Dr. Peppa

Is thymosin alpha-1 FDA approved? No, and the confusion is understandable

Published by Dr. Peppa ·

Disclosure: Dr. Peppa is owned and operated by Medtruva LLC, which sells peptide products, including some compounds discussed on this site. Advertisements are labeled.

The short answer

  • Not FDA approved. FDA's own documents say so directly.
  • It is approved in a number of other countries, sold as Zadaxin, mainly for hepatitis B.
  • It has more human trial data behind it than most peptides discussed online.
  • It's 28 amino acids long, not 21, a detail that's frequently misstated.

What FDA says

FDA's Pharmacy Compounding Advisory Committee reviewed thymosin alpha-1 in December 2024. The agency's own presentation slides state that it "is not approved in the United States, Japan, or Europe (except Italy)."

There is no listing for thymalfasin or Zadaxin in Drugs@FDA, the database of approved products.

Where the "approved" claim comes from

Three things feed the confusion.

It's approved elsewhere. The manufacturer states that Zadaxin is approved in countries across Asia, Latin America, Eastern Europe and the Middle East, mainly for hepatitis B and C and as an adjunct in some other settings. FDA quotes that claim in its review and adds that it "is unable to independently verify" it.

Orphan drug designation isn't approval. Secondary sources report that FDA granted orphan designation for DiGeorge anomaly, a condition where children are born without a working thymus. Designation is a status that encourages development of drugs for rare diseases. It is not permission to market. We weren't able to confirm the designation in FDA's database.

It has real human trials. Unlike most peptides in this conversation, thymosin alpha-1 has been tested in randomized trials, including a sepsis trial and later meta-analyses. Having trial evidence and having FDA approval are different things.

The other detail people get wrong

Thymosin alpha-1 is frequently described as a 21-amino-acid peptide. The original 1977 paper from Allan Goldstein's lab, which first described it, says it is "composed of 28 amino acid residues." FDA's slides also say 28.

What it is

Thymosin alpha-1 comes from the thymus, the gland that trains immune cells and shrinks with age. It was isolated from a preparation called thymosin fraction 5. Research interest centers on immune function, which is why it's been studied in infections and as a vaccine adjuvant.

Compounding status in the US

Thymosin alpha-1 was among the peptides FDA placed in its restricted category in 2023. Following the 2024 advisory committee review and later nomination withdrawals, it appears on FDA's "nominated but withdrawn" list rather than the list pharmacies may compound from.

Sources