Immune Peptide Research

Thymosin Alpha-1 Benefits and Side Effects: Research Data

What immune studies and clinical trials report on thymosin alpha-1 (thymalfasin), which large trials were negative, what side effects were recorded, and where it is approved.

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Fact-checked · Reviewed by Remy Research Editorial Board
Update History ▾
October 27, 2026: Initial publication, built from FDA’s 2024 thymosin alpha-1 briefing document and committee minutes, current approval records and the fact-checked thymosin alpha-1 source set.
Research-use-only framing applied throughout in line with Remy editorial standards.
TL;DR — Research Summary

The thymosin alpha 1 benefits claimed for the immune system rest on a real but mixed record: thymalfasin (Zadaxin) is approved in China, Italy and several other countries, yet its largest modern trials were negative.[1][2][3] Cell and mouse studies link it to dendritic cell activation, and older trials in chronic hepatitis B gave mixed results.[4][5][6] The 1,106-patient TESTS sepsis trial found no reduction in 28-day mortality, and a 508-patient pancreatitis trial also missed its primary endpoint.[7][8]

Thymosin alpha 1 side effects in trials were mostly mild, mainly local discomfort and passing liver-enzyme rises in hepatitis B.[1] It is not FDA approved, and FDA found a lack of evidence of effectiveness for every use it reviewed. Remy Research supplies thymosin alpha-1 for in-vitro laboratory research only.

Compliance note: this page is a research review, not a treatment guide. It does not provide human-use dosing, therapeutic recommendations, or any clinical-use instructions, and should be read in the same non-therapeutic frame required across Remy's research content.

What Is Thymosin Alpha-1 (Thymalfasin)?

Thymosin alpha-1 (Tα1) is a 28-amino-acid peptide with an acetyl group at its start; its drug name is thymalfasin. PubChem lists it as C129H215N33O55, about 3,108 g/mol, CAS 62304-98-7.[9] Allan Goldstein’s group isolated and sequenced it from calf thymus in 1977, as one of several peptides in the thymus gland preparation thymosin fraction 5.[10]

It is often called a naturally occurring peptide. Its sequence matches residues 2–29 of prothymosin α, a natural protein, but a 1984 study found prothymosin α, not free Tα1, to be the main form in rat thymus, so whether free Tα1 circulates is still debated.[11][12] The drug version was developed and marketed by SciClone as Zadaxin.[1]

How Thymosin Alpha 1 Works: Immune Modulation

Tα1 is described as an immune modulator that augments T-cell function, possibly by helping thymocytes mature into active T cells.[13] Most of the mechanistic work comes from a few groups, many in Perugia and Rome:

This dual action, activating immune responses while also limiting chronic inflammation, is why researchers describe Tα1 as restoring immune homeostasis rather than simply boosting immunity.[16] A 2017 review from the same Rome network describes thymosin alpha 1 as acting differently depending on the host’s state of inflammation or immune dysfunction, in infection, cancer, immunodeficiency, vaccination and aging.[17] No specific high-affinity receptor has been established.[4]

Potential Thymosin Alpha 1 Benefits in Research

The table lists each claimed benefit, what the best available study reported and the type of evidence.

Thymosin Alpha-1 — Claimed Benefits and the Evidence
Claimed benefit What was reported Evidence type
Immune function Dendritic cell and T-cell activation Cell, animal
Chronic hepatitis B Mixed: US phase III negative, Taiwan positive Human trials
Chronic hepatitis C No benefit added to standard treatment Human trial
Severe sepsis No reduction in 28-day mortality Human phase 3 trial
COVID-19 Mixed: retrospective benefit, pilot null Human, mostly observational
Long COVID T-cell changes in blood samples Ex vivo (lab)

Chronic Hepatitis B and Other Chronic Viral Infections

Chronic hepatitis B is Tα1’s main approved indication in China, for adults with compensated liver disease and evidence of hepatitis B virus replication.[2] The trial record is split: a US multicentre, double-blind phase III trial did not confirm efficacy, while a smaller randomised Taiwanese trial reported a higher delayed virological response.[5][6] In chronic hepatitis C, a 552-patient trial adding Tα1 to peginterferon and ribavirin did not meet its primary endpoint.[18] A 2001 review summed up the hepatitis trials as mixed, with effects on illness and mortality still to be shown.[13]

HIV, Vaccine Response and Chronic Infections

In HIV, antiretroviral treatment often leaves immune reconstitution incomplete, and Rome researchers have studied thymosin alpha 1 in vitro and in vivo as a way to restore immune function in that setting.[17] For vaccine response, the Chinese label reports that in haemodialysis patients given influenza vaccine, 65% of those also given Tα1 had a fourfold or greater antibody rise, against 24% on placebo.[2] FDA nonetheless found a lack of evidence of effectiveness for HIV infection and for poor vaccine response.[1]

