Read This First
This page is not built on clinical evidence. There are no trials of gray-market TB-500 because there is no standardized product to trial. What exists is regulatory statements, analytical chemistry, and the structural facts of an unregulated market.
TB-500 is not approved for human use by any global regulatory authority and is prohibited in sport under WADA section S2, where it is named explicitly.4
Legal Status
Where Does TB-500 Stand?
Not approved anywhere for human use. It is sold labeled for research, which is a liability position taken by the seller rather than a regulatory category that makes a product suitable for human use.
What Did the July 2026 FDA Meeting Change?
On 23 July 2026 the FDA's Pharmacy Compounding Advisory Committee discussed TB-500 free base and TB-500 acetate, among seven peptides, for possible inclusion on the 503A Bulks List, which governs what pharmacies may compound.3
Two details get dropped in most coverage. The use the FDA evaluated for TB-500 was wound healing, not tendon or sports injury. And the FDA states on its own meeting page that advisory committees make non-binding recommendations which the agency is not legally bound to follow.3
Inclusion on a compounding list is not drug approval, and compounded preparations are not reviewed by the FDA for safety, effectiveness or quality.
Does Any of This Change Sport Status?
No. Thymosin beta-4 and its derivatives, with TB-500 given as the example, have been prohibited growth factors under section S2.3 since the 2018 list.4 That remains current. For 2026 the only S2 change was the addition of pegmolesatide, and one substance moved from permitted to prohibited across the whole list, in section M.1.64 S2 turns on approval status, not on compounding permissions.
Because the rule names both the parent protein and its derivatives, buying the fragment rather than the protein does not sit outside it.
Product Identity
Why Identity Matters More Here Than Usual
TB-500 is Ac-LKKTETQ. Seven amino acids, with an acetyl group on the front.1
Short peptides are cheap to synthesize and easy to substitute. A vial could contain a closely related fragment, an unacetylated version, a partial sequence, or the parent protein, and still present plausibly on a certificate that reports purity without confirming identity.
This is the specific reason to insist on identity testing for this compound rather than accepting a purity figure.
Purity Testing Versus Identity Testing
| Test | Question it answers | Question it cannot answer |
|---|---|---|
| HPLC purity | What proportion of this sample is one substance | Which substance that is |
| Mass spectrometry identity | Whether the molecule matches the expected structure | How much of the sample it represents |
| Endotoxin assay | Whether bacterial cell wall fragments are present | Identity or potency |
A sample can be 99 percent pure and be the wrong molecule. A certificate reporting purity alone leaves that possibility open.
Is It TB-500 or Thymosin Beta-4?
These get sold interchangeably and they are not the same thing. Thymosin beta-4 is a naturally occurring 43 amino acid protein. TB-500 is a synthetic seven-amino-acid fragment corresponding to its actin-binding region.1
The commercial consequence: research on the parent protein is routinely used to sell the fragment. ONPEPS grades them separately, B for thymosin beta-4 and D for TB-500, because their research records are different in size and quality. The detail is on the TB-500 library entry.
Free Base or Acetate?
The FDA treated these as distinct substances in its July 2026 review, listing TB-500 free base and TB-500 acetate separately, as it did for every peptide on the agenda.3 A label that does not specify the form is giving an incomplete identity.
Certificates of Analysis
What a Certificate Is
A document reporting laboratory results for a specific batch, usually identity and purity, sometimes more.
Read it for four things: which laboratory ran the analysis, the batch or lot number and whether it matches the vial in hand, the date, and which tests were actually performed as opposed to which the seller mentions in marketing.
What It Cannot Establish
It describes the batch tested, which may not be the vial received. And its value rests on a chain of custody between laboratory, seller and buyer that an end purchaser cannot independently verify. A certificate is a PDF, and nothing about that format prevents reuse across batches or fabrication.
Endotoxin
Endotoxins are fragments of bacterial cell wall left behind after the bacteria themselves are killed. They survive processes that sterilize a product, so a sterile preparation can still contain them. Injected, they can provoke fever and inflammatory reactions.
Endotoxin testing is a separate assay from purity and identity, and it is frequently absent from vendor certificates. Its absence is not evidence of contamination. It is an untested question.
Blended Products
What a Blend Changes
Blended vials combine TB-500 with another compound, most often BPC-157, at a ratio the seller has fixed. Three consequences follow.
The ratio cannot be adjusted afterwards. Neither component can be stopped independently if a problem develops. And the identity question doubles, because two unverified substances share one container and usually one certificate.
