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PeptideMostly animalNot FDA approved

TB-500

Synthetic fragment of thymosin beta 4

Last reviewed October 27, 2026 · 24 sources · Written for general readers · Compare with another compound →

The bottom line

TB-500 is not thymosin beta 4. It is a seven amino acid piece of that protein, made in a lab and sold under a nickname, and FDA found no human studies of it by any route.[1] The studies people cite were mostly done on the full protein, and even the full protein has mixed results in small human trials.[2][3] One 2026 rat study found stronger repaired tendons with TB-500, but nobody has tested it in people.[4]

Where the evidence stands

What it is

TB-500 is a synthetic peptide of seven amino acids, LKKTETQ, with an acetyl group added to the front end. It matches positions 17 to 23 of a natural human protein called thymosin beta 4. Its identifier is CAS 885340-08-9 and its weight is about 889 g/mol. The acetate salt form weighs about 949 g/mol.[1]

FDA points out that TB-500 is a common nickname, not an official drug name, so different sellers may ship different things under it. The nomination FDA reviewed even listed a CAS number and formula that conflicted with reference data and with the supplier's certificate.[1] When doping scientists tested products sold online as TB500 and TB1000, the contents did not match how those products had been described.[11]

This matters when reading claims. Thymosin beta 4 is a full protein of 43 amino acids and has been tested in a few small human trials. TB-500 is a small fragment of it and has not, and a 2026 orthopaedic review warned that the two are often mixed up.[1][12]

Name
TB-500 (Synthetic fragment of thymosin beta 4)
Other names
LKKTETQ fragment, acetylated thymosin beta 4 (17 to 23)
Type
Peptide
Sequence
LKKTETQ
CAS number
885340-08-9
Formula
C38H68N10O14
Molecular weight
About 889.0 g/mol

What it does in the body

TB-500 does not occur in the body as a drug. It copies positions 17 to 23 of thymosin beta 4, a natural protein found in many cells and in blood, saliva, tears and wound fluid, with an acetyl cap added to the front.[1] The natural protein holds on to actin, the building block of the cell skeleton, and the stretch TB-500 copies is the part thought to grab actin.[1]

This is the biology, area by area. A change measured in the body, like a higher blood level, does not always mean a person feels a benefit. The claims check below covers that.

Cells and tissue repair

Well established

Inside cells, the full thymosin beta 4 protein binds single actin units, a step FDA describes as essential for building and keeping up the cell skeleton that cells need in order to move and repair tissue.[1] FDA says it is still unknown whether actin binding has anything to do with any healing effect of the short TB-500 piece.[1]

Skin and wounds

Lab finding

In scratched skin cells in a dish, TB-500 itself did not meaningfully speed closure. One of its breakdown pieces, called Ac-LKKTE, did, which led the authors to suggest earlier healing reports may come from that piece instead.[5] In old mice, a version of the same chain without the acetyl cap, put on skin wounds, sped closure and raised collagen.[1]

Joints and tendons

Seen in animals

In a 2026 study of 32 rats with cut and repaired Achilles tendons, tendons from rats given TB-500 by injection over four weeks took about 39% more force to break than untreated tendons, and tissue scores were better. TB-500 also raised an early repair type of collagen, which the authors said is not clearly a good sign.[4]

Brain and mood

Seen in animals

In mice bred to develop Alzheimer type brain changes, TB-500 and a related thymosin piece called Ac-SDKP improved memory tests and calmed immune cells in the brain. They did not reduce the amyloid plaque that marks the disease.[6]

Eyes

Seen in animals

A 2025 lab team built a gel carrying TB-500 that sets at the site of an eye injury. In animals with chemical burns of the eye surface, it sped regrowth of the clear outer layer and reduced inflammation.[7] This was a specially engineered gel, not the plain peptide.[7]

Absorption and breakdown

Seen in animals

In horses given TB-500 under the skin, blood levels peaked within one to two hours and became unmeasurable within 6 to 10 hours. In rats and in human liver and serum in a dish, it was trimmed into shorter pieces, some of which lingered in rats for up to 72 hours.[1][5]

How it works

The proposed mechanism is borrowed from the parent protein rather than shown for the fragment.

  • Thymosin beta 4 binds actin, a building block cells use to move and rebuild tissue, and the LKKTETQ stretch is the part thought to do that binding.[1]
  • In a laboratory dish, TB-500 did not meaningfully speed up closure of scratched skin cells. One of its breakdown products did show a small effect.[5]
  • In lab tests with human liver and blood serum, and in rats, TB-500 was trimmed into shorter pieces such as Ac-LK and Ac-LKK, whose activity in the body is unknown.[1][5]
  • In mouse brain cells, TB-500 lowered inflammation signals and pushed immune cells away from an inflamed state.[6]

There is no evidence that these actions produce any benefit in a person.