Severe Sepsis and Critical Illness

Sepsis is a life-threatening response to infection. The TESTS trial randomised 1,106 adults with sepsis across 22 Chinese centres, double-blind and placebo-controlled. 28-day mortality was 23.4% with Tα1 and 24.1% with placebo, with a corrected hazard ratio of 0.97; a correction was published after the original paper.[7][19] An earlier single-blind trial in severe sepsis had a borderline, non-significant result, and a 2025 meta-analysis found no significant benefit when only high-quality or multicentre trials were pooled.[20][21] In a 508-patient double-blind trial in predicted severe pancreatitis, Tα1 did not reduce infected pancreatic necrosis.[8]

COVID-19 and Long COVID

A small retrospective Wuhan series reported lower mortality and recovery of depleted T cells, but a larger propensity-matched cohort found no difference in mortality, and a small US randomised pilot found no significant clinical benefit.[22][23][24] For long COVID, a 2023 Rome study found that Tα1 added to blood cells taken from patients shifted T cell subsets toward a more normal pattern and lowered pro-inflammatory cytokines, most clearly in people who had more severe disease or specific systemic and psychiatric symptoms; it was an ex vivo study with no patients treated.[16]

Cancer, Immune Surveillance and the Immune System

In a 488-patient randomised melanoma study, arms with Tα1 had more tumour responses, but survival differences were not statistically significant.[25] FDA’s 2024 review found a lack of evidence of effectiveness for melanoma, liver cancer and lung cancer, as for every other use it examined.[1]

Clinical Evidence: How Strong Is It?

Tα1 has far more clinical data than most research peptides: ClinicalTrials.gov lists 68 studies.[26] But across several trials, positive results come mostly from smaller, open-label or retrospective work, while the largest double-blind trials were null.[7][8][5] FDA concluded in 2024 that evidence was lacking for its use in hepatitis B and C, HIV, COVID-19, vaccine response, sepsis and cancer.[1]

Thymosin Alpha 1 Side Effects and Safety

Is Thymosin Alpha-1 FDA Approved?

Where thymosin alpha-1 stands as of October 28, 2026.
  • FDA approval. No. FDA states that it has approved no drug products containing Tα1, and Drugs@FDA lists no thymalfasin application.[1][27]
  • Compounding. FDA’s Category 2 page lists “Thymosin-alpha 1 (Ta1)” under “nominated but withdrawn,” and FDA’s May 2026 list of nominated substances does not include it.[28][29] In December 2024 FDA’s advisory committee voted 4–17 against adding thymosin alpha-1 acetate to the list compounding pharmacies may use, and a majority also voted against the free base in a separate vote.[30]
  • Approved markets. China approves thymalfasin for chronic hepatitis B and as a vaccine enhancer in people with weak immune function.[2] In the EU it is authorised only in Italy, as an influenza-vaccine adjuvant.[3] FDA’s 2024 review also lists authorisations in India, Hong Kong, Singapore and Mexico.[1]
  • Sport. Thymosin alpha-1 is not named on WADA’s 2027 Prohibited List; thymosin beta-4 and TB-500 are prohibited by name.[31]
  • UAE. Thymosin alpha-1 is not a registered medicine; a randomised IVF trial is recruiting in Abu Dhabi.[32] Remy Research sells it for in-vitro laboratory research only, not for human or veterinary use.

Thymosin Alpha-1 vs Thymosin Beta-4 and TB-500

Thymosin alpha-1 and thymosin beta-4 share a name only because both were first isolated from the same thymus extract; thymosin beta-4 was sequenced from that fraction in 1981.[33] They are different molecules from different genes: Tα1 is studied for immune function, while thymosin beta-4 and its fragment TB-500 are studied for actin binding and tissue repair. See TB-500 benefits and side effects, the TB-500 and thymosin beta-4 review and the KPV research review for another peptide studied for inflammation.

What the Research Does Not Yet Show

Thymosin Alpha-1 for Laboratory Research

Remy Research supplies thymosin alpha-1 for in-vitro research as the Genovare Thymosin Alpha-1 25mg AQ pen. The product page carries its batch testing details. For the full trial-by-trial review, read the thymosin alpha-1 research review.

Our Research Standards

This article prioritizes randomised trials, regulator documents and primary literature, and reports null primary endpoints alongside positive findings. Where evidence is weak, we say so directly. No therapeutic, dosing or administration guidance is given. Read our editorial policy →

RP
Editorial Review

Editorial Board, Remy Research

The Remy Research Editorial Board reviews Remy's peptide research library, with a focus on analytical verification, clinical-trial interpretation, and compliance-safe scientific communication.

