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TB-500

aka Thymosin beta-4, Tbeta4, TB4, Ac-LKKTETQ, fequesetide, RGN-137, RGN-259

Tissue RepairTissue RepairInjury RecoveryCardiac RecoveryCorneal InjuryHair GrowthWound ClosureActin-bindingAngiogenesisAnti-inflammatoryMusculoskeletalSkin Repair

Last reviewed April 27, 2026 by Doserr editorial team · 21 references on this page

Information on this page is sourced from published research and is for educational purposes only. It does not constitute medical advice.

TL;DR

  • What it is: A synthetic peptide fragment of thymosin beta-4, a naturally occurring actin-binding protein found in most mammalian cells.
  • What it's used for: Most studied for tissue repair, cardiac recovery, and corneal injury in animal models, human trials are topical only.
  • Evidence level:limitedLimited -- no controlled human trials for injectable use published.

Dose at a glance

BeginnerCommonHigher end
Per dose500 mcg - 1 mg2-4 mg4-5 mg
Daily total500 mcg - 1 mg (every 2-3 days)4-8 mg/week split across 2 injections8-10 mg/week split across 2 injections
ScheduleEvery 2-3 days2x weekly2x weekly
Cycle length4-6 weeks4-6 weeks loading, then 2 mg/week maintenance8-12 weeks

Synthesized from community-reported ranges. Not a recommendation. Route varies by compound — see Common route in What people report below.

Half-life
Not characterized for subcutaneous injection in humans. In mice given 400 mcg IP, serum levels were elevated for approximately 40 minutes with rapid renal clearance (PMID: 9226473). A community-cited value of 2-3 hours is extrapolated from rodent data and has not been confirmed in a human pharmacokinetic study. The published human IV trial (PMID: 20536472) showed dose-proportional pharmacokinetics at very large doses (42-1,260 mg) but did not report a specific terminal half-life.
Typical dose range
Doses below are from published research, not recommendations. Rodent studies: 400 mcg IP single dose (biodistribution), 1.6 mg/kg/day IP via osmotic minipump (cardiac MI model). Human IV pharmacokinetics trial: 42, 140, 420, or 1,260 mg single IV dose, then daily for 14 days (PMID: 20536472). Human topical wound trials: 0.01%, 0.03%, or 0.1% topical gel once daily for up to 84 days. Human ophthalmic trials: 0.1% RGN-259 eye drops 6 times daily for 28 days (PMID: 25826322). No dose-ranging human trial exists for subcutaneous or intramuscular injection.
Route
Intraperitoneal (IP) in rodent efficacy studies, intravenous in human pharmacokinetics and cardiac safety trials, topical gel in human dermal wound trials, topical ophthalmic drops in human corneal and dry eye trials. Subcutaneous injection is the route most commonly reported in self-reported community use, this route has not been studied in controlled human trials.
Evidence tier
limited

Animal or in-vitro studies only — no published human efficacy data.

What the research shows

Each topic links to the studies behind it. Click a topic to expand.

What we don't know yet

  1. No controlled human efficacy data exist for injectable use, the clinical trial program has focused on topical formulations only
  2. Human pharmacokinetics after subcutaneous or intramuscular injection are not characterized, community-cited half-life values are extrapolated from rodent data
  3. Most products sold as 'TB-500' are full-length Tbeta4 (CAS 77591-33-4), not the 7-amino-acid Ac-LKKTETQ fragment (CAS 885340-08-9), whether the fragment recapitulates the full protein's biological activity is unestablished
  4. Long-term safety in injectable human use is unknown, preclinical work has raised questions about Tbeta4 expression in certain cancer cell lines
  5. TB-500 and Tbeta4 are prohibited by WADA and major equine sport authorities, detection windows in humans have not been formally published

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