U.S. regulatory status

Thymosin Alpha-1

Also known as Thymalfasin · Zadaxin · Tα1

In limboOff Category 2, never in Category 1; PCAC declined Dec 2024

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 It was removed from Category 2 in late 2024 after its nomination was withdrawn, but that removal did not authorize compounding.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 7, 2026 (ET) · status held since Dec 4, 2024

Primary source: FDA All 4 sources

Where it sits in the process

  1. Nominated
  2. Under review
  3. Rulemaking
  4. Compounding-legal

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

  1. FDA advisory committee reviewed thymosin alpha-1 and did not recommend adding it to the 503A list.

    Not legalizedView on federalregister.gov

Status elsewhere

JurisdictionStatusNote
United States (FDA)In limboRemoved from Category 2 (2024); PCAC declined to recommend it on Dec 4, 2024; not on the 503A list; no approved U.S. product.
Australia (TGA)RestrictedRegulated as Schedule 4 (prescription-only); the TGA has enforced against unlawful advertising.
Sport / anti-doping (WADA)UnscheduledNot specifically named on the Prohibited List (distinct from thymosin beta-4, which is prohibited).

Sources & transparency

Sources for this entry

Last verified by a human
Jul 7, 2026 (ET) · how we verify
Who runs this
Peptlas Research Team - independent. About us.
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Confidence
medium - some facts here rest on secondary reporting. Always confirm against the primary source before you rely on it.

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