TB-500

What it is

TB-500 is a synthetic peptide of seven amino acids (leucine, lysine, lysine, threonine, glutamic acid, threonine and glutamine, written LKKTETQ) with an acetyl group, a small chemical cap, on the first one¹. The sequence matches residues 17 to 23 of thymosin beta-4, a 43-amino-acid protein found in many cell types and body fluids¹. Anti-doping labs that analyzed TB-500 products identified this acetylated fragment, Ac-LKKTETQ, as the key ingredient¹²¹³. The fragment contains the part of thymosin beta-4 that binds actin, a protein that forms the cell’s internal scaffolding and lets cells move. Researchers have proposed that the fragment acts on actin the way the full protein does, but FDA says it remains to be determined whether actin binding explains any healing effect¹. The body cuts TB-500 into shorter pieces, and in a 2024 cell study one of those pieces (Ac-LKKTE), not TB-500 itself, helped close scratch wounds⁶. ‘TB-500’ is a common name, not an official drug name, and anti-doping researchers report that products sold online claim to contain either the acetylated fragment or full-length thymosin beta-4¹¹⁴.

FDA’s review says TB-500 appears to have first been made in 2003, citing a study in which researchers made the fragment LKKTETQ (without the acetyl group) and applied it to skin wounds in aged mice¹¹⁵. A veterinary preparation called TB-500 appeared around 2011 and was marketed to boost performance in horse and greyhound racing; anti-doping labs identified its key ingredient as the acetylated fragment in 2012¹¹²¹³. It is now sold on ‘research use only’ peptide websites aimed at people¹. A compounding pharmacy nominated TB-500 for FDA’s compounding list and later withdrew the nomination; FDA evaluated it anyway and recommended against listing it in a review dated 15 May 2026¹.

Benefits: what the research shows

FDA’s 2026 review found no clinical trial, case report or other human exposure data for TB-500 by any route, and no human data on how the body absorbs or clears it¹. A PubMed search on 8 October 2026 found no study that gave it to people either³⁹. The only ClinicalTrials.gov record we found that names TB-500 (NCT07487363, first posted 23 March 2026) calls itself ‘fictional’ in its own summary¹⁶. A 2021 chart review from a Florida clinic reported that 3 of 4 knee-pain patients given injections of BPC-157 plus ‘TB4’ said their pain improved, but it had no control group; the paper and FDA’s BPC-157 review both name the second peptide as thymosin beta-4, not TB-500¹⁷¹⁸. Trials of full-length thymosin beta-4, such as a 700-person Phase 3 trial of eye drops for dry eye, tested a different molecule and are not evidence for TB-500⁴. The animal and cell data are thin and point in different directions. In a 2026 rat study (8 rats per group), TB-500 injected into the abdominal cavity (intraperitoneal injection) daily for four weeks after Achilles tendon repair gave stronger tendons and better tissue scores than controls, and adding BPC-157 gave no extra benefit; the authors called the study exploratory and described the peptide as ‘synthetic thymosin beta-4 (TB-500)’, so it is unclear whether they used the 7-amino-acid fragment or the full protein⁵. The often-cited 2003 mouse wound study used the non-acetylated fragment, which FDA says cannot be assumed to act like TB-500¹¹⁵. In a 2024 cell study, TB-500 itself did not speed the closure of scratch wounds, while one of its breakdown products (Ac-LKKTE) had a small effect¹⁶. A 2026 study in a mouse model of Alzheimer’s disease reported better memory-test performance with ‘TB500’, again without the chemical form stated in the abstract¹⁹. FDA found no animal studies of TB-500’s toxicity of any kind¹.

Key human studies

No completed human studies were found.

Doses studied

Doses below are what studies used or what a label says. They are not advice, and gray-market products may not contain what their label says.

Half-life

No human value found¹FDA found no human exposure data for TB-500 by any route¹. In horses given 10 mg under the skin, blood levels peaked at 0.05 to 0.08 ng/mL between 1 and 2 hours after the dose and could no longer be measured 6 to 10 hours after it. FDA’s review gives no half-life value.

