TB-500: uses, evidence and status | Inside Your Peptides

compound file

The answer, first. A seven-residue acetylated fragment of thymosin beta-4, residues 17 to 23, sold since the late 2000s as an injectable for injury repair. The strongest evidence is for venous ulcer closure, graded C — small or open-label human only.

Topical full-length thymosin beta-4, 73 patients randomised across eight European sites: complete healing within three months in about 25% at the best-performing dose ⁴.

Dose-escalation, never replicated. The rest of what it is sold for — tendon repair, skin wound healing, muscle repair — grade D or E: animal or mechanism data with no controlled human outcome.

What it is used for

Every use graded on its own evidence, not the compound as a whole. 6 outcomes, ranked by what the human record supports.

#outcome · human · animal · gradewhat the best evidence actually shows

01Venous ulcer closure1 phase 2, n=73 · replicated rodent wound modelsgrade CTopical full-length thymosin beta-4, 73 patients randomised across eight European sites: complete healing within three months in about 25% at the best-performing dose ⁴. Dose-escalation, never replicated.

02Neurotrophic keratopathy1 phase 3, n=18 · corneal modelsgrade C0.1% thymosin beta-4 eye drops, randomised placebo-controlled double-masked: complete healing at four weeks in 6 of 10 versus 1 of 8 on placebo, P=0.0656 ⁵. Eighteen patients, primary endpoint missed.

03Severe dry eye1 phase 2, n=9 · corneal modelsgrade C0.1% eye drops six times daily: 35.1% less ocular discomfort and 59.1% less corneal fluorescein staining versus vehicle at day 56, P=0.0141 and P=0.0108 ⁶. Nine patients, eye drops only.

04Tendon repairno trial · 1 controlled rat studygrade DRat Achilles transection, TB-500 at 60 micrograms per kilogram daily for four weeks. Load to failure beat saline, P<0.05, with lower Bonar and Movin degeneration scores, n=8 per arm ³. No human trial.

05Skin wound healingno trial of the fragment · diabetic and aged micegrade DThe seven-residue fragment matched full-length thymosin beta-4 for wound contracture and collagen deposition in 26-month-old mice ². Every human wound trial dosed the full 43-residue protein, not the fragment.

06Muscle repairno trial · 1 six-month mouse study, null on functiongrade DSix months of thymosin beta-4 in dystrophic mice raised regenerating fibre counts but did not improve grip strength, cardiac shortening fraction or fibrosis ⁸. No human trial of either molecule.

gradewhat it means

ARegulatory approval, or multiple adequately-powered trials agreeing with each other

BAt least one well-powered human randomised trial, with the direction replicated

CSmall or open-label human trials only

DAnimal or mechanism data only, with no controlled human outcome

EA claim the human trials have already killed

How it works

The proposed mechanism, in three steps. A mechanism is a reason to run a trial, never a substitute for one.

1targetThymosin beta-4 sequesters G-actin. LKKTETQ is its central actin-binding site at residues 17 to 23, and TB-500 is that site alone ¹⁹.

2signalThat short sequence drives cell migration, angiogenesis and wound closure. The separate N-terminal Ac-SDKP site carries the anti-fibrotic activity ⁹.

3effectLaminin-5, matrix metalloproteinases and angiogenesis genes rise, and ILK and Akt signalling is activated. Mapped in cells and rodents ⁹.

What it does not do

Claims the current record does not support. Worth knowing before you set expectations.

not supported by the evidence

TB-500 is thymosin beta-4. It is residues 17 to 23 with an acetyl group on the front. Every human trial dosed the full 43-residue protein ¹.
Human trials prove TB-500 heals injury. No human has received the fragment in a published trial. FDA states it has identified no human exposure data at all ¹¹.
Injection is the route the studies used. Every positive human result came from eye drops or a topical gel. The intravenous work measured safety, not healing ⁵⁶⁷.
A WADA ban shows it works. S2.3 lists thymosin-beta-4 and its derivatives with TB-500 as the worked example. The list keys on structure, not on evidence ¹².

How it is used

What published protocols administered, and what the community reports doing. Descriptive on both counts, and never a recommendation.

routeReported subcutaneous, near the injury or systemically. Every published human study used eye drops, a topical gel, or intravenous infusion.

formatLyophilised powder in a vial, reconstituted with bacteriostatic water.

published dosesNo published study dosed the fragment in a human. Full-length thymosin beta-4 was given intravenously at 42 to 1260 mg daily for 14 days in a phase 1 ⁷. A dose-escalating venous ulcer trial applied it topically, where 0.03% performed best ⁴. Eye-drop trials used 0.1% ⁵⁶. The rat tendon study used 60 micrograms per kilogram daily ³.

human pharmacokineticsNo human pharmacokinetic data published for the fragment. Intravenous full-length thymosin beta-4 showed dose-proportional exposure and a half-life that lengthened with dose ⁷¹⁰.

reported conventionsAs reported on peptide forums and Reddit, 2015 to 2026: a front-loaded block of roughly 2 to 2.5 mg twice weekly. That block runs four to six weeks, then the same amount weekly or fortnightly. Subcutaneous, often near the injury, frequently alongside BPC-157. Convention, not guidance.

commonly paired withBPC-157

This site does not publish protocols to follow. The doses above are what studies administered or what users report, stated as facts about the literature and the market. How protocols are structured, mixing and storage and the reconstitution calculator cover the arithmetic.

