Skip to content

Reference information only. Therapept does not sell peptides and does not provide medical advice.Research-use notice

Therapept

Synthetic 28-residue N-acetylated peptide corresponding to the N-terminal fragment of prothymosin alpha

Thymosin alpha-1 — evidence

What has been published, classified by the kind of document it is. This is not a protocol, not a score, and not a recommendation for use.

Evidence overview

3 records in this file

  • REVIEW1
  • REGULATORY2

Research areas. Immunology review; United States approval; United States compounding.

Publication span. 2016–2026.

What we know

  • Marketed in some jurisdictions outside the United States (thymalfasin / Zadaxin). No Drugs@FDA approval record.
  • FDA's withdrawn nomination cites immunogenicity risk and inadequate safety information for compounding.
  • A 2016 review by manufacturer-affiliated authors summarises preclinical and clinical immune-cell findings; it is not a US label and not an independent safety assessment.

Editorial reading of the records below, labelled as Therapept analysis. How records are built

What remains uncertain

  • How non-US labelled use should be read against US compounding policy — they are different systems.

Regulatory notes

No FDA-approved product

  • No record found in Drugs@FDA under thymalfasin. Not approved in the United States.
  • Listed on FDA's table of bulk substances nominated for compounding and withdrawn by the nominator.
  • FDA's published concerns state that compounded thymosin alpha-1 may pose significant risk for immunogenicity, and that available safety information is inadequate for the agency to understand the extent of any safety issues.
  • Not named on the WADA 2026 Prohibited List.

Regulatory status describes how a substance is classified. It is not a safety assessment of any particular material.

Studies and documents

  1. REGULATORY2026Negative regulatory search

    Drugs@FDA — no thymalfasin / Zadaxin record

    U.S. Food and Drug AdministrationDrugs@FDA

    Objective
    To record the absence of a United States approval.
    Endpoint investigated
    Marketing authorisation (none found)

    No record found in Drugs@FDA under thymalfasin. Not approved in the United States, though the substance is marketed in some other jurisdictions.

    Limitations. Absence of a record is not a safety study.

    Drugs@FDA — approved drug productsReviewed 12 September 2026

  2. REGULATORY2026Regulatory listing

    FDA table of bulk drug substances nominated for compounding and subsequently withdrawn

    U.S. Food and Drug AdministrationFDA compounding communications

    Objective
    To record FDA's published compounding position.
    Endpoint investigated
    Compounding classification

    Nomination withdrawn. FDA's published concerns state that compounded thymosin alpha-1 may pose significant risk for immunogenicity, and that available safety information is inadequate for the agency to understand the extent of any safety issues. Not approved in the United States.

    Limitations. US compounding classification. Non-US marketing is a separate fact.

    FDA — Certain bulk drug substances for use in compounding may present significant safety risksReviewed 12 September 2026

  3. REVIEW2016Narrative review (manufacturer-affiliated authors)

    Immune modulation with thymosin alpha 1 treatment

    King R, Tuthill CVitamins and Hormones

    Objective
    To summarise preclinical and clinical literature on the immune effects of thymosin alpha 1.
    Endpoint investigated
    Immune-cell subsets and proposed applications, as described by the authors

    Review of thymosin alpha 1 (thymalfasin) pharmacology and of preclinical and clinical studies of its effects on immune-cell subsets, including action through Toll-like receptors on dendritic cells. Both authors list SciClone Pharmaceuticals affiliations. The paper summarises a literature; it is not an independent safety assessment.

    Limitations. Narrative review by manufacturer-affiliated authors, not a systematic analysis. Not a United States labelling document, and it does not establish a US approval.

    DOI 10.1016/bs.vh.2016.04.003King and Tuthill, Vitam Horm (2016)Reviewed 15 September 2026

Last reviewed 3 September 2026 · Compiled by Therapept Editorial · How these records are built