What the research shows

We keep animal and human evidence apart. A result in animals is a reason to study something in people, not proof that it works in people.

Animal and lab studies

Thin animal evidence, and much of it used a different molecule

  • A 2026 study in 32 rats with repaired Achilles tendons was, by its authors' account, the first to compare TB-500 and BPC-157 directly in that model.[4] TB-500 gave about 39% stronger tendons than no treatment after four weeks, and combining it with BPC-157 gave no extra benefit.[4]
  • A 2003 mouse wound study used the plain LKKTETQ chain without the acetyl group. Applied to the skin of aged mice, it sped wound closure. FDA said this cannot be carried straight over to the acetylated version sold as TB-500.[1]
  • In Alzheimer model mice, TB-500 improved memory tests and reduced brain inflammation without lowering amyloid plaque.[6] A gel carrying TB-500 sped healing of chemical eye burns in animals.[7]
  • In horses and rats, TB-500 was absorbed and quickly broken into smaller pieces that appeared in urine. No absorption study used the injection into muscle many users describe.[1]
  • The well known heart repair results come from mice given the full thymosin beta 4 protein after a blocked heart artery, not from TB-500.[9]
  • No studies of single dose toxicity, repeat dose toxicity, gene damage, pregnancy effects or cancer risk were found for TB-500.[1]

Limit: The animal record for TB-500 itself is tiny, mostly from single small studies, and includes no safety testing at all.

Human studies

There are no human studies of TB-500 alone

  • FDA searched for clinical trials, absorption studies, safety reports and published case reports of TB-500 by any route and found none.[1] A 2026 primer for sports medicine doctors also found no human orthopaedic data for TB-500.[8]
  • FDA's adverse event database returned no reports for TB-500 alone through March 2025. Its food complaint system held two cases involving blends of TB-500 and BPC-157, with no safety details.[1]
  • One FDA adverse event report described a 40 year old woman who injected a research labelled blend of BPC-157 and TB-500 under the skin. After about a week her skin and gums darkened, the same reaction came back when she used it again, and it cleared after she stopped. Because the product held two peptides, the cause could not be pinned down.[13]
  • A 2026 report described three dental patients with jaw nerve damage given gum injections of a mix that included TB-500, BPC-157, another peptide, a steroid and a numbing drug over four weeks. All regained most feeling and no side effects were recorded, but natural recovery could not be ruled out and no single ingredient could be credited.[14]
  • The parent protein, thymosin beta 4, was given as an IV drip to 40 healthy volunteers for up to 14 days in a placebo controlled safety study. There were no serious side effects, and the few side effects were mild or moderate.[15] A 2021 Chinese study of a gene engineered version gave IV drips to 84 healthy volunteers, with similar results.[16]
  • The parent protein was tested as a skin gel in 73 people with venous leg ulcers at eight European sites. Safety was similar to placebo, and one of the strengths tested may have sped healing, with about a quarter fully healed within three months.[2]
  • Eye drops of the parent protein were tested in 72 people with dry eye for 28 days. The drops missed both main goals. Eye side effects, mostly mild, occurred in 2 of 36 people on the drops and 5 of 36 on placebo.[3]
  • In a Phase 3 trial of the parent protein as eye drops in 18 people with a nerve damage eye disease, 6 of 10 on the drops had fully healed eye surfaces at four weeks versus 1 of 8 on placebo, a gap just short of statistical significance. Three authors worked for the developer or its parent company.[17]
  • None of those trials tested TB-500, and none tested an injection of the kind sold online.[1]

Limit: No human has been studied on TB-500 alone in a published trial, so nothing is known about its safety or effect in people.

Claims check

The most common claims about this compound, and what studies actually found. Verdicts rate the evidence, not whether you should use it.

