> ## Content Index > Fetch the complete content index at: https://compoundcodex.org/llms.txt > Use this file to discover other available public pages before exploring further. # TB-500 for injury recovery - URL: https://compoundcodex.org/tb-500/ - Published: 2026-08-22T06:35:07.000Z - Updated: 2026-08-24T08:07:19.000Z - Description: Does TB-500 accelerate healing of muscle, tendon or ligament in humans? - Author: The Archivist - Tags: peptides, grade-preliminary, verdict-untested, tb-500 Preliminary evidence Untested in humans ⚑ Not characterised Marks reviewed Aug 2026 4 sources cited Next review Aug 2027 --- ## The substitution at the centre of this one TB-500 is usually described as "thymosin beta-4," and the research cited for it is research on thymosin beta-4\. That research is real. It is also research on a different molecule. Thymosin beta-4 is a naturally occurring protein, 43 amino acids long, with several functional regions. TB-500 is a synthetic fragment of it — a short sequence, LKKTETQ, corresponding to the actin-binding region. The FDA's own listing names it precisely this way: *"Thymosin beta-4, fragment (LKKTETQ), also known as TB-500."*[1](#c1) A seven-amino-acid fragment is not an abbreviation of a 43-amino-acid protein any more than a sentence is an abbreviation of a chapter. It may retain some of the parent molecule's activity. Whether it does, in a person, is an empirical question — and it is the question nobody has answered. ## Two molecules, side by side | | TB-500 — what people inject | Thymosin beta-4 — what was studied | | ------------------- | ------------------------------- | ------------------------------------------------- | | Molecule | 7-amino-acid fragment (LKKTETQ) | Full-length 43-amino-acid protein | | Human exposure data | none identified by FDA[1](#c1) | Phase III trials completed | | Route studied | none | Topical eye drop, five times daily[2](#c2) | | Condition studied | none | Neurotrophic keratopathy — corneal wounds[2](#c2) | | Trial size | — | 18 subjects (10 treated, 8 placebo)[2](#c2) | | Result | — | Primary endpoint not met, p=0.0656[2](#c2) | Read the right-hand column carefully, because it is doing all the persuasive work in every article you have seen about this compound — and it does not say what it is used to imply. The 2022 Phase III trial of RGN-259, a synthetic full-length thymosin beta-4, was an **eye drop**, applied to the **cornea**, for a **corneal disease**, in **eighteen people**. Complete healing occurred in 60% of treated subjects versus 12.5% on placebo — an encouraging trend that the authors report plainly did not reach statistical significance.[2](#c2) So the strongest human evidence in this entire story is: a different molecule, given by a different route, for a different condition, in eighteen people, missing its primary endpoint. None of that is a criticism of the researchers, who ran a legitimate trial in a rare disease and reported the result honestly. It is a description of how far that evidence has been stretched to justify injecting a fragment into a shoulder. ## What exists for TB-500 itself Nothing that we or the FDA could locate. When the agency assessed the fragment as a bulk drug substance for pharmacy compounding, its finding was unambiguous: > FDA has not identified any human exposure data drug products containing Thymosin Beta-4, Fragment. FDA lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans. US Food and Drug Administration[1](#c1) Note the phrasing: not "limited data," not "insufficient trials." *No human exposure data*. The agency looked and found none. This places TB-500 in the same position as BPC-157, which it is very often sold alongside: an animal-and-laboratory literature, a plausible mechanism, and an entirely empty human column. ## What happens to people who use it There is one place where the consequences of taking TB-500 are documented precisely, and it is not the medical literature. It is anti-doping enforcement. In 2025 a US triathlete accepted a sanction for using a stack that will look familiar to anyone who has browsed a peptide forum. #### USADA sanction — triathlon, 2025 SubstancesBPC-157 · TB-500 · CJC-1295 ipamorelin · tesamorelin TB-500 classificationNon-Specified Substance — Peptide Hormones, Growth Factors Sanction4 years reduced from 5 for early acceptance Results disqualified from1 June 2024 Additional violationpromoting prohibited substances on social media — attempted complicity Five compounds, four of them from the exact queue of peptides the FDA has flagged.[3](#c3) TB-500 is prohibited at all times, in and out of competition, as a non-Specified Substance — the class carrying a default four-year sanction. USADA's guidance on this whole category is worth quoting because it is the plainest statement any authority has made about research-chemical peptides: the substances are not FDA-approved for self-treatment, "the safety of such products has not been established, therefore, athletes should avoid these products," and "it is illegal to sell peptide hormones in dietary supplements."[4](#c4) ## Safety and unknowns - Adverse events reported None can be reported, because no human trial data exists to report them from.[1](#c1) This is an absence of information, not a finding of safety. - Longest human exposure studied None. FDA identified no human exposure data via any route of administration.