TB-500 (Thymosin Beta-4): The Complete Research Guide, Checked Against the Evidence

What TB-500 is, and what it is not

TB-500 is a name used by sellers of research peptides, not a drug name. What it refers to is the first thing to settle, because the answer decides which research applies. Our TB-500 entry and the regulatory tracker treat it as a synthetic fragment of thymosin beta-4: LKKTETQ, the seven amino acids (residues 17 to 23) that hold on to actin. Many listings instead describe their TB-500 as the full thymosin beta-4 protein (listings read on September 26, 2026 for our blends guide). WADA's Prohibited List takes no side; it names "Thymosin-ß4 and its derivatives e.g. TB-500" together ¹.

Thymosin beta-4 itself is a 43-amino-acid protein found in almost every cell and released by platelets at wounds ². It is the major actin-sequestering molecule inside cells: it holds a reserve of single actin units that cells draw on to change shape and move ³. See our thymosin beta-4 entry.

The two are easy to tell apart in a laboratory. The fragment weighs about 889 daltons (C38H68N10O13); the full protein about 4,963.5 (C212H350N56O78S). A certificate of analysis that reports a measured mass tells you which one a vial holds, and our COA Decoder checks a stated mass against both.

At a glance

What thymosin beta-4 does in the laboratory

Because nearly all the research is on the parent protein, this section describes thymosin beta-4. None of it was done with the fragment unless we say so.

Wound healing and blood vessels

In rats with full-thickness skin wounds, thymosin beta-4 applied to the wound or injected into the abdomen increased re-epithelialisation by 42% over saline at day 4 and by up to 61% at day 7, wounds contracted at least 11% more, and treated wounds showed more collagen and new blood vessels. In a migration assay it made skin cells (keratinocytes) move two to three times faster ⁴. Later work found faster dermal healing across normal, steroid-treated, diabetic and aged rodents ².

The heart

In mice, thymosin beta-4 formed a complex with the proteins PINCH and integrin-linked kinase, switched on the survival kinase Akt, helped heart muscle and vessel cells migrate and survive, and after a coronary artery was tied off improved early heart-cell survival and heart function ⁵. In pigs, 15 mg infused into a coronary vein after 55 minutes of blocked blood flow cut infarct size from 54% to 37% of the area at risk and improved wall motion ⁶. A 2011 mouse study found that thymosin beta-4 given before a heart attack primed resident progenitor cells in the heart's outer layer to form new heart muscle cells afterwards ⁷. Priming before an injury is a different situation from treating one.

The nervous system

In mice with an experimental model of multiple sclerosis, 30 days of thymosin beta-4 improved neurological scores and increased new myelin-forming cells ⁸. In rats with an embolic stroke, injections starting 24 hours later improved recovery at 2 and 12 mg/kg but not at 18 mg/kg, and the authors estimated 3.75 mg/kg as the optimal dose ⁹.

Hair

In rats and mice it stimulated hair growth, apparently by activating stem cells in the hair follicle bulge and raising the matrix enzyme MMP-2 ¹⁰. No human study has tested this.

The only study of TB-500 itself

One published experiment gave the product sold as TB-500. Thirty-two rats had an Achilles tendon cut and repaired, then received BPC-157, TB-500, both, or nothing, injected into the abdomen daily for four weeks. Compared with untreated rats, only the TB-500 group showed a statistically significant gain in the load the tendon could bear before breaking; the combination scored better on one tissue-structure scale ¹¹.

That is a single, small animal study. It supports the idea that TB-500 is biologically active in a tendon model; it cannot supply a human dose, a safety profile or a result in people.

Human evidence: all of it is thymosin beta-4

No human trial has tested TB-500. These are the human studies of the parent protein.

• Safety. Forty healthy volunteers in four cohorts received intravenous thymosin beta-4 at 42, 140, 420 or 1,260 mg as a single dose and then daily for 14 days, or placebo. Adverse events were infrequent and mild or moderate ¹².
• Skin ulcers. A double-blind, placebo-controlled dose-escalation trial at ten sites in Italy and Poland tested topical thymosin beta-4 on venous leg ulcers ¹³. In two phase 2 trials in stasis and pressure ulcers, it sped healing by almost a month in the patients who healed ².
• The eye. Nine patients with chronic neurotrophic corneal defects used thymosin beta-4 drops on a compassionate basis; the six with large (geographic) defects healed dramatically ¹⁴. In a phase 2 trial in severe dry eye, nine patients using 0.1% drops (RGN-259) had 35.1% less ocular discomfort at day 56 than on vehicle ¹⁵. In a small randomised, double-masked phase 3 trial in neurotrophic keratopathy (18 patients), 6 of 10 treated and 1 of 8 placebo patients healed completely at four weeks (p = 0.066), and healing was significant by day 43 ¹⁶.
• Phase 3. ClinicalTrials.gov lists two completed phase 3 dry-eye trials ^{17 18}, a neurotrophic keratopathy trial terminated in 2020 ¹⁹ and another recruiting ²⁰ (records read September 27, 2026). None has produced an approval.

