Reviewed & approved by Dr. Nova Reyes · Last checked 2026-10-15. ← Back to Evidence Library

TB-500 and thymosin beta-4: what the evidence says

Legend: HUMAN data · ANIMAL / LAB data · UNKNOWN · UNVERIFIED: not yet confirmed against a primary source

---

What is it?

Two molecules share the name "TB-500". The full protein (thymosin beta-4, 43 amino acids) and a 7-amino-acid fragment (Ac-LKKTETQ, amino acids 17–23 of the protein) are different molecules. Research on one doesn't automatically apply to the other. Seller pages mix them up (see Combining peptides).

Thymosin beta-4 is a protein your own cells make, 43 amino acids long once its starting methionine is removed (UniProt P62328). It helps control actin, the scaffolding that lets cells move. Drug companies have tested the full protein as an eye drop, a skin gel and an IV (into a vein) drug. ^{R1, R2}

TB-500 is not the same molecule. It is a short piece, 7 amino acids long. It comes from the part of Tβ4 thought to drive its healing effects. Doping-control scientists found it in a product called "TB-500." That product was suspected of being used to cheat in sport. ^R1

Why this matters: almost all the research people quote for "TB-500" was done on the full Tβ4 protein. Results from the full protein don't automatically apply to the fragment. ^{R1, R3}

Does it work?

Animal Full Tβ4, in animals: rats and mice given Tβ4 healed skin wounds faster. Mice also had better heart function after a heart attack. ^R3

Animal TB-500 fragment, in animals: one rat study measured how the body breaks it down. In cell tests, the fragment itself showed no significant wound-healing effect. Only one of its breakdown products did. ^R3

Human Full Tβ4, in people: small randomized trials (studies that compare against a placebo, assigned by chance) tested Tβ4 eye drops for dry eye. One with 72 people missed both of its main goals. It did improve some secondary (less important) measures. One with 9 people reported improvements. Both were run by the company developing the eye drop. Caution [UNVERIFIED: sponsor role, see R2] Skin-ulcer trials were reported only in summaries. ^R2

Human TB-500 fragment, in people: essentially untested in people. We found no human study. ^R2

Is it safe?

• Human Two placebo-controlled safety studies gave the full Tβ4 protein by IV to healthy volunteers (40 people in the US, 84 in China). Side effects were mild to moderate. There were no serious adverse events (serious medical problems during the study). These were short studies of a pharmaceutical-grade product. ^R2
• Unknown No human safety data exist for the TB-500 fragment. ^R2
• Caution Theoretical concern: Tβ4 helps cells move and new blood vessels form, which helps healing but could in theory also help tumors grow and spread. Reviews report higher Tβ4 levels in some metastatic tumors (cancers that have spread). That shows the two go together, which doesn't prove one causes the other. It does not show that taking Tβ4 causes cancer. No one has tested this in people. ^R4
• Unknown No formal animal toxicology for TB-500 (testing for serious harm, like organ damage) was found on PubMed. ^R5

What we don't know

• Unknown A safe or effective human dose of either molecule
• Unknown Any human data at all for the TB-500 fragment
• Unknown Whether the fragment does what the full protein does
• Unknown Long-term safety (including cancer and pregnancy)
• Unknown How injected "TB-500" behaves in the human body

Is it legal?

Neither Tβ4 nor TB-500 is FDA-approved. WADA's 2026 Prohibited List bans "Thymosin-β4 and its derivatives e.g. TB-500" at all times, under S2.3 (growth factors and growth factor modulators). FDA lists the TB-500 fragment among compounding substances (pharmacies preparing custom medicines for individual patients, with a prescription) that it flagged for safety risks. It noted it found no human exposure data. As of Oct 15, 2026. ^{R7, R8}

What's in the vial?

Labs that test for doping found that products sold as "TB-500" contained the 7-amino-acid fragment, not the full protein. A vial labeled "TB-500" might hold the fragment, the full protein, something else, or the wrong amount. It could also contain impurities, bacterial toxins or heavy metals. We test retail vials blind under the Open Peptide Standard. See results at /tests/. A passing test covers one batch, tested on one date. It does not mean the compound itself is safe. ^{R1, R10}

What do users report?

