Evidence signal01
The fragment has a defined biological rationale
TB-500 is connected to the actin-binding region of thymosin beta-4, and FDA reviewed nonclinical pharmacology and pharmacokinetic material.
FDA briefing pp. 6–7, 28–29Day 1 recordPCAC favorable
Peptide dossier / July 23–24, 2026TB-500
The central technical issue is identity: FDA treated the seven-amino-acid TB-500 fragment as distinct from full-length thymosin beta-4 and found no direct human TB-500 evidence.
Decision boundaryPCAC advice is not FDA approval, does not establish safety or effectiveness, and did not itself place either form on the 503A Bulks List.
Editorial review
The central tension in this record.
FDA staff recommended against both forms; PCAC voted favorably on both form-level questions.
Decisive limitation02
Related-molecule evidence cannot close the identity gap
FDA’s evaluation repeatedly separated TB-500 from full-length thymosin beta-4 and found no direct human evidence for the nominated wound-healing use.
FDA briefing pp. 20–33PeptideBase read
The committee outcome belongs beside the evidence record—not on top of it. A favorable advisory vote describes the panel’s recommendation on compounding eligibility; it does not erase FDA’s characterization, route-match or human-evidence concerns.
The case made in the room
Named speakers. Their strongest argument. Then the record check.
These are attributed testimony arguments, not PeptideBase endorsements. Each one is paired with the most relevant FDA answer and an explicit assessment of what the evidence can—and cannot—carry.
2named speaker moments
100%recording checked
Only named, source-reconciled speaker moments that were checked against the recording appear here. Statements remain attributed arguments unless the underlying evidence was independently established; no machine-caption wording is published as a quotation.
01Supports listing
Alex Tatem, MD
Board-certified urologist; fellowship-trained in male fertility, microsurgery and sexual medicine
Verify credentialsAttributed testimony
The identity-and-transfer argument
Tatem described TB-500 as a short active fragment of thymosin beta-4 and used human thymosin beta-4 studies as indirect safety context. He acknowledged that the formal human trials he cited involved the parent peptide rather than TB-500 itself.
tb-500 session · attributed argument, not an established factAudio-checked paraphrasePlay the source08:42:53–08:43:45
02Opposes listing
Peter Lurie, MD, MPH
President and Executive Director, Center for Science in the Public Interest; former FDA Associate Commissioner
Verify credentialsAttributed testimony
The hearing-wide case against all seven
Lurie said CSPI opposed adding all seven substances. He argued that the FDA criteria had not been met, that compounded products could create consumer risks, and that listing could weaken incentives for development through the standard drug-approval pathway.
Opening public hearing · explicitly applied to all seven substancesAudio-checked paraphrasePlay the source00:57:09–00:57:55
Evidence about thymosin beta-4 can inform the safety and identity case for TB-500.
Related-molecule evidenceWhat supports it
Human thymosin beta-4 studies are relevant background if TB-500 is the proposed active fragment. The hearing itself disputed whether evidence for the parent molecule transfers to the exact nominated material.
FDA’s answer
FDA considered both TB-500 forms not well characterized and found a lack of direct clinical and nonclinical safety information.
FDA Day 1 presentation · 09:05:56PeptideBase assessment
Parent-peptide evidence can generate a hypothesis. It cannot establish molecular equivalence or allow TB-500 to inherit thymosin beta-4’s human record.
Why the judgments diverged
The panel and FDA drew the transfer line in different places.
The favorable majority appears to have given some weight to thymosin beta-4 literature and supervised-access arguments. FDA kept the parent peptide and exact TB-500 material analytically and evidentially separate.
Editorial inference from the hearing record—not an attributed rationale for every voterClaim versus record
What the official material supports—and what it does not.
These are recurring propositions in the wider peptide discussion, not attributed speaker quotations.
Recurring claim
Evidence for thymosin beta-4 is evidence for TB-500.
Official record
FDA described TB-500 as a seven-amino-acid synthetic fragment of thymosin beta-4 and explicitly stated that the two are not the same substance.
