Endogenous 43-amino-acid actin-sequestering peptide
Thymosin beta-4 is a naturally occurring 43-amino-acid peptide involved in actin regulation. Several investigational formulations have reached human studies, but results are early, route- and condition-specific, and do not apply to the seven-amino-acid TB-500 fragment.
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Depth and confidence summarize the research record—not effectiveness, safety, or a recommendation.
Controlled human studies exist for full-length synthetic or recombinant products, but they remain small, formulation-specific, and outcome-limited.
Research depth describes how large and mature the overall record is. It does not tell you whether the results were positive.
IV exposure and short-term tolerability are documented; clinical benefit remains preliminary, mixed, or confined to very small studies.
Confidence describes how reliable and consistent the conclusions are. It can be high for one outcome and low for another.
The strongest evidence type shows what the best-supported conclusions are actually based on.
Human findings are more directly relevant than animal or laboratory results, but they still apply only to the populations and outcomes studied.
Route-specific record
These are exposures used in cited research for a specific route and population—not a suggested amount.
Half-life describes how long it takes the measured amount in the body to fall by half. It is not a dosing recommendation.
Evidence can change by administration method. Findings from one route should not automatically be applied to another.
Evidence boundary: The products, manufacturing methods, concentrations, and clinical contexts differ. Full-length IV findings do not establish SubQ use and do not apply to TB-500. Amounts shown describe cited research exposure—not a dosage recommendation.
Practical starting point
Common goals and questions—not recommendations or promises of benefit.
The overview, studies, and source ledger below explain what supports each label—and where the evidence stops.
The short version
Thymosin beta-4 is a naturally occurring 43-amino-acid peptide involved in actin regulation. Several investigational formulations have reached human studies, but results are early, route- and condition-specific, and do not apply to the seven-amino-acid TB-500 fragment.
Includes IV Phase 1 studies, a nine-patient Phase 2 ophthalmic trial, a 2025 randomized STEMI report, wound-healing literature, FDA's 2026 identity review, and the 2026 WADA list.
What the evidence says
Multiple controlled studies exist, but each is limited: short Phase 1 IV safety studies, a nine-patient ophthalmic Phase 2 trial, and a 96-person STEMI trial with a timing-dependent subgroup result but no significant overall infarct-area difference.
This is the strongest supported conclusion in the current human evidence—not a summary of every claim made about the compound.
Which formulation-specific findings replicate in larger trials, long-term safety, whether any benefit generalizes beyond the studied route and condition, and how investigational products differ.
Keeping the main uncertainty visible prevents an early or promising finding from looking more settled than it is.
The evidence story
Importance shows how much an item changes the evidence story. Quality shows how much confidence the design deserves. A strong negative study can score highly on both.
Importance and quality answer different questions. A rigorous study can be highly important even when it challenges a popular claim.
The overall infarct-area difference was not significant. A reported subgroup first treated within eight hours after PCI showed a smaller infarcted area at 90 days.
Reported adverse events were mild to moderate, with no dose-limiting toxicity or serious adverse events. Exposure increased with dose and no obvious accumulation was reported.
The small trial reported improvements in discomfort and corneal staining at several time points, including day 56.
Adverse events were infrequent and mild or moderate, with no dose-limiting toxicities or serious adverse events reported during the short study. Exposure increased with dose.
Administration and handling
Human studies used protocol-defined intravenous synthetic or recombinant thymosin beta-4, topical RGN-259 eye drops, and other condition-specific formulations. These trial arms are not consumer dosing guidance and do not establish injectable use outside research.
No FDA-approved thymosin beta-4 product label, consumer reconstitution procedure, or universal storage instruction was located. Handling must remain tied to the exact investigational formulation; instructions should not be transferred between TB-500, RGN-259, NL005, or another product.
Primary-source ledger
2026-07-21
2026-01-01
2025-12-31 · PMID 41229390 · NCT05485818 · DOI 10.1093/cvr/cvaf223
2021-08-02 · PMID 34346165 · DOI 10.1111/jcmm.16693
2015-05-01 · PMID 25826322 · NCT01393132 · DOI 10.1097/ICO.0000000000000379
2012-10-01 · PMID 23050815 · DOI 10.1111/j.1749-6632.2012.06717.x
2010-04-01 · PMID 20536472 · DOI 10.1111/j.1749-6632.2010.05474.x