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Thymosin alpha-1 regulatory status

Current status of Thymosin alpha-1 in the United States: Removed from Category 2 (Apr 2026). In sport: WADA status unclear. Details, sources, and the dated timeline follow.

By the PeptideAgent Editorial Team. Draft, pending editorial review.  Last verified

What is the current status of Thymosin alpha-1?

Regulatory: Removed from Category 2 (Apr 2026)WADA: WADA status unclearVerified: Verified Sep 22, 2026
FDA and compounding
Not FDA approved, although approved as Zadaxin (thymalfasin) in more than 30 countries. FDA placed thymosin alpha-1 in 503A Category 2 in 2023, citing immunogenicity risk and inadequate safety information for compounded product. FDA's Category 2 page (current as of April 22, 2026) now lists it under bulk drug substances nominated but withdrawn, so it is no longer in Category 2 but has no active nomination and is not on the 503A bulks list. That leaves US compounding pharmacies without a lawful basis to make it. It was not among the peptides reviewed by the advisory committee in July 2026.
WADA
WADA status unclear
Access path
  1. No lawful United States access path identified on the last verified date; the 503A nomination was withdrawn and it is not on the bulks list.
  2. Not available as an FDA approved product in the United States, although approved abroad as Zadaxin (thymalfasin).
  3. Products labeled research use only are not lawful for human use and are not verified for identity or purity.

Full Thymosin alpha-1 page: evidence, dosing in the literature, and sources

How has the status of Thymosin alpha-1 changed over time?

  1. FDA

    FDA lists BPC-157 and 16 other peptides as withdrawn from 503A Category 2

    FDA's Category 2 page, revised in April 2026 and current as of April 22, 2026, moved BPC-157, AOD-9604, CJC-1295, dihexa, DSIP, epitalon, injectable GHK-Cu, ipamorelin, KPV, LL-37, melanotan II, MOTS-c, PEG-MGF, selank, semax, thymosin alpha-1, and thymosin beta-4 fragment (TB-500) to a list of bulk drug substances nominated but withdrawn by their nominators. A withdrawn substance is no longer in 503A Category 2, but withdrawal is not an approval and does not place a substance on the 503A bulks list; a 503A pharmacy still needs a listing before it may compound it. Ipamorelin acetate remains in 503B Category 2. Seven of the withdrawn peptides (BPC-157, KPV, TB-500, MOTS-c, semax, epitalon, and DSIP) were taken to the Pharmacy Compounding Advisory Committee in July 2026.

    Regulatory: Removed from Category 2 (Apr 2026)Source: FDA: Certain bulk drug substances for use in compounding may present significant safety risks (503A and 503B Category 2 lists and withdrawn nominations, content current as of April 22, 2026)
  2. FDA

    FDA places a batch of nominated peptides in 503A Category 2

    In September 2023 FDA updated its 503A bulk drug substances category lists to place a group of nominated peptides in Category 2, which means FDA identified significant safety risks and the substances may not be used in 503A compounding while the evaluation continues. Kisspeptin-10 and ibutamoren (MK-677) were added on September 29, 2023 and remain in Category 2 on the FDA page current as of April 22, 2026. BPC-157, CJC-1295, ipamorelin, AOD-9604, dihexa, DSIP, epitalon, KPV, MOTS-c, selank, semax, melanotan II, LL-37, thymosin alpha-1, and thymosin beta-4 fragment (TB-500) were also placed in Category 2 under the 503A interim policy; that same page now lists them as nominated but withdrawn (see the April 2026 event). Hexarelin, PNC-27, and 5-amino-1MQ have never appeared on the FDA category lists.

    Regulatory: Not eligible for compoundingSource: FDA: Certain bulk drug substances for use in compounding may present significant safety risks (503A and 503B Category 2 lists and withdrawn nominations, content current as of April 22, 2026)

Sources

Numbered citations in the answers above point here, followed by the regulatory sources on record for Thymosin alpha-1 and the source of each dated event.

  1. [1]FDA: Certain bulk drug substances for use in compounding may present significant safety risks (Category 2 list and withdrawn nominations, content current as of April 22, 2026)FDA, 2026
  2. [2]FDA: Bulk drug substances used in compounding under section 503A of the FD&C ActFDA, 2026
  3. [3]FDA: July 23-24, 2026 meeting of the Pharmacy Compounding Advisory Committee (BPC-157, KPV, TB-500, MOTS-c, DSIP, semax, epitalon)FDA, 2026
  4. [4]WADA Prohibited ListWADA, 2026

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