A 7-amino-acid piece of thymosin beta-4 sold for injury recovery. No completed human study has tested it; a small heart trial began in 2026.
Also called Ac-LKKTETQ, Thymosin beta-4 fragment 17-23, Thymosin Beta-4, Fragment (LKKTETQ), TB4 fragment
TB-500 is a short synthetic peptide, Ac-LKKTETQ: amino acids 17 through 23 of thymosin beta-4 with an acetyl group on the front. Thymosin beta-4 itself is a 43-amino-acid protein found in nearly every human cell, where it holds onto actin, the protein cells use to change shape and crawl. The 17-23 stretch is the part that grips actin. Vendors and many websites use 'TB-500' and 'thymosin beta-4' as if they were the same thing. They are not, and some vials sold as TB-500 contain the full protein instead.
Almost all the research people quote for TB-500 was done on full-length thymosin beta-4. That protein has real human trial data: a 40-person IV safety study, topical gel trials in leg ulcers, and eye-drop trials in dry eye, with mixed results. The fragment has none. FDA reviewers searched in 2026 and found no study of TB-500 in humans for any purpose. One 2024 cell study found TB-500 itself did nothing for wound closure, while one of its breakdown products did.
TB-500 is not approved anywhere. WADA names it under S2 growth factors, banned at all times. It first drew attention as a veterinary product used to dope racehorses and greyhounds around 2011. In July 2026 an FDA advisory panel voted 8 to 6 to recommend allowing pharmacies to compound it for wound healing, against FDA staff advice; FDA had not acted on that vote as of October 2026.
What it binds to, and what happens inside the body after that, step by step.
The LKKTET stretch inside thymosin beta-4 is its actin-binding site. Full-length thymosin beta-4 holds single actin units in reserve so cells can build filaments quickly when they need to move, which is how it is thought to speed cell migration into wounds and new blood vessel growth. Whether the short acetylated TB-500 fragment does the same in a living body has not been shown.
Human results and animal results are kept apart below. A result in rats tells you a mechanism is plausible. It does not tell you what happens in a person.
There are no published human studies of TB-500. FDA reviewers in 2026 found no clinical or nonclinical toxicity data and no animal study showing the acetylated fragment heals wounds. The human trials people cite were done with full-length thymosin beta-4 as IV infusions, skin gel or eye drops, and those show good tolerability but only modest or inconsistent benefits.
72 adults with moderate to severe dry eye
Both primary endpoints missed; discomfort during a dry-air challenge on day 28 was 27% lower than placebo, a secondary endpoint. No adverse events.
Read the study73 patients with venous leg ulcers at 8 European sites
Safety was comparable to placebo. Efficacy was only suggestive: the authors said the 0.03% gel may speed healing, with about 25% of patients fully healed within 3 months, mostly those with smaller ulcers.
Read the study40 healthy adults in 4 dose cohorts, 14 days of daily IV dosing
No dose-limiting toxicity or serious adverse events with full-length thymosin beta-4; half-life increased with dose.
Read the studyHuman serum, human and rat enzyme systems, rats, cultured fibroblasts
TB-500 itself did not speed scratch-wound closure in fibroblasts; only its breakdown product Ac-LKKTE did. Ac-LKK was detectable in rat urine up to 72 hours.
Read the studyDiabetic db/db mice and 26-month-old aged mice, punch wounds
Full-length thymosin beta-4 increased wound contraction and collagen in both groups of mice; non-acetylated LKKTETQ matched it in aged mice. Neither is the acetylated TB-500 molecule.
Read the studyThoroughbred geldings given a subcutaneous dose
Plasma TB-500 peaked 1 to 2 hours after injection and was unquantifiable by 6 to 10 hours; breakdown fragments appeared in urine.
Read the studyThese are questions the published research has not answered.
No product containing TB-500 is approved as a medicine by the FDA.
No regulator has approved TB-500 or full-length thymosin beta-4. EMA lists no authorized product. WADA names 'Thymosin-beta-4 and its derivatives e.g. TB-500' under S2 (peptide hormones, growth factors), banned in and out of competition. A small industry-sponsored phase 1/2 trial of TB-500 in stable cardiovascular disease (80 people, sites in China) was registered and recruiting in 2026; no results exist.
No human half-life has been published for TB-500, so we do not draw a clearance curve. Half-lives quoted online for it are usually estimates from animal data.
No human study or approved label has published a dose for TB-500, so there is no table to show.
No dose of TB-500 has been tested in a published human study or approved on a label. Numbers that circulate online come from animal studies scaled up by guesswork or from sellers. We do not reproduce them.
Which symptoms are expected and which mean stop and get help: side effects and red flags.
Tap a claim to see what the studies found.
TB-500 is a 7-amino-acid acetylated fragment; thymosin beta-4 is a 43-amino-acid protein. FDA's 2026 review states plainly they are not the same substance, and results from one cannot be transferred to the other.
The trials people cite used full-length thymosin beta-4 as eye drops, skin gel or IV infusion. No trial has given TB-500 to people.
The heart findings come from mice given full-length thymosin beta-4. A human IV safety study was run with heart attack in mind, but no efficacy trial followed, and TB-500 was never part of it.
The acetylated 17-23 fragment is not a known natural circulating peptide, and acetylation changes how a peptide behaves. FDA found no toxicity studies of TB-500.
Mice engineered to overproduce full-length thymosin beta-4 grew hair faster. No human study of either thymosin beta-4 or TB-500 has tested hair growth.
These pairings come up often. Almost none have been tested together in a trial, and the evidence note on each says so plainly.
Sold for tendon, ligament and joint injuries on the theory that TB-500 helps cells migrate while BPC-157 drives local blood vessel growth.
EvidenceNo controlled study has tested the combination. One uncontrolled knee survey gave a BPC-157 and thymosin beta-4 combination to 4 people, and it is unclear whether that was TB-500 or the full protein. An FDA report links a research-label blend to skin and gum darkening.
No published stability data for TB-500. Pharmacy practice for lyophilized peptides is frozen or refrigerated storage, dry and away from light.
No published stability data. Peptide solutions are generally refrigerated at 2 to 8 C; in a lab study, small amounts of TB-500 broke down into shorter fragments even without liver enzymes present.
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