Home / Peptides / TB-500: What FDA and HHS Say, and What the Evidence Shows
TB-500: What FDA and HHS Say, and What the Evidence Shows
TB-500 is not FDA-approved and is not thymosin beta-4. What FDA found in people, the Tβ4 eye trials, and where HHS's policy and FDA's review differ.
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Quick facts
Fact sheet
- U.S. status
- Strongest evidence
- Animal studies
- Status verified
TB-500 is sold as if it were thymosin beta-4, and the trials of thymosin beta-4 are quoted as if they were about TB-500. They are not. This guide separates the two and looks at what is known about each.
Key takeaways
- TB-500 is not FDA-approved. FDA says thymosin beta-4 and TB-500 are not the same substance.
- FDA’s 2026 review identified no clinical studies or human exposure data for TB-500.
- We found no real registered clinical trial of TB-500; the only ClinicalTrials.gov record describes itself as fictional.
- The human trials people cite are of thymosin beta-4, mostly as eye drops or skin treatments, and they do not tell us about injected TB-500.
- HHS’s October 2026 interim policy says it does not intend to take enforcement action against 503A compounding of TB-500 acetate under conditions. That is enforcement discretion, not FDA approval.
- HHS and FDA’s reviewers see the evidence differently. We lay out both below.
Is TB-500 the same as thymosin beta-4?
No. FDA wrote that “thymosin beta-4 and TB-500 are not the same substance.”
| Thymosin beta-4 | TB-500 | |
|---|---|---|
| What it is | A natural, much longer protein | A short synthetic fragment: an acetylated chain of seven amino acids, residues 17 to 23 of thymosin beta-4 |
| Human clinical trials | Yes, mostly eye and skin uses (below) | None identified by FDA |
| Source | FDA briefing | FDA briefing |
Many websites use the two names as synonyms. They are not. A separate point from FDA: the pharmacology of the non-acetylated seven-amino-acid fragment “cannot be directly extrapolated” to TB-500. That sentence is about the fragment, not about the full protein. For a head-to-head look at TB-500 and BPC-157, see our BPC-157 vs TB-500 comparison.
Is TB-500 FDA-approved?
TB-500 is not FDA-approved. A search of Drugs@FDA on Nov. 6, 2026 found no product listed for TB-500 or for thymosin beta-4. That search shows approved products, not pending applications.
FDA’s page on substances that may present significant safety risks listed the fragment, as “thymosin Beta-4, Fragment (LKKTETQ),” among nominations that were withdrawn (FDA). FDA’s page, updated April 22, 2026, lists the nomination as withdrawn, and HHS says TB-500 was in Category 2 until that date. We did not find it in FDA’s 503A categories list. FDA’s drug center proposed not adding it to the compounding list; the advisory committee voted 8–6–1 in favor of listing it, according to a law-firm account (secondary source).
In a January 2026 warning letter to a company that repackages drugs, FDA cited “Thymosin Beta-4” as an unapproved new drug and a biological product (FDA). We found no FDA warning letter from 2025 or 2026 that names TB-500. A warning letter states FDA’s position on one company; it is not a court ruling.
What does the HHS policy cover?
HHS’s October 2026 interim policy says it does not intend to take enforcement action against 503A compounding of TB-500 acetate under conditions. That is enforcement discretion, not FDA approval. As we read the policy:
- It covers TB-500 acetate, by subcutaneous or intramuscular routes only, as a single active ingredient, under its other conditions.
- It does not name full-length thymosin beta-4. We do not infer that it covers it.
- It does not cover blends. A product containing TB-500 and another peptide has two active ingredients; a law-firm analysis (secondary source) says the policy does not cover blends, and the single-ingredient condition is in HHS’s text.
- It does not replace state law. Before the policy, boards in Alabama and Mississippi told licensees they may not compound, administer or dispense non-FDA-approved or research-grade peptides, and it isn’t clear how those notices apply to compounding under the HHS policy.
For the six peptides in the policy and the 503A/503B rules, see 503A compounding of peptides and are peptides legal in the US.
