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US Peptide Guide

Last reviewed May 21, 2026·Editorial Board

TB-500 (Thymosin Beta-4 Fragment)

Also known as TB500, Thymosin beta-4 fragment, Tβ4 active fragment, LKKTETQ peptide

TB-500 is a synthetic 7-amino-acid peptide (Ac-LKKTETQ) corresponding to the actin-binding region of thymosin β4, a naturally-occurring 43-amino-acid protein studied for cell migration, angiogenesis, and tissue repair in animal models.[1]

Tier 4 — Animal Data OnlyCompounding: Category 1(2026-04-23)Not FDA-Approved
Class
Heptapeptide fragment
Parent peptide
Thymosin β4 (43 aa)
Sequence
Ac-LKKTETQ
Half-life
~2 hours (SC, est.)
Human RCTs
0 (fragment)
WADA status
Prohibited

What TB-500 actually is

TB-500 is not thymosin β4. It is a synthetic heptapeptide — seven amino acids, Ac-LKKTETQ — that corresponds to residues 17 to 23 of the full thymosin β4 sequence, the region identified as the actin-binding domain.[1] The marketing convention of using "TB-500" and "thymosin β4" interchangeably is pharmacologically incorrect: the full peptide is 43 amino acids and roughly six times the molecular weight of the fragment, and the two have different pharmacokinetics and likely different biological reach.

This distinction matters because most of the human clinical data marketed as TB-500 evidence comes from trials of the full-length thymosin β4 (developed as RGN-352 by RegeneRx for cardiac, dermal, and ocular indications), not from the LKKTETQ fragment that compounding pharmacies and gray-market suppliers sell.[2] No published randomized controlled trial has tested the TB-500 fragment specifically in humans.

Mechanism of action

Thymosin β4 binds monomeric G-actin in a 1:1 stoichiometric ratio, sequestering it and preventing polymerization into filamentous F-actin.[1] This maintains a reservoir of unpolymerized actin that cells can mobilize on demand for migration, division, and cytoskeletal reorganization. TB-500 contains the segment of thymosin β4 identified as responsible for this actin-binding activity.

Downstream effects observed in animal models include accelerated migration of fibroblasts, endothelial cells, and keratinocytes to wound sites; promotion of angiogenesis; and modulation of inflammatory signaling.[3] A 2012 review synthesizes the basic and translational research and identifies cell migration, angiogenesis, and anti-inflammatory activity as the three mechanistic pillars of the thymosin β4 literature.[4] Whether the seven-amino-acid TB-500 fragment reproduces all of these effects with equivalent potency, or only a subset, has not been established in controlled human studies.

What the evidence shows

We separate the evidence by study type because thymosin β4 marketing routinely combines full-peptide trial data with fragment animal data — and that produces a misleading picture of what has actually been tested.

Human randomized trials (TB-500 fragment specifically)
0 published trials

No published randomized controlled trial has tested the Ac-LKKTETQ fragment in humans. The fragment has not progressed through Phase 1 pharmacokinetic studies in any indication available in the published literature.

Sources:4
Human trials of full-length thymosin β4 (a different molecule)
2 Phase 2 trials, stasis and pressure ulcers

Two Phase 2 trials of full-length thymosin β4 (RGN-352) reported accelerated dermal healing in stasis ulcers and pressure ulcers by approximately one month in patients who healed. These trials used the 43 amino acid parent peptide, not the TB-500 fragment, and the data does not transfer directly to the fragment marketed as TB-500.

Sources:2
Animal data
50+ studies across multiple injury models

Animal studies — primarily rodent — have shown accelerated dermal wound closure, increased angiogenesis at injury sites, faster epithelial migration, and promotion of hair follicle development. Most of this work used full-length thymosin β4. A smaller subset specifically tested the LKKTETQ fragment with broadly similar but less extensively characterized results.

Sources:534

What experts say

We track positions from clinicians and researchers who have publicly evaluated TB-500 with attention to the underlying evidence. Quotes are paraphrased to their published positions; original sources are linked.

A
Andrew Huberman, PhDProfessor of Neurobiology, Stanford School of Medicine

Discusses TB-500 alongside thymosin β4 for tissue repair and recovery; notes that despite extensive animal data and widespread anecdotal use, conclusive human clinical trials of the fragment remain lacking.

P
Peter Attia, MDInternal medicine, longevity-focused practice

Categorizes TB-500 alongside BPC-157 in the lowest evidence tier of his peptide framework — biologically plausible based on animal data, but without the human evidence needed to recommend.

T
Taradaj et al.Peer-reviewed orthopaedic primer, JAAOS

Includes TB-500 in their review of injectable peptides used in orthopaedic contexts; concludes the human evidence base relies on extrapolation from animal studies and from trials of the full-length parent peptide rather than the fragment itself.

Marketed claims vs. published evidence

The gap between what TB-500 vendors and biohacking communities claim and what has actually been tested in humans is wider than for almost any peptide on the market — primarily because the marketing routinely substitutes thymosin β4 trial data for fragment evidence that does not exist.

