Questions readers actually ask, answered with citations.

What is TB-500 and how is it different from full-length Thymosin Beta-4?

TB-500 is a synthetic seven-amino-acid peptide with the sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH (Ac-LKKTETQ-OH), CAS 885340-08-9, molecular weight 889.0 Da. It corresponds to residues 17 through 23 of full-length human Thymosin Beta-4 ^{[1] [2]}. Thymosin Beta-4 itself is a 43-amino-acid intracellular peptide, molecular weight roughly 4,921 Da, encoded by the TMSB4X gene and expressed in essentially every nucleated cell type.

The practical difference: TB-500 is the actin-binding warhead in isolation. The full parent protein carries that warhead plus most of the downstream interaction surface that the published clinical and preclinical record actually measures — the PINCH-Integrin-Linked-Kinase-Akt complex, NF-κB binding, Meprin-α / Prolyl Oligopeptidase processing into Ac-SDKP, and Notch / VEGF / HIF-1α induction in endothelium ^{[6] [7] [10] [13]}. Every registered human trial labelled "thymosin beta-4" uses the full 43-amino-acid recombinant peptide, not the seven-amino-acid synthetic ^[25].

How does TB-500 work at the molecular level?

The LKKTET central motif binds a single G-actin monomer in a 1:1 complex, sequestering monomeric actin and maintaining the dynamic G-actin pool that cells use for cytoskeletal remodelling, migration, and tissue repair ^{[1] [2]}. The C-terminal α-helix in the full parent protein stabilises the complex and sterically blocks both barbed-end and pointed-end filament addition ^[2].

That is the biochemistry the TB-500 synthetic preserves. What it does not preserve from the parent are the downstream signalling activities: the PINCH-ILK-Akt cardiomyocyte survival axis ^[6], the Notch1 / Notch4 / VEGF / HIF-1α endothelial cascade ^[13], NF-κB binding and IL-8 suppression ^[10], and enzymatic cleavage to the anti-fibrotic tetrapeptide Ac-SDKP. Vendor literature commonly attributes parent-protein activities to the fragment by association; the published literature does not support that mapping for most endpoints ^[25].

What does the research say about TB-500 and tissue repair?

The body of evidence is large for full-length Thymosin Beta-4 and small for the seven-amino-acid synthetic. Topical Tβ4 at 5 μg per wound accelerated rat dermal punch-wound re-epithelialisation by 42% at day 4 and up to 61% at day 7 ^[3]. Topical Tβ4 at 5 μg twice daily accelerated mouse corneal re-epithelialisation after alkali burn and reduced IL-1β, KC, and MIP-2 ^[4]. Tβ4 improved fractional shortening in mouse coronary ligation ^[6] and mobilised adult epicardial progenitor cells at 150 μg IP every 3 days ^[7]. Tβ4 at 3.75 mg/kg IV improved functional neurological recovery in rat embolic stroke ^{[8] [9]}.

Philp 2003 specifically tested a synthetic peptide containing only the actin-binding domain in db/db diabetic and aged mice and showed comparable activity to full-length Tβ4 in those impaired-healing dermal models ^[5]. That paper is the closest published evidence for activity at the fragment level. Outside of that and the engineered tandem-repeat tTB4 construct ^[21], strict head-to-head studies between full Tβ4 and short LKKTET-containing fragments remain sparse ^[25].

Are there any human clinical trials of TB-500 or Thymosin Beta-4?

Of full-length Thymosin Beta-4, yes — multiple. Ruff 2010 ran a US Phase I IV safety study in 40 healthy adults at single doses up to 1,260 mg with a multiple-dose extension, no SAEs and no DLTs ^[13]. Wang 2021 ran a Chinese Phase I IV study in 84 healthy adults at 0.05–25 μg/kg single doses and 0.5–5 μg/kg/day for 10 days, dose-linear PK and no SAEs ^[14]. The RGN-259 0.1% Tβ4 ophthalmic programme ran Phase II/III in dry eye (ARISE) and Phase III in neurotrophic keratopathy (NCT02600429, n=18 — 60% vs 12.5% complete healing at day 29, p=0.066) ^{[15] [22]}. The RGN-352 IV Tβ4 programme ran a Phase II in roughly 75 post-acute-myocardial-infarction patients at 450 mg or 1,200 mg daily × 3 then weekly × 4 ^[25].

Of the seven-amino-acid TB-500 synthetic, no registered human efficacy or pharmacokinetic study has been published in the peer-reviewed literature ^{[16] [25]}. The only published primary-source human-adjacent PK work is the equine doping-control study by Esposito 2012 ^[16].

What were the results of the RGN-259 Phase III trials?

The neurotrophic keratopathy Phase III (NCT02600429, n=18, published in 2022) produced complete corneal healing at day 29 in 60% of treated subjects versus 12.5% of placebo. The prespecified primary endpoint missed statistical significance narrowly (p=0.066). The same endpoint was significant at day 43 (p=0.036), and the benefit was durable after washout ^[15].

The dry eye programme (ARISE-1 / ARISE-2 / ARISE-3) missed prespecified primary endpoints but produced positive secondary signals — ocular grittiness improvement and two-week central corneal staining ^[22]. The narrative review of the programme attributed part of the primary endpoint miss to high placebo response. A planned 46-subject SEER expansion in neurotrophic keratitis was terminated early due to slow rare-disease recruitment. None of these trials used the seven-amino-acid TB-500 heptapeptide; all used full-length 0.1% recombinant Tβ4 ophthalmic solution.

What are typical research doses of TB-500 in animal studies?

