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No. 040 · Longevity & Immune · Immune Peptide

Thymosin Alpha-1

ThymalfasinZadaxinTα1

A Tier A · Controlled human trials how tiers work →
  • Not FDA approved
  • WADA — not listed
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28 residues C129H215N33O55
O O O O O O O O O H O O O O H O O O O O H O H O O H O O O O H O H O H O O O O O H O H O O O H O O O O O O H O O H O O H O O O O O O H O O H O N H N H N H N H N H N H N H N H N H N H N H N H N H N H N H N H N 2 H N 2 H N 2 H N H N 2 H N H N H N H N H N H N H N H N H N H N 2 H N H N H

2D structure from PubChem CID 16130571 (Thymalfasin), matched by molecular formula. Hydrogens on carbon are implied.

Thymosin Alpha-1 sequence fingerprint
  • Nonpolar 8
  • Polar 7
  • Positive charge 4
  • Negative charge 9

Each dot is a residue placed around the ring from N- to C-terminus; its distance from the centre reflects its chemistry.

01

Quick answers

What is Thymosin Alpha-1?
A thymic peptide that enhances T-cell maturation and dendritic cell function.
How strong is the evidence for Thymosin Alpha-1?
Tier A (controlled human trials) on the peptidemeta evidence scale. Many randomized trials, including the phase 3 TESTS trial in sepsis (BMJ 2025, no mortality benefit shown) and earlier RCTs in chronic hepatitis B. It is approved outside the US and EU but not by the FDA or EMA.
Is Thymosin Alpha-1 FDA-approved?
No. Thymosin Alpha-1 is not approved by the FDA for any use. Outside the US: China (1996) — Zadaxin (thymalfasin); Singapore — Zadaxin injection, prescription-only, for chronic hepatitis B and C.
Is Thymosin Alpha-1 banned in sport?
No. Thymosin Alpha-1 is not on the World Anti-Doping Agency Prohibited List.
How does Thymosin Alpha-1 work?
Thymosin alpha-1 is a 28-amino-acid thymic peptide that activates toll-like receptors (TLR2, TLR9) on dendritic cells, promoting MHC class I expression and antigen presentation. It enhances CD4+ and CD8+ T-cell maturation, stimulates NK cell cytotoxicity, and shifts the immune balance toward a Th1 response, improving antiviral and antitumor immunity.
What is known about the safety of Thymosin Alpha-1?
Approved outside the US/EU (Zadaxin) with clinical safety data from hepatitis trials; in the 1,106-patient TESTS sepsis RCT no safety outcome differed from placebo. FDA orphan drug designation (not an approval).

Last reviewed · editorial policy · markdown

02

Evidence

  1. D In vitro
  2. C Animal
  3. B Human pilot
  4. A RCT
  5. S Approved

TIER A — At least one published randomized controlled trial in humans.

Many randomized trials, including the phase 3 TESTS trial in sepsis (BMJ 2025, no mortality benefit shown) and earlier RCTs in chronic hepatitis B. It is approved outside the US and EU but not by the FDA or EMA.

Tiers rate the strength of published evidence — not effectiveness, safety, or a recommendation.

03

At a glance

Residues
28 amino acids, N→C
Molecular weight
3,108.3 Da
Formula
C129H215N33O55
Routes studied
Subcutaneous, Intramuscular Routes used in published research
FDA
Not approved
Other approvals
  • China (1996) — Zadaxin (thymalfasin)
  • Singapore — Zadaxin injection, prescription-only, for chronic hepatitis B and C
WADA
Not on the Prohibited List
04

Sequence

N → C · 28 residues · hover, tap, or use arrow keys to inspect

Note N-terminally acetylated; corresponds to residues 2–29 of human prothymosin α.

05

Overview

A thymic peptide that enhances T-cell maturation and dendritic cell function. Sold as Zadaxin (thymalfasin), it is approved outside the US and EU (e.g. China, Singapore) for chronic hepatitis B, but not by the FDA or EMA.

Research status Approved as Zadaxin in several countries outside the US/EU (e.g. China since 1996, Singapore); many RCTs, including the phase 3 TESTS sepsis trial (BMJ 2025), which found no 28-day mortality benefit

06

Mechanism

Thymosin alpha-1 is a 28-amino-acid thymic peptide that activates toll-like receptors (TLR2, TLR9) on dendritic cells, promoting MHC class I expression and antigen presentation. It enhances CD4+ and CD8+ T-cell maturation, stimulates NK cell cytotoxicity, and shifts the immune balance toward a Th1 response, improving antiviral and antitumor immunity.

07

Effects reported in research

Reported outcomes, not promises. Some come from controlled human trials; others may be from smaller or preclinical studies — check the studies below.

  • Enhanced T-cell and NK cell activity
  • Improved vaccine response rates
  • Modulated Th1/Th2 immune balance
  • Supported immune function in immunocompromised patients
08

Safety & unknowns

Approved outside the US/EU (Zadaxin) with clinical safety data from hepatitis trials; in the 1,106-patient TESTS sepsis RCT no safety outcome differed from placebo. FDA orphan drug designation (not an approval). Generally well-tolerated; reported side effects include mild injection site discomfort. Has been used in immunocompromised populations including cancer and hepatitis patients.

Unknowns. Trial safety data apply to the populations, formulations and conditions studied.

Informational only — not medical advice. peptidemeta publishes no dosing, protocols, or sourcing. Talk to a qualified clinician about any treatment decision.

09

Studies [2]

  1. Clinical trial 2025

    The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial

    Wu J, Pei F, Zhou L, et al. BMJ

    Phase 3 RCT in 1,106 adults with sepsis: 28-day mortality was 23.4% with thymosin α1 versus 24.1% with placebo, with no significant difference.

    [pubmed] [doi]

  2. Review 2007

    Thymosin alpha1: a historical overview

    Garaci E. Annals of the New York Academy of Sciences

    Historical overview of thymosin alpha 1 since its 1977 characterization, focusing on its use combined with cytokines and chemotherapy in cancer and infectious disease.

    [pubmed] [doi]

11

Status sources

Sources behind the tier, regulatory status, sequence and dates on this page.

12

Cite this entry

$ cite --format=apa

peptidemeta. (2026). Thymosin Alpha-1. In peptidemeta: The peptide library, ranked by evidence. Retrieved November 8, 2026, from https://peptidemeta.com/p/thymosin-alpha-1/

$ cite --format=bibtex 
@misc{peptidemeta-thymosin-alpha-1,
  title = {Thymosin Alpha-1},
  author = {{peptidemeta}},
  year = {2026},
  howpublished = {\url{https://peptidemeta.com/p/thymosin-alpha-1/}},
  note = {Accessed 2026-11-08}
}

Accessed date reflects when you opened this page. Cite primary studies for scientific claims.

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