No human dataTB-500 is not FDA-approved. The FDA wrote in 2026 that it "has not identified, any clinical studies or human exposure data using TB-500 via any ROA" (route of administration).[2] This calculator converts numbers you enter. It cannot make an untested substance safer to measure.
The TB-500 peptide is not thymosin beta-4
The name invites confusion. Thymosin beta-4 is a natural 43-amino-acid protein. TB-500 is a short synthetic piece of it.
| TB-500 | Thymosin beta-4 | |
|---|---|---|
| What it is | Residues 17–23 of thymosin beta-4, acetylated: Ac-LKKTETQ[2] | The full natural protein[8] |
| Length | 7 amino acids | 43 amino acids |
| Molecular weight | 889.0 g/mol[7] | 4,963 g/mol |
| Official name | None. The FDA notes "TB-500 is a common name and not a United States Adopted Name"[2] | Timbetasin |
| Human trials | None published | Yes, as IV infusion, eye drops and skin gel (below) |
The FDA adds that different salts and derivatives are "sold commercially under the same common name", so a vial labeled TB-500 may not all be the same molecule.[2] Under U.S. law a chain longer than 40 amino acids counts as a protein,[9] which puts full-length thymosin beta-4 on the protein side of the line and TB-500 well on the peptide side.
Regulatory status in November 2026
TB-500 is not FDA-approved, is not on the 503A bulks list, and is banned in sport.
- FDA approval: none, for TB-500 or for thymosin beta-4.[1]
- FDA safety wording: compounded TB-500 "may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation as well as peptide-related impurities."[3] It was in 503A Category 2 from September 2023 until April 22, 2026, when the nomination was withdrawn.
- FDA's 2026 review: FDA proposed not adding TB-500 to the 503A bulks list and wrote that it is "particularly concerned about the absence of human data".[2]
- HHS policy (Oct 30, 2026): a draft, non-binding enforcement-discretion policy covers TB-500 acetate for injection under the skin or into muscle, under ten conditions. HHS based this partly on the parent protein's human safety record.[4]
- Research-use sellers: FDA has warned a seller of injectable and nasal-spray TB-500 marketed "for research purposes only".[6]
- Sport: WADA 2026 S2.3 names "Thymosin-ß4 and its derivatives e.g. TB-500", prohibited at all times.[5] See peptides banned in sport.
What the human evidence says
For TB-500 itself: nothing. FDA's adverse event database had no TB-500 reports through March 2025, and its food and supplement complaint system held 2 reports of blended TB-500 and BPC-157.[2] One phase 1/2 trial was registered in 2026 with no results.[15]
The studies below used full-length thymosin beta-4, a different molecule. FDA cautions that data on one form "cannot be directly extrapolated" to another.[2]
| Study | Design | Amount and route studied | Reported |
|---|---|---|---|
| Ruff 2010[10] | Phase 1, placebo-controlled, 40 healthy adults | 42–1,260 mg IV, single dose then daily for 14 days | "No dose limiting toxicities or serious adverse events" |
| Wang 2021[11] | Phase 1, 84 healthy adults (recombinant form) | 0.05–25 µg/kg IV single; 0.5–5 µg/kg daily for 10 days | Adverse events mild to moderate; none serious |
| Guarnera 2010[12] | Phase 2, about 72 people with venous leg ulcers | 0.01–0.1% gel on the skin, daily up to 84 days | Safety comparable to placebo |
| Sosne & Ousler 2015[13] | Phase 2, 72 people with dry eye | 0.1% eye drops for 28 days | Primary endpoints not met |
| Sosne 2022 (SEER-1)[14] | Phase 3, 18 people with neurotrophic keratopathy | 0.1% eye drops | Complete healing 6/10 vs 1/8 (p = 0.0656) |
TB-500 side effects: what is known
TB-500's side effects in people are unknown, because it has never been tested in a published human study.[2]
- Reports to the FDA: none for TB-500 alone in the adverse event database through March 2025; 2 complaint reports involving blended TB-500 and BPC-157.[2]
- FDA's concern: possible immune reactions, "due to the potential for aggregation as well as peptide-related impurities".[3]
- Full-length thymosin beta-4 is not a proxy: its trials reported few problems (no dose-limiting toxicity IV; gel safety comparable to placebo),[10][12] but the FDA says such data "cannot be directly extrapolated" to TB-500.[2]
TB-500 concentration chart
No dose of TB-500 has been tested in people, so this chart shows only what each syringe unit holds. Nanomoles use the free-base weight of 889.0 g/mol: 100 mcg is 112.5 nmol. TB-500 is a smaller molecule than BPC-157, so the same number of micrograms is more molecules.
