ImmuneNot approvedEvidence tier: Human RCT

Thymosin Alpha-1

Last updated October 21, 2026. Approval line checked October 21, 2026. Compounding sources checked October 10, 2026.

FDA status

Not approved

Not approved. This record is not an FDA-approved drug product. Approval, where it exists, is specific to a drug product, indication, and route.

FDA primary source on file

Evidence tier

Human RCT. The tier is the highest indexed study type. It is not a safety rating and it is not an FDA approval. Confidence score 4/5. 856 PubMed citations indexed.

Thymosin Alpha-1 in the literature

28-aa thymic peptide promoting T-cell maturation, enhancing dendritic cell function, and modulating innate/adaptive immunity through TLR signaling and MHC class I upregulation.

What the literature studies

Immune Modulation & T-Cell Support

Evidence tier

Human RCT

Compounding record

Nomination withdrawn

Confidence
4/5

Regulatory record

Nomination withdrawn. FDA substance context: Thymosin alpha-1. Previously in Category 2; FDA still identifies potential significant safety risks. Withdrawal is not FDA approval or a determination of safety or compounding eligibility. Research information is not evidence of FDA approval. Approval, where applicable, is specific to a drug product, indication and route.

Regulatory source checked October 10, 2026. This compounding label is separate from the approval line above.

FDA primary source 1

landmark TESTS RCT (n=1106) found no overall sepsis mortality benefit.

Questions

Educational only. Not medical advice. This page does not give doses or sourcing. See the medical and editorial disclaimer.

Short answer

Thymosin alpha-1 (thymalfasin, Zadaxin outside the US) is an immunomodulatory peptide with orphan designation but no FDA approval in the US; hepatitis B trials are mixed-to-positive, a large 2025 sepsis Phase 3 trial found no mortality benefit, and FDA/PCAC have weighed against 503A compounding listing.

What it is

28-amino-acid thymic peptide (thymalfasin) used internationally as Zadaxin for selected immune/viral indications; not a US-approved drug [R1][FDA-ORPHAN].

Legal / FDA status (as of Oct 27 2026)

Not FDA-approved for any indication. Orphan designation exists for chronic active hepatitis B (designated 1991) with status "Not FDA Approved for Orphan Indication" [FDA-ORPHAN]. FDA lists thymosin-alpha-1 under nominated-but-withdrawn with immunogenicity/characterization concerns and inadequate safety information for proposed compounded uses [FDA-RISK]. At the Dec 4 2024 PCAC, FDA proposed against 503A listing for free base and acetate; secondary reports cite committee votes against inclusion (commonly 4-17) [PCAC-2024].

Human evidence

  • Chronic hepatitis B: randomized trial data exist, including a Japanese RCT of thymosin alpha-1 reporting antiviral/biochemical endpoints with generally mild adverse effects; results across the hepatitis B literature are mixed by regimen and endpoint [R2].
  • Sepsis: earlier multicenter work suggested a possible mortality signal; the large double-blind Phase 3 TESTS trial (n=1,089 analyzed) found 28-day mortality 23.4% vs 24.1% placebo (HR 0.99, 95% CI 0.77-1.27, p=0.93) - no clear benefit [R3].
  • A 2025 meta-analysis of RCTs reported an overall 28-day mortality odds reduction that disappeared in high-quality and multicenter subgroups; authors urge personalized immunotherapy research and note sample-size limits on TSA [R4].

Animal / lab evidence

Extensive immunology literature on T-cell maturation/modulation. Not a substitute for clinical outcomes.

Risks and unknowns

Injection-site and flu-like reactions reported in product literature outside the US; US compounding safety package inadequate per FDA [FDA-RISK]. Gray-market products unverified. Foreign approval is not US approval.

What's coming

No US NDA approval pending based on public TESTS-negative sepsis result for that indication. Compounding pathway remains closed pending any future rulemaking contrary to Dec 2024 trajectory.

Sources

  1. [FDA-ORPHAN] FDA OOPD. Thymalfasin orphan designation for chronic active hepatitis B (designated May 3 1991). https://www.accessdata.fda.gov/scripts/opdlisting/oopd/detailedIndex.cfm?cfgridkey=52990
  2. [R2] Iino S et al. The efficacy and safety of thymosin alpha-1 in Japanese patients with chronic hepatitis B; results from a randomized clinical trial. J Viral Hepat 2005;12:300-306. PMID 15850471
  3. [R3] Wu J, Pei F et al. TESTS trial - thymosin alpha-1 in sepsis. BMJ 2025. doi:10.1136/bmj-2024-082583
  4. [R4] Gu B et al. Efficacy of thymosin alpha-1 for sepsis: systematic review and meta-analysis of RCTs. Front Cell Infect Microbiol 2025. PMID 40969554
  5. [FDA-RISK] FDA. Certain Bulk Drug Substances... (Thymosin-alpha 1 entry). https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
  6. [PCAC-2024] FDA. December 4, 2024 Pharmacy Compounding Advisory Committee meeting materials. https://www.fda.gov/advisory-committees/pharmacy-compounding-advisory-committee/2024-meeting-materials-pharmacy-compounding-advisory-committee

Last checked 2026-10-27

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