Region — International. Neutral scientific reference — not offered for sale here.

Set region

Explore Shop Tools Journal Trust

Explore  /  Thymosin Alpha-1 (Thymalfasin / Zadaxin)

Research reference — not for sale

Thymosin Alpha-1 (Thymalfasin / Zadaxin)

B

lead outcome

Chronic hepatitis B (approved indication)

grades vary by outcome ↓

Peptide

also called — Thymosin Alpha-1 · Tα1 · thymalfasin · INN thymalfasin · brand Zadaxin · a thymic immune peptide. INCI: none

immune modulationantiviral (hepatitis)vaccine adjuvant(studied:) sepsis, cancer, COVID-19

Reference entry — not sold here. The strong-evidence immune peptide and a deliberate contrast to DSIP (#45): where DSIP is "50 years, still unproven," Thymosin Alpha-1 is approved in ~35 countries with a large clinical database. A prescription/compounded drug, not a wellness supplement. No dosing published here.

In brief

Thymosin Alpha-1 (thymalfasin / Zadaxin) is a 28-amino-acid thymic immune-modulating peptide and one of the most clinically validated peptides in this register — approved in ~35 countries, with a 2024 review documenting >30 clinical trials in >11,000 people. Its strongest evidence is chronic hepatitis B and immune modulation. It is not FDA-approved for marketing in the US (orphan designations and Phase 3 that stalled commercially, not on safety), and its US compounding status has been unsettled. The general "immune-boosting" wellness use is extrapolated. It is distinct from the tissue-repair peptide TB-500 (#12) despite the shared "thymosin" name.

Legal standing, by region

European Union

not EMA-centrally approved (used in some countries' clinical

not EMA-centrally approved (used in some countries' clinical practice/trials).

United States

Not FDA-approved (under review)

not FDA-approved for marketing (orphan designations + stalled Phase 3). Historically dispensed via 503A/503B compounding; its compounding status has been in flux through the 2023–2026 FDA peptide review — confirm current status.

Evidence, by outcome

How we grade →

An honest grade per outcome — drawn from the evidence, not any catalogue. Hype and undemonstrated marketing claims grade low.

OutcomeEvidence base · effectGrade

Chronic hepatitis B (approved indication)

Strongest use; approved widely but not FDA-approved (US)

Pivotal trials; approved in ~35 countries; part of a >30-trial / >11,000-subject database · Antiviral / immune benefit

B

Immune modulation / vaccine response (elderly, immunocompromised)

Benefit clearest in immunocompromised; context-dependent

RCTs (co-administration with influenza, hep B, COVID vaccines) · Improved antibody titres / durability

B

Sepsis

Aggregate evidence re-evaluated; context-dependent

Multiple RCTs + systematic review/meta-analysis · Suggestive / mixed

C

Cancer immunotherapy adjunct

Adjuvant use; results mixed across cancers

>40 adjuvant trials (melanoma, HCC, NSCLC); 2006 NSCLC (n=95, +21% 12-mo survival) · Mixed

C

COVID-19 (severe/hospitalised)

Observational/pilot; not definitive

Zhang 2020 (China); Shehadeh 2023 US pilot (hypoxemia + lymphocytopenia) · Encouraging but preliminary

C

General "immune boosting" (healthy people / wellness)

Not proven for healthy-person immune enhancement

Extrapolated from mechanism + age-related decline · Plausible

D

Safety

Very well tolerated; minimal side effects

Millions treated; approved-drug record · Excellent

—

Disclosure

Vallydia sells its own cosmetic serums, and some ingredients graded here belong to the same categories as those products. Grades are drawn from the published evidence by the method we publish, and applied to our own ingredients on the same terms — our copper-peptide serum is graded no more kindly than the peptides it competes with. We disclose the interest so you can weigh it.

Trade names shown here (for example Matrixyl, Argireline, Syn-Ake) are the property of their respective owners and are used only to identify the ingredient under discussion. Their appearance implies no affiliation with, or endorsement by, the proprietor.

Evidence changes

Get notified if this changes

We track new research and update these grades as the evidence moves. Leave your email and we'll tell you if the evidence for Thymosin Alpha-1 (Thymalfasin / Zadaxin) changes - nothing else.