Self-report, not evidence.

Unknown TBD. We'll only list this once we can cite a public source.

Study details

^R2 Human Human studies: full table (all are the full Tβ4 protein, none are TB-500)

Human studies used pharmaceutical Tβ4 (synthetic or recombinant), mostly developed by one company program (RegeneRx-linked authors such as Crockford D, Sosne G, Goldstein AL). UNVERIFIED Company affiliations of individual authors were not checked against the full texts. No human study of the TB-500 fragment was found on PubMed (searched Oct 15, 2026).

Study	People	Route	Dose used	Follow-up	Reported	Limitations	Citation
Ruff 2010, healthy volunteers	40 (4 cohorts of 10, with placebo)	IV	42, 140, 420 or 1260 mg; single dose then daily for 14 d	14 d dosing	AEs infrequent, mild/moderate; no dose-limiting toxicity or serious AEs	Small; healthy people only; run by a contract research firm, co-author Crockford D Caution [UNVERIFIED: sponsor]	PMID 20536472
Wang 2021, healthy volunteers (recombinant NL005)	54 single-dose + 30 multiple-dose, with placebo	IV	0.05–25 µg/kg single; 0.5, 2, 5 µg/kg daily for 10 d	28 d	AEs mild/moderate; no serious AEs	Three authors are sponsor employees (Beijing Northland Biotech, per the paper's disclosure); healthy people	PMID 34346165
Sosne & Ousler 2015, dry eye	72, randomized 1:1	Eye drops	0.1% solution	28 d	Missed both primary endpoints; some secondary measures improved (e.g., 27% less discomfort in a challenge chamber)	Single center; secondary outcomes	PMID 26056426
Sosne 2015, severe dry eye	9 (18 eyes), randomized	Eye drops	0.1%, 6×/day	28 d + 28 d follow-up	Less discomfort and corneal staining vs vehicle	Very small	PMID 25826322
Guarnera 2007, venous ulcers	Planned 72, 21 enrolled at writing	Topical	Caution "Increasing doses", not in abstract UNVERIFIED	84 d	Design report only; no results in abstract	Interim	PMID 17495250
Treadwell 2012 (review of two phase 2 ulcer trials)	Caution Not in abstract	Topical	Caution Not in abstract	—	"Accelerate[d] healing by almost a month in those patients that did heal"	Review by program investigators; full trial results UNVERIFIED	PMID 23050815

^R3 Animal Animal and lab studies: dose table

These are doses researchers used, not recommendations. Animal doses don't convert simply to people. Most work is on the full Tβ4 protein. Several key papers share authors (Kleinman HK, Goldstein AL).

Molecule	Species	Model	Route	Doses	Duration	Outcome	Citation
Full Tβ4	Rat	Full-thickness skin wound	Topical or i.p.	Caution Not in abstract UNVERIFIED	7 d	Re-epithelialization +42% (d4), up to +61% (d7)	PMID 10469335
Full Tβ4	Mouse	Coronary artery ligation (heart attack)	Caution Not in abstract	Caution Not in abstract	—	Better early heart-cell survival and function	PMID 15565145
TB-500 fragment	Rat (+ human serum, cells)	Metabolism	Caution Not in abstract	Caution Not in abstract	Up to 72 h	Main metabolite Ac-LK; Ac-LKK detectable to 72 h. In fibroblasts, only metabolite Ac-LKKTE showed significant wound-healing activity	PMID 38382158

^R4–R6 Safety evidence and theoretical concerns

• ^R4 Cancer concern: review describes Tβ4 as facilitating tumor metastasis and angiogenesis, with increased expression in several metastatic tumors (Xiao 2012, PMID 22856429). Mechanistic/associational only; no human data on supplemental use.
• ^R5 Animal toxicology: Unknown none found for TB-500 on PubMed.
• ^R6 Human IV safety of the full protein: see R2 (PMIDs 20536472, 34346165).