What studies of TB-500 exist?
| Type | What was found | Source |
|---|---|---|
| Randomized trial in people | None | FDA |
| Other human studies | FDA identified no clinical studies or human exposure data. FDA also identified no published human pharmacokinetic data | FDA |
| Animals | In horses and rats, it reaches the bloodstream and breaks into fragments. FDA identified no published in vivo studies of wound healing or toxicity, and says it is unknown whether it heals wounds in animals | FDA |
| Cells | In fibroblasts, it did not promote closure of scratch “wounds” (a 2024 study, as described by FDA) | FDA |
| Registered trials | A ClinicalTrials.gov search returns one record with “TB-500.” It describes itself as a fictional study, so we do not count it | ClinicalTrials.gov |
FDA concluded there is a “lack of evidence to evaluate the effectiveness” of TB-500 for wounds, and that its risks in humans are “unknown.” That is what FDA identified, not a statement that no person has ever used it. In our review of BPC-157, we found a report of a person using BPC-157 with TB-500 who developed skin and gum darkening, and FDA’s TB-500 briefing lists two reports about a blended product, with no safety assessment. These are safety mentions, not evidence of benefit.
What do the thymosin beta-4 eye and skin trials show?
These are trials of the full protein, not of TB-500. They tested it as an eye drop or a skin treatment. We read the registry entries, not published papers; our PubMed searches returned no useful publications for them.
| Trial | Use and phase | People | What the registry shows |
|---|---|---|---|
| NCT03937882 | Dry eye, eye drop, phase 3 | 700 | RGN-259 (thymosin beta-4) and placebo changed by similar amounts on the primary measures we read: staining −0.41 vs −0.46, and discomfort −0.4 vs −0.4. No apparent difference; we did not review all results |
| NCT02974907 | Dry eye, phase 3 | 601 | Small changes with RGN-259 and with placebo: discomfort 0.07 vs −0.04, staining 0.07 vs −0.01 |
| NCT00832091 | Venous leg ulcers, applied to the skin, phase 2 | 72 | Primary outcome was safety |
| NCT00382174 | Pressure ulcers, applied to the skin, phase 2 | 72 | Primary outcome was safety |
| NCT04555824, NCT04555850 | Healthy volunteers, phase 1 | 54 and 30 | No results posted in the registry |
| NCT05555589 | Eye, phase 3 | 70 | Completed; no results posted when we checked (Nov. 6, 2026) |
Three things follow:
- They do not support TB-500. An eye drop of the full protein tells us nothing about injecting a seven-amino-acid fragment.
- The eye trials did not show a clear difference in the measures we read, and we did not find a thymosin beta-4 product approved by FDA for any use.
- A search of the registry for “thymosin beta 4” returns 18 records. Apart from the fictional TB-500 record, they are of the full protein, mostly an eye drop.
Where do HHS and FDA’s reviewers disagree?
We present both and do not choose. FDA’s review (July 2026) came before HHS’s policy (October 2026), so FDA has not answered HHS’s points directly.
| Question | HHS (policy) | FDA (briefing, slides) |
|---|---|---|
| Human safety evidence | Points to a “controlled human safety record” of the parent protein | Says TB-500 and thymosin beta-4 are not the same substance, and identified no clinical studies or human exposure data for TB-500 |
| What happens in the body | Says the fragment “is rapidly truncated in human serum” and does not cite the source in the text we read | Identified no published human pharmacokinetic data |
| Historical use | Describes use as “documented and quantified”; the usage data are not published in the text we read | Says “no pharmacies were found that compound products containing TB-500-related” bulk substances, and that it was “unable to identify any pharmacies” |
Whether the safety record of a whole protein applies to one of its fragments is an open question. We do not say FDA refuted HHS, because it has not responded to it.
What are the risks?
- Unknown in people. FDA says it has no clinical data and no nonclinical toxicity data for TB-500.
- Immune reactions. FDA points to potential immunogenicity with injected routes, made worse by aggregation and impurities.
- No reports is not safety. FDA’s adverse event system had no TB-500-specific reports, and FDA notes that this does not mean the product is safe.
- Source and quality. FDA identified no pharmacies compounding it, even though websites claim to obtain it from one.
