TB-500.

thymosin β4 fragment
FTier · 30/100Research / preclinicalHealing & recovery

TB-500 is a synthetic peptide sold for research use and widely marketed as "thymosin beta-4 (Tβ4)." Naturally occurring Tβ4 is a 43-amino-acid, ~4.9 kDa actin-sequestering peptide found in nearly all mammalian cells and at high concentration in platelets and wound fluid.

Quick answer

TB-500 is a synthetic peptide sold for research use and widely marketed as "thymosin beta-4 (Tβ4)." Naturally occurring Tβ4 is a 43-amino-acid, ~4.9 kDa actin-sequestering peptide found in nearly all mammalian cells and at high concentration in platelets and wound fluid. TB-500 is research / preclinical, and PepCue grades its published evidence F tier (30/100). Also known as thymosin β4 fragment. This is a research reference, not medical or dosing advice.

What it is

TB-500 is a synthetic peptide sold for research use and widely marketed as "thymosin beta-4 (Tβ4)." Naturally occurring Tβ4 is a 43-amino-acid, ~4.9 kDa actin-sequestering peptide found in nearly all mammalian cells and at high concentration in platelets and wound fluid. Notably, many products labeled "TB-500" are actually a shorter synthetic fragment built around the active actin-binding motif (LKKTET/LKKTETQ) rather than the full-length Tβ4 molecule, so the name is used loosely in the research-chemical market and the exact identity of a given vial is often unverified.

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How it works

The best-characterized function of thymosin beta-4 is binding monomeric G-actin in a 1:1 complex, acting as the principal intracellular actin-sequestering peptide that buffers the pool of unpolymerized actin and thereby modulates cytoskeletal assembly, cell shape, and migration. Through the LKKTET motif and downstream signaling, Tβ4 has been reported in preclinical models to promote keratinocyte and endothelial cell migration, angiogenesis, anti-inflammatory and anti-apoptotic effects, and activation of integrin-linked kinase (ILK)/Akt and laminin-5 pathways relevant to wound repair. These mechanisms are mostly established in cell and animal systems; the degree to which a synthetic LKKTET-type fragment reproduces full-length Tβ4 biology is not firmly established.

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Mechanism pathways

Angiogenesis and tissue repair

Promoting new blood-vessel formation, cell migration, and repair signalling.

Wound healing proceeds through overlapping phases: haemostasis, inflammation, proliferation, and remodelling. Angiogenesis, the growth of new capillaries from existing vessels, is essential to the proliferative phase because new tissue cannot be built or sustained without perfusion. It is driven largely by vascular endothelial growth factor acting on VEGFR2 on endothelial cells, with nitric oxide serving as a downstream and permissive signal that governs vessel dilation, endothelial survival, and sprouting. Cell migration is the other requirement: keratinocytes, fibroblasts, and endothelial cells must physically move into the wound bed, which depends on rapid reorganisation of the actin cytoskeleton. Compounds grouped here engage different points in that sequence. One acts most consistently through the nitric oxide system, promoting endothelial nitric oxide production, with protective effects that are blunted when nitric oxide synthase is blocked. It has been reported to activate a signalling chain involving Src, caveolin-1, and endothelial nitric oxide synthase, and to enhance VEGFR2-driven signalling, which is the proposed basis for its pro-angiogenic effects. It also has reported effects on gut mucosal protection and on tendon fibroblast behaviour. Others derive from a naturally occurring intracellular protein whose best-characterised function is binding monomeric actin in a one-to-one complex. By buffering the pool of unpolymerised actin, it modulates cytoskeletal assembly and therefore cell shape and motility. A short conserved motif within the protein has been reported to promote keratinocyte and endothelial migration, angiogenesis, and anti-inflammatory and anti-apoptotic effects in preclinical models. The relationship between the full protein and the fragment sold under a separate name is a frequent source of confusion, since they are related but not identical entities. This is a pathway where the gap between mechanism and proof is unusually wide, and it deserves plain statement. The molecular actions above are documented, but overwhelmingly in cell culture and rodent models of injury. Controlled human trials are sparse to absent for these compounds, none is an approved medicine for tissue repair in major jurisdictions, and material sold under these names is unregulated with uncertain identity and purity. Promoting angiogenesis is also not universally desirable, since the same signals that build capillaries into healing tissue could in principle support other proliferating tissue, and that question has not been addressed in humans.

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The evidence

Human evidence comes almost entirely from the full-length Tβ4 molecule developed pharmaceutically by RegeneRx and partners, not from research-chemical "TB-500." Topical Tβ4 (RGN-137) was tested in completed Phase 2 dermal-wound trials including a randomized, placebo-controlled study in venous stasis ulcers (ClinicalTrials.gov NCT00832091), and ophthalmic Tβ4 (RGN-259) has advanced to Phase 3 for neurotrophic keratopathy (e.g., the SEER-2 trial, NCT05555589). Preclinical support for dermal, corneal, and cardiac repair is substantial and replicated across labs, as reviewed by Kleinman and Sosne (Vitamins and Hormones, 2016). However, there are no controlled human trials of injectable "TB-500" as sold in the peptide market for musculoskeletal healing, tendon/ligament injury, or athletic recovery; those uses rest on animal data and extrapolation, and the human-vs-preclinical gap is wide.

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The evidence, in brief

TB-500 is a synthetic fragment related to thymosin β4. Thymosin β4 has been studied preclinically for wound and tissue repair, but TB-500 itself has minimal human evidence and is not approved. Most claims rest on animal data.