^R7–R8 Regulatory status (as of Oct 15, 2026)

• ^R7 FDA: not approved as a drug (no approved label found). Compounding: "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500" is on FDA's list of substances previously in Category 2 (significant safety risks) whose nominations were withdrawn. FDA states it "may pose risk for immunogenicity... due to the potential for aggregation as well as peptide-related impurities" and that FDA "has not identified any human exposure data" (FDA page, content current as of 04/22/2026). Not on the 503A bulks list, so not lawfully compoundable under 503A. On July 23, 2026, FDA's advisory committee (PCAC) reviewed TB-500 for wound healing; FDA staff proposed that it NOT be added (FDA briefing). UNVERIFIED STAT, July 24, 2026 reports the committee voted in favor; FDA has not posted minutes on its meeting page (checked Oct 15, 2026), so the count is from news coverage only. The vote is advice only.
• ^R8 WADA: 2026 Prohibited List, S2.3 (growth factors and growth factor modulators): "Thymosin-ß4 and its derivatives e.g. TB-500", prohibited at all times (WADA 2026 list). Detection methods exist (Esposito 2012, PMID 22962027; Rahaman 2024, PMID 38382158). Unknown Re-check against the 2027 list.

^{R1, R9, R10} Background, pharmacokinetics, product quality

• ^R1 TB-500 identified as the N-terminal acetylated 17–23 fragment of human Tβ4 (Ac-LKKTETQ) in a product suspected of doping use (Esposito 2012, PMID 22962027). The fragment's biological effects "have not been documented" per Rahaman 2024 (PMID 38382158). Length of full Tβ4 confirmed by UniProt P62328 (44 residues including the initiator methionine, which is removed; mature chain 43 aa; LKKTETQ = mature residues 17–23), checked Oct 15, 2026.
• ^R9 Full Tβ4 IV PK in humans: dose-proportional, half-life increasing with dose (PMID 20536472); no accumulation (PMID 34346165). TB-500 PK: rat metabolism only (PMID 38382158).
• ^R10 Open Peptide Standard panel: identity (mass spec, which can tell the fragment from the full protein), purity (HPLC), content, endotoxin, heavy metals, and sterility where offered; ISO/IEC 17025 lab; blind samples; results tied to a batch, and they expire. Unknown TB-500 results pending the first batch.

Full reference list (all verified on PubMed, Oct 15, 2026)

• Malinda KM, et al. J Invest Dermatol. 1999;113(3):364-8. doi:10.1046/j.1523-1747.1999.00708.x. PMID 10469335
• Bock-Marquette I, et al. Nature. 2004;432(7016):466-72. doi:10.1038/nature03000. PMID 15565145
• Guarnera G, et al. Ann N Y Acad Sci. 2007;1112:407-12. doi:10.1196/annals.1415.003. PMID 17495250
• Ruff D, et al. Ann N Y Acad Sci. 2010;1194:223-9. doi:10.1111/j.1749-6632.2010.05474.x. PMID 20536472
• Xiao Y, et al. Crit Rev Eukaryot Gene Expr. 2012;22(2):109-16. doi:10.1615/critreveukargeneexpr.v22.i2.30. PMID 22856429
• Esposito S, et al. Drug Test Anal. 2012;4(9):733-8. doi:10.1002/dta.1402. PMID 22962027
• Treadwell T, et al. Ann N Y Acad Sci. 2012;1270:37-44. doi:10.1111/j.1749-6632.2012.06717.x. PMID 23050815
• Sosne G, et al. Cornea. 2015;34(5):491-6. doi:10.1097/ICO.0000000000000379. PMID 25826322
• Sosne G, Ousler GW. Clin Ophthalmol. 2015;9:877-84. doi:10.2147/OPTH.S80954. PMID 26056426
• Wang X, et al. J Cell Mol Med. 2021;25(17):8222-8228. doi:10.1111/jcmm.16693. PMID 34346165
• Rahaman KA, et al. J Chromatogr B Analyt Technol Biomed Life Sci. 2024;1235:124033. doi:10.1016/j.jchromb.2024.124033. PMID 38382158

---

Disclaimer

This page is for education and harm reduction. It is not medical advice and not a recommendation to use TB-500 or thymosin beta-4. Their safety in humans is not established (the TB-500 fragment has no human data at all). Please talk to a clinician you trust, especially if you have or have had cancer, are pregnant or breastfeeding, or are a tested athlete. Seek care right away for a serious reaction, and report it to FDA MedWatch (https://www.fda.gov/safety/medwatch).