Routes

• Subcutaneous injection (the usual community route; no human data found; the only drug-level data we found are from horses)
• Intramuscular injection (proposed in the withdrawn compounding nomination; no human data or animal drug-level data found)
• Intraperitoneal injection (rats only)
• Nasal spray (sold in blends with BPC-157; no data found)
• Topical (only the non-acetylated fragment, in mice)

Every dose studied for TB-500, with sources →

Legal status

United States

Not approved for any use. TB-500 has no official (USAN) name and no USP monograph, and it is not a component of any FDA-approved drug¹. FDA has said that ‘research purpose only’ and ‘not for human consumption’ labels do not stop such products from being drugs when the evidence shows they are meant for people; its 2023 warning letter to one online seller named TB-500 among the seller’s unapproved new drugs²⁰. On 1 April 2026 federal prosecutors in Utah announced the indictment of an osteopathic physician accused of receiving misbranded drugs from China, including TB500, and supplying them to more than 200 patients; these are allegations, not findings of guilt²¹.

US pharmacies

Under section 503A, a pharmacy may compound from a bulk ingredient only if it has a USP monograph, is part of an approved drug, or is on FDA’s 503A bulks list. TB-500 meets none of these, so it cannot be lawfully compounded¹²². FDA’s safety-risk page lists ‘Thymosin beta-4, fragment (LKKTETQ), also known as TB-500’ as nominated but withdrawn (previously Category 2) and warns of possible immune reactions²; it is in no category of FDA’s current list⁹. No outsourcing facility has reported compounding it¹. At the Pharmacy Compounding Advisory Committee (PCAC) meeting on 23 July 2026, FDA staff recommended against listing it, but the panel voted 8-6 with 1 abstention to recommend both the free base and the acetate¹⁷. The vote is advisory. According to the FDA Law Blog, FDA said it would announce any final decision through notice-and-comment rulemaking, and told the panel that listing would be the ‘first time creating legal access’, not a restoration of past access⁷²². The blog also notes a faster route: FDA could place TB-500 in Category 1 of its interim policy, as it has done with other substances it reviewed, and it has not acted against pharmacies compounding Category 1 substances while rulemaking is pending⁷²². As of 30 September 2026 FDA had posted no minutes, proposed no rule and changed no category⁸⁹. Full-length thymosin beta-4 is a separate case: FDA treats it as a biological product (federal rules define a protein as a chain of more than 40 amino acids), and biological products are not eligible for the 503A or 503B compounding exemptions²³²⁴.

Other countries

FDA found no approved TB-500 product in Canada, Australia, the UK, Belgium, Ireland, France, Norway, Germany, Spain or Italy, none authorized by the European Medicines Agency, and no entry in the European or Japanese pharmacopeias¹. Australia: the Poisons Standard in force from 1 October 2026 lists TB-500 and thymosin beta 4 as prescription-only (Schedule 4) and in Appendix D clause 5, which covers poisons that must not be possessed without authority such as a prescription²⁵. Canada: Health Canada says peptides are generally regulated as prescription drugs, lists TB-500 among unauthorized injectable peptides it has seized, and says ‘research use only’ labels do not make such products legal²⁶. Products seized from a wellness center in Calgary, in a warning Health Canada published in April 2025, included ones named ‘Frag 17-23 of Thymosin-β4 without Mannitol’ and ‘Thymosin-β4 (TB4 or TB-500)’²⁷. Other UK and EU legal details were not verified.

Sport

Prohibited at all times, in and out of competition, under S2.3, which names ‘Thymosin-ß4 and its derivatives e.g. TB-500’. All S2 substances are non-Specified¹⁰. The 2027 List, in force from 1 January 2027, keeps the same entry²⁸. USADA says use or possession of a non-Specified substance carries a default four-year ban. In 2025 a US triathlete accepted a four-year ban for possessing and using BPC-157 and TB-500 and for attempted complicity, because he promoted prohibited peptides to his social-media followers; USADA had asserted five years and cut one because he admitted the violations and accepted the sanction promptly¹¹. A Canadian university volleyball player received four years for using both in 2024²⁹.

