unrelated peptides studied separately. TB-500 is the Ac-LKKTETQ fragment of thymosin beta-4, an actin-binding peptide ^[1]; BPC-157 is a distinct gastric pentadecapeptide. Both are unapproved, WADA-relevant research compounds with mostly animal data.

Legal and regulatory

Is TB-500 legal?

TB-500 occupies a narrow status. It is not an FDA-approved drug, and FDA lists the LKKTETQ fragment as TB-500 and placed it in 503A Category 2 — bulk substances that may present significant safety risks — so it is not within FDA's enforcement-discretion policy for routine 503A compounding while that status stands [reg1][reg3]. It is supplied as a research and veterinary-context chemical, is WADA-prohibited in sport, and is a prescription medicine in some jurisdictions. "TB-500 (free base)" and "TB-500 acetate" are on the published agenda of the July 23–24, 2026 PCAC meeting as substances under evaluation — a scheduled discussion, not a change in status [reg2].

Can you get TB-500 from a compounding pharmacy?

Legally compounded medications follow a defined pathway: a licensed prescriber evaluates a patient (telehealth can be the front-end channel), issues a patient-specific prescription, and a 503A pharmacy or 503B outsourcing facility compounds it — but only if the ingredient is eligible under the bulk-substance rules [reg3][reg4]. Because FDA placed TB-500 in Category 2, it is not eligible for routine 503A compounding while that status stands [reg4]. This is general information, not medical advice, and not an offer to supply anything.

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, citing concerns including potential immunogenicity for certain routes and a lack of important safety information [reg1]. Category 2 substances are not afforded FDA's enforcement discretion for 503A compounding [reg3]. The substance is on the July 2026 PCAC agenda for evaluation, which is a discussion and not a decision [reg2].

Is TB-500 banned by WADA?

Yes. TB-500 and thymosin beta-4 fall under WADA prohibited peptide, growth-factor, and tissue-repair categories, banned in and out of competition, and are detectable by LC-MS anti-doping assays.

Why is TB-500 associated with racehorses?

TB-500 has been encountered as a designer substance in equine sport, which is why the first validated LC-MS detection methods (limits of detection around 0.01–0.02 ng/mL) were developed in horses. It is prohibited in regulated racing.