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It was removed from Category 2 in September 2024 after its nomination was withdrawn, but that removal did not authorize compounding.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: Moved on paper - nominated, removed from a restricted list, or recommended by an FDA committee - but not added to the 503A list. The headline implies a change; the legal status has not moved.

Verified Sep 22, 2026 (ET) · status held since Dec 4, 2024

Primary source: FDA All 7 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 (Sept 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.
United Kingdom (MHRA)RestrictedNo UK marketing authorisation; supply for human use treated as an unlicensed medicine.
European Union (EMA)RestrictedNo EU-wide EMA marketing authorisation - thymalfasin holds only an orphan designation (EU/3/02/110) - and is reported as nationally authorised on prescription in Italy as Zadaxin.
Canada (Health Canada)RestrictedNot authorized for sale; no Drug Product Database listing, and Health Canada named thymosin alpha-1 among unauthorized injectable peptides seized in April 2025.
Sport / anti-doping (WADA)UnscheduledNot specifically named on the Prohibited List (distinct from thymosin beta-4, which is prohibited).

The U.S. status is watched by automation every six hours. Statuses elsewhere change less often and are covered by a monthly wide-net sweep, then re-verified whenever a lead surfaces - this entry’s last-verified date covers every row above. How we track it

Sources & transparency

Sources for this entry

Last verified by a human
Sep 22, 2026 (ET) · how we verify
Who runs this
Peptlas Research Team - independent. About us.
What we sell
Nothing. No products, no affiliates, no sponsored placements.

This page reports publicly available regulatory status for information only. It is not medical or legal advice and makes no health claim. See our full disclaimer.