TB-500 is sold with thymosin beta-4's biology and none of its trials. The hyphen is not load-bearing: TB500 and TB-500 are written for the same fragment. The fragment itself, Ac-LKKTETQ, has no human study, and the paper that worked out how to detect it in urine says its biological effects have not been documented. So every dose figure for TB-500 is a convention, and the trials people cite for it used a different molecule at doses hundreds of times larger, intravenously, for the heart and the eye. This page keeps the two apart and reports both. It does not recommend anything. Our guide to reading a dosing claim sets out what separates a label figure from a convention. How brands appear on this site is set out on our disclosure page.
What it is, and its status
TB-500 is "Ac-LKKTETQ, derived from the active site of thymosin β4", a synthetic acetylated seven-residue peptide; "the biological effects of TB-500, however, have not been documented" (Rahaman et al., Journal of Chromatography B 2024). PubMed lists no human trial of it (search on 2026-09-05: TB-500 AND humans returned reviews and doping-detection papers only). It is named as the example under "Thymosin-β4 and its derivatives e.g. TB-500" in S2.3 of the 2026 WADA Prohibited List, prohibited at all times, and appears by name on the NCAA's 2026-27 banned classes. On 2026-07-23 FDA's Pharmacy Compounding Advisory Committee voted 8 to 6 to recommend TB-500 for the 503A bulks list, against FDA staff's position; the vote is advisory and FDA has not acted. MuscleLedger's Wolverine-stack page counts the human evidence for TB-500 and BPC-157 together; on the registry side, what a peptide stack actually is records that the pairing has never been registered as a combination anywhere. Another short peptide fragment cut from a larger parent molecule, the alpha-MSH tripeptide KPV, shows the same pattern in its literature — an active fragment with a clear mechanism and no registered trial. The similarly named thymosin alpha 1 is an unrelated peptide with a different sequence and a far deeper file: 66 registered studies and a dose used consistently since 2001, which is the opposite position to this one and a reason the shared family name misleads.
The dose table
| Source | What it states | Kind of source | Date opened and link |
|---|---|---|---|
| Peptide Dosing Protocols | Loading "approximately 2–2.5 mg subcutaneous twice weekly" for 4–6 weeks; maintenance "approximately 2–2.5 mg subcutaneous once weekly"; cycles "4–12 weeks"; states the planning is "community-derived and not validated by a published human RCT of the TB-500 fragment" | Protocol site | Reviewed September 2026 |
| Tucson Wellness MD | "TB-500 2–5 mg weekly" in a combination protocol with BPC-157 | Clinic guide | Page dated 2025-10-30 |
| Other clinic and vendor pages returned by a 2026-09-05 search (PeakedLabs, Peptide Nerds, Path to Peptides, Peptide Deck) | Loading 2–5 mg twice weekly for 4–6 weeks, then 2 mg weekly; 8–12 weeks on, 4 off | Vendor and clinic guides, as summarized in search results; not individually opened | Not quoted beyond the range |
The convention is narrow, 2 to 2.5 mg with an upper tail to 5 mg, and it is the same on every page because the pages descend from the same forum posts. There is no trial behind any of it, and the site that publishes the most detailed version says so. Because the fragment weighs about a fifth as much as the full protein, a milligram figure means something different for each — see TB-500 vs thymosin beta-4.
What the full protein was given at
Thymosin beta-4, the 43-amino-acid protein, has real human trials, none of them about TB-500 and none about tendons or muscle:
| Trial | Substance and route | Doses | Population and purpose |
|---|---|---|---|
| Ruff et al., Ann N Y Acad Sci 2010 | Synthetic Tβ4, intravenous | 42, 140, 420 or 1,260 mg, single dose then daily for 14 days | 40 healthy volunteers; safety for a cardiac-ischemia program; no dose-limiting toxicity |
| Wang et al., J Cell Mol Med 2022 | Recombinant Tβ4 (NL005), intravenous | 0.05 to 25 mcg/kg single; 0.5, 2.0 and 5.0 mcg/kg daily for 10 days | 84 healthy Chinese volunteers; phase 1 for myocardial infarction; well tolerated |
| Sosne et al., Cornea 2015 | Tβ4 0.1% eye drops (RGN-259) | Six times daily for 28 days | 9 patients with severe dry eye; symptoms and staining improved versus vehicle |
The intravenous doses in the 2010 study are roughly a thousand times the weekly subcutaneous figures on TB-500 pages; the 2022 doses, per kilogram, are roughly a thousand times smaller. Neither is a reference point for a different molecule by a different route, which is the point.
Reconstitution arithmetic as the guides state it
A 10 mg vial with 2 mL of bacteriostatic water gives 5 mg/mL (5,000 mcg/mL, 50 mcg per unit on a U-100 syringe): 10 units is 500 mcg, 50 units is 2.5 mg, and a 2 mg quantity is 40 units. A 5 mg vial with 1 mL gives the same concentration. Because the quantities on TB-500 pages are in milligrams rather than micrograms, they occupy a large share of a syringe, which is why the guides describe 10 mg vials and small diluent volumes. Our the arithmetic of reconstitution has the procedure as an FDA label describes it and the arithmetic for any combination.
Detection
The 2024 analytical study found Ac-LKK, a TB-500 metabolite, detectable in rat urine up to 72 hours after administration, and Ac-LK as the main early metabolite. Anti-doping laboratories screen for TB-500 by mass spectrometry in urine and, since 2026, in dried blood spots. MuscleLedger's drug-testing page covers which tests look for it.
What is not known
Whether the fragment does anything in a human; whether any of the weekly figures has a basis beyond convention; and what the fragment's safety profile is at any dose. Nothing on this page is a recommendation. FDA's 2026 review of that last question, and what the adverse-event database holds, are set out in our record of TB-500 side effects.
A muscle-directed compound one shelf over shows what a registered trial can look like and still leave the product form undosed: follistatin has five of them, and every one administers a gene rather than the protein that is sold, with doses counted in vector genomes per kilogram. A registration is not automatically a dose record for the thing in the vial.
Since this page was written the fragment has gained a registered study of its own: a Hudson Biotech dose-escalation trial, NCT07487363, whose three dose arms carry no milligram amounts. It is examined alongside the matching BPC-157 filing in the dose record for the BPC-157 and TB-500 pairing.
Sources and dates
Opened 2026-09-05: Rahaman et al. 2024 (PMID 38382158); Ruff et al. 2010 (PMID 20536472); Wang et al. 2022 (PMID 34346165); Sosne et al. 2015 (PMID 25826322); Peptide Dosing Protocols TB-500 page (September 2026); Tucson Wellness MD guide (2025-10-30); the 2026 WADA Prohibited List; FDA PCAC July 2026 meeting page and press coverage of the vote. Corrections go to the contact page.