None of these studies is about tendons, ligaments, joints or muscle, and none used the fragment. That gap, between a substantial record for the protein in wounds and eyes and nothing for TB-500 in the injuries people use it for, is the central fact about this compound.

Dosing: what circulates, and what has been tested

No study has given TB-500 to a person, so no human dose has been tested for safety or effect. The figures that circulate in the peptide community are listed here so they can be read critically, not followed.

The community schedules are sometimes explained by a "24-hour half-life", but no half-life has been measured for TB-500 in people, and none is reported in the abstracts we hold for thymosin beta-4. Whether the injection site matters has not been studied either.

If you are checking a prescription's arithmetic, a 5 mg vial mixed with 2 mL of water holds 2.5 mg per mL, so 2.5 mg is 1.0 mL (100 units on a U-100 syringe) and 1.5 mg is 0.6 mL (60 units). The calculator below does the conversion for any vial.

Safety and the cancer question

The only controlled human safety data are for intravenous thymosin beta-4 in healthy volunteers over two weeks ¹². There is no systematic safety information on TB-500 as sold, and no long-term data for either.

The cancer question comes from biology: thymosin beta-4 helps cells move, and tumours spread by moving. In colorectal cancer cells, overexpressing thymosin beta-4 triggered an epithelial-mesenchymal transition, the change associated with invasion and metastasis ²¹. The evidence does not all point one way: in multiple myeloma, patients whose cancer cells expressed more thymosin beta-4 lived longer, and adding it to mouse myeloma cells slowed their growth ²². Neither study gave the peptide to people. Our peptides and cancer guide sets out the evidence compound by compound; people with an active cancer have a reason for extra caution that no study has yet resolved.

Legal status in the US and in sport

United States. TB-500 has never been approved by FDA. It was placed in 503A Category 2 in 2023; when its nomination was withdrawn, FDA removed it from Category 2 in April 2026 without placing it in Category 1 ²³. On July 23, 2026 FDA's Pharmacy Compounding Advisory Committee voted 8 to 6, with one abstention, to recommend it for the 503A bulk substances list; FDA's briefing found a lack of historical use of TB-500 in compounding ²⁴. FDA had not acted on the vote as of September 28, 2026.

Sport. WADA's 2026 Prohibited List names "Thymosin-ß4 and its derivatives e.g. TB-500" under S2.3, prohibited at all times; it is a non-specified substance, which carries a heavier default sanction, and the 2027 List keeps it unchanged ^{1 25}.

Elsewhere. No regulator has approved TB-500 or thymosin beta-4 as a medicine. Country rules differ; our legal guide covers the EU, UK, Canada and Australia with dated sources.

Stacks and blends

TB-500 is often sold mixed with other peptides, most often BPC-157. No study has tested any combination in people. The rat tendon study above gave BPC-157 and TB-500 together ¹¹, and a 2021 chart review of knee injections included 4 patients who received BPC-157 with thymosin beta-4, without a control group ²⁶. Our KLOW, GLOW and Wolverine guide covers the named blends, and the interaction checker marks such pairs as complementary in theory and untested in practice.

Frequently asked questions

Is TB-500 the same as thymosin beta-4?

Not as our encyclopedia defines it. TB-500 is a sellers' name that we and the regulatory tracker treat as the seven-residue fragment LKKTETQ (about 889 daltons); thymosin beta-4 is the natural 43-amino-acid protein (about 4,963 daltons). Many listings describe TB-500 as the full protein, and a certificate of analysis with a measured mass shows which one a vial holds.

Has TB-500 been tested in humans?

No. The human studies are of thymosin beta-4: an intravenous safety study in 40 volunteers and small trials in skin ulcers and eye disease. The only study of TB-500 itself is a 2026 rat tendon experiment.

What is the TB-500 dose?

No dose has been tested in people. Community schedules of about 2 to 2.5 mg twice a week, then weekly, are community practice. The intravenous safety study gave 42 to 1,260 mg a day of the full protein for two weeks.

Do I need to inject TB-500 near the injury?

No study has compared injection sites for TB-500. The claim that it works anywhere in the body is not based on any human study.

Is TB-500 legal in the US?

It is not FDA-approved. It left FDA's 503A Category 2 in April 2026 when its nomination was withdrawn, and FDA's advisory committee voted 8 to 6 on July 23, 2026 to recommend it for the 503A list; FDA had not acted as of September 28, 2026.

Is TB-500 banned in sport?

Yes. WADA's Prohibited List names thymosin beta-4 and its derivatives, including TB-500, under S2.3, prohibited at all times, in the 2026 and 2027 Lists.

Is TB-500 the same as thymosin alpha-1?

No. Thymosin alpha-1 is a different peptide with a different role in the immune system; see its encyclopedia entry.