Research-context only. Topical Tβ4 at 5 μg per wound twice daily in rat and mouse dermal and corneal models ^{[3] [4] [5]}. Intraperitoneal Tβ4 at 150 μg every three days in mouse cardiac models ^[7]. Intravenous Tβ4 at 3.75 mg/kg as a single dose 24 hours post-stroke in rats ^{[8] [9]}. Local Tβ4 at 1 μg in fibrin sealant in rat MCL transection ^[23]. Intravenous recombinant Tβ4 in human Phase I at 42–1,260 mg in the US ^[13] and 0.05–25 μg/kg in China ^[14]. Topical 0.1% RGN-259 ophthalmic in the RGN-259 programmes ^{[15] [22]}.

The "2–10 mg/week subcutaneous" range commonly cited in vendor and research-chemical literature for the TB-500 heptapeptide is not anchored to any registered clinical trial or peer-reviewed PK study ^[26]. None of the numbers in this answer is a recommendation for human use.

Is there published pharmacokinetic data on TB-500 in humans?

Not on the seven-amino-acid TB-500 heptapeptide specifically. The two published human Phase I PK datasets — Ruff 2010 in the US ^[13] and Wang 2021 in China ^[14] — both used full-length recombinant Thymosin Beta-4 administered intravenously. Both showed dose-proportional Cmax and AUC, biphasic plasma decline, no accumulation after repeat dosing, and no dose-limiting toxicities ^{[13] [14]}.

The only published primary-source PK work on the TB-500 heptapeptide is the equine doping-control LC-MS study by Esposito 2012, which detected TB-500 in horse plasma at a lower limit of approximately 0.02 ng/mL and in urine at approximately 0.01 ng/mL after intravenous administration, and explicitly documented plasma instability ^[16]. The commonly cited "1.5–3 hour half-life" figure for TB-500 in rodents originates from vendor and aggregated commercial sources, not from a primary peer-reviewed PK study ^[26].

Is TB-500 FDA-approved or legal to compound?

TB-500 is not FDA-approved for any human indication ^{[25] [26]}. Full-length recombinant Thymosin Beta-4 — the molecule used in RGN-259 ophthalmic and RGN-352 IV — remains investigational after multiple Phase II and Phase III trials and has not received marketing authorisation ^{[15] [22] [25]}.

On compounding: TB-500 (free base and acetate forms) was nominated for the FDA Section 503A Bulks List and is scheduled for Pharmacy Compounding Advisory Committee review on 23 July 2026 (FDA docket FDA-2025-N-6895) ^[26]. TB-500 has no USP monograph and is not a component of any FDA-approved drug, so its legal compounding pathway under Section 503A depends entirely on whether the PCAC recommends inclusion. The 503A status is pending at the time of writing and may change after the July 2026 review.

Is TB-500 on the WADA Prohibited List?

Yes, at all times. TB-500 and Thymosin Beta-4 derivatives are listed under both S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics) and the catch-all S0 (Non-Approved Substances) of the World Anti-Doping Agency Prohibited List in the 2024, 2025, and 2026 editions ^{[16] [26]}. Multiple athlete sanctions including multi-year ineligibility have been issued. Equine doping-control LC-MS detection methods for the heptapeptide are published with lower limits of approximately 0.01 ng/mL in urine and 0.02 ng/mL in plasma ^[16].

How does TB-500 compare with BPC-157 in the research literature?

BPC-157 and TB-500 are the two most-discussed companion research peptides in the tissue-repair literature, and both appear on the FDA's 503A bulk-drug compounding nomination docket scheduled for the July 2026 PCAC review ^[26]. The molecules are structurally and mechanistically unrelated — BPC-157 is a 15-amino-acid pentadecapeptide derived from a human gastric juice protein, while TB-500 is the seven-amino-acid LKKTETQ fragment of Thymosin Beta-4. Both have substantial rodent musculoskeletal-repair preclinical literatures. Neither is FDA-approved for any human indication. Both are prohibited under WADA at all times ^[26].

The research records are not equivalent: BPC-157's mechanism is incompletely characterised but extensively studied across rodent models; TB-500's actin-binding mechanism is structurally resolved at atomic resolution ^[2] but the seven-amino-acid synthetic specifically has no registered human PK or efficacy trial ^[25]. Read the molecules separately, not as interchangeable "healing peptides."

What are the safety and contamination concerns with research-chemical-grade TB-500?

The published human safety data on full-length recombinant Tβ4 is reassuring within the studied dose range — no dose-limiting toxicities and no serious adverse events in Phase I IV dosing up to 1,260 mg in the US ^[13] and up to 25 μg/kg in China ^[14]. That dataset says nothing about research-chemical-grade TB-500 sold by unregulated vendors ^[26].

Underground TB-500 is manufactured without GMP standards, lot-release testing, endotoxin control, sterility assurance, or potency verification. Contamination and purity risks routinely dwarf the peptide's own pharmacology in unregulated use. The molecule also promotes angiogenesis and cell migration; theoretical concerns about effects on occult or pre-existing tumours have been raised in the literature, though no clinical signal of tumour promotion has been reported in the published Phase I/II/III safety data to date ^{[24] [25]}. The biology is also context-dependent — Lee 2023 showed Tβ4 conditional deletion in hepatic stellate cells reduces liver fibrosis, indicating that Tβ4 is pro-fibrotic in that compartment, the opposite direction of its dermal and cardiac biology ^[19].

Why is this site called "Clinic TB-500" if it is not a clinic?

The "clinic" in the domain name is editorial framing — the stance the publisher takes toward the literature, not a description of the site's services. This project is an annotated bibliography of the research on TB-500 and Thymosin Beta-4. It keeps no clinical staff, gives no medical advice, makes and sells nothing, and points no reader to a vendor. The about page treats this distinction explicitly. The dark-mode console aesthetic is deliberate — it is meant to read as a research-platform interface rather than a treatment-services page.