Peptide Protocol IQ
Unapproved research chemicalNo human evidenceProhibited in sport

TB-500 / Thymosin beta-4

Also referred to as TB4, Tβ4 fragment

Frequently marketed as interchangeable with thymosin beta-4. It is not. TB-500 is a fragment, and most of the research concerns the full-length protein.

Molecule class
Actin-sequestering peptide (TB-500 is a fragment, not the full protein)
Category
Repair
Last evidence review
2026-08-24
Compare this compoundCheck interactionsSolution calculator
2
Human studies
1
Animal / in vitro
1
Graded claims
156
Participants

Derived from qualifying human evidence

  • Most commonly studied duration: 2 weeks. Most frequently reported duration among 2 qualifying human studies with a stated duration.
  • Longest qualifying human study: 4 weeks. Longest duration among qualifying human studies with a stated duration.

These figures are computed from the study records shown below. Records without a verified source identifier are excluded from the calculation.

Mechanism

What is being studied

Thymosin beta-4 sequesters G-actin and has been studied for effects on cell migration, angiogenesis, and inflammation in repair models.

Evidence

Claims, graded individually

Each statement below carries its own evidence level, its own confidence rating, and its own account of what remains unestablished. A compound does not have a single grade.

Musculoskeletal Recovery Research

DPreclinicalLow confidenceNo human evidence

Thymosin beta-4 has been reported to influence repair endpoints in animal models, and small human trials exist for topical dermal and ophthalmic formulations.

What is not established

The commercially sold fragment is not the researched full-length protein. Systemic human use is not studied.

Supporting sources (3)
Pharmacokinetic studyHuman Identifier verified

First-in-human study of recombinant human thymosin beta-4: safety, tolerability and pharmacokinetics

Multiple · Journal of Cellular and Molecular Medicine · 2021 · n = 84

Population
Healthy Chinese adult volunteers
Endpoint
Safety, tolerability and pharmacokinetics
Route
Intravenous
Quantity as reported
Single ascending amounts of 0.05, 0.25, 0.5, 2.0, 5.0, 12.5 and 25.0 µg/kg; a multiple-dose phase used 0.5, 2.0 and 5.0 µg/kg once daily for 10 consecutive days
Frequency
Single, then once daily for 10 days
Duration
2 weeks

Result. Well tolerated across the range studied, with no dose-limiting toxicity reported.

Adverse events. No dose-limiting toxicity reported.

Limitations. Read the units carefully. This is µg/kg intravenous full-length thymosin beta-4, roughly 0.035 to 1.75 mg per administration for a 70 kg adult. The fragment sold as TB-500 is a different molecule and is injected subcutaneously at amounts many times larger. This record is the reason that comparison can be made at all.

PMID34346165DOI10.1111/jcmm.16693
Randomised controlled trialHuman Identifier verified

Thymosin beta-4 ophthalmic solution for dry eye: a randomised, placebo-controlled, phase 2 clinical trial

Sosne G, Ousler GW · Clinical Ophthalmology · 2015 · n = 72

Population
Adults with moderate to severe dry eye
Endpoint
Ocular discomfort and corneal fluorescein staining
Route
Topical ophthalmic
Quantity as reported
0.1% thymosin beta-4 ophthalmic solution
Frequency
As specified in the trial protocol
Duration
4 weeks

Result. Both primary endpoints were missed. Several secondary endpoints favoured treatment.

Adverse events. No significant safety signal reported over 28 days.

Limitations. A topical ophthalmic formulation. It carries no information about subcutaneous use for soft-tissue repair, which is what the compound is sold for.

PMID26056426DOI10.2147/OPTH.S80954
Animal studyAnimalNo verified identifier on file

Thymosin beta-4 in tissue repair and cardiac models

Multiple · Annals of the New York Academy of Sciences and related · 2012

Population
Rodent and porcine injury models; small human dermal-wound trials
Endpoint
Wound closure, cardiac repair, corneal healing
Route
Intravenous, intraperitoneal, and topical by model
Quantity as reported
Model-dependent; human topical trials used formulated concentrations
Frequency
Varies

Result. Positive findings in animal repair models. Human work is largely limited to topical dermal and ophthalmic formulations.

Adverse events. Not characterised for systemic use in humans.

Limitations. TB-500 as sold is a fragment and is not identical to full-length thymosin beta-4 used in much of the research. This distinction is frequently ignored.

Search PubMed for this literature →

Last evidence review: 2026-08-23

Human evidence

2 human studies catalogued

Human and non-human evidence are kept strictly separate. They are never pooled, averaged, or presented as a single body of support.