Is There a Reason to Combine Them?
The only controlled comparison that exists is a 2026 rat study of Achilles tendon repair, which tested BPC-157 alone, TB-500 alone, and both together. The authors reported that combined treatment did not confer additional benefits compared with either agent alone.2
That is a rat study with eight animals per group over four weeks, described by its authors as exploratory. It is not a reason to rule the combination out. It is the only controlled evidence on the question, and it does not support the combination being better.
The stacking discussion in full is in the ONPEPS TB-500 versus BPC-157 article.
Storage and Handling
What Is Known
For TB-500 specifically, no manufacturer-validated storage specification exists, because no approved product exists. There is no stability dataset for any given preparation.
What can be stated is general peptide chemistry. Lyophilized powder is more stable than peptide in solution. Heat accelerates degradation. Repeated freeze-thaw cycles stress peptides. Light is a degradation route for many peptides, which is why amber vials and opaque packaging are common.
Every specific duration circulating online is extrapolated from other compounds. None of it is measured data for this one.
Signs to Stop Rather Than Proceed
Incomplete dissolution, persistent cloudiness or visible particulate after gentle mixing. Discoloration. A package that arrives warm when cold-chain materials were promised. Powder that is wet or clumped where a dry cake is expected.
None of these distinguishes between a different compound, degradation and contamination. What they share is that the material is not behaving as the label predicts. Appearance rules out some problems and confirms nothing, since a solution can lose potency or grow organisms with no visible change.
Sharps Disposal
Used needles go into a rigid, puncture-resistant sharps container, never household waste or recycling
Do not recap, bend or break needles before disposal
Do not overfill the container, and seal it before disposal
Disposal routes vary by jurisdiction and commonly include pharmacy take-back, household hazardous waste collection or a local sharps program
Detection
Can Testing Find It?
Yes. Doping control analysis of TB-500 in equine urine and plasma by liquid chromatography-mass spectrometry was published in 2012, detecting the parent peptide at 0.02 ng/mL in plasma and 0.01 ng/mL in urine after a single 10 mg dose in horses.5 A 2024 study developed and validated simultaneous quantification of TB-500 and its metabolites, explicitly framed around detection in urine.1
One detail from that work matters for anyone assuming a short window. The metabolite Ac-LKK was detectable up to 72 hours and is described by the authors as the long-term metabolite, which makes metabolites a useful detection target alongside the peptide itself.1
Community Language
TB-500
Ac-LKKTETQ. A synthetic seven amino acid fragment of thymosin beta-4.
TB-4
Thymosin beta-4. The naturally occurring 43 amino acid parent protein. A different molecule.
Blend
A vial containing more than one compound at a ratio fixed by the seller.
Loading phase
An initial period at a higher amount or frequency before reducing. A convention in circulation, not a validated schedule.
Free base and acetate
Two forms of the substance, treated separately by the FDA in its 2026 review.
Research use only
A seller's liability position, not a regulatory category permitting human use.
Related ONPEPS Coverage
Sources
Rahaman KA, Muresan AR, Min H, Son J, Han HS, Kang MJ, Kwon OS. 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. Free article. pubmed.ncbi.nlm.nih.gov/38382158
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. Free article. pubmed.ncbi.nlm.nih.gov/42542926
US Food and Drug Administration. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee. Agenda and evaluated uses. Docket FDA-2025-N-6895. fda.gov
United States Anti-Doping Agency. 2018 Prohibited List: Summary of Major Changes. Archived advisory; see reference for current-year status. Accessed 12 August 2026. usada.org
Ho EN, Kwok WH, Lau MY, et al. Doping control analysis of TB-500, a synthetic version of an active region of thymosin beta-4, in equine urine and plasma by liquid chromatography-mass spectrometry. J Chromatogr A. 2012;1265:57-69. Paywalled. pubmed.ncbi.nlm.nih.gov/23084823
United States Anti-Doping Agency. Athlete Advisory: What's New on the 2026 WADA Prohibited List? Accessed 12 August 2026. Records that for 2026 only one substance or method changed from permitted to prohibited, in section M.1, and that the sole S2 addition was pegmolesatide. usada.org
Not Medical Advice
TB-500 is not approved for human use in any jurisdiction and is prohibited in sport. If you are already using a product obtained outside a pharmacy, the route back to oversight is a clinician who knows what you have taken.
Regulatory sources verified 12 August 2026. Compounding status is unsettled following the July 2026 advisory recommendation and should be re-checked against FDA docket FDA-2025-N-6895.