Related on Grey Peptides

• TB-500 encyclopedia entry
• Thymosin beta-4 encyclopedia entry
• BPC-157 vs TB-500
• KLOW vs GLOW vs Wolverine
• Do peptides cause cancer?
• The July 2026 compounding committee votes
• COA Decoder
• Reconstitution calculator

Sources

1. World Anti-Doping Agency. The 2026 Prohibited List, section S2.3 (read September 27, 2026). WADA 2026 List
2. Treadwell, T. et al. (2012). The regenerative peptide thymosin β4 accelerates the rate of dermal healing in preclinical animal models and in patients. Ann N Y Acad Sci, 1270, 37-44. PMID: 23050815
3. Goldstein, A. L. et al. (2005). Thymosin beta4: actin-sequestering protein moonlights to repair injured tissues. Trends Mol Med, 11(9), 421-9. PMID: 16099219
4. Malinda, K. M. et al. (1999). Thymosin beta4 accelerates wound healing. J Invest Dermatol, 113(3), 364-8. PMID: 10469335
5. Bock-Marquette, I. et al. (2004). Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature, 432(7016), 466-72. PMID: 15565145
6. Hinkel, R. et al. (2008). Thymosin beta4 is an essential paracrine factor of embryonic endothelial progenitor cell-mediated cardioprotection. Circulation, 117(17), 2232-40. PMID: 18427126
7. Smart, N. et al. (2011). De novo cardiomyocytes from within the activated adult heart after injury. Nature, 474(7353), 640-4. PMID: 21654746
8. Zhang, J. et al. (2016). Thymosin beta4 promotes oligodendrogenesis in the demyelinating central nervous system. Neurobiol Dis, 88, 85-95. PMID: 26805386
9. Morris, D. C. et al. (2014). A dose-response study of thymosin β4 for the treatment of acute stroke. J Neurol Sci, 345(1-2), 61-7. PMID: 25060418
10. Philp, D. et al. (2004). Thymosin beta4 increases hair growth by activation of hair follicle stem cells. FASEB J, 18(2), 385-7. PMID: 14657002
11. Biçer, O. et al. (2026). Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study. Jt Dis Relat Surg, 37(3), 822-837. PMID: 42542926
12. Ruff, D. et al. (2010). A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Ann N Y Acad Sci, 1194, 223-9. PMID: 20536472
13. Guarnera, G. et al. (2007). Thymosin beta-4 and venous ulcers: clinical remarks on a European prospective, randomized study on safety, tolerability, and enhancement on healing. Ann N Y Acad Sci, 1112, 407-12. PMID: 17495250
14. Dunn, S. P. et al. (2010). Treatment of chronic nonhealing neurotrophic corneal epithelial defects with thymosin beta4. Ann N Y Acad Sci, 1194, 199-206. PMID: 20536469
15. Sosne, G. et al. (2015). Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea, 34(5), 491-6. PMID: 25826322
16. Sosne, G. et al. (2022). 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. Int J Mol Sci, 24(1). PMID: 36613994
17. ClinicalTrials.gov. NCT02974907: RGN-259 ophthalmic solution in dry eye (phase 3), completed. Record read September 27, 2026. ClinicalTrials.gov NCT02974907
18. ClinicalTrials.gov. NCT03937882: RGN-259 ophthalmic solution in dry eye (phase 3), completed. Record read September 27, 2026. ClinicalTrials.gov NCT03937882
19. ClinicalTrials.gov. NCT02600429: RGN-259 in neurotrophic keratopathy (phase 3), terminated. Record read September 27, 2026. ClinicalTrials.gov NCT02600429
20. ClinicalTrials.gov. NCT05555589: RGN-259 in neurotrophic keratopathy (phase 3), recruiting. Record read September 27, 2026. ClinicalTrials.gov NCT05555589
21. Huang, H. C. et al. (2007). Thymosin beta4 triggers an epithelial-mesenchymal transition in colorectal carcinoma by upregulating integrin-linked kinase. Oncogene, 26(19), 2781-90. PMID: 17072345
22. Caers, J. et al. (2010). Thymosin beta4 in multiple myeloma: friend or foe. Ann N Y Acad Sci, 1194, 125-9. PMID: 20536459
23. U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (current as of April 22, 2026), and Bulk Drug Substances Nominated for Use in Compounding Under Section 503A (updated May 14, 2026). FDA Category 2 page
24. U.S. Food and Drug Administration. July 23-24, 2026 Meeting of the Pharmacy Compounding Advisory Committee: briefing materials and votes. FDA meeting page
25. World Anti-Doping Agency. The 2027 Prohibited List, in force January 1, 2027 (read September 27, 2026). WADA 2027 List
26. Lee, E. & Padgett, B. (2021). Intra-Articular Injection of BPC 157 for Multiple Types of Knee Pain. Altern Ther Health Med, 27(4), 8-13. PMID: 34324435

This article is for education. It is not medical or legal advice, and it is not a guide to buying or using any peptide. TB-500 is not approved as a medicine anywhere and is prohibited in sport.