TB-500 half-life: what do the studies show?

What is the half-life of TB-500?

The FDA's briefing document (memo dated 15 May 2026) reports that its search found no clinical study of TB-500's pharmacokinetics (what the body does to a compound over time) or pharmacodynamics (what a compound does in the body) by any route, so it gives no human half-life. The only plasma time course it cites is a 2012 study in thoroughbred geldings, in which plasma TB-500 peaked at 0.05 to 0.08 ng/mL between 60 and 120 minutes after treatment and became unquantifiable between 6 and 10 hours after it; the FDA summary gives no number of horses and no half-life, and the result describes one animal species (Ho et al., Journal of Chromatography A, 2012, as summarised by the FDA).

That time course is not a half-life. The FDA's summary of the horse study gives when levels peaked and when they fell below the quantifiable limit, and it gives no half-life. The FDA also says the study did not include the comparison needed to work out absolute bioavailability, the share of a compound that reaches the blood (FDA briefing document, memo dated 15 May 2026).

The horse study used a veterinary preparation sold as TB-500, and its aim was anti-doping detection. The authors built a method that found N-acetylated LKKTETQ in horse urine at 0.01 ng/mL and in horse plasma at 0.02 ng/mL, a detection limit for horse samples that says nothing about how long the peptide persists in people (Ho et al., 2012). The TB-500 research guide gathers the published studies in one place.

Evidence limits

What has not been measured about TB-500 in the body?

A search of the FDA's adverse event database through 26 March 2025 retrieved no reports for TB-500, and the FDA notes that such data have limits, so the empty result does not show safety or clearance (FDA briefing document, memo dated 15 May 2026). The FDA's search also did not find published case reports of TB-500 in people.

What does the body do to TB-500?

In horse liver tissue tested in the laboratory, TB-500 was cut into shorter pieces, called metabolites: N-acetylated LKKTET, LKKTE, LKKT, LKK and LK, a result that does not show what happens inside a living horse or a person (Ho et al., Journal of Chromatography A, 2012, as summarised by the FDA). Shortened pieces were also found in plasma and urine from horses treated with TB-500, a result in horses (number not stated in the FDA summary) that does not describe people (Ho et al., 2012, as summarised by the FDA).

In urine from treated rats (number not stated in the abstract), Ac-LK was the breakdown product at the highest concentration over the first 0 to 6 hours and Ac-LKK was detected up to 72 hours, detection windows for breakdown products in one species that are not the half-life of TB-500 and do not establish a result in people (Rahaman et al., Journal of Chromatography B, 2024).

In a laboratory comparison, human kidney and liver preparations showed high metabolic activity against TB-500 and human serum produced fewer breakdown products (number of preparations not stated in the abstract), a dish result that does not show how fast a body clears TB-500 or establish a result in people (Zvereva et al., Journal of Proteomics, 2016). Kidney microsomes are small particles of kidney cell membrane that carry its enzymes. They show how a peptide can be broken down, not how fast a body clears it.

In cultured fibroblasts with scratch wounds, one breakdown product, Ac-LKKTE, was the only one with significant wound-closure activity compared with control, while the parent TB-500 did not show significant activity in the same test; that is a cell result and it does not establish an effect in any animal or person (Rahaman et al., 2024).

How long did studies take to measure an effect of TB-500?

The FDA's briefing document (memo dated 15 May 2026) reports that its literature search found no article in which TB-500 was given to humans, and no human study was found in the sources opened for this page on 14 October 2026, so this page reports no timed effect of TB-500 in people. The time points reported on this page come from animals and cells, and they show when researchers measured, not when an effect starts. In a rat Achilles tendon study of 32 rats, outcomes were measured at four weeks, a measurement point in one animal model that does not describe people (Biçer et al., Joint Diseases and Related Surgery, 2026). In cultured fibroblasts (number of cultures not stated in the FDA summary), wound closure after 8 hours with TB-500 was not significantly different from vehicle, a cell result that does not establish an effect in any animal or person (Rahaman et al., Journal of Chromatography B, 2024, as summarised by the FDA).

In 32 male rats, eight per group, after Achilles tendon transection and repair, maximum load to failure at four weeks (measured on four tendons per group) was higher in the group treated with TB-500 than in controls and reached statistical significance (p < 0.05), in what the authors call an exploratory study that does not establish a result in people; the paper labels its test substance synthetic thymosin beta-4 (TB-500) without stating a sequence, and the study did not measure how quickly any change began (Biçer et al., 2026).

A 2003 mouse study used the non-acetylated fragment LKKTETQ, not TB-500, and checked wounds at day 7 in aged mice (number not stated in the FDA summary), so its result cannot be moved across to TB-500 (Philp et al., Wound Repair and Regeneration, 2003, as summarised by the FDA). The FDA warns that acetylation changes a peptide's charge, size and binding. The FDA also found websites that market TB-500 for many conditions and found no human article behind those claims (FDA briefing document, memo dated 15 May 2026).

What is known about thymosin beta-4's half-life in people?

Full-length thymosin beta-4 has been measured in healthy volunteers. In the first part of a 2021 first-in-human trial of recombinant human thymosin beta-4 in 54 healthy Chinese volunteers (44 treated, 10 placebo), peak times ranged from 3 to 15 minutes and half-lives from 0.5 to 2.08 hours across the six cohorts with pharmacokinetic sampling, in a trial sponsored by the product's maker that tested safety and blood levels and gave no TB-500 (Wang et al., Journal of Cellular and Molecular Medicine, 2021). Thymosin beta-4 is the 43-amino-acid parent protein, and the trial's product was a 44-amino-acid recombinant version, not TB-500, so those numbers describe a different molecule.

The 2021 trial had a second part of 30 healthy volunteers (24 treated, 6 placebo), and every volunteer was followed for 28 days. In the two healthy-volunteer parts of that trial of recombinant thymosin beta-4 (54 and 30 volunteers), the authors reported adverse events that were mild to moderate and no serious adverse events, in a sponsor-run trial of healthy Chinese adults that did not test TB-500 (Wang et al., 2021). In the second part (30 volunteers, 24 of them treated), the authors reported no obvious accumulation of recombinant thymosin beta-4, a healthy-volunteer result for a different molecule that does not describe TB-500 (Wang et al., 2021). An earlier randomised trial in four groups of 10 healthy volunteers reported that blood levels rose in proportion to the amount given and that half-life rose with the amount, with a synthetic form of full-length thymosin beta-4, not TB-500; its abstract gives no single half-life value (Ruff et al., Annals of the New York Academy of Sciences, 2010).

A shorter, acetylated fragment need not behave like its parent protein. The TB-500 and thymosin beta-4 page sets the two side by side.

Is research-use TB-500 the same material the studies measured?

The studies opened for this page did not measure the contents of any catalogue vial. The horse study used a veterinary preparation sold as TB-500 (Ho et al., Journal of Chromatography A, 2012). The FDA's briefing document (memo dated 15 May 2026) says it found several salts and derivatives sold under the TB-500 name, that the free base and the acetate salt are different bulk drug substances, and that inconsistent naming leaves a reference standard hard to match to a product. Research material is not a medicine and is not for human or animal use.

The catalogue lists TB-500 reference material as laboratory stock. Reading its paperwork is a skill of its own; the peptide quality and verification hub explains what a certificate records and what it cannot show. The Australian status of TB-500 is a separate question from any measurement on this page.