Is TB-500 Legal or FDA-Approved? Thymosin Beta-4 Fragment Status, November 2026

Key takeaways

TB-500 is not FDA-approved and is not on the 503A bulks list as of 11 November 2026.
HHS defines TB-500 as TB-500 acetate, a seven-residue acetylated fragment of thymosin beta-4 (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH), with a molecular weight of 949.1 g/mol. It is not the full-length protein.
Under the 30 October 2026 HHS policy, the covered routes are subcutaneous or intramuscular injection only. Blends such as BPC-157 with TB-500 fall outside it.
FDA’s drug centre recommended against listing TB-500, and the advisory committee voted in favour. Research-use-only TB-500 is unaffected. In sport, TB-500 is prohibited under WADA class S2.

Is TB-500 legal in the US?

It depends on who is selling it and how. TB-500 is not an FDA-approved drug and is not on FDA’s 503A bulks list (FDA). Since 30 October 2026, however, an HHS enforcement discretion policy says HHS does not intend to take action against 503A compounders, meaning state-licensed pharmacies, federal facilities and licensed physicians, that compound TB-500 acetate for subcutaneous or intramuscular injection on a valid prescription when all ten of the policy’s conditions are met (HHS policy).

Outside that channel nothing has changed. TB-500 sold as a “research chemical” can still be treated by FDA as an unapproved new drug when the seller’s site shows it is meant for people (FDA warning letter 733652). State law and sports rules apply on top of all of this.

What exactly does “TB-500” mean in the HHS policy?

The name is used loosely online, so the definition matters. HHS’s Appendix B defines the covered substance as TB-500 acetate, with molecular formula C₃₈H₆₈N₁₀O₁₄·CH₃COOH, molecular weight 949.1 g/mol, and amino acid sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH (HHS Appendix B). FDA’s compounding page uses the same identity, listing it as “Thymosin beta-4, fragment (LKKTETQ), also known as TB-500” (FDA).

Three practical points follow:

It is a fragment, not thymosin beta-4 itself. HHS refers to thymosin beta-4 as the “parent protein”. A product described as full-length thymosin beta-4 is a different substance from the one HHS defined.
The salt form is specified. The policy names the acetate. Material made as a different salt does not match the identity in Appendix B.
Identity has to be shown on a COA. The policy requires a certificate of analysis whose results match the defined identity. Our testing-standard explainer describes what that COA has to contain.

What is TB-500’s regulatory timeline?

Date	Event	Source
29 Sep 2023	TB-500 placed in 503A category 2 (“may present significant safety risks”)	HHS Appendix B
22 Apr 2026	Removed from category 2 after its nomination was withdrawn. HHS notes that neither the placement nor the removal changed its status under section 503A	FDA; HHS
Jun–Jul 2026	FDA’s drug centre (CDER) recommended against listing TB-500. The Pharmacy Compounding Advisory Committee, meeting on 23–24 July, voted in favour	HHS Appendix B
28–30 Oct 2026	HHS policy issued, then published in the Federal Register (FR Doc. 2026-22192). TB-500 is sixth in Appendix A	Federal Register
13 Nov 2026	Public comment deadline on docket HHS-OASH-2026-0496	regulations.gov

FDA’s safety statement on TB-500 is still on its category 2 page. It says compounded drugs containing the fragment “may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation as well as peptide-related impurities”, and that FDA “has not identified any human exposure data” on drug products containing it (FDA).

Why did HHS include TB-500 when FDA staff advised against it?

Appendix B gives a “threefold” justification for TB-500 (HHS Appendix B):

Characterisation. “Lot-specific certificates from FDA-registered manufacturers supply the identification, assay, impurity, endotoxin, microbial, and residual solvent results CDER found missing.”
Historical use. Use “is now documented and quantified, where CDER could not identify any pharmacy compounding TB-500.”
Safety reasoning. HHS says CDER’s concerns “are inferential rather than observed”, that “the parent protein has a controlled human safety record across several routes”, and that “the fragment is rapidly truncated in human serum.”

These are HHS’s reasons for an enforcement decision. They are not an FDA finding that TB-500 is safe or effective, and FDA’s own statement quoted above has not been withdrawn. This page makes no health claims about TB-500.

What conditions apply to compounded TB-500?

