TB-500

What it is

TB-500 is a synthetic peptide of seven amino acids: residues 17 to 23 of the natural protein thymosin beta-4, with an acetyl group on the first amino acid (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln) [1]. It is not the same thing as thymosin beta-4, which is a 43-amino-acid protein found in blood, tears and wound fluid [1]. FDA notes that many websites use the two names interchangeably, but they are different substances [1]. Full-length thymosin beta-4 has been through human trials, including an intravenous study in healthy volunteers and eye-drop trials for corneal disease; the seven-amino-acid fragment has not [7][8][1]. “TB-500” is a common name, not a United States Adopted Name, and FDA has found multiple salts and derivatives sold under it [1]. There is no USP or NF monograph for it and it is not part of any approved drug [1].

How it works

The proposed mechanism is borrowed from the parent protein. The LKKTETQ sequence contains the segment of thymosin beta-4 that binds monomeric actin, and researchers have hypothesised that this binding underlies effects on cell migration and wound healing seen with the full protein [1]. In an old-mouse study, topical non-acetylated LKKTETQ increased wound closure and collagen, but FDA cautions that this cannot be extrapolated directly to the acetylated TB-500 [1]. In an in-vitro scratch-wound test, TB-500 free base at 50 µg/mL did not speed closure of fibroblast wounds, though one of its metabolites did slightly [1]. FDA concluded that “nonclinical pharmacological evidence is currently lacking to support the potential for TB-500 to promote wound healing” [1]. In horse liver preparations the peptide is trimmed one amino acid at a time from its C-terminal end [1].

What the evidence shows

There are no human studies of TB-500. FDA’s 2026 review states that the nominator did not provide, and FDA did not find, any information on TB-500 administered to humans, and that no clinical studies or human exposure data exist for any route [1]. FDA therefore concluded there is “a lack of evidence to evaluate the effectiveness” of TB-500 for the nominated use, wound healing [1]. The human data that do exist concern full-length thymosin beta-4, a different molecule. In a 2010 study, 40 healthy volunteers received single and then 14 daily intravenous doses of synthetic thymosin beta-4 (42–1260 mg) with infrequent, mild-to-moderate adverse events and no serious adverse events [7]. A small phase III trial of 0.1% thymosin beta-4 eye drops (RGN-259) in 18 people with neurotrophic keratopathy reported a healing trend that missed statistical significance at four weeks [8]. A planned phase 2 trial of injectable thymosin beta-4 after heart attack was withdrawn before enrolling anyone [9].

Regulatory status

Not an FDA-approved drug. On Jul 23–24 2026 the FDA Pharmacy Compounding Advisory Committee voted to recommend adding it to the 503A bulk drug substances list; FDA has not finalized that listing (as of Sep 24 2026). FDA brought both the free base and the acetate to the committee for the use of wound healing [11][2]; the vote was 8 in favour, 6 against, with 1 abstention, against FDA staff’s proposal that the criteria weigh against listing [4][1]. The votes are recommendations; FDA must complete rulemaking before any listing, possibly in 2027 or later, and a listing is not FDA approval [3][4]. In September 2023 FDA had put “Thymosin beta-4, fragment (LKKTETQ), also known as TB-500” into 503A Category 2, citing immunogenicity and no human exposure data; it was removed in April 2026 after the nomination was withdrawn [5][6]. The World Anti-Doping Agency lists “Thymosin-β4 and its derivatives e.g. TB-500” as prohibited at all times [10].

Half-life and what it means for a level curve

STACK has no reference half-life for this compound because no human value has been published; you can enter your own estimate. FDA did not identify any clinical study measuring TB-500 pharmacokinetics in humans by any route [1]. The only in-vivo data come from thoroughbred geldings: after a 10 mg subcutaneous dose, plasma levels peaked at 0.05–0.08 ng/mL between 60 and 120 minutes and were unquantifiable by 6 to 10 hours [1]. No intravenous arm was run, so bioavailability is unknown [1]. Note also that the intravenous half-life reported for full-length thymosin beta-4 in people rose with dose and belongs to a different molecule, so it should not be used for TB-500 [7]. If the horse pattern held in humans, an estimated level would rise over the first hour or two and fall to nothing the same day, with no build-up between doses. STACK’s curve is an estimate from this published half-life, not a blood level.

