U.S. regulatory status
Thymosin Alpha-1
Also known as Thymalfasin · Zadaxin · Tα1
Is Thymosin Alpha-1 legal right now?
Thymosin alpha-1 is not on the FDA's 503A Bulk Drug Substances List and was never in Category 1, so it is not eligible for compounding under Section 503A. It was removed from Category 2 in September 2024 after its nomination was withdrawn, but that removal did not authorize compounding. The FDA's advisory committee reviewed it on December 4, 2024 and did not recommend adding it to the list, citing immunogenicity and characterization concerns and the absence of an approved U.S. indication. There is no FDA-approved thymosin alpha-1 product in the United States (the branded product Zadaxin is approved in some other countries), leaving it in regulatory limbo.
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 Jul 16, 2026 (ET) · status held since Dec 4, 2024
Where it sits in the process
- Nominated (stalled here - not advancing)
- Under review (not reached)
- Rulemaking (not reached)
- Compounding-legal (not reached)
Not on a path to the 503A list right now. The process stalled or reversed at this stage - read the status above. Sitting at an earlier step is not a sign it will advance.
What changed last
FDA advisory committee reviewed thymosin alpha-1 and did not recommend adding it to the 503A list.
Status elsewhere
| Jurisdiction | Status | Note |
|---|---|---|
| United States (FDA) | In limbo | Removed from Category 2 (Sept 2024); PCAC declined to recommend it on Dec 4, 2024; not on the 503A list; no approved U.S. product. |
| Australia (TGA) | Restricted | Regulated as Schedule 4 (prescription-only); the TGA has enforced against unlawful advertising. |
| Sport / anti-doping (WADA) | Unscheduled | Not specifically named on the Prohibited List (distinct from thymosin beta-4, which is prohibited). |
Sources & transparency
Sources for this entry
- FDA - 503A bulk drug substances: Category 1 & Category 2 lists FDA · primaryThymosin alpha-1 is not on the 503A list and was never in Category 1, per the FDA 503A categories.
- FDA - PCAC December 4, 2024 meeting materials FDA · primaryDec 4, 2024 PCAC reviewed thymosin alpha-1 and did not recommend adding it to the 503A list.
- TGA - enforcement re: thymosin alpha-1 advertising TGA · primaryIndicates prescription-only (Schedule 4) status in Australia.
- National Law Review - What FDA's latest actions mean for peptide compounding analysisRemoval from Category 2 does not authorize compounding; substances not moved into Category 1.
- Last verified by a human
- Jul 16, 2026 (ET) · how we verify
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- Peptlas Research Team - independent. About us.
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