TB-500 in the legal tracker →

Quality and the gray market

What testing finds

Finnrick Analytics, a US testing service that sends samples to third-party labs, lists 282 TB-500 tests covering 58 vendors from 16 May 2025 to 25 September 2026³³¹. Of the 200 most recent tests shown on 1 October 2026, dated 29 January 2026 to 25 September 2026, 113 failed, 83 passed and 4 were incomplete under its default ‘purity focus’ standard: purity of at least 99.5% and an amount within 35% of the label³. A sample with the wrong identity also fails, but a fail can simply mean purity slightly under 99.5%³¹. Among those 200 samples, 68 had product names containing ‘TB-500 (Thymosin Beta-4)’ and 12 ‘TB-500 (Fragment 17-23)’, which shows how sellers mix the two molecules’ names³. A 2023 anti-doping lab analysis of products sold online as TB500 and TB1000 found their contents did not consistently match their descriptions³². FDA found that a public certificate of analysis (a supplier’s test report) for TB-500 covered only appearance, identity and purity, not assay, impurities, bacterial endotoxins or aggregates¹.

How it is sold

When FDA checked in February 2024, several websites sold TB-500 as 2 to 15 mg powders labeled for research use only, and several offered consultations about using it¹. It is often combined with other peptides. Supporters at the July 2026 FDA panel described the BPC-157 + TB-500 ‘Wolverine stack’⁷, and FDA’s BPC-157 review found injectable and nasal-spray blends of BPC-157 with ‘Thymosin Beta 4 Fragment 17-23’ or ‘TB 500’¹⁸. On one US-facing vendor’s shop page sorted by popularity (checked 1 October 2026), a four-peptide blend containing TB-500 and a 20 mg BPC-157 + TB-500 ‘Wolverine Stack’ vial ranked 4th and 5th of 41 products. The Wolverine vial was listed at $90 on sale ($149.99 regular), and the site says its products are ‘Not for Human consumption’³³. Finnrick’s chart of test requests shows 546 for TB-500 from May 2025 to May 2026, about 2.6% of all 21,253 requests (share calculated by us). TB-500 requests ran at 19 to 74 a month from June 2025 and were 68 in May 2026, after only 3 in May 2025, when Finnrick received 302 requests for all products, against 1,604 in June³⁴. Interest is not new: a veterinary TB-500 product appeared around 2011, and a study of 13 doping forums found TB-500 among the two most-mentioned peptide and growth-factor names, with discussion rising after 2010¹.

Side effects and risks

• No human safety data: FDA found no trial, case series or dose-finding study, so side effects and safe doses are unknown. FDA’s adverse-event database had no TB-500 reports through 26 March 2025, but FDA notes that such reporting is voluntary and incomplete¹.
• No toxicology: FDA found no acute, repeat-dose, genetic-toxicity, reproductive or cancer studies of TB-500 in animals¹.
• Immune reactions: FDA warns that injected peptides can trigger immune responses ranging from harmless antibodies to life-threatening reactions, and that aggregation (peptide molecules clumping together) and impurities can add to that risk¹².
• Wrong product: ‘TB-500’ is a common name, not a standard. FDA has seen different salts and even different active molecules sold under it, and told its 2026 panel that inconsistent naming can contribute to a safety risk for patients¹³⁸.
• Cancer questions: according to the FDA Law Blog’s account of the 2026 panel, FDA and several panelists focused on a possible cancer signal, and dissenting panelists cited overlap with tumor progression⁷. FDA’s review found no cancer studies of TB-500 in animals¹.
• Unclear activity: the body breaks TB-500 into shorter fragments, and in a cell study only one fragment, not TB-500 itself, helped close wounds¹⁶.
• Blends: products that combine TB-500 with BPC-157 or other peptides make it impossible to tell which ingredient caused a reaction, as FDA noted in one adverse-event report¹⁸.
• Anti-doping tests: labs have methods to detect TB-500 and its breakdown products, and in rats one breakdown product stayed detectable in urine for up to 72 hours⁶¹³.
• Legal: possession without authority is illegal in Australia, and ‘research use only’ labels do not make these products legal in Canada or exempt them from US drug law²⁰²⁵²⁶.

Documented harms

• 11 May 2026FDA’s review of BPC-157 describes an FDA Adverse Event Reporting System (FAERS) report of a 40-year-old woman who injected a ‘research purposes only’ BPC-157 + TB-500 product under the skin for joint and wound healing. After a week of use she developed diffuse skin darkening and darkened gums. The same reaction returned when she used the product again, and it did not recur after she stopped. FDA judged the reaction likely due to the product but could not tell which peptide caused it¹⁸.

