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Clinician reference, evidence review

Thymosin Alpha-1

Zadaxin (approved outside the US)

Immunomodulatory peptide, not FDA approved in the US, orphan drug status

Reviewed by: Sabrina Runbeck, PA-C, MHS, MPH, Co-Founder, Scriptura Health. Physician assistant, public health master's, health sciences master's. Sabrina reviews the clinical layer of Scriptura Health, and she reviews every compound reference on this site.

Published: 2026-07-08. This page is an evidence review, not clinical instruction, and does not recommend dosing, cadence, routes, or prescribing decisions. Prescribing is the responsibility of a licensed clinician evaluating a specific patient.

Regulatory posture

Thymosin alpha-1 is not approved by the FDA for general use in the United States, though it has received orphan drug designation for certain conditions and is approved and marketed in several other countries, for example as Zadaxin. Because there is no broadly approved US product, its compounding status is uncertain and subject to ongoing FDA scrutiny of peptide compounding. It is not a controlled substance under the DEA.

Mechanism, plain English

Thymosin alpha-1 is a small protein originally found in the thymus, a gland that helps train the immune system. It is thought to help the immune system respond more effectively by supporting T cells, a type of white blood cell that fights infection, and by adjusting inflammation. Because of these effects it has been studied in infections and conditions where the immune response is weakened or unbalanced.

Evidence landscape

Thymosin alpha-1 has a more developed clinical evidence base than most research-grade peptides, but results across conditions are mixed. A large multicenter Phase 3 randomized controlled trial in sepsis, the TESTS trial, did not show a clear mortality benefit, which tempers earlier optimism. A systematic review and meta-analysis of randomized trials in sepsis suggested possible benefit in some pooled analyses while noting variable trial quality. A separate systematic review and meta-analysis in COVID-19 reported potential benefit in moderate to critical patients but emphasized heterogeneity and the need for higher quality trials. Overall the evidence is meaningful yet inconsistent, and firm efficacy conclusions depend on the specific condition studied.

Primary PubMed citations

  1. 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. PMID: 39814420
  2. Efficacy of thymosin alpha1 for sepsis: a systematic review and meta-analysis of randomized controlled trials , Gu B et al, Frontiers in Cellular and Infection Microbiology, 2025. PMID: 40969554
  3. The efficacy of thymosin alpha-1 therapy in moderate to critical COVID-19 patients: a systematic review, meta-analysis, and meta-regression , Soeroto AY et al, Inflammopharmacology, 2023. PMID: 37845598

Citations selected from the PubMed literature. Every URL was checked at publication time. Scriptura's daily PubMed scan surfaces new studies for each compound as they index. See the regulatory and literature layers on the demo.

Scope of this page

This is a plain English summary of the peer reviewed literature and current regulatory posture. It is not a substitute for a licensed clinician's judgment on a specific patient. It does not recommend dosing, cadence, or route. Where the literature is limited or preclinical, this page says so, so a prescriber can weigh marketing claims against what the trials actually show.

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Thymosin Alpha-1 clinician reference: evidence review and regulatory posture | Scriptura Health | Scriptura Health