Identity

a 28-amino-acid, N-terminally acetylated peptide (~3,108 Da; < 40 aa → peptide), a fragment of prothymosin alpha, produced by thymic epithelial and peripheral immune cells. Its international non-proprietary name (INN) is thymalfasin, and it has been marketed as Zadaxin. Serum levels decline ~40–60% with age (thymic involution). Discovered by Allan Goldstein's lab at George Washington University (Goldstein et al., 1977) — the same lab associated with thymosin beta-4 / TB-500 (#12) — but Tα1 and Tβ4 have fundamentally different biology (Tα1 = immune modulator; Tβ4 = actin-sequestering tissue repair).

Development & history

Isolated by Goldstein's group in the 1970s from thymic tissue (thymosin fraction 5) — one of the first demonstrations that the thymus secretes soluble immune-modulating factors. Synthetic Tα1 was made by solid-phase synthesis in the early 1980s, freeing production from tissue extraction.
SciClone Pharmaceuticals developed the synthetic version as Zadaxin and pursued international approvals: China approved it for hepatitis B in 1996, and it went on to marketing authorisation in ~35–37 countries across Asia, South America, the Middle East and parts of Europe.
US: the FDA granted orphan-drug designations (hepatitis B in 1991, plus melanoma, DiGeorge anomaly, hepatocellular carcinoma), and SciClone ran US Phase 3 trials (hepatitis C, melanoma) — but these did not lead to US marketing approval. (Widely attributed to commercial/regulatory economics, not a safety signal.)

Mechanism (as proposed)

an immune modulator acting largely through Toll-like receptors TLR2 and TLR9 on dendritic and myeloid antigen-presenting cells → activates T-cell / cell-mediated immunity. It promotes T-cell maturation (upregulating CD3/CD4/CD8), dendritic-cell maturation and Th1 polarisation, and enhances NK-cell function, helping restore immune competence in immunosuppressed states while also contributing to control of inflammation and tolerance.

Chemical identifiers

Cross-reference identifiers for the authoritative external databases — not a recipe, and nothing about how to use it.

PubChem CID16130571

InChIKeyNZVYCXVTEHPMHE-ZSUJOUNUSA-N

SMILESCC[C@H](C)[C@@H](C(=O)N[C@@H]([C@@H](C)O)C(=O)N[C@@H]([C@@H](C)O)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CC(=O)O)C(=O)N[C@@H](CC(C)C)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](C(C)C)C(=O)N[C@@H](C(C)C)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](C)C(=O)N[C@@H](CCC(=O)O)C(=O)N[C@@H](CC(=O)N)C(=O)O)NC(=O)[C@H](CCC(=O)O)NC(=O)[C@H](CO)NC(=O)[C@H](CO)NC(=O)[C@H]([C@@H](C)O)NC(=O)[C@H](CC(=O)O)NC(=O)[C@H](C(C)C)NC(=O)[C@H](C)NC(=O)[C@H](C)NC(=O)[C@H](CC(=O)O)NC(=O)[C@H](CO)NC(=O)C

ChEMBLCHEMBL2103979

via PubChem exact-name match (Thymosin Alpha-1) · high confidence

Sources — 5 cited

01Goldstein AL, Low TL, et al. (Isolation and characterisation of thymosin alpha-1.) 1977.

02Romani L, et al. (Dendritic-cell maturation / Th1 polarisation; TLR mechanism.) 2004.

03Zadaxin (thymalfasin) pivotal hepatitis-B / hepatitis-C trials; sepsis RCT meta-analysis.

04Shehadeh F, et al. A pilot trial of thymalfasin (thymosin-alpha-1) in hospitalised COVID-19 patients with hypoxemia and lymphocytopenia. J Infect Dis. 2023.

05Comprehensive review (2024) — >30 clinical trials, >11,000 subjects; PMC7747025 (literature review).

Updated 2026-07-13 (US compounding status evolving — re-check)

Grades reflect the published evidence, not our interest. No dosing, reconstitution, or administration is published for research compounds — that restraint is deliberate.

Related compounds

TB-500 (Thymosin Beta-4 fragment)C

Explore by goal

Immune & thymic →

A neutral reference and a lawful-lane shop. Information for those who seek it — never promotion.

Region — International

ExploreRegister The Register — full index Categories Trust & COA How we grade Open data Brands

ShopCosmetic peptides Journal Quizzes

TermsPrivacyCookiesReturnsShippingImprint

This site provides neutral scientific reference and sells only products lawful in your region. Nothing here is medical advice, a recommendation, or an offer to supply unapproved medicines. No dosing or administration is published for research compounds. Cosmetic peptides per Regulation (EC) 1223/2009. Unapproved injectable peptides are neither sold nor advertised in the EU (Directive 2001/83/EC, Title VIII). © 2026 Vallydia.