[1](#c1) - Known interactions and at-risk groups Not characterised. FDA flags risk of immunogenicity for certain routes of administration, arising from the potential for aggregation and peptide-related impurities.[1](#c1) - Regulatory status Not approved by the FDA for any indication. Appears on FDA's list of bulk drug substances placed in category 2 and subsequently withdrawn by the nominator.[1](#c1) Prohibited by WADA at all times as a non-Specified Substance under Peptide Hormones, Growth Factors, Related Substances and Mimetics.[3](#c3) USADA states it is illegal to sell peptide hormones in dietary supplements.[4](#c4) - What has not been characterized Everything in humans: efficacy, safety, pharmacokinetics, dose, duration, interactions. Separately, whether the fragment reproduces any of the full-length protein's activity in a person is unknown — the parent molecule's other functional regions are simply absent from it. And material sold as a research chemical carries no pharmaceutical quality assurance, so what is in a given vial is its own open question. **The standing rule, applied:** the safety profile of TB-500 in humans *has not been characterized*. Not "well tolerated," not "no side effects reported" — those sentences require data that does not exist. If you are considering this compound, that conversation belongs with a clinician, and if you compete in a tested sport it will end your season and the three after it. ## How this was graded #### Evidence strength — Preliminary, criteria checked Completed qualifying trials of TB-500 in humans0 ✗ Human exposure data identified by FDAnone ✗ Trials of the full-length parent moleculeexist — different claim ✓ Systematic review of TB-500 in humansnone possible ✗ Trials of thymosin beta-4 do not count toward TB-500's grade, and this is the entire methodological point of the breakdown. Our rubric grades a **specific claim about a specific substance**. Evidence about a related molecule, given by another route for another condition, is evidence about that molecule. Letting it count here would be exactly the error the marketing depends on. ## What would change this grade One completed, published, placebo-controlled human trial of the LKKTETQ fragment — for any indication, with any result — moves TB-500 from Preliminary to Emerging. That is the whole bar, and in the seventeen years the compound has circulated, nobody has cleared it. Short of that, a pharmacokinetic study establishing that injected TB-500 reaches tissue in humans at all would be a meaningful first step. So would any published characterisation of what commercial material actually contains. ## Bottom line TB-500 is a seven-amino-acid fragment sold on the reputation of a 43-amino-acid protein. The FDA looked for human exposure data on the fragment and found none — no trials, no safety data, nothing. The research the marketing borrows is real, and it is about the full-length molecule: an eye drop, for corneal wounds, in eighteen people, which missed its primary endpoint. That is a long way from a shoulder injection. Meanwhile the consequences of using it are precisely documented, just not in a journal. A four-year ban, results wiped back eighteen months, for a stack of five peptides that a great many people are currently taking on the assumption someone has checked. peptides grade-preliminary verdict-untested tb-500 ## Sources 1. US Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Entry: "Thymosin beta-4, fragment (LKKTETQ), also known as TB-500," listed under nominations subsequently withdrawn. Content current as of 22 April 2026\. [fda.gov](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks?ref=compoundcodex.org) 2. Sosne G, Kleinman HK, Springs C, Gross RH, Sung J, Kang S. 0.1% RGN-259 (Thymosin β4) ophthalmic solution promotes healing and improves comfort in neurotrophic keratopathy patients in a randomized, placebo-controlled, double-masked Phase III clinical trial. *International Journal of Molecular Sciences*. 2022;24(1):554\. [PMC9820614](https://pmc.ncbi.nlm.nih.gov/articles/PMC9820614/?ref=compoundcodex.org) 3. US Anti-Doping Agency. Anthony McCauley accepts doping sanction. Triathlon; BPC-157, TB-500, CJC-1295, ipamorelin and tesamorelin; four-year sanction commencing 9 September 2025\. [usada.org](https://www.usada.org/sanction/anthony-mccauley-accepts-doping-sanction/?ref=compoundcodex.org) 4. US Anti-Doping Agency. 6 things to know about peptide hormones and releasing factors. [usada.org](https://www.usada.org/spirit-of-sport/6-things-know-peptide-hormones/?ref=compoundcodex.org) As with every peptide we cover, search results for this compound are dominated by vendor and marketing pages. Under our sourcing standard none are usable as evidence for any mark, and none were used here. **The Compound Codex** — every mark on this page is assigned under our [public editorial standards](https://compoundcodex.org/editorial-standards/). The rubric is versioned, its revisions are logged, and any grade here is open to challenge. This breakdown summarizes published research and regulatory records for informational purposes only. It is not medical advice and does not endorse the use of any compound discussed. No dose or protocol for human use is described anywhere on this page. TB-500 is an unapproved drug, prohibited at all times in tested sport, and appears on FDA's list of bulk substances flagged for potential significant safety risks. © 2026 The Compound Codex · Every claim cited, none of them prescriptive.