U.S. regulatory status

TB-500 (Thymosin Beta-4)

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

Under reviewRemoved from Category 2 in April 2026; now before the FDA committee, 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 503A Bulk Drug Substances List, so pharmacies are not authorized to compound it. In April 2026 the FDA removed it from Category 2 (the "significant safety risks" bucket) after nominations were withdrawn - but it was never in Category 1, the category that permits compounding, so that removal did not change its legal status. It is scheduled for FDA advisory committee (PCAC) evaluation on July 23, 2026, where the FDA's briefing materials propose not adding it to the list.

Under review: Actively before the FDA advisory committee; a decision is pending and the status can move.

Verified Jul 7, 2026 (ET) · status held since Apr 16, 2026

Primary source: Federal Register All 4 sources

Where it sits in the process

Nominated(completed)
Under review(current stage)
Rulemaking(upcoming)
Compounding-legal(upcoming)

Next milestoneFDA advisory committee (PCAC) evaluates TB-500 for the 503A list - Jul 23, 2026 (in 15 days)

What changed last

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Removed from FDA Category 2 after nominations were withdrawn - but it was never in Category 1, so it is still not legal to compound.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)	Under review	Never in Category 1; removed from Category 2 in April 2026; before PCAC July 23-24, 2026 (Docket FDA-2025-N-6895).
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.
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.

Last verified by a human: Jul 7, 2026 (ET) · how we verify
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