The six / TB-500
TB-500
Also: Thymosin beta-4 fragment, Ac-LKKTETQ
A fragment of a protein found in nearly every cell, borrowing its reputation from the full-length parent.
Class
Synthetic fragment of thymosin beta-4 (Tβ4), a 43-amino-acid protein
Sequence
Ac-LKKTETQ, the actin-binding region of Tβ4 (grey-market labelling varies)
Origin
Tβ4 isolated from calf thymus in 1981; the fragment characterised in doping-control work, 2012
Policy form
TB-500 acetate
Permitted routes
Subcutaneous or intramuscular injection only
Human evidence
Limited: none for the fragment; small trials of full-length Tβ4
What people ask for it for
Soft-tissue injury, recovery after training and the 'healing stack' with BPC-157. It is the second name a gym member mentions after BPC-157.
What the policy allows
TB-500 acetate. Subcutaneous or intramuscular injection only. No oral, nasal or topical form is covered.
Strength of the evidence
LimitedEvery human trial is of the full-length protein, mostly as eye drops or a wound gel. No completed human efficacy trial of the TB-500 fragment has been published. The animal evidence is substantial for the parent protein and thin for the fragment.
Where it comes from
Thymosin beta-4 is a 43-amino-acid protein present in almost every human cell, where its main job is to bind actin, the protein that forms the cell's internal scaffolding and lets it move. It was first isolated from calf thymus in 1981 and later found to be one of the most abundant small proteins in wound fluid and platelets.
TB-500 is a synthetic fragment covering the actin-binding region of that protein, usually written Ac-LKKTETQ. It was characterised in 2012 by doping-control laboratories, which tells you where it was being used. What is sold as TB-500 on the grey market is inconsistent: some vials contain full-length Tβ4, some the fragment, some other fragments.
The full-length protein has been through a real drug development programme. RegeneRx has tested it as eye drops (RGN-259) in dry eye and neurotrophic keratopathy and as a dermal gel in wounds and epidermolysis bullosa. None of that has produced an approved product, and none of it was done with the fragment.
How it is thought to work
From cell and animal models unless stated
Tβ4 binds monomeric actin and regulates how it assembles, which is central to cell migration. In repair models that translates into cells moving into a wound, new blood vessels forming, and inflammation and scarring being reduced.
A 2004 study in mice reported that Tβ4 improved cardiac repair after induced heart attack, which started the interest in it as a systemic repair agent rather than a topical one.
The fragment is assumed to carry the actin-binding activity of the parent. That assumption is reasonable and largely untested: most of what is written about TB-500's mechanism is extrapolated from full-length Tβ4.
What the research shows
Study by study, labelled by what it was. The third column is the citation; the full references are at the foot of the page.
In cells and animals
Dermal wound healing in rodents
Faster wound closure and reduced scarring with full-length Tβ4, the foundation of the dermal gel programme.
Goldstein et al., review, 2012
Corneal injury
Improved epithelial healing in several animal models, which led to the eye-drop trials.
RegeneRx, 2018 and 2022
Cardiac ischaemia in mice
Improved cardiac function and cell survival after induced infarction with full-length Tβ4.
Bock-Marquette et al., Nature, 2004
The fragment itself
Far less dedicated study than the parent. The published animal work on Ac-LKKTETQ is limited.
Superpower guide, 2026
In people
Venous leg ulcers, randomised dose-escalation study of Tβ4 gel
Designed for safety and tolerability. No efficacy conclusion.
PubMed 17495250
Neurotrophic keratopathy, Phase 3 of 0.1% RGN-259 eye drops, 18 patients
Complete healing at four weeks in 6 of 10 treated versus 1 of 8 on placebo (60% versus 12.5%, p = 0.066). Symptom improvements reported. No significant adverse effects.
Int J Mol Sci 2023; PubMed 36613994
Dry eye disease, Phase 2 and 3 of RGN-259
RegeneRx reports over 1,700 subjects exposed across dry eye and keratopathy with 'various degrees of efficacy'. No approval has followed.
RegeneRx
The TB-500 fragment
No completed human efficacy trial published. FDA identified no human exposure data for it.
FDA briefing, 2026
Safety, and what is not known
- For the fragment there are no published human safety data at all. For full-length Tβ4, the eye-drop and gel trials reported no significant adverse effects, which is reassuring about a topical protein and says little about an injected fragment.
- The policy's own Appendix B describes TB-500's safety concerns as inferential rather than observed: nobody has reported harm, and nobody has looked properly.
- Because Tβ4 drives cell migration and blood-vessel growth, the same theoretical tumour-promotion question raised about BPC-157 applies. There is no human evidence either way.
