For clinicians
TB-500 for prescribers: status, evidence and what FDA has said
A neutral reference. It reports TB-500's regulatory status, the quality of its human evidence and what FDA has said about it. It does not suggest a dose, a protocol or a source.
Status reviewed 2026-10-01 · By the Grey Peptides Editorial Board · Regulatory fields generated from our tracker
| Also known as | Thymosin β4 fragment, Tβ4 (17-23) |
| Substances FDA reviewed | TB-500 (free base) and TB-500 acetate |
| FDA approval | Not FDA-approved |
| Compounding (503A) | Not compoundable; PCAC recommended it 8–6 (Jul 2026), FDA has not acted |
| Outsourcing (503B) | No 503B status recorded |
| FDA advisory committee | Reviewed July 23–24, 2026 (docket FDA-2025-N-6895): recommended, 8–6, 1 abstention |
| WADA 2026 List | Prohibited (S2.3) |
| WADA 2027 List | Prohibited (S2.3) |
| Evidence grade | Low |
| Status reviewed | 2026-10-01 |
What FDA has said
FDA staff's position, in its briefing for the July 23–24, 2026 committee meeting: FDA proposes not adding either TB-500 substance to the 503A Bulks List, citing a lack of physicochemical data, a lack of historical use in compounding, and no information on use in humans — plus a specific immunogenicity concern about the proposed injectable route.
The use FDA evaluated. Nominated for wound healing.
FDA's objections
FDA says TB-500 (free base) is not physically and chemically well characterised, citing naming that does not follow INN, USAN or IUPAC standards and missing critical characterisation data.
Unlike most of the seven, FDA found a lack of historical use in compounding for TB-500 specifically.
There was a lack of any evidence of effectiveness for either form.
FDA describes the information on human use as non-existent, and adds that peptides given by the proposed injectable routes may pose a significant risk for immunogenicity.
Specific to TB-500
TB-500 is on the World Anti-Doping Agency's prohibited list under section S2.3. WADA approved a project in 2013 to determine detection limits for TB-500 metabolites and build them into peptide screening methods. Anyone subject to anti-doping testing should treat any change in compounding status as irrelevant to their situation — the two regimes are unrelated.
TB-500 is a short fragment of thymosin β4, not thymosin β4 itself. Full-length thymosin β4 has been studied in FDA-registered trials; that record does not transfer to the fragment, and FDA's evaluation does not treat it as if it does.
FDA describes websites selling TB-500 in 2 mg to 15 mg vials stating the products are for research use only, and at least one providing reconstitution and administration instructions. It also cites published analysis of online forum discussion in which TB-500 was among the most frequently mentioned substances, trending upward after 2010.
FDA lists Thymosin beta-4, fragment (LKKTETQ), also known as TB-500 among substances it has identified as potentially presenting significant safety risks outside Category 2 (page current as of 2026-04-22). In FDA's words:
Compounded drugs containing thymosin Beta-4, Fragment (LKKTETQ) may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation as well as peptide-related impurities. 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.
Monitoring: what the literature does and does not say
- No label. TB-500 has no FDA-approved label, and therefore no labelled guidance on monitoring.
- What FDA has said about its risks is quoted above, from its list of bulk substances that may present significant safety risks.
- Immunogenicity. FDA's July 2026 review found no adequate information to assess the risk that TB-500 provokes an immune response.
- What is in the vial. FDA judged the substance not well characterised physically and chemically — the property FDA relies on to know what a compounded product actually contains.
- Findings specific to TB-500. FDA's review also describes points particular to this compound, some of them safety signals; they are set out above in FDA's own terms.
These are gaps, not a monitoring schedule. This page does not supply one, and for a compound in this position the human evidence would not support one.
Compounding: where it stands
Today's position for TB-500: Not compoundable; PCAC recommended it 8–6 (Jul 2026), FDA has not acted. An FDA advisory committee's vote is a non-binding recommendation; until FDA acts, a vote does not change what may be compounded. Our explainer on the 503A and 503B categories sets out what each status means, and the regulatory tracker is updated as FDA acts.
The evidence
Grey Peptides grades TB-500's evidence base as low. Human data is effectively absent. The frequent conflation of TB-500 with full-length thymosin β4 is the single most common factual error made about this compound.
The encyclopedia entry lists the human and animal studies we hold, each with its PMID and FDA's full briefing is summarised on our page for the July 2026 review.
What this page leaves out
Doses, regimens, cycle lengths and sources. That is deliberate. A reference that reports status and evidence is useful only if it is not also a protocol, and for a compound in this position there is no approved one to report.
Sources
- US Food and Drug Administration. Pharmacy Compounding Advisory Committee meeting, July 23–24, 2026: briefing documents, docket FDA-2025-N-6895. FDA
- US Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Content current as of 2026-04-22; read 2026-10-01. FDA
- Grey Peptides regulatory tracker, row for TB-500, reviewed 2026-10-01. Tracker · dataset
- World Anti-Doping Agency. Prohibited List 2027, dated August 26, 2026, in force January 1, 2027. WADA
This page is a reference for qualified professionals. It is not medical advice, it does not recommend any treatment, and it is not a substitute for the prescriber's own judgement and their state and federal obligations.
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