Thymosin Alpha-1 Thymalfasin · Tα1

What is thymosin alpha-1?

Allan Goldstein’s group isolated thymosin alpha-1 in 1977 from “thymosin fraction 5”, a calf-thymus extract, and sequenced it: 28 amino acids, very acidic, with an acetylated serine at the N-terminus. A chemically synthesised version was as active as the natural one in their assays, and synthetic thymosin alpha-1 is what the drug name thymalfasin refers to. In 1984 the same sequence was found at the start of a larger protein, prothymosin alpha, which is the main form in thymus tissue.

No dedicated receptor has been identified. The best-characterised mechanism is signalling through Toll-like receptors: in a 2004 study it matured dendritic cells and drove interleukin-12 production through the MyD88-dependent pathway. Despite the shared name it is unrelated to thymosin beta-4, the actin-binding protein that TB-500 comes from; both names come from the thymus extract they were first found in.

Thymosin alpha-1 identity

Sources: the FDA substance registry (GSRS UNII W0B22ISQ1C), UniProt, PubChem and The chemistry and biology of thymosin. II. Amino acid sequence analysis of thymosin alpha1 and polypeptide beta1, Low TL, Goldstein AL. Journal of Biological Chemistry, 1979.

Certificate for the current lot

The current lot was analysed by ILS Laboratories in San Diego, which states ISO/IEC 17025 accreditation for activities within its published scope. The certificate reports HPLC purity, net peptide content and identity:

Thymosin alpha-1 price

Price per vial and per milligram, read live from the store:

Published research on thymosin alpha-1

Thymosin alpha-1 has decades of clinical literature, much of it from China and Italy. The larger, better-controlled trials have mostly been negative or null on their primary end points, and the list below says so.

• Isolation and sequence (1977, 1979). The 28-residue peptide from thymosin fraction 5, its acetylserine N-terminus and its activity in thymocyte assays. Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide. Goldstein AL, et al. PNAS, 1977; Low TL, et al., 1979.
• The parent protein (1984). Prothymosin alpha, a protein of about 112 residues carrying the thymosin alpha-1 sequence at its N-terminus, was the main immunoreactive form in rat thymus. Prothymosin alpha: isolation and properties of the major immunoreactive form of thymosin alpha 1 in rat thymus. Haritos AA, et al. PNAS, 1984.
• Toll-like receptor signalling (2004). In fungus-pulsed dendritic cells it induced maturation and interleukin-12 production through p38 MAPK, NF-κB and MyD88-dependent Toll-like receptor signalling. Thymosin alpha 1 activates dendritic cells for antifungal Th1 resistance through toll-like receptor signaling. Romani L, et al. Blood, 2004.
• Hepatitis B (1998, 1999). A randomised trial in Taiwan and a US phase 3 placebo-controlled trial in 97 patients; the US trial did not reach significance on its primary end point. Chien RN, et al., 1998; Mutchnick MG, et al., 1999.
• Hepatitis C add-on (2012). A 552-patient phase 3 trial with peginterferon and ribavirin in prior non-responders missed its intention-to-treat end point. Ciancio A, et al. Journal of Viral Hepatitis, 2012.
• Metastatic melanoma (2010). A 488-patient, five-arm randomised study in combination with dacarbazine, with tumour response as the primary measure. Maio M, et al. Journal of Clinical Oncology, 2010.
• Sepsis, TESTS (2025). A double-blind, placebo-controlled phase 3 trial in 1,106 patients at 22 centres in China found no difference in 28-day mortality (hazard ratio 0.99), after an earlier single-blind trial (ETASS, 2013) had reported a marginal result. The efficacy and safety of thymosin alpha1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. Wu J, et al. BMJ, 2025; Wu J, et al. Critical Care, 2013.

FDA’s 2024 review reports a short elimination half-life, about 2 hours.

Regulatory status

Thymalfasin is not approved in the United States. It is sold as Zadaxin in a number of other countries, including China, where it is approved for hepatitis B; EMA states that in the EU it is authorised in Italy. In the US it holds four orphan designations (hepatitis B, DiGeorge anomaly, hepatocellular carcinoma and melanoma), none of them an approval. FDA placed it in its 503A compounding category 2 in September 2023 and removed it in September 2024 when the nomination was withdrawn; at FDA’s Pharmacy Compounding Advisory Committee in December 2024 the members voted 17 to 4 against adding it to the compounding bulks list. FDA briefing document, December 2024; committee minutes; EMA orphan designation EU/3/02/110. Clean Peptide’s thymosin alpha-1 is a laboratory reference material, not Zadaxin, and is not for human or veterinary use.

Related research

• TB-500, a fragment of the unrelated thymosin beta-4.
• KPV and BPC-157, with their own certificates.
• Peptide testing: what a certificate’s purity, content and identity lines show.
• All longevity and mitochondrial peptides.