A 28-amino-acid thymus peptide that modulates immune responses. It is approved in some countries but not in the U.S.
Key takeaway
Thymosin alpha-1 occurs naturally in the thymus. As thymalfasin, it is approved outside the U.S. for uses such as hepatitis B and as an immune adjuvant.
At a glance
| FDA status | Not FDA-approved |
|---|---|
| 503A compounding | No 503A pathway: nomination withdrawn after FDA safety review |
| Body areas | Immune & inflammation |
| Through ScriptMates | Information only |
| Open questions | None noted |
What is thymosin alpha-1?
Thymosin alpha-1 occurs naturally in the thymus. As thymalfasin, it is approved outside the U.S. for uses such as hepatitis B and as an immune adjuvant.
It has no U.S. approval. FDA flagged a significant risk of immunogenicity and impurities in compounded versions.
Dosage forms
No FDA-approved dosage form. A standardized dosage form for human use was not confirmed from the sources below.
Is thymosin alpha-1 FDA-approved?
Not FDA-approved. Thymosin alpha-1 was nominated for the 503A bulks list and placed in Category 2 over safety concerns; the nomination was later withdrawn. FDA notes it has no, or only limited, safety information for the proposed uses.
Can it be prescribed through ScriptMates?
No 503A pathway: nomination withdrawn after FDA safety review. A partner pharmacy lists it, but it has no lawful 503A pathway today (nomination withdrawn after FDA safety review).
Sources
- FDA: Bulk substances that may present significant safety risks (Category 2 and withdrawn nominations)
- FDA: Bulk drug substances nominated under 503A, Categories 1–3 (May 14, 2026)
Checked October 27, 2026. FDA updates these pages, so confirm before relying on them.