Questions people ask

What is still unknown

• What vials sold as TB-500 actually contain: the acetylated 7-residue fragment, its acetate salt, full-length thymosin beta-4 or something else. Public tests report purity and amount, but rarely say which molecule was found.
• Whether TB-500 itself has any healing effect in living animals, or whether any effect comes from its breakdown products.
• Whether the 2026 rat Achilles study, which calls its peptide ‘synthetic thymosin beta-4 (TB-500)’, used the acetylated fragment or the full protein, and whether its results can be replicated.
• Which molecule FDA staff meant when, according to an FDA Law Blog account of the 24 July 2026 panel session, they said ‘TB500’ typically refers to a 17-amino-acid fragment. FDA’s written review and its 23 July 2026 slides describe a 7-amino-acid fragment.
• Whether concerns about thymosin beta-4 and tumor growth apply to the TB-500 fragment. FDA found no study testing this.
• How TB-500 behaves in the human body (absorption, clearance, immune response) and what dose, if any, is safe. FDA found no study of any of this.
• Whether and when FDA will propose a rule on TB-500 after the 23 July 2026 panel vote.
• Whether ‘TB4’ in the 2021 knee-pain chart review meant TB-500 or full-length thymosin beta-4.
• Whether the two reports on ‘blended TB-500 and BPC-157’ in FDA’s food and supplement complaint system (through 10 March 2025) involved any harm; FDA says they contained no safety assessment.
• Who is behind ClinicalTrials.gov record NCT07487363, which names TB-500 but calls itself fictional, and why it is listed as recruiting.
• Legal status in the UK, the EU and New Zealand beyond the absence of approved products was not verified.

