U.S. regulatory status

TB-500 (Thymosin Beta-4)

Also known as TB-500 · Thymosin Beta-4 · TB-4 · Timbetasin · Thymosin Beta-4 fragment

In limboPCAC recommended listing (8-6, Jul 23, 2026) - advisory only; still not on the 503A list

Is TB-500 (Thymosin Beta-4) legal right now?

TB-500 (a synthetic fragment associated with thymosin beta-4) is not an FDA-approved drug and is not on the Section 503A Bulk Drug Substances List, so pharmacies are not authorized to compound it. On July 23, 2026 the FDA's Pharmacy Compounding Advisory Committee voted 8-6, with 1 abstention, to recommend adding it - despite the FDA's own reviewers reporting that they could not identify a single human clinical study of the substance. The vote is advisory and does not bind the FDA. Nothing about TB-500's legal status changed on the day of the vote. Before it could be compounded lawfully the FDA would have to accept the recommendation and complete notice-and-comment rulemaking - a process the agency has not begun and that is generally estimated at 12 to 24 months. Its earlier removal from the interim Category 2 list, in April 2026, likewise did not authorize compounding: it was never in Category 1, the category that does.

In limbo: Nominated or removed from a restricted list but NOT approved - the headline implies a change, but the legal reality did not move.

Verified Aug 11, 2026 (ET) · status held since Jul 23, 2026

Primary source: Federal Register All 9 sources Reconstitution calculator Compared: vs BPC-157

The committee vote

July 23, 2026 ET

Question put to the FDA Pharmacy Compounding Advisory Committee (PCAC)“Should TB-500 (free base) be placed on the list? - and, as a separate vote, TB-500 acetate?”

Recommended by the committee

8 in favour
6 against
1 abstained

15 votes recorded. Tally reported by Healio and the FDA Law Blog (Hyman, Phelps & McNamara). The panel was not the same size for every substance - the meeting roster seats temporary voting members for single topics - so the totals legitimately differ between votes - the FDA has not yet published the meeting minutes, so treat the counts as reported rather than official.

What this does not do: an advisory committee recommendation is not an FDA decision and does not bind the agency. TB-500 (Thymosin Beta-4) is not on the 503A Bulk Drug Substances List, and a pharmacy compounding it today has no more federal authorisation than it did the day before the vote. Only a completed FDA rulemaking can change that.

Where it sits in the process

Nominated (completed)
Under review (advisory committee recommended it - not yet legal)
Rulemaking (upcoming)
Compounding-legal (upcoming)

Recommended by the advisory committee - and still not legal to compound. The vote is advisory and does not bind the FDA. Nothing changes until the FDA accepts the recommendation and completes notice-and-comment rulemaking. This is real forward motion, not a green light.

What changed last

Jul 23, 2026
FDA advisory committee (PCAC) voted 8-6, with 1 abstention, to recommend adding TB-500 to the 503A list - despite FDA reviewers reporting they could not identify a single human clinical study. Advisory only: TB-500 is still not on the list and still not legal to compound.
Not legalizedView on healio.com
Apr 22, 2026
Removed from FDA Category 2 after nominations were withdrawn - but it was never in Category 1, so it is still not legal to compound.
Not legalizedView on orrick.com
Apr 16, 2026
Placed on the July 23, 2026 FDA advisory committee agenda for possible inclusion on the 503A list.
Review scheduledView on federalregister.gov

Status elsewhere

TB-500 (Thymosin Beta-4): regulatory status by jurisdiction
Jurisdiction	Status	Note
United States (FDA)	In limbo	Not on the 503A Bulks List. PCAC recommended adding it on Jul 23, 2026 (8-6, 1 abstention); the recommendation is advisory and the FDA has not acted.
Australia (TGA)	Restricted	Thymosin beta-4 treated as Schedule 4 (prescription-only) under the Poisons Standard.
Sport / anti-doping (WADA)	Restricted	Prohibited at all times as a growth factor / non-approved substance.

Sources & transparency

Sources for this entry

Federal Register - PCAC notice of meeting (Docket FDA-2025-N-6895) Federal Register · primaryTB-500 (free base and acetate) on the July 23, 2026 agenda.
FDA - PCAC meeting page, July 23-24, 2026 FDA · primaryOfficial meeting record. FDA has not yet published the minutes or vote tallies.
FDA - PCAC July 23-24, 2026: questions put to the committee FDA · primaryFDA's own vote questions. Confirms each substance was voted on twice - free base and acetate separately - and gives the session order.
FDA - PCAC July 23-24, 2026: meeting roster FDA · primaryVoting members plus temporary voting members seated for single topics, which is why the vote totals differ between substances.
RAPS - FDA considers adding a dozen peptides to its bulk compounding list analysisConfirms TB-500 among the peptides under PCAC review and the prior Category 2 history.
FDA Law Blog - FDA's Pep(tide) Rally (Hyman, Phelps & McNamara) analysisRemoval from Category 2 did not make these peptides compoundable; they were never in Category 1.
BSCG - TB-500 status in sport analysisProhibited at all times under the WADA Prohibited List.
Healio - FDA committee recommends looser restrictions for several peptides analysisReported per-substance vote tallies; also records that FDA review staff recommended against all seven.
Mintz - FDA's Advisory Committee Votes on Peptides: What It Does and Doesn't Do analysisLegal analysis: the vote is not an agency action and nothing has legally changed.

Last verified by a human: Aug 11, 2026 (ET) · how we verify
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