  1. Thymosin β4 Promotes Dermal HealingVitamins and Hormones, 2016 (PMID 27450738)
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Evidence maturity

An evidence-only reading: approval status, human vs preclinical data, mechanism and safety. Popularity never raises it. Research file #062

Preliminary1.8/5 composite

Mostly preclinical or mechanistic; little human data.

Human evidence1/5
Preclinical depth3/5
Mechanism3/5
Safety clarity1/5
Regulatory1/5
Practical relevance2/5
Where it sits on the evidence ladder
AnecdoteMechanismAnimalEarly humanClinical trialsApproved use

Findings come mainly from animal models, not people.

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Claim receipts

Popular claims about TB-500, checked against the state of the evidence. The verdict describes evidence maturity, never an invented study result.

~ Too early“Speeds muscle and injury recovery”

Support is preclinical/mechanistic; human recovery outcomes are not established.

! Safety caveat“Safe for regular use”

Human safety data is sparse; it is research-only and not approved for human use.

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Safety profile

There is no established human safety profile for research-chemical "TB-500"; it is not a licensed drug and is not manufactured to pharmaceutical quality, so identity, purity, sterility, and endotoxin content of marketed vials are unverified. Pharmaceutical full-length Tβ4 has been reasonably well tolerated in controlled topical and ophthalmic trials, but those findings do not transfer to unregulated injectable products. A recurring theoretical concern is that a peptide promoting angiogenesis and cell migration could be undesirable in the setting of occult malignancy, though this is not established as a clinical harm. Contamination, dosing errors, and injection-related risks are the most concrete real-world hazards.

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Compound notes

  • TB-500 is a synthetic version of a fragment of Thymosin Beta-4, a naturally occurring actin-binding peptide.
  • Mechanistically it is studied for cell migration, actin regulation, and angiogenesis, processes relevant to wound healing and recovery.
  • Support is largely preclinical/mechanistic; human recovery outcomes are not established.
TB-500 vs. Thymosin Beta-4

TB-500 is a synthetic fragment marketed as a research chemical; Thymosin Beta-4 (Tβ4) is the full natural peptide studied in formal trials. They are related but not identical.

Safety notes
  • Not FDA-approved; research-only. Prohibited in sport under WADA.
  • Human safety data is sparse; long-term effects are unknown.
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Regulatory status

TB-500/thymosin beta-4 is not approved by the FDA or EMA for any indication; full-length Tβ4 remains investigational (RegeneRx/ReGenTree ophthalmic and dermal programs), and material sold as "TB-500" is research-use-only and not a dietary supplement or medicine. It is prohibited in sport at all times by the World Anti-Doping Agency under class S2 (peptide hormones, growth factors, related substances and mimetics).

Research / preclinical

Sold research-use-only; human evidence is limited or preclinical.

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By the numbers

  • 01Naturally occurring thymosin beta-4 is a 43-amino-acid (~4.9 kDa) intracellular actin-sequestering peptide abundant in platelets and wound fluid
  • 02The peptide's active region is the LKKTET/LKKTETQ motif; many 'TB-500' products are a fragment around this motif rather than full-length Tβ4
  • 03Human clinical data exist for pharmaceutical full-length Tβ4 (RGN-137 topical, RGN-259 ophthalmic), not for injectable research-chemical TB-500
  • 04Phase 3 ophthalmic trials (RGN-259, e.g. SEER-2) are ongoing for neurotrophic keratopathy
  • 05WADA-prohibited at all times under class S2
  • 06Not FDA- or EMA-approved; sold as research-use-only material

TB-500: research formats

Choose the format you are researching to see route-specific notes.

Primary research format; sometimes administered IM. Larger doses than most peptides.

TB-500 is typically sold as a 5 mg or 10 mg vial. A common reconstitution is 5 mg + 2.5 mL BAC water for 2,000 mcg/mL (2 mg/mL). Research designs frequently use doses in the low-mg range per injection, spaced weekly or biweekly, making the vial math different from most other peptides.

Example math: 5 mg vial + 2.5 mL BAC water (2,000 mcg/mL)
PHASEDAILY DOSEUNITS ON U-100VOLUME
Per injection (low)2.5 mg (2,500 mcg)125 units*1.25 mL
Per injection (high)5.0 mg (5,000 mcg)250 units*2.50 mL†
* A standard 1 mL U-100 syringe holds 100 units (1.0 mL). Volumes above 1 mL require a larger syringe. † Two 5 mg vials needed per injection at this level. This is not a dosing recommendation. Amounts shown are illustrative examples of the concentration math.

The larger injection volumes typical in TB-500 research sometimes favour intramuscular (IM) administration over SC to accommodate volume and reduce discomfort. Spread across multiple SC sites is also used.

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Sources

Every factual claim above resolves to a real, published source.

  1. Thymosin β4 Promotes Dermal HealingKleinman HK, Sosne G. Vitamins and Hormones, 2016. PMID: 27450738
  2. Safety and Efficacy of Thymosin Beta 4 (RGN-137) in Patients With Venous Stasis Ulcers (Phase 2)RegeneRx Biopharmaceuticals; ClinicalTrials.gov NCT00832091 (completed)
  3. Safety and Efficacy of 0.1% RGN-259 (Thymosin Beta 4) Ophthalmic Solution for Neurotrophic Keratopathy: SEER-2 (Phase 3)ReGenTree, LLC; ClinicalTrials.gov NCT05555589 (recruiting)
  4. PubMed: thymosin beta-4 actin sequestration (mechanism literature)PubMed search, NCBI
Cite this page

PepCue. “TB-500: the evidence.” PepCue, reviewed June 1, 2026. https://www.pepcue.app/p/tb-500.

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Compounds