| Vial + liquid | mg/mL | mcg per unit | nmol per unit | Units per 100 mcg |
|---|---|---|---|---|
| 2 mg + 1 mL | 2 | 20 | 22.5 | 5 |
| 2 mg + 2 mL | 1 | 10 | 11.25 | 10 |
| 2 mg + 3 mL | 0.667 | 6.67 | 7.5 | 15 |
| 5 mg + 1 mL | 5 | 50 | 56.24 | 2 |
| 5 mg + 2 mL | 2.5 | 25 | 28.12 | 4 |
| 5 mg + 3 mL | 1.667 | 16.67 | 18.75 | 6 |
| 10 mg + 1 mL | 10 | 100 | 112.49 | 1 |
| 10 mg + 2 mL | 5 | 50 | 56.24 | 2 |
| 10 mg + 3 mL | 3.333 | 33.33 | 37.5 | 3 |
Example arithmetic: a 5 mg vial with 2 mL holds 25 mcg per unit, so 100 mcg is 4 units. For vials that contain TB-500 together with BPC-157, use the blend calculator.
Other peptide pages
The peptides most often looked up alongside this one. Each page gives that peptide's FDA status, compounding status and published human evidence, with sources; the status table has all 23 in one place.
- BPC-157Not approved 15-amino-acid peptide. Human data: a few tiny, uncontrolled studies.
- BPC-157 + TB-500 blendNot approved Two peptides in one vial: the arithmetic of a fixed ratio.
- GHK-CuNot approved Copper peptide. Studied on skin; injectable use has no published trials.
- KPVNot approved Lys-Pro-Val tripeptide. No human data by any route.
- LL-37Not approved Human cathelicidin. Topical wound trials; FDA cites tumor concerns.
- TesamorelinFDA-approved Egrifta SV and Egrifta WR. Labeled doses, diluents and volumes.
Frequently asked questions
Is TB-500 the same as thymosin beta-4?
No. TB-500 is a 7-amino-acid acetylated fragment (Ac-LKKTETQ) of the 43-amino-acid protein thymosin beta-4. Trials of thymosin beta-4 do not tell you how TB-500 behaves.
Has TB-500 been tested in humans?
No published trial was found, and the FDA said in 2026 that it had identified no clinical studies or human exposure data for TB-500 by any route.[2]
How many units is 1 mg of TB-500?
It depends on the mix. From a 5 mg vial with 2 mL of liquid, 1 mg is 40 units; with 1 mL it is 20 units. This is arithmetic, not a suggested amount.
Is TB-500 banned in sport?
Yes. WADA's 2026 list names it under S2.3, growth factors, prohibited at all times.[5]
Sources
- openFDA Drugs@FDA searches for BPC-157, thymosin, CJC-1295, ipamorelin, MOTS-c and prezatide (no application found)
- FDA briefing document: TB-500-related bulk drug substances
- Certain bulk drug substances for use in compounding that may present significant safety risks
- Enforcement discretion policy regarding 503A compounding using certain peptide bulk drug substances (91 FR 68526)
- World Anti-Doping Code: Prohibited List 2026
- Warning letter: Warrior Labz SARMS
- PubChem CID 62707662: TB-500 (Ac-LKKTETQ)
- PubChem CID 16132341: thymosin beta-4 (timbetasin)
- Final rule: Definition of the term "biological product" (85 FR 10057)
- Ruff D et al. Phase 1 safety of intravenous thymosin beta-4 in healthy volunteers (Ann N Y Acad Sci 2010;1194:223–9)
- Wang X et al. Phase 1 trial of recombinant thymosin beta-4 (NL005) (J Cell Mol Med 2021;25:8222–8)
- Guarnera G et al. Thymosin beta-4 gel (RGN-137) for venous stasis ulcers: phase 2 (Ann N Y Acad Sci 2010;1194:207–12)
- Sosne G, Ousler GW. Thymosin beta-4 eye drops (RGN-259) in dry eye: phase 2 (Clin Ophthalmol 2015;9:877–84)
- Sosne G et al. RGN-259 in neurotrophic keratopathy: SEER-1 phase 3 (Int J Mol Sci 2022;24:554)
- NCT07487363: TB-500 phase 1/2 registered 2026 (no results)