- TB-500 is detectable in blood and urine; detection methods were developed for horse racing and human doping control. If you are drug-tested, you need to know that.
What the HHS policy says about TB-500
TB-500 acetate
Subcutaneous or intramuscular injection only. No oral, nasal or topical form is covered.
- Appendix B records that updated characterisation data now exist and that use is documented, which addresses the identity question that made grey-market TB-500 so unreliable.
- One peptide per product: the popular BPC-157 and TB-500 blend is outside the policy.
All ten conditions of the policy →
Sport
Prohibited at all times under S2 of the 2026 Prohibited List, alongside other growth factors and modulators. Detectable, and tested for.
Regulatory status
-
Never
FDA approval. No application for approval of this substance has been filed in the US, and no trial exists that could support one.
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September 2023
Placed in Category 2 of FDA's interim 503A bulk substances list, the category for substances where FDA identified significant safety risks. Reputable pharmacies stopped compounding it.
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April 2026
Removed from the active Category 2 table after the Federal Register notice announcing advisory committee review.
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July 2026
Pharmacy Compounding Advisory Committee recommended TB-500 (free base and acetate) for the 503A bulks list for wound healing on July 23, by 8 votes to 6 with one abstention.
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October 28, 2026
Covered by the HHS enforcement discretion policy. Compoundable by state-licensed pharmacies and physicians that meet all ten of the policy's conditions, for an individual patient on a valid prescription. Still not on the 503A bulks list and still not approved.
Getting TB-500 through Healthy Peptides
You complete a health intake. An independent clinician at Beluga Health reviews it and decides whether TB-500 is appropriate for you, and by which permitted route. If prescribed, a state-licensed pharmacy that meets every condition of the HHS policy compounds the single-ingredient product and ships it to you. Healthy Peptides sells you the program; Local Healthcare bills you as its agent.
What we will and will not tell you
- WillWhat the research on TB-500 actually shows, graded honestly, and the routes a pharmacy may prepare.
- WillWho made it, who prescribed it, who billed you, and how to report a problem.
- Will notCall TB-500 approved, proven, safe or natural, or promise a result.
- Will notPublish a dose or protocol. That is between you, the clinician and the pharmacy label.
Questions about TB-500
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is the full 43-amino-acid protein. TB-500 is a synthetic fragment covering its actin-binding region. The clinical trials are of the full protein as eye drops and a wound gel; the fragment has no completed human trial. Grey-market products labelled TB-500 may contain either.
What is the evidence it helps injuries heal?
Animal studies of the full-length protein show faster wound closure and better cardiac repair. In people, the strongest result is a small eye-drop trial in corneal defects that just missed statistical significance. There is no human evidence for injected TB-500 in muscle or tendon injury.
Why injection only?
Because that is the route Appendix B of the HHS policy names for TB-500 acetate, reflecting the documented use the policy relied on. An oral or nasal TB-500 product is outside the policy.
Can it be combined with BPC-157?
Not in one product. The policy allows a single active ingredient per compounded product. Whether a clinician prescribes two products is a clinical decision, not a menu option.
Is it banned in sport?
Yes, at all times, under WADA's S2 category, and it is detectable. A tested athlete should not be anywhere near it.
TB-500 is not FDA-approved and no clinical trial has established that it is safe or effective for any use. The research described on this page is reported as what it is, cell, animal or small human studies, and is not a benefit you should expect. Programs are provided only where an independent, licensed clinician determines they are clinically appropriate after reviewing your health history, and not everyone qualifies. Compounded TB-500 is prepared by a state-licensed pharmacy under a patient-specific prescription and the conditions of the HHS enforcement discretion policy of October 28, 2026, which is not an approval and may be withdrawn. Availability varies by state. This page is general information, not medical advice. Last reviewed October 29, 2026.
Sources
- 0.1% RGN-259 (thymosin ß4) ophthalmic solution in neurotrophic keratopathy: randomised, placebo-controlled, double-masked Phase 3. Int J Mol Sci 2023
- RegeneRx: publication of RGN-259 Phase 3 results (January 2023)
- Goldstein AL et al. Thymosin β4: a multi-functional regenerative peptide. Expert Opin Biol Ther 2012
- Randomised dose-escalation study of Tβ4 in venous ulcers
- Identification and detection of the TB-500 fragment, Drug Testing and Analysis 2012
- Superpower peptide guide: TB-500
- HHS: Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances, with Appendices A and B (October 28, 2026)
- AJMC: FDA panel backs 6 peptides for compounding (July 2026)
- FDA: Bulk drug substances used in compounding under section 503A
- WADA: 2026 Prohibited List