The TB-500 FDA review hasn't ended, and it was never about approving a drug. TB-500 has never had an FDA-approved product in the United States. The question FDA has been working through since 2022 is narrower: whether TB-500 belongs on the 503A Bulks List, the federal list of raw ingredients a pharmacy may use to prepare a medicine for one patient's prescription. FDA's own reviewers said no in May 2026. An outside advisory committee said yes on July 23. FDA hasn't acted on that advice yet.
Here is each step, with the date its own document carries.
2022: a pharmacy nominates TB-500 for the 503A Bulks List
TB-500 is a lab-made fragment of thymosin beta-4, a 43-amino-acid protein found in most of the body's cells. The fragment is seven amino acids long (positions 17 to 23) with a small chemical cap on the front, written Ac-LKKTETQ. A Belgian doping-control lab identified that sequence in a product sold as TB-500 in 2012 (Esposito et al., Drug Testing and Analysis). The naming story lives in who discovered TB-500.
Wells Pharmacy Network's nomination was posted to FDA's public docket on August 29, 2022. It asked FDA to add "Thymosin Beta-4, Fragment (LKKTETQ)" to the 503A Bulks List as an injectable for wound healing. A nomination starts a review. It doesn't put anything on the list.
2023: FDA places TB-500 in Category 2
In its category document marked "Updated September 29, 2023", preserved by the Alliance for Pharmacy Compounding, FDA added the fragment to Category 2: its interim holding group for nominated ingredients it believes raise significant safety concerns. BPC-157, KPV and MOTS-c went in with the same update.
FDA's reasoning, still on its safety-risks page, is short. For certain routes of use, TB-500 may pose a risk of immunogenicity, meaning the immune system reacts to the drug itself, because peptides can clump and carry impurities. And "FDA has not identified any human exposure data" for it.
Category 2 was a policy position while the review went on. It wasn't a final rule, and it wasn't a ruling on anyone's prescription.
April 2026: the nomination is withdrawn, the review goes on
On April 14, 2026, Wells withdrew 12 peptide nominations at once, TB-500 among them. FDA's safety-risks page, current as of April 22, 2026, now lists TB-500 under "bulk drug substances nominated but withdrawn," and the nominations document marked "Updated May 14, 2026" places it in no category.
That can look like a step forward. It isn't. TB-500 left Category 2 without entering Category 1 or the list, and FDA's safety text stayed up. The agency kept evaluating it on its own initiative, and an April 16 notice in the Federal Register, the government's daily journal of rules and notices, scheduled the advisory meeting.
What FDA's staff review found
FDA's TB-500 briefing document, dated May 15, 2026, reviewed two chemical forms of the peptide, TB-500 free base and TB-500 acetate, for wound healing, since the nomination hadn't made clear which one it meant.
| What FDA asked | What the staff review found |
|---|---|
| Is the ingredient clearly defined? | No. "TB-500" is a common name, not an official drug name, and different salts and derivatives have been sold under it |
| Has it been given to people? | FDA found no study in which TB-500 was given to humans, by any route |
| Do lab and animal studies support wound healing? | FDA identified no animal study of TB-500 itself for wound healing; in one cell study it did not speed wound closure |
| Is it safe to inject? | Unknown; FDA flagged a risk of immune reactions to the proposed injections |
In that cell study, TB-500 didn't close scratch wounds in cultured fibroblasts (connective-tissue cells) faster than the control, while one of its breakdown products did (Rahaman et al., Journal of Chromatography B).
The naming point matters to anyone who has seen TB-500 sold online: FDA wrote that inconsistent names mean a patient may be dosed with a different ingredient than the physician ordered.
The staff's summary: "FDA is particularly concerned about the absence of human data on drug products containing these substances administered via any route of administration." Its conclusion: "we propose not adding TB-500 (free base) or TB-500 acetate to the 503A Bulks List."
The TB-500 PCAC vote on July 23
The Pharmacy Compounding Advisory Committee (PCAC) is an outside panel. FDA's meeting page says such committees "make non-binding recommendations to the FDA, which generally follows the recommendations but is not legally bound to do so."
TB-500 came up on the afternoon of July 23. The final agenda lists a public hearing, a presentation by three FDA reviewers including Emily Kneeream, PharmD, then the vote. FDA's question sheet posed two questions: should the free base go on the list, and should the acetate?
The committee said yes. With no written tally or minutes posted, FDA's official recording is the primary record. PharmExec's July 24 report put the count at 8 in favor, 6 against and 1 abstention, the same split it reported for BPC-157 and KPV. Our overview of the July peptide decision sets all seven votes side by side.
One detail matters for the Wolverine blend, which pairs BPC-157 with TB-500. The panel weighed each ingredient separately, for different uses: TB-500 for wound healing, BPC-157 for ulcerative colitis. It didn't review the pair.
Where the TB-500 FDA review stands today
As of September 22, 2026, the day this article was written, FDA had published no proposed or final rule adding TB-500 to the 503A Bulks List. A Federal Register search for TB-500 since April returns only the April 16 notice. The meeting page, current as of August 6, 2026, holds slides and recordings but no minutes. The comment docket, which closed July 22 and covered all seven peptides, shows 2,641 posted comments.
What would change the record is a document: a proposed rule in the Federal Register, then a public comment period, then a final rule. There is no published deadline, and FDA isn't bound by the vote.
New research hasn't closed the gap FDA described. A study published the day of the vote gave TB-500 to 32 rats after Achilles-tendon repair (Biçer et al., Joint Diseases and Related Surgery). An August 2026 review of six popular peptides, TB-500 included, found human studies "limited to a handful of investigations, most lacking robust controls" (Tewari et al., American Journal of Sports Medicine). Neither is a human trial of TB-500.
What the review does and doesn't change for a patient
TB-500 has never had an FDA-approved product in the United States, and nothing above changed that. The 503A list governs which raw ingredients a pharmacy may start from; it isn't drug approval, and the July vote covered wound healing only. The thymosin beta-4 explainer covers why studies of the full parent protein can't be credited to the fragment.
Regulatory status is one input, not a verdict on a person. A licensed provider may still prescribe a compounded formulation, and that decision is between you and your doctor. Federal and state compounding rules still apply to the pharmacy that fills it. TB-500 is coming soon to Promise as a compounded medication — add me to the list — and the formulation Promise will offer is not FDA-approved.
Why the naming problem favors a prescription
FDA's naming finding is the plainest case for a prescription over a vial ordered from a website, whose "TB-500" label may not say which salt or derivative is inside. A prescription names what the provider ordered, a licensed U.S. compounding pharmacy dispenses a labeled preparation, and there's a clinician to contact if something feels wrong. At Promise, a licensed provider reviews every request, and not everyone qualifies.
WADA's list is separate, and unchanged for 2027
WADA's 2026 Prohibited List names "Thymosin-ß4 and its derivatives e.g. TB-500" under S2.3, growth factors and growth factor modulators, a class prohibited at all times, in and out of competition.
As of September 22, 2026, the day this article was written, WADA had published its 2027 List on September 21, taking effect January 1, 2027, with the TB-500 entry in S2.3 unchanged. A favorable FDA vote doesn't change an athlete's anti-doping status, so anyone in tested sport has a separate question to raise with the provider.