Sources

1. 1FDA Briefing Document, Pharmacy Compounding Advisory Committee meeting of July 23-24, 2026: TB-500-related bulk drug substances U.S. Food and Drug Administration, 15 May 2026. fda.gov
2. 2Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks U.S. Food and Drug Administration, 22 Apr 2026. fda.gov
3. 3TB-500: safety testing results and vendor ratings Finnrick, 25 Sep 2026. finnrick.com
4. 4Assessment of the Safety and Efficacy of RGN-259 Ophthalmic Solutions for Dry Eye Syndrome: ARISE-3, NCT03937882 ClinicalTrials.gov, 28 Aug 2026. clinicaltrials.gov
5. 5Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study Joint Diseases and Related Surgery, 23 Jul 2026. pubmed.ncbi.nlm.nih.gov
6. 6Simultaneous 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 Journal of Chromatography B, 1 Mar 2024. pubmed.ncbi.nlm.nih.gov
7. 7PEPTIDE-L WAVE! PCAC Approves Four Bulk Drug Substances for the 503A List FDA Law Blog (Hyman, Phelps & McNamara), 24 Jul 2026. thefdalawblog.com
8. 8July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee U.S. Food and Drug Administration, 6 Aug 2026. fda.gov
9. 9Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act (categories list) U.S. Food and Drug Administration, 14 May 2026. fda.gov
10. 10World Anti-Doping Code International Standard: Prohibited List 2026 World Anti-Doping Agency, 24 Sep 2025. wada-ama.org
11. 11Triathlon Athlete Accepts Sanction for Anti-Doping Rule Violations U.S. Anti-Doping Agency, 17 Sep 2025. usada.org
12. 12Synthesis 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 Drug Testing and Analysis, Sep 2012. pubmed.ncbi.nlm.nih.gov
13. 13Doping 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 Journal of Chromatography A, 23 Nov 2012. pubmed.ncbi.nlm.nih.gov
14. 14Equine Doping Controls of Thymosin β 4: A Population Study and Strategy for Misuse Detection Drug Testing and Analysis, Jul 2025. pubmed.ncbi.nlm.nih.gov
15. 15Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice Wound Repair and Regeneration, 2003. pubmed.ncbi.nlm.nih.gov
16. 16TB-500 (Thymosin Beta 4 17-23 Fragment) for Cardiovascular Biomarkers in Stable ASCVD (NCT07487363) ClinicalTrials.gov, 23 Mar 2026. clinicaltrials.gov
17. 17Intra-Articular Injection of BPC 157 for Multiple Types of Knee Pain Alternative Therapies in Health and Medicine, Jul 2021. pubmed.ncbi.nlm.nih.gov
18. 18FDA Briefing Document, Pharmacy Compounding Advisory Committee meeting of July 23-24, 2026: BPC-157-related bulk drug substances U.S. Food and Drug Administration, 11 May 2026. fda.gov
19. 19Thymosin β4-derived peptides alleviate neuroinflammation and neurite atrophy in both in vitro models and in vivo 5 × FAD mice: A potential therapy for memory improvement in Alzheimer’s disease International Immunopharmacology, 1 Feb 2026. pubmed.ncbi.nlm.nih.gov
20. 20Warning letter to Warrior Labz SARMS (MARCS-CMS 655280) U.S. Food and Drug Administration, 12 Jun 2023. fda.gov
21. 21Utah Licensed Osteopathic Physician Indicted for Allegedly Receiving Misbranded Drugs from China and Selling them to Patients U.S. Attorney’s Office, District of Utah, 1 Apr 2026. justice.gov
22. 22The PEPTIDE-L Wave Rolls On! PCAC Adds Two More Bulk Drug Substances for the 503A List FDA Law Blog (Hyman, Phelps & McNamara), 28 Jul 2026. thefdalawblog.com
23. 23Warning letter to GenoGenix LLC (MARCS-CMS 718739) U.S. Food and Drug Administration, 20 Jan 2026. fda.gov
24. 2421 CFR 600.3, Definitions (eCFR, as of 25 September 2026) Electronic Code of Federal Regulations (eCFR), 25 Sep 2026. ecfr.gov
25. 25Therapeutic Goods (Poisons Standard—October 2026) Instrument 2026 (F2026L01327) Federal Register of Legislation, Australian Government, 28 Sep 2026. legislation.gov.au
26. 26Think twice before injecting peptides bought online: unauthorized products can seriously harm you (RA-81874) Health Canada, 9 Apr 2026. recalls-rappels.canada.ca
27. 27Unauthorized injectable peptide drugs seized from Optimum Wellness Centre in Calgary, Alberta may pose serious health risks (RA-77218) Health Canada, 1 Apr 2025. recalls-rappels.canada.ca
28. 28World Anti-Doping Code International Standard: Prohibited List 2027 World Anti-Doping Agency, 21 Sep 2026. wada-ama.org
29. 29U SPORTS Volleyball Athlete Suspended for the Use of BPC-157 and TB-500 Sport Integrity Canada, 7 Apr 2025. sportintegrity.ca
30. 30TB-500 5 mg Dosage: Vial Chart & Protocol PeptideDosages, 28 Sep 2026. peptidedosages.com
31. 31Methodology Finnrick, accessed 30 Sep 2026. finnrick.com
32. 32TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs Drug Testing and Analysis, Apr 2023. pubmed.ncbi.nlm.nih.gov
33. 33Ascension Peptides shop page sorted by popularity Ascension Peptides (vendor), accessed 1 Oct 2026. ascensionpeptides.com (seller page, deliberately not linked)
34. 34We’d Rather Buy the Future Than Wait For It Finnrick, 10 Jun 2026. finnrick.com
35. 35Peptide Supplements and Their Therapeutic Applications in Sports Medicine The American Journal of Sports Medicine, 11 Aug 2026. pubmed.ncbi.nlm.nih.gov
36. 36PubMed search: TB-500 with testosterone, androgens, the testes, luteinizing hormone, sex hormones or gonads (4 results, all on drug testing in sport) National Library of Medicine (PubMed), accessed 7 Oct 2026. pubmed.ncbi.nlm.nih.gov
37. 37Thymosin stimulates secretion of luteinizing hormone-releasing factor Science, 6 Nov 1981. pubmed.ncbi.nlm.nih.gov
38. 38FDA presentations, July 23, 2026, Pharmacy Compounding Advisory Committee meeting U.S. Food and Drug Administration, 23 Jul 2026. fda.gov
39. 39PubMed search: TB-500, TB500, TB 500 or Ac-LKKTETQ in titles and abstracts (33 results; none gave TB-500 to people) National Library of Medicine (PubMed), accessed 8 Oct 2026. pubmed.ncbi.nlm.nih.gov