Marketed claims
  • Heals tendon and ligament injuries in weeks
    anecdotal
  • Stacks with BPC-157 for synergistic recovery
    anecdotal
  • Repairs torn rotator cuffs and chronic injuries
    anecdotal
  • Regrows hair and reverses hair loss
    animal only
  • Reduces scarring after surgery
    animal only
Published evidence
  • Wound healing acceleration in rodent models[5]
    animal only
  • Angiogenesis and hair follicle activity (animal)[3]
    animal only
  • Phase 2 dermal healing — full thymosin β4, not fragment[2]
    human RCT
  • No published human TB-500 fragment RCT
    no data
  • No published human tendon repair data
    no data

Risks, side effects, and contraindications

The risk profile of TB-500 mirrors BPC-157 in structure but differs in detail: pharmacological risks inherent to the compound class, and supply chain risks specific to how most users obtain it.

Pharmacological. Thymosin β4 promotes angiogenesis — the formation of new blood vessels — through both VEGF-dependent and independent pathways.[3] As with BPC-157, this raises a theoretical concern about accelerating tumor vascularization in patients with active cancer or significant cancer history. Long-term human safety data for the TB-500 fragment specifically is not available because long-term human studies have not been conducted on the fragment. Reported side effects from animal studies and anecdotal human use include injection site reactions, transient fatigue, and headache.

Supply chain. Like other "research use only" peptides, a substantial portion of TB-500 in circulation reaches users through suppliers operating outside pharmaceutical quality controls. Gray-market peptide products in this category have documented issues with content variability, bacterial endotoxin contamination, and in some cases incorrect or substituted compounds.[9] Compounding pharmacies under USP 797/795 standards provide a substantially better quality assurance pathway, which is why the April 2026 Category 1 reclassification has clinical significance beyond the regulatory technicality.

Access and sourcing

The legal landscape for TB-500 changed in early 2026 in lockstep with BPC-157 and roughly a dozen other peptides.

In late 2023, the FDA placed TB-500 on its Category 2 restricted compounding list, blocking licensed 503A compounding pharmacies from preparing it for patients.[10] On February 27, 2026, HHS Secretary Robert F. Kennedy Jr. announced that approximately 14 of those peptides, including TB-500, would return to Category 1 status. The reclassification became effective April 23, 2026.[11]

Licensed 503A compounding pharmacies can again prepare TB-500 for individual patients with a valid, patient-specific prescription. The Pharmacy Compounding Advisory Committee will conduct a formal review at its July 23–24, 2026 meeting.[11] Category 1 status permits compounding while a substance remains under FDA evaluation; it is not FDA approval.[12]

WADA status. TB-500 is prohibited at all times under section S2 of the World Anti-Doping Agency Prohibited List (peptide hormones, growth factors, related substances). Athletes subject to WADA testing should treat use as a sanction risk regardless of dose or timing.[13]

We do not recommend specific vendors on this page. Vendor-related guidance lives in a separate, clearly-labeled section of this site, with a different editorial process and disclosure standards.

Frequently asked

BPC-157Thymosin alpha-1GHK-CuCompare BPC-157 vs TB-500comparisonRecovery peptides hubhub

References

  1. Sanders MC, Goldstein AL, Wang YL. Thymosin beta 4 (Fx peptide) is a potent regulator of actin polymerization in living cells. Proceedings of the National Academy of Sciences USA. 1992. PMID 1584803
  2. Treadwell T, Kleinman HK, Crockford D, Hardy MA, Guarnera GT, Goldstein AL. The regenerative peptide thymosin β4 accelerates the rate of dermal healing in preclinical animal models and in patients. Annals of the New York Academy of Sciences. 2012. PMID 23050815 Phase 2 trials are for full-length thymosin β4 (RGN-352), not the TB-500 fragment.
  3. Philp D, Goldstein AL, Kleinman HK. Thymosin beta4 promotes angiogenesis, wound healing, and hair follicle development. Mechanisms of Ageing and Development. 2004. PMID 15037013
  4. Goldstein AL, Hannappel E, Sosne G, Kleinman HK. Thymosin β4: a multi-functional regenerative peptide. Basic properties and clinical applications. Expert Opinion on Biological Therapy. 2012. PMID 22074294
  5. Malinda KM, Sidhu GS, Mani H, et al. Thymosin beta4 accelerates wound healing. Journal of Investigative Dermatology. 1999. PMID 10469335
  6. Huberman A. Benefits & risks of peptide therapeutics for physical & mental health. Huberman Lab. 2024. ↗ Source podcast
  7. Attia P. AMA #83: Peptides — evaluating the science, safety, and hype in a rapidly growing field. The Peter Attia Drive. 2026. ↗ Source podcast
  8. Author group, JAAOS. Injectable peptide therapy: a primer for orthopaedic and sports medicine physicians. Journal of the American Academy of Orthopaedic Surgeons. 2024. PMID 41476424
  9. Peptide Database editorial. FDA peptide reclassification 2026: which peptides are coming back. peptide-db.com. 2026. ↗ Source industry-analysis
  10. Beverly Hills Rejuvenation Center editorial. Potential FDA peptide reclassification 2026: what it means for patients. bhrcenter.com. 2026. ↗ Source industry-analysis
  11. Amanecia Health editorial. FDA peptide reclassification 2026. amaneciahealth.com. 2026. ↗ Source industry-analysis
  12. OpenLoop Health editorial. What peptides are becoming legal in 2026? openloophealth.com. 2026. ↗ Source industry-analysis
  13. World Anti-Doping Agency. The 2026 Prohibited List — S2 Peptide Hormones, Growth Factors, Related Substances and Mimetics. wada-ama.org. 2026. ↗ Source wada
Revision history
  • 2026-05-21Page first published. Reflects April 23, 2026 Category 1 reclassification and the editorial distinction between TB-500 fragment and full-length thymosin β4.