What it does not establish
FDA briefing pp. 6–10, 20–23Parent-molecule or full-length-peptide evidence is indirect unless the exact TB-500 substance, form, dose and route are studied.
Recurring claim
Direct experiments showed TB-500 closes wounds.
Official record
FDA identified an in-vitro fibroblast scratch study in which TB-500 at the tested concentration did not induce wound closure.
What it does not establish
FDA briefing pp. 28–29A single negative in-vitro concentration does not settle all possible biological activity, but it also does not support a clinical wound-healing claim.
Evidence architecture
Eight questions applied consistently.
“Absent” means FDA said it did not identify that evidence within this evaluation. It is not a universal claim that no evidence exists anywhere.
| Evidence question | Status | FDA-record summary | Locator |
|---|---|---|---|
| Human clinical evidence | absent | FDA found no studies in which TB-500 was administered to humans. | Briefing pp. 20–23, 32–33 |
| Nonclinical evidence | limited | A direct fibroblast scratch study was negative at the tested concentration; other material often concerned related molecules. | Briefing pp. 28–29 |
| Exact-form match | contested | The nomination and certificate of analysis conflicted on free base versus acetate and other identity fields. | Briefing pp. 9–10 |
| Nominated-route match | indirect | Nonclinical pharmacokinetic work used SC and IP routes; no human evidence matched the nominated SC/IM products. | Briefing pp. 28–29, 33 |
| Evaluated-use match | absent | FDA found no adequate direct evidence for wound healing with either TB-500 form. | Briefing pp. 22–24 |
| Product characterization | limited | FDA considered both forms not well characterized and identified identity, impurity and aggregate-control gaps. | Briefing pp. 7–19 |
| Human safety | absent | FDA identified no human safety data by any route. | Briefing pp. 29–33 |
| Historical compounding use | limited | FDA found the extent of compounding use unclear. | Briefing pp. 20–22 |
Qualitative evidence map · no numerical score · scoped to FDA’s July 2026 evaluation
FDA findings
Five parts of the staff case.
01characterizationBoth TB-500 free base and TB-500 acetate were considered not well characterized.Day 1 pp. 100, 103
09:05:5602effectivenessFDA found a lack of evidence to evaluate effectiveness for wound healing.Day 1 p. 107
09:12:3003safetyFDA found a lack of clinical and nonclinical safety information.Day 1 pp. 108–112
09:14:3904historical useFDA found the extent of historical use in compounding unclear.Day 1 pp. 113–117
09:17:1205recommendationFDA proposed that neither TB-500 free base nor TB-500 acetate be included on the 503A Bulks List.Day 1 pp. 117–118
09:18:09
09:05:5602effectivenessFDA found a lack of evidence to evaluate effectiveness for wound healing.Day 1 p. 107
09:12:3003safetyFDA found a lack of clinical and nonclinical safety information.Day 1 pp. 108–112
09:14:3904historical useFDA found the extent of historical use in compounding unclear.Day 1 pp. 113–117
09:17:1205recommendationFDA proposed that neither TB-500 free base nor TB-500 acetate be included on the 503A Bulks List.Day 1 pp. 117–118
09:18:09
What changes the assessment
Open evidence gaps and direct sources.
A useful dossier should show the reader what evidence could materially strengthen or weaken the current read.
01
A definitive identity and nomenclature record for each nominated form
02
Direct TB-500 studies rather than extrapolation from thymosin beta-4
03
Prospective human safety and effectiveness evidence for wound healing
Decision boundaryPCAC advice is not FDA approval, does not establish safety or effectiveness, and did not itself place either form on the 503A Bulks List.
Continue the record
View all sevenRelated peptide dossiers
Day 1
BPC-157
The official record contains a limited human signal and substantial nonclinical literature, but the exact form, dosage form, route, duration and safety questions remain unresolved.
Open dossierDay 1KPV
KPV’s official-record case is primarily mechanistic and nonclinical. FDA said it found no human administration or exposure data by any route.
Open dossierDay 1MOTS-c
The scientific premise is mitochondrial and metabolic, but FDA said it found no clinical study or human-administration evidence and no adequate nonclinical toxicity package.
Open dossier