Reported side effects

There is no human safety data for TB-500 at all. FDA states that potential safety risks in humans “are unknown” because no clinical studies or exposure data exist [1]. A search of FDA’s adverse event reporting system through March 26 2025 retrieved no reports for TB-500, and the published literature contained no case reports [1]. FDA’s Human Foods Program had two complaint reports about “blended TB-500 and BPC-157” products, but they included no safety assessment [1]. FDA’s separate BPC-157 review describes one person who developed diffuse skin darkening and gum darkening after a combined BPC-157 and TB-500 product, which recurred on rechallenge; the two-peptide product made it impossible to tell which substance was responsible [6]. FDA’s main stated concern is immunogenicity: an injected seven-amino-acid peptide with possible aggregates and impurities may provoke immune responses ranging from harmless antibodies to severe reactions, and no study has looked [1]. Report any injection-site reaction or new symptom to your prescriber.

Storage and handling

There is no approved label, so the label from the pharmacy that dispensed your product governs. FDA’s review reports that TB-500 free base is stable when stored below −20 °C in sealed containers away from moisture and light, and that the acetate salt is reported stable below −15 °C in a tightly closed container protected from light [1]. FDA also notes that peptide stability, activity and immunogenic properties are highly sensitive to manufacturing process and handling, so a product’s behaviour after mixing is not predictable from the raw material [1]. Practically: store unopened vials as your pharmacy states, keep them out of light, and do not use a vial that looks cloudy. If your product is a powder that needs mixing, STACK’s reconstitution calculator turns the label’s numbers into a concentration and volume; it never suggests a dose.

What STACK tracks for it

STACK logs each TB-500 dose as your prescriber wrote it, with the date, time, route and injection site. Because no human half-life exists, STACK draws no estimated level curve unless you supply your own estimate, and it labels that curve as user-entered [1]. You can log the injury or wound your prescriber is treating and rate pain, function or healing over time, since there is no trial evidence to compare against [1]. Side-effect logging covers injection-site reactions, skin changes and anything new, the gaps FDA identified in its safety review [1]. STACK tracks vial inventory and mixing dates. If TB-500 is used alongside BPC-157, each compound is logged separately, which matters because FDA’s adverse event reports involved combined products and could not tell them apart [6].

The reference half-life in STACK

STACK ships TB-500 without a default half-life: No human value; only a horse study, levels gone by 6–10 h. You enter your own estimate before a curve is drawn. Measured in: Thoroughbred geldings, subcutaneous; no human pharmacokinetics published for the fragment.

Estimate only. Modelled from the published half-life you selected and the doses you logged — not a measured blood level. Do not use it to make medication decisions.

Free tools for TB-500

Read next

Sources

Every URL below was fetched and checked on 2026-09-24. Bracketed numbers in the text link here.

1. FDAFDA Briefing Document for TB-500-Related Bulk Drug Substances (TB-500 (free base) and TB-500 acetate), Pharmacy Compounding Advisory Committee, July 23–24 2026
2. FDAJuly 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee
3. OtherFDA advisory committee backs two more peptides, rejects one for compounding list (RAPS, Jul 27 2026)
4. OtherBulk List Bound: PCAC backs majority of peptides in two-day public meeting (McDermott Will & Schulte)
5. OtherFDA Announces Removal of 12 Peptides from Category 2 and Schedules PCAC Meetings (Orrick, Apr 16 2026)
6. FDACertain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks
7. TrialA randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers (Ruff et al., Ann N Y Acad Sci 2010)
8. Trial0.1% RGN-259 (Thymosin ß4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial (Sosne et al., Int J Mol Sci 2023)
9. TrialNCT01311518 — Study of the Safety and Efficacy of RGN-352 in Subjects With an Acute ST Elevation Myocardial Infarction
10. OtherThe Prohibited List — World Anti-Doping Agency
11. FDAFDA Briefing Document, Pharmacy Compounding Advisory Committee Meeting, July 23–24 2026 (introduction)