Pharmacokinetic studyHuman Identifier verified

First-in-human study of recombinant human thymosin beta-4: safety, tolerability and pharmacokinetics

Multiple · Journal of Cellular and Molecular Medicine · 2021 · n = 84

Population
Healthy Chinese adult volunteers
Endpoint
Safety, tolerability and pharmacokinetics
Route
Intravenous
Quantity as reported
Single ascending amounts of 0.05, 0.25, 0.5, 2.0, 5.0, 12.5 and 25.0 µg/kg; a multiple-dose phase used 0.5, 2.0 and 5.0 µg/kg once daily for 10 consecutive days
Frequency
Single, then once daily for 10 days
Duration
2 weeks

Result. Well tolerated across the range studied, with no dose-limiting toxicity reported.

Adverse events. No dose-limiting toxicity reported.

Limitations. Read the units carefully. This is µg/kg intravenous full-length thymosin beta-4, roughly 0.035 to 1.75 mg per administration for a 70 kg adult. The fragment sold as TB-500 is a different molecule and is injected subcutaneously at amounts many times larger. This record is the reason that comparison can be made at all.

PMID34346165DOI10.1111/jcmm.16693
Randomised controlled trialHuman Identifier verified

Thymosin beta-4 ophthalmic solution for dry eye: a randomised, placebo-controlled, phase 2 clinical trial

Sosne G, Ousler GW · Clinical Ophthalmology · 2015 · n = 72

Population
Adults with moderate to severe dry eye
Endpoint
Ocular discomfort and corneal fluorescein staining
Route
Topical ophthalmic
Quantity as reported
0.1% thymosin beta-4 ophthalmic solution
Frequency
As specified in the trial protocol
Duration
4 weeks

Result. Both primary endpoints were missed. Several secondary endpoints favoured treatment.

Adverse events. No significant safety signal reported over 28 days.

Limitations. A topical ophthalmic formulation. It carries no information about subcutaneous use for soft-tissue repair, which is what the compound is sold for.

PMID26056426DOI10.2147/OPTH.S80954

Preclinical evidence

Animal and in-vitro research

Kept separate deliberately. Most preclinical findings do not translate to humans, and animal quantities expressed per kilogram do not convert to human quantities by simple arithmetic.

Animal studyAnimalNo verified identifier on file

Thymosin beta-4 in tissue repair and cardiac models

Multiple · Annals of the New York Academy of Sciences and related · 2012

Population
Rodent and porcine injury models; small human dermal-wound trials
Endpoint
Wound closure, cardiac repair, corneal healing
Route
Intravenous, intraperitoneal, and topical by model
Quantity as reported
Model-dependent; human topical trials used formulated concentrations
Frequency
Varies

Result. Positive findings in animal repair models. Human work is largely limited to topical dermal and ophthalmic formulations.

Adverse events. Not characterised for systemic use in humans.

Limitations. TB-500 as sold is a fragment and is not identical to full-length thymosin beta-4 used in much of the research. This distinction is frequently ignored.

Search PubMed for this literature →

Pharmacology

Reported parameters

Half-life

Not characterised

Human pharmacokinetics for the marketed fragment are not adequately characterised.

Routes studied

  • Intravenous (research)
  • Topical (human dermal and ophthalmic trials)

Evidence from one route does not transfer to another. Topical, oral, and injected administration can produce entirely different exposure from the same quantity.

Regulatory status

Not approved for human use. Prohibited in sport. FDA removed thymosin beta-4 from the Category 2 list effective 22 April 2026, and the Pharmacy Compounding Advisory Committee voted favourably on 23-24 July 2026. Neither is an approval, and FDA has not acted on the committee's recommendation.

Storage as documented

No approved labelling exists.

Safety

Signals reported in the literature

This lists what has been reported. It is not a complete safety profile, and for several compounds in this catalogue no systematic safety surveillance exists at all.

  • Systemic human safety is not characterised
  • Theoretical concern regarding angiogenesis in the presence of undetected malignancy is raised in the literature and remains unresolved

Limitations

What the evidence cannot tell you

Given as much prominence as the findings, because for most compounds in this category it is the more important half.

  • The fragment sold commercially is not identical to the researched full-length protein
  • Human evidence is largely confined to topical dermal and ophthalmic formulations

Reference

Evidence grading key

AStrong

Multiple high-quality human trials, or strong systematic-review or meta-analytic evidence.

BModerate

Human controlled evidence exists, but replication or sample size is limited.

CPreliminary

Small human studies, observational evidence, or early-phase clinical work.

DPreclinical

Predominantly animal or in-vitro evidence. No adequate human outcome data.

EMechanistic

Biological plausibility or mechanistic reasoning without adequate outcome evidence.

XInsufficient / conflicting

Evidence is absent, irreconcilable, or too weak to support any directional statement.

Related

Other compounds studied in the same research areas

BPC-157

One of the most discussed compounds in this category and one of the least supported by human evidence. The published record is overwhelmingly animal work.