TB 500.

TB 500 is a research compound in the thymic & immune-modulating peptides.

Promoting new blood-vessel formation and repair signalling.

It draws interest for thymic & immune-modulating peptides.

F-tier evidence: human evidence is limited; most support is preclinical.

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.

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.

What the evidence shows

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.

Safety considerations

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.

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).

1. [1]Thymosin β4 Promotes Dermal Healing — Kleinman HK, Sosne G. Vitamins and Hormones, 2016. PMID: 27450738
2. [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. [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. [4]PubMed: thymosin beta-4 actin sequestration (mechanism literature) — PubMed search, NCBI

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

Stack fit

Why not D: held back by human evidence, safety clarity, regulatory clarity, practical relevance.

What would move it up: Larger controlled human trials, clearer long-term safety, replicated findings, and regulatory progress.

What would move it down: Failed confirmatory trials, new safety signals, or evidence that popular claims don't translate.

• TB 500 is not FDA-approved for human use; it is discussed in a research context.
• It belongs to the Thymic & immune-modulating peptides class.
• Its principal mechanism is characterized in the literature.

• Whether observed effects reliably translate to humans at large.
• Long-term safety in healthy users, and full drug-interaction risk.
• Optimal studied parameters outside any approved indication.
• Claim-by-claim verdicts — these are authored against verified sources and shown when complete.
• Quality and purity of material from non-pharmaceutical sources.

1. What it is
2. The Angiogenesis & tissue repair mechanism
3. The preclinical evidence lane
4. Why Preliminary, and not higher or lower
5. Proven lane vs speculative lane
6. What people report
7. Regulatory status
8. What changed recently