- Sport. TB-500 is prohibited by the World Anti-Doping Agency (class S2) (WADA 2026 list).
Which claims are not supported?
- “TB-500 is synthetic thymosin beta-4.” FDA says they are not the same substance.
- “Proven to repair tendons and muscle in people.” FDA identified no human studies of TB-500.
- “FDA approved it.” It is not approved.
- “No adverse events, so it’s safe.” The absence of reports does not show safety.
- “The BPC-157 and TB-500 stack is backed by research.” We found no controlled trial of the combination, and a blend is outside the HHS policy.
- “The eye-drop trials prove TB-500 works.” They tested a different substance, for a different use.
What should you ask your doctor?
- What is behind my injury or pain, and what evidence-based options exist?
- If TB-500 is suggested, what human evidence supports it for my goal, given that FDA identified none?
- Is the product a compounded one made under a patient-specific prescription, who made it, and does it contain one active ingredient?
- Could it interact with my medicines or affect my sport’s anti-doping status?
We do not give doses, cycles or preparation instructions, and we do not recommend sellers.
Frequently asked questions
Is TB-500 FDA-approved?
No. TB-500 is not FDA-approved. FDA says thymosin beta-4 and TB-500 are not the same substance.
Is TB-500 the same as thymosin beta-4?
No. Thymosin beta-4 is a natural, much longer protein. TB-500 is a short synthetic fragment. The human trials that exist are of thymosin beta-4.
Does TB-500 heal injuries?
FDA’s 2026 review identified no clinical studies or human exposure data for TB-500, and said it is unknown whether it heals wounds in animals.
Is TB-500 legal?
We give no legal conclusion. HHS says it does not intend to take enforcement action against 503A compounding of TB-500 acetate under conditions, on an interim basis. That is not FDA approval, and state rules are separate.
Is there a clinical trial of TB-500?
We found no real registered clinical trial of TB-500; the only ClinicalTrials.gov record describes itself as fictional.
From Best Peptides Today
Sources we checked
- FDA briefing document on TB-500FDA. Accessed .
- FDA presentations to the Pharmacy Compounding Advisory Committee (July 23, 2026)FDA. Accessed .
- FDA CDER proposal on seven peptides (July 2026)FDA. Accessed .
- FDA: bulk drug substances that may present significant safety risks (Category 2)FDA. Accessed .
- FDA: bulk drug substances nominated under section 503A, by category (updated May 14, 2026)FDA. Accessed .
- Drugs@FDA (searched Nov. 6, 2026; no product listed as TB-500 or thymosin beta-4)FDA. Accessed .
- Federal Register: HHS enforcement discretion policy on 503A peptide compounding (Oct. 30, 2026)Other. Accessed .
- HHS: Enforcement Discretion Policy, with Appendices A and BOther. Accessed .
- McDermott+: PCAC votes on peptides (secondary source)Other. Accessed .
- Frier Levitt: HHS peptide compounding enforcement discretion policy (secondary source)Other. Accessed .
- ClinicalTrials.gov search for TB-500 (searched Nov. 6, 2026)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT03937882 (thymosin beta-4 eye drop, dry eye, phase 3)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT02974907 (thymosin beta-4 eye drop, dry eye, phase 3)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT00832091 (thymosin beta-4, venous ulcers, phase 2)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT00382174 (thymosin beta-4, pressure ulcers, phase 2)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT04555824 (thymosin beta-4, healthy volunteers, phase 1)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT04555850 (thymosin beta-4, healthy volunteers, phase 1)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT05555589 (thymosin beta-4, eye, phase 3)ClinicalTrials.gov. Accessed .
- FDA Warning Letter 718739 (Jan. 20, 2026)FDA. Accessed .
- Alabama Board of Medical Examiners: notice on prescribing non-FDA-approved research-grade peptidesOther. Accessed .
- Mississippi nursing, pharmacy and medical licensure boards: joint statement on peptides (Aug. 19, 2026)Other. Accessed .
- WADA 2026 Prohibited ListOther. Accessed .
Written and maintained by the Best Peptides For Editorial Team. How we rate evidence.