About the editorial team →

Thymosin Alpha-1 Benefits and Side Effects FAQ

What are the benefits of thymosin alpha 1?

Studies link it to dendritic cell and T-cell activation, and it is approved in China for chronic hepatitis B. Its largest trials in sepsis and pancreatitis were negative, and FDA found a lack of evidence of effectiveness for every use it reviewed.[4][2][7][1]

What are the side effects of thymosin alpha-1?

Trials mostly report local irritation, mild fever, nausea and temporary liver-enzyme rises in hepatitis B. Labels advise against use in children, pregnancy and transplant recipients.[1]

Is thymosin alpha-1 FDA approved?

No. FDA has approved no product containing it, and in 2024 an FDA advisory committee voted 4–17 against adding the acetate form to the compounding list, with a majority also against the free base.[1][30]

Is thymosin alpha-1 safe?

In approved-drug trials it was generally well tolerated, but FDA concluded that compounded Tα1 may raise safety concerns, and one sepsis subgroup had a mortality signal that did not hold after adjustment.[1][7]

Does thymosin alpha 1 boost the immune system?

Reviews describe it as augmenting T-cell function, and mouse studies show dendritic cell activation, but large trials have not shown that this prevents infection or improves disease outcomes.[13][4][7]

What is Zadaxin used for?

Zadaxin is the brand name of thymalfasin. In China it is approved for chronic hepatitis B and as a vaccine enhancer; in Italy it is authorised as an influenza-vaccine adjuvant.[2][3]

Is thymosin alpha 1 the same as TB-500?

No. TB-500 is a fragment of thymosin beta-4, a different molecule. WADA bans TB-500 by name but does not name thymosin alpha-1.[33][31]

What contraindications do thymalfasin labels list?

Labels list childhood, pregnancy and breastfeeding, and deliberate immune suppression such as in transplant recipients as contraindications.[1]

Does thymosin alpha 1 help in sepsis?

The largest trial says no: 28-day mortality was 23.4% with Tα1 and 24.1% with placebo.[7]