What to expect

Where a trial measured it, the trial. Where only the community reports it, that is said out loud.

onsetNo trial has measured onset for the fragment. In the eye-drop trials full-length thymosin beta-4 separated from placebo on staining and comfort inside 28 days ⁵⁶. As reported for injected use: two to four weeks before anything is noticed. No trial measured that.

most common reportAs reported: less soreness at an old injury site after a few weeks. Many report nothing.

adverse effectsIntravenous full-length thymosin beta-4 up to 1260 mg daily for 14 days gave infrequent mild-to-moderate adverse events and no dose-limiting toxicity in 40 subjects ⁷. As reported for the fragment: injection-site redness, transient fatigue, a head-rush on dosing. FDA cites immunogenicity risk from aggregation and impurities ¹¹.

the stop signalAs reported: the end of the front-loaded block, or the injury settling. No published stopping rule exists, because no trial has run the fragment in a person.

Approval and status

What regulators and sport bodies have actually said, separately from what the evidence shows.

approvalNot approved anywhere. Full-length thymosin beta-4 reached phase 3 in ophthalmology and remains unapproved.

FDACategory 2 on FDA's compounding safety-risk list as thymosin beta-4, fragment [LKKTETQ], also known as TB-500, with no human exposure data identified ¹¹.

sport [WADA]Prohibited at all times. S2.3 growth factors, TB-500 named ¹².

sold asresearch chemical

Check the vial

The grade above describes a molecule studied under controlled conditions. It says nothing about the powder in a particular vial.

That gap is the one part of this market a reader can actually close. How to read a certificate of analysis covers the five measures in five minutes, and the 2026 audit grades vendors on the documents they publish against a rubric printed in full.

Questions we get

What is TB-500 used for?

It is sold for injury recovery, mostly tendon, ligament and muscle. The animal record for the fragment is one controlled rat Achilles study. Load to failure beat saline at four weeks, eight rats per arm.

The human trials people cite were run on full-length thymosin beta-4, in eye drops and topical gels, for corneal and ulcer healing. Nobody has tested the fragment in a person for anything.

How is TB-500 used?

Descriptively, and labelled as such. No published human protocol exists for the fragment. As reported on peptide forums between 2015 and 2026, the convention is a front-loaded block of roughly 2 to 2.5 mg twice weekly.

That block runs four to six weeks, then weekly or fortnightly. Injections are subcutaneous and often near the injury. The published human doses belong to a different molecule and different routes: intravenous, topical gel and eye drops.

How long does TB-500 take to work?

No trial has measured that for the fragment. In the eye-drop trials, full-length thymosin beta-4 separated from placebo on corneal staining and comfort within 28 days. Complete healing in neurotrophic keratopathy was assessed at four weeks.

Those numbers describe a drop in an eye, not an injection near a tendon. As reported, users describe two to four weeks before noticing anything, which no trial has checked.

Is TB-500 the same as thymosin beta-4?

No. Thymosin beta-4 is a 43-residue protein present in most human cells. TB-500 is a synthetic seven-residue piece of it, residues 17 to 23, with an acetyl group on the front.

An anti-doping laboratory synthesised that exact fragment out of a commercial TB-500 preparation in 2012 and characterised it. FDA names the substance on its list as thymosin beta-4, fragment [LKKTETQ]. The human trials all used the whole protein.

How do I know what is actually in a vial of TB-500?

You do not, unless a certificate of analysis for that specific lot says so. A certificate worth trusting covers five measures [identity, purity, measured net content, endotoxin and a microbial screen].

It names the lab that ran them, and carries an accession number you can verify with that lab. Most certificates on this market cover one to three of the five. Purity alone is one number and is not a quality programme.

References

Esposito S, et al. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500. Drug Test Anal. 2012. PMID 22962027
Philp D, et al. Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair Regen. 2003. PMID 12581423
Bicer O, et al. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats. Jt Dis Relat Surg. 2026. PMID 42542926
Guarnera G, DeRosa A, Camerini R. The effect of thymosin treatment of venous ulcers. Ann N Y Acad Sci. 2010. PMID 20536470
Sosne G, et al. 0.1% RGN-259 [Thymosin beta-4] ophthalmic solution in neurotrophic keratopathy: phase III trial. Int J Mol Sci. 2022. PMID 36613994
Sosne G, Dunn SP, Kim C. Thymosin beta-4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea. 2015. PMID 25826322
Ruff D, Crockford D, Girardi G, Zhang Y. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Ann N Y Acad Sci. 2010. PMID 20536472
Spurney CF, et al. Evaluation of skeletal and cardiac muscle function after chronic administration of thymosin beta-4 in the dystrophin deficient mouse. PLoS One. 2010. PMID 20126456
Sosne G, Qiu P, Goldstein AL, Wheater M. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB J. 2010. PMID 20179146
Wang X, et al. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin beta-4 in healthy Chinese volunteers. J Cell Mol Med. 2021. PMID 34346165
FDA. Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks. Content current as of 22 April 2026. fda.gov
World Anti-Doping Agency. The Prohibited List, section S2.3 Growth Factors and Growth Factor Modulators. wada-ama.org

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