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Thymosin Beta-4: quick citable summary
Thymosin Beta-4 is listed by PeptaHub as a recovery peptide with a research only legal-status classification. The page summarizes mechanism, research context, common routes, safety notes, and references for writers and AI answer engines.
PeptaHub. “Thymosin Beta-4: Mechanism, Research Context, Safety.” peptahub.com, 2026. https://peptahub.com/peptides/thymosin-beta-4. Licensed CC BY 4.0.
License: Creative Commons Attribution 4.0 International. Link back to https://peptahub.com/peptides/thymosin-beta-4.
What is Thymosin Beta-4?
Thymosin Beta-4 is a 43-amino acid endogenous protein that regulates actin dynamics, tissue repair, cardiac regeneration, and immune modulation. It is distinct from the shorter TB-500 fragment and is uniquely studied for its ability to mobilize cardiac progenitor cells after myocardial infarction.
Overview
Thymosin Beta-4 is a 43-amino acid endogenous protein ubiquitously expressed in mammalian tissues, encoded by the TMSB4X gene. It is distinct from TB-500, which is a shorter synthetic heptapeptide fragment derived from its actin-binding domain. TB4 plays a fundamental role in actin dynamics, tissue repair, cardiac regeneration, and immune modulation, with research applications spanning wound healing, cardiac injury, and neurological recovery.
Mechanism of action
Thymosin Beta-4 functions through several coordinated mechanisms. Its primary structural role is G-actin sequestration — TB4 binds globular actin monomers, preventing uncontrolled polymerization and regulating the dynamic equilibrium between G-actin and F-actin required for cell motility and structural integrity. Beyond actin dynamics, TB4 acts extracellularly to promote cell migration, angiogenesis, and stem cell maturation. It upregulates integrin-linked kinase (ILK) expression, activating downstream Akt and PI3K signaling that drives cardiomyocyte survival, reduces apoptosis, and promotes progenitor cell recruitment to sites of injury. Anti-inflammatory effects include downregulation of NF-κB signaling and reduction of pro-inflammatory cytokine production including TNF-α and IL-1β. In cardiac injury models, TB4 mobilizes epicardial progenitor cells and promotes their differentiation into cardiomyocytes, positioning it uniquely among peptides studied for cardiac regeneration.
Reported study ranges
| Purpose | Route | Reported range | Frequency | Notes |
|---|---|---|---|---|
| Wound healing / tissue repair | subcutaneous | 2–5 mg | twice weekly | Loading phase: 2–5 mg twice weekly for 4–6 weeks. Maintenance: 2–6 mg per month. Do not use more than 3 months without cycling (3 months on, 6 weeks off). |
| Cardiac / systemic regenerative research | intramuscular | 2–5 mg | twice weekly | Protocols mirror subcutaneous administration and come from community practice, not from trials. No published human study establishes an intramuscular or subcutaneous dose of thymosin beta-4; the completed Phase 2 trial used a topical gel. |
Reported ranges are for research context only. Consult a qualified healthcare professional before using any peptide.
Convert Thymosin Beta-4 research-range units
Need to convert mg to mcg, dose volume, or U-100 syringe units? The Thymosin Beta-4 dose calculator is preloaded with these ranges, or use the general dose unit converter.
Research summary
Preclinical research spanning over two decades reports that TB4 accelerates healing of dermal wounds, burns, and corneal injuries in rodent and rabbit models, including diabetic (db/db) and aged mice (Philp et al., Wound Repair Regen 2003). Cardiac studies in animals report improved post-MI functional recovery and reduced infarct size. The one completed human trial we could verify is NCT00832091 (RegeneRx), a Phase 2 randomized, double-blind, placebo-controlled dose-response study of topical thymosin beta-4 gel (RGN-137) at 0.01%, 0.03% and 0.1% in 72 patients with venous stasis ulcers, applied once daily for up to 84 days. That trial was topical, not systemic, and its primary outcome was safety and tolerability rather than healing. No large-scale human efficacy trial of TB4 by any route has been completed as of 2026.[1][2][3][4]
Evidence grading
Each claimed benefit is graded by the strength of available evidence. Grades reflect study quality, not effect size.
Strong = multiple RCTs · Moderate = limited trials or observational · Preliminary = animal or in vitro only · Insufficient = anecdotal or no published data
Side effects
Side effects vary by individual. This is not an exhaustive list. Report unusual symptoms to a healthcare professional.
Common stacks
Peptides commonly paired with Thymosin Beta-4 for synergistic effects.
Legal status
Thymosin Beta-4 cannot legally be compounded in the US today. The FDA's April 15, 2026 action and both Pharmacy Compounding Advisory Committee agendas name the substance as TB-500 (TB-500 free base and TB-500 acetate), not as thymosin beta-4, and the agency's own review documents cite inconsistent naming conventions across peptide bulk substances as a specific deficiency. Because the full 43-amino-acid protein and the shorter fragment sold as TB-500 are not clearly the same substance in the public record, this entry does not claim that thymosin beta-4 is covered by the PCAC review; see the TB-500 profile for the substance the FDA actually named. Either way, thymosin beta-4 is not on the Section 503A Bulks List and is not eligible for compounding. It is not FDA-approved for any indication, and research supply chains remain active. Verify current federal and state rules before relying on access claims.
Sourcing & access
Research compound
Thymosin Beta-4 is classified as a research compound. Regulatory status varies by jurisdiction. Always verify current legal status and source from vendors providing third-party certificates of analysis (COA).
Frequently asked questions
Thymosin Beta-4 (TB4) is a 43-amino acid endogenous protein encoded by the TMSB4X gene, ubiquitously expressed in mammalian tissues. It is distinct from TB-500, which is a shorter synthetic heptapeptide fragment derived from its actin-binding domain.
TB4 sequesters G-actin monomers to regulate cell motility, promotes angiogenesis and stem cell maturation, upregulates integrin-linked kinase for cardiomyocyte survival via Akt/PI3K signaling, and downregulates NF-kB to reduce inflammation. It uniquely mobilizes cardiac epicardial progenitor cells.
Human safety data is thin. The one completed trial used a topical gel, so there is no controlled safety data for injected thymosin beta-4 at any dose. Reported side effects from research and community use include injection site reactions, transient fatigue, headache, rare nausea, and dizziness. Thymosin beta-4 is not FDA-approved and is not on the Section 503A Bulks List, so it cannot legally be compounded in the US. The FDA's 2026 peptide actions named TB-500 rather than thymosin beta-4, and the agency has not stated that the two are the same substance.
TB-500 is a shorter synthetic heptapeptide fragment derived from TB4's actin-binding domain. Full TB4 has a broader mechanistic profile, particularly for cardiac progenitor mobilization, while TB-500 focuses on the actin-related tissue repair pathway. Many suppliers sell TB-500 as a proxy for full TB4.
Research references
- Thymosin beta4 accelerates wound healingPubMed
- Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged micePubMed
- Thymosin β4: a multi-functional regenerative peptide. Basic properties and clinical applicationsReview
- Thymosin beta4: actin-sequestering protein moonlights to repair injured tissuesReview