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Peptides · Thymosin beta-4 (and its synthetic fragment TB-500)

TB-500 / Thymosin beta-4: what the studies show

Every line below comes from a study, label or regulator record, checked by two models, with the source linked. Information, not medical advice. For adults 18+.

What it is

  • Thymosin beta-4 (Tβ4) is a 43-amino-acid protein the body makes. 'TB-500' is a different, much smaller thing: a synthetic, N-acetylated 7-amino-acid fragment of Tβ4 (Ac-LKKTETQ, residues 17-23) sold as a veterinary or 'research' product.[1][2][3]
  • Most human trials listed below tested full-length thymosin beta-4 (RGN-259 eye drops, RGN-352 IV, recombinant NL005, topical gel for venous ulcers), not the TB-500 fragment. Their results do not show that TB-500 works or is safe.[4][5][6][7][3]
  • Products sold online as TB500 or TB1000 have been found not to match their descriptions. A lab analysis of such products found contents not consistently as labelled.[8]

Bottom line

  • TB-500 has no published human study of its own. Studies of full-length thymosin beta-4 in people (eye drops, IV in healthy volunteers, topical for leg ulcers) are small to mid-size, mixed in result, and cannot be transferred to the fragment. FDA's reviewers found no report of TB-500 being given to patients for any condition.[9][4][10]

What the human studies found

  • Thymosin beta-4, not TB-500. In a phase 3 randomised, placebo-controlled trial of 0.1% RGN-259 eye drops (Tβ4) in 18 people with stage 2-3 neurotrophic keratopathy, complete healing at 4 weeks occurred in 6 of 10 treated and 1 of 8 on placebo (p = 0.0656, not significant at 0.05). The sponsor's earlier registered trial of the same design (SEER-1, 18 enrolled) was terminated.[4][11]
  • Thymosin beta-4, not TB-500. In a phase 2 trial of 72 people with moderate-to-severe dry eye, RGN-259 0.1% for 28 days did not beat placebo on either primary endpoint (ocular discomfort, inferior corneal staining). Some secondary measures did. A separate phase 2 trial of 9 people reported better dry-eye signs and symptoms with RGN-259 6 times daily for 28 days.[10][12]
  • Thymosin beta-4, not TB-500. Phase 3 dry-eye trials ARISE-2 (601 enrolled) and ARISE-3 (700 enrolled) of RGN-259 eye drops are registered as completed. The efficacy results are not in the records held here.[13][14]
  • Thymosin beta-4, topical, not TB-500. A double-blind dose-escalation phase 2 trial in 73 people with venous leg ulcers found acceptable safety. The authors said the 0.03% dose 'may have the potential' to speed healing, with complete healing within 3 months in about 25% of patients.[7]
  • Thymosin beta-4, intravenous, not TB-500. In four cohorts of 10 healthy volunteers given synthetic Tβ4 by IV at 42 to 1260 mg (single dose, then the same dose daily for 14 days), adverse events were mild to moderate with no dose-limiting toxicity.[5]
  • Recombinant human thymosin beta-4 (NL005), not TB-500, in healthy Chinese volunteers: 54 people had a single IV dose of 0.05 to 25 µg/kg, and 30 people had 0.5 to 5 µg/kg daily for 10 days. Adverse events were mild to moderate only.[3]

Known risks and side effects

  • FDA's reviewers found a lack of both clinical and nonclinical safety information for TB-500 and no toxicity studies. They were particularly concerned about the absence of human data by any route, and about immune reactions from injected peptides because of aggregation and impurities.[9]
  • For full-length thymosin beta-4, the human trials above reported mostly mild to moderate adverse events at the doses studied, in small groups over days to weeks. That is not long-term safety data and not data for the fragment.[5][3][4]
  • TB-500 is detectable in doping control and is the subject of doping-control methods in horses.[2][1]

Legal status

  • As of 2026-10-09 no TB-500 product is approved. FDA's category 2 page lists thymosin beta-4 fragment (LKKTETQ), also known as TB-500, among nominated-but-withdrawn substances, citing immunogenicity risk.[15]
  • FDA's briefing document for the July 23-24, 2026 advisory committee proposed not adding TB-500 (free base or acetate) to the 503A bulks list. It said FDA found no medical literature in which TB-500 was given to patients for any condition, and found that its historical use in compounding was unclear.[9]
  • ABC News reportedly said the committee narrowly voted to recommend adding TB-500 and five other peptides to the 503A list, against FDA staff advice. This is a secondary report. FDA had not posted minutes as of 2026-10-09. The vote is advisory and non-binding.[16]

Sources

  1. [1] Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential.
  2. [2] Doping control analysis of TB-500, a synthetic version of an active region of thymosin β₄, in equine urine and plasma by liquid chromatography-mass spectrometry.
  3. [3] A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers.
  4. [4] 0.1% 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.
  5. [5] A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers.
  6. [6] A Study of the Safety and Efficacy of Injectable Thymosin Beta 4 for Treating Acute Myocardial Infarction
  7. [7] The effect of thymosin treatment of venous ulcers.
  8. [8] TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs.
  9. [9] July 23-24, 2026, Meeting of the Pharmacy Compounding Advisory Committee – FDA Briefing Document for TB-500-Related Bulk Drug Substances (TB-500 (free base) and TB-500 acetate)
  10. [10] Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial conducted using the controlled adverse environment (CAE™) model.
  11. [11] Assessment of the Safety and Efficacy Study of RGN-259 Ophthalmic Solutions for Neurotrophic Keratopathy : SEER-1
  12. [12] Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial.
  13. [13] Assessment of the Safety and Efficacy of RGN-259 Ophthalmic Solutions for Dry Eye Syndrome : ARISE-2
  14. [14] Assessment of the Safety and Efficacy of RGN-259 Ophthalmic Solutions for Dry Eye Syndrome: ARISE-3
  15. [15] FDA: Certain bulk drug substances for use in compounding that may present significant safety risks (503A/503B category 2)
  16. [16] ABC News: FDA advisers narrowly vote to add 6 peptides to drug compounding list (2026-07-24)