Speeds healing of injuries and wounds

Only in animals

In scratched skin cells in a dish, TB-500 itself did not meaningfully speed closure, though one of its breakdown pieces did.[5] The skin wound study in old mice used the same chain without the acetyl cap that TB-500 carries.[1] No human study has tested wound healing with TB-500.[1]

Repairs muscles, tendons and joints

Only in animals

In a 2026 rat study, repaired Achilles tendons treated with TB-500 for four weeks took about 39% more force to break than untreated ones, with better tissue scores. Each test group had only four tendons.[4] No study has tested TB-500 for muscle, tendon or joint injury in people.[8]

Works better stacked with BPC-157

Not tested

The only study that tested the pair head to head, in rats with repaired Achilles tendons, did not support this claim: TB-500 alone improved tendon strength, while BPC-157 plus TB-500 gave no extra benefit over either one alone.[4] No human study has compared the mix with either peptide alone.[1]

Repairs the heart after a heart attack

Not tested

In mice with a blocked heart artery, the full 43 amino acid thymosin beta 4 protein helped heart muscle cells survive and improved heart function.[9] That was not TB-500, and FDA found no heart study of TB-500 at all.[1]

Heals chronic wounds and leg ulcers

Not tested

The full protein, not TB-500, was tested as a skin gel in 73 people with leg ulcers caused by poor vein circulation, at eight sites in Europe. Safety looked similar to placebo, and one of the strengths tested may have sped healing, with about a quarter of patients fully healed within three months.[2] No such trial exists for TB-500.[1]

Treats dry eye and eye injuries

Only in animals

A gel carrying TB-500 sped healing of chemical eye burns in animals.[7] Eye drops made with the full protein, not TB-500, gave mixed results in people: one trial of 72 people missed both main goals, while a tiny trial of 9 people with severe dry eye reported 35% less discomfort than placebo drops.[3][10]

Protects the brain and memory

Only in animals

In Alzheimer model mice, TB-500 improved memory tests and calmed brain inflammation but did not clear amyloid plaque.[6] No human study has looked at the brain.[1]

Known risks and side effects

  • No safety testing at all. FDA found no toxicity studies of any kind for TB-500, in animals or people, so long term risks are completely unknown.[1] A 2026 journal review raised the theoretical concern that, like its parent protein, it could help hidden tumor cells move and spread.[18]
  • Immune reactions. FDA judged that an injected peptide of this kind carries a meaningful risk of provoking an immune response, made worse by clumping and by peptide impurities.[1]
  • Products may not contain what the label says. The certificates of analysis FDA reviewed did not test for bacterial toxins or clumping for either form, and one form skipped tests for impurities and strength.[1] Doping lab tests of online TB500 and TB1000 products found contents that did not match their descriptions.[11]
  • Unregulated products and blends. TB-500 is sold online as research material, often blended with BPC-157. FDA lists a blend case with skin and gum darkening that returned when the product was used again.[13] Blends do not qualify for the October 2026 HHS compounding policy, which covers only single ingredient products.[19]
  • Banned in sport. The World Anti Doping Agency list bans thymosin beta 4 and its derivatives, naming TB-500 directly, in section S2.3 on growth factors, at all times.[20] The 2027 list keeps that wording.[21]

Regulatory status

Today: TB-500 is not an approved drug in the United States and no product containing it has FDA approval.[1] It sat in FDA's category 2, the significant safety concerns group, from September 2023 until April 22, 2026.[19] On July 23, 2026 the Pharmacy Compounding Advisory Committee voted 8 to 6 with one abstention to recommend adding TB-500 to the 503A compounding list, against FDA staff advice.[22] On October 28, 2026 HHS filed a policy saying it will not take action against licensed pharmacies and doctors that compound TB-500 for a named patient, as a single ingredient injection under the skin or into muscle, from an FDA registered maker, with testing for identity, purity, strength and harmful contaminants and reporting of serious side effects.[19][23] This is not FDA approval and lasts only until FDA finishes formal rulemaking.[24]

  1. FDA places TB-500 in category 2 of the nominated bulk substances list.[19]
  2. TB-500 leaves category 2 on April 22, 2026.[19]
  3. Advisory committee votes 8 to 6 with one abstention to recommend adding TB-500 to the 503A list. FDA staff had proposed against it.[1][22]
  4. HHS files an enforcement discretion policy covering TB-500 and five other peptides, limited to single ingredient injections, set for publication on October 30.[23][19]
  5. The 2027 anti doping list takes effect and still names TB-500 as banned at all times.[21]