Condition	What it means for TB-500
Identity	TB-500 acetate as defined in Appendix B (Ac-LKKTETQ, 949.1 g/mol)
Routes	Subcutaneous or intramuscular injectable forms only. Oral, topical and intranasal TB-500 are outside the policy
Single API	TB-500 on its own. Blends with BPC-157, GHK-Cu or anything else are excluded
Bulk source	The original manufacturer must be FDA-registered and CGMP-compliant, with its physical location on the COA. A reseller must have validated that manufacturer
Reporting	Products compounded, serious adverse events and quality problems reported to FDA’s MedWatch and to the states where products are compounded and sent
Device and label	Only an FDA 510(k)-cleared syringe may be co-packaged. Label: “This is a compounded drug product. Not for resale.”
Prescription	A valid patient-specific prescription, as section 503A requires

Condition summary from the HHS policy and NABP’s 28 October memo to state boards (HHS; NABP memo). All ten conditions are set out in HHS’s peptide compounding policy explained. This page gives no dosing or administration information.

Blends are an easy mismatch to miss

Some online catalogues, including several we reviewed this month, sell TB-500 in named combinations with BPC-157 or GHK-Cu. The single-API condition puts every one of those outside the HHS policy, even when both ingredients are individually listed in Appendix A.

What about research-use-only TB-500?

The policy does not apply to it. HHS’s discretion covers state-licensed pharmacies, federal facilities and licensed physicians compounding on a prescription, so a website selling vials “for research use only” is not in that group (HHS). FDA’s August 2026 warning letters treated research-use disclaimers as not controlling when other site content showed products were intended for human use (FDA warning letter 733652).

The three channels are compared in research-use-only vs compounded vs FDA-approved peptides. Suppliers who sell for laboratory research are listed, with their published testing evidence, in our supplier directory.

Does the HHS policy apply in every state?

Not automatically. NABP told state boards on 28 October that “Boards should evaluate whether state law permits compounding with these substances” (NABP memo). Some states have said they will mirror the federal approach and others have pre-existing restrictions. The state picture is covered in does the HHS peptide policy apply in your state?

Is TB-500 allowed in sport?

No. USADA’s advisory on the 2027 Prohibited List names TB-500 as “Prohibited under S2” and thymosin-beta 4 as prohibited under S2 (USADA). Under the World Anti-Doping Code athletes are strictly liable for what is in their system. A prescription or a compounding policy does not change that.

What could change next?

Comments close 13 November 2026. HHS called the document interim and says it may revisit the policy if a safety signal or product quality issue appears (HHS).
Rulemaking. The policy lasts until TB-500 is addressed in a final rule as either included in or excluded from the 503A bulks list. No proposed rule has been published (FDA).
Supply. NABP has asked how long it will take before supply chains carry bulk material that meets the conditions (NABP memo). Any change will appear on our regulatory tracker.

Sources

Checked 11 November 2026. This page describes regulatory status only. It is not medical or legal advice and does not suggest that TB-500 is safe or effective.

Reader Question

“Is TB-500 legal now that HHS changed the peptide rules?”

Short Answer

Only for 503A compounders working on a prescription, as TB-500 acetate for injection, sold alone, under ten conditions. It is not FDA-approved, it is not on the bulks list, and research-use-only sales are unaffected.

Practical Recommendation

Check the identity on the COA against Appendix B: Ac-LKKTETQ, acetate salt, 949.1 g/mol.
Treat any TB-500 blend as outside the HHS policy, because the policy requires a single active ingredient.
Ask your state board of pharmacy whether it follows the federal policy before relying on it.

What we learned

With TB-500 the first question is what the product actually is. The HHS policy covers one specific molecule: the acetylated seven-residue fragment, as the acetate salt, injected, and sold alone. Many products sold as “TB-500” fail one of those tests before anyone gets to the sourcing and reporting conditions.

Frequently asked

Is TB-500 FDA-approved?

No. There is no FDA-approved drug containing TB-500, and it is not on the 503A bulks list.

Is TB-500 the same as thymosin beta-4?

No. HHS defines TB-500 acetate as a seven-residue acetylated fragment of thymosin beta-4 (Ac-LKKTETQ). It refers to thymosin beta-4 as the parent protein.

Can a pharmacy compound TB-500 now?

HHS says it will not act against 503A compounders using TB-500 acetate for subcutaneous or intramuscular injection on a prescription when all ten conditions of its 30 October 2026 policy are met. State law can still restrict it.

Are BPC-157 and TB-500 blends covered?

No. The policy requires a single active ingredient, so blends fall outside it.

Does the HHS policy cover oral or nasal TB-500?

No. For TB-500 acetate, the policy covers subcutaneous or intramuscular injectable dosage forms only. Other routes are outside it.

Does the policy change anything for research-use-only TB-500?

No. It covers state-licensed pharmacies, federal facilities and licensed physicians compounding on a prescription, not websites selling vials for research use.

Is TB-500 banned in sport?

Yes. USADA lists TB-500 as prohibited under WADA class S2.

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Is TB-500 Legal? Its US Regulatory Status After the HHS Peptide Policy (November 2026)