Overview
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In plain language
Thymosin alpha-1 is a natural peptide of 28 amino acids first found in the thymus, the organ where immune T cells mature.
A lab-made version called thymalfasin (Zadaxin) is approved in a number of countries for hepatitis B and C and to help the immune system respond to vaccines. It is not FDA-approved in the United States.
For students
Thymosin alpha-1 (about 3,108 Da) was isolated in 1977 by Allan Goldstein and colleagues from thymosin fraction 5, a calf thymus extract. Its N-terminus is acetylated. It comes from a larger protein, prothymosin alpha.
It is reported to promote T-cell maturation and to act on dendritic cells through Toll-like receptors (TLR2 and TLR9), enhancing antiviral and Th1-type responses.
For researchers and instructors
Human evidence. Controlled trials in chronic hepatitis B, as a vaccine adjuvant and in severe infections such as sepsis have produced mixed results; meta-analyses are limited by trial quality.
Regulatory. Approved outside the U.S. (as thymalfasin); not FDA-approved. Products sold online in the U.S. are unregulated.
Status. Graded Controlled trials.
Molecular identity
- Amino acids
- 28
- Molecular weight
- ~3,108.3 Da
- Formula
- Form-dependent; verify
- Sequence
- Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN
Sequence map
N-terminus is acetylated (Ac-).
Hydropathy
Kyte–Doolittle score per residue. Positive values are water-repelling.
Origin and history
Thymosin alpha-1 was the first peptide purified from thymosin fraction 5, reported by Allan Goldstein’s group in 1977. It is a 28-amino-acid peptide that helps mature and activate immune T cells.
SciClone Pharmaceuticals developed a synthetic version, thymalfasin (Zadaxin), which was approved in a number of countries, including China and Italy, for hepatitis B and as an immune booster. It was never approved by the FDA. It drew new attention when it was used in China during the COVID-19 pandemic.
Key people
- Allan L. GoldsteinLed the team that isolated it
- SciClone PharmaceuticalsDeveloped thymalfasin (Zadaxin)
Timeline
- 1977
Isolated and sequenced from thymosin fraction 5
- 1990s
Approved outside the U.S. as Zadaxin
- 2020
Used in China during COVID-19
- Today
Not FDA-approved
See every peptide on one history timeline.
Human evidence
Human studies exist in selected infectious disease and oncology settings, with mixed and indication-specific evidence.
Study design, enrollment, endpoints, outcomes and limitations must be assessed individually; registration is not proof of efficacy.
Explore the literature for Thymosin alpha-1 and distinguish in-vitro, animal, and human findings.
Safety and regulatory status
See every compound on the regulatory tracker.
Approved in some countries; not FDA-approved as a drug in the United States.
Long-term risks, formulation differences, and human safety evidence require careful review. Educational content only; not medical advice.
Sources
Hernandez Gener, E. (2026, November 7). Thymosin alpha-1: molecular data, research history and evidence. VALREXA Biosciences. https://valrexa.com/peptides/thymosin-alpha-1.html
APA style · Last reviewed November 7, 2026 · Our editorial standardsLast reviewed November 7, 2026. Trial and regulatory status can change; confirm in the linked registries. This profile is educational and is not medical advice, a treatment recommendation, or dosing or sourcing guidance. Report an error · Corrections policy