Sources

  1. U.S. Food and Drug Administration. FDA Briefing Document for TB-500-Related Bulk Drug Substances. Pharmacy Compounding Advisory Committee Meeting, July 23-24, 2026. FDA briefing document, TB-500
  2. Guarnera G, DeRosa A, Camerini R, et al. The effect of thymosin treatment of venous ulcers. Ann N Y Acad Sci. 2010;1194:207-212. PMID 20536470
  3. Sosne G, Ousler GW, et al. Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial conducted using the controlled adverse environment (CAE) model. Clin Ophthalmol. 2015;9:877-884. doi 10.2147/OPTH.S80954
  4. Biçer O, Adanir O, Güleryüz Y, et al. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study. Jt Dis Relat Surg. 2026;37(3):822-837. PMID 42542926
  5. Rahaman KA, Muresan AR, Min H, et al. Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro. J Chromatogr B Analyt Technol Biomed Life Sci. 2024;1235:124033. PMID 38382158
  6. Ou H, Chen R, Zhou L, Zhang Y, Zhao S, Yang Z. Thymosin beta4-derived peptides alleviate neuroinflammation and neurite atrophy in both in vitro models and in vivo 5xFAD mice: A potential therapy for memory improvement in Alzheimer's disease. Int Immunopharmacol. 2026;170:116097. PMID 41443105
  7. Lu P, Shan M, Peng C, Ji W, Yang T, Yang Z, et al. Alkaline Phosphatase-Triggered Spatiotemporal Repair of Corneal Injury with TB500 Peptide Hydrogel. ACS Appl Mater Interfaces. 2025;17(50):67503-67518. PMID 41359360
  8. Mayfield CK, Bolia IK, Feingold CL, Lin EH, Liu JN, Rick Hatch GF, et al. Injectable Peptide Therapy: A Primer for Orthopaedic and Sports Medicine Physicians. Am J Sports Med. 2026;54(1):223-229. PMID 41476424
  9. Bock-Marquette I, Saxena A, White MD, DiMaio JM, Srivastava D. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466-472. doi 10.1038/nature03000
  10. Sosne G, Dunn SP, Kim C. Thymosin beta4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea. 2015;34(5):491-496. PMID 25826322
  11. Delcourt V, Garcia P, Chabot B, et al. TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs. Drug Test Anal. 2023;15(4):458-464. PMID 36482504
  12. Tham A, Hodgkins CW, Kennedy JG. Investigational Peptides in Orthopaedic Practice: Evidence, Safety, and Patient Counseling for BPC-157, Thymosin Beta-4, and TB-500. J Am Acad Orthop Surg. 2026. Online ahead of print. PMID 42937313
  13. U.S. Food and Drug Administration. FDA Briefing Document for BPC-157-Related Bulk Drug Substances. Pharmacy Compounding Advisory Committee Meeting, July 23-24, 2026. FDA briefing document, BPC-157
  14. Froum S, Estrin N, Pico G, Yakubov M, Ahmad P, LaValle J. Case Report: Regenerative peptides for Inferior alveolar nerve injury: a narrative review with hypothesis-generating three clinical cases. Front Oral Health. 2026;7:1907109. PMID 42876687
  15. Ruff D, Crockford D, Girardi G, Zhang Y. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Ann N Y Acad Sci. 2010;1194:223-229. PMID 20536472
  16. Wang X, Liu L, Qi L, Lei C, Li P, et al. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin beta4 in healthy Chinese volunteers. J Cell Mol Med. 2021;25(17):8222-8228. PMID 34346165
  17. Sosne G, Kleinman HK, Springs C, Gross RH, Sung J, Kang S. 0.1% RGN-259 (Thymosin beta 4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial. Int J Mol Sci. 2022;24(1):554. PMID 36613994
  18. Moiz A, O'Keefe EL, O'Keefe JH. Dangers of Injectable Peptides and Other Unregulated "Biohacking" Drugs. Mo Med. 2026;123(4):337-343. PMID 42757290
  19. U.S. Department of Health and Human Services. HHS Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances, with Appendices A and B. October 2026. HHS policy document
  20. World Anti-Doping Agency. The 2026 Prohibited List. Effective 1 January 2026. WADA 2026 List
  21. World Anti-Doping Agency. The 2027 Prohibited List. Comes into effect 1 January 2027. WADA 2027 List
  22. Steinzor P. FDA Panel Backs 6 Peptides for Compounding. The American Journal of Managed Care. July 31, 2026. PCAC vote coverage
  23. Department of Health and Human Services, Office of the Secretary. Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances. Federal Register notice of availability, FR Doc. 2026-22192, filed October 28, 2026. Federal Register 2026-22192
  24. Steinzor P. 5 Things to Know About HHS's Interim Peptide Compounding Policy. The American Journal of Managed Care. October 29, 2026. HHS policy coverage
Medical disclaimer

This page is educational information only. It is not medical advice and does not replace care from a licensed medical provider. Do not use this page to decide whether to take any substance. Talk to a licensed medical provider first.

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