Sources

  1. U.S. Food and Drug Administration. FDA Evaluation of thymosin alpha-1 (free base) and thymosin alpha-1 acetate, briefing document for the December 4, 2024 Pharmacy Compounding Advisory Committee meeting, dated November 15, 2024. Checked October 28, 2026. fda.gov/media/183820 ↩
  2. Thymalfasin for injection, approval number H20193180: Chinese package insert (indications: chronic hepatitis B; vaccine-response enhancer in immunocompromised patients). Checked October 28, 2026. package insert ↩
  3. European Medicines Agency. EU/3/02/110: orphan designation of thymalfasin for hepatocellular carcinoma (July 30, 2002); “In the European Union thymalfasin is authorised in Italy”, as an influenza-vaccine adjuvant. Checked October 28, 2026. ema.europa.eu ↩
  4. Romani L, Bistoni F, Gaziano R, et al. Thymosin alpha 1 activates dendritic cells for antifungal Th1 resistance through toll-like receptor signaling. Blood. 2004;103(11):4232-4239. doi: 10.1182/blood-2003-11-4036 · PMID: 14982877 ↩
  5. Mutchnick MG, Lindsay KL, Schiff ER, et al. Thymosin alpha1 treatment of chronic hepatitis B: results of a phase III multicentre, randomized, double-blind and placebo-controlled study. J Viral Hepat. 1999;6(5):397-403. doi: 10.1046/j.1365-2893.1999.00181.x · PMID: 10607256 ↩
  6. Chien RN, Liaw YF, Chen TC, et al. Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial. Hepatology. 1998;27(5):1383-1387. doi: 10.1002/hep.510270527 · PMID: 9581695 ↩
  7. Wu J, Pei F, Zhou L, et al. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ. 2025;388:e082583. doi: 10.1136/bmj-2024-082583 · PMID: 39814420 ↩
  8. Ke L, Zhou J, Mao W, et al. Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial. Intensive Care Med. 2022;48(7):899-909. doi: 10.1007/s00134-022-06745-7 · PMID: 35713670 ↩
  9. National Center for Biotechnology Information. PubChem Compound Summary for CID 16130571, Thymalfasin. pubchem.ncbi.nlm.nih.gov/compound/16130571 ↩
  10. Goldstein AL, Low TL, McAdoo M, et al. Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide. Proc Natl Acad Sci U S A. 1977;74(2):725-729. doi: 10.1073/pnas.74.2.725 · PMID: 265536 ↩
  11. UniProt. P06454 — Prothymosin alpha (PTMA_HUMAN); residues 2–29 form thymosin alpha-1. uniprot.org ↩
  12. Haritos AA, Goodall GJ, Horecker BL. Prothymosin alpha: isolation and properties of the major immunoreactive form of thymosin alpha 1 in rat thymus. Proc Natl Acad Sci U S A. 1984;81(4):1008-1011. doi: 10.1073/pnas.81.4.1008 · PMID: 6583693 ↩
  13. Ancell CD, Phipps J, Young L. Thymosin alpha-1. Am J Health Syst Pharm. 2001;58(10):879-885. doi: 10.1093/ajhp/58.10.886 · PMID: 11381492 ↩
  14. Bozza S, Gaziano R, Bonifazi P, et al. Thymosin alpha1 activates the TLR9/MyD88/IRF7-dependent murine cytomegalovirus sensing for induction of anti-viral responses in vivo. Int Immunol. 2007;19(11):1261-1270. doi: 10.1093/intimm/dxm097 · PMID: 17804687 ↩
  15. Romani L, Bistoni F, Perruccio K, et al. Thymosin alpha1 activates dendritic cell tryptophan catabolism and establishes a regulatory environment for balance of inflammation and tolerance. Blood. 2006;108(7):2265-2274. doi: 10.1182/blood-2006-02-004762 · PMID: 16741252 ↩
  16. Minutolo A, Petrone V, Fanelli M, et al. Thymosin alpha 1 restores the immune homeostasis in lymphocytes during Post-Acute sequelae of SARS-CoV-2 infection. Int Immunopharmacol. 2023;118:110055. doi: 10.1016/j.intimp.2023.110055 · PMID: 36989892 ↩
  17. Matteucci C, Grelli S, Balestrieri E, et al. Thymosin alpha 1 and HIV-1: recent advances and future perspectives. Future Microbiol. 2017;12:141-155. doi: 10.2217/fmb-2016-0125 · PMID: 28106477 ↩
  18. Ciancio A, Andreone P, Kaiser S, et al. Thymosin alpha-1 with peginterferon alfa-2a/ribavirin for chronic hepatitis C not responsive to IFN/ribavirin: an adjuvant role? J Viral Hepat. 2012;19 Suppl 1:52-59. doi: 10.1111/j.1365-2893.2011.01524.x · PMID: 22233415 ↩
  19. BMJ. Correction: The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ. 2025;389:r1098. doi: 10.1136/bmj.r1098 · PMID: 40447307 ↩
  20. Wu J, Zhou L, Liu J, et al. The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial. Crit Care. 2013;17(1):R8. doi: 10.1186/cc11932 · PMID: 23327199 ↩
  21. Gu B, Zhou Y, Nie Y, et al. Efficacy of thymosin α1 for sepsis: a systematic review and meta-analysis of randomized controlled trials. Front Cell Infect Microbiol. 2025;15:1673959. doi: 10.3389/fcimb.2025.1673959 · PMID: 40969554 ↩
  22. Liu Y, Pan Y, Hu Z, et al. Thymosin Alpha 1 Reduces the Mortality of Severe Coronavirus Disease 2019 by Restoration of Lymphocytopenia and Reversion of Exhausted T Cells. Clin Infect Dis. 2020;71(16):2150-2157. doi: 10.1093/cid/ciaa630 · PMID: 32442287 ↩
  23. Sun Q, Xie J, Zheng R, et al. The effect of thymosin α1 on mortality of critical COVID-19 patients: A multicenter retrospective study. Int Immunopharmacol. 2021;90:107143. doi: 10.1016/j.intimp.2020.107143 · PMID: 33208294 ↩
  24. Shehadeh F, Benitez G, Mylona EK, et al. A Pilot Trial of Thymalfasin (Thymosin-α-1) to Treat Hospitalized Patients With Hypoxemia and Lymphocytopenia Due to Coronavirus Disease 2019 Infection. J Infect Dis. 2023;227(2):226-235. doi: 10.1093/infdis/jiac362 · PMID: 36056913 ↩
  25. Maio M, Mackiewicz A, Testori A, et al. Large randomized study of thymosin alpha 1, interferon alfa, or both in combination with dacarbazine in patients with metastatic melanoma. J Clin Oncol. 2010;28(10):1780-1787. doi: 10.1200/JCO.2009.25.5208 · PMID: 20194853 ↩
  26. ClinicalTrials.gov API search for thymalfasin OR "thymosin alpha", run October 28, 2026 (68 records). clinicaltrials.gov ↩
  27. U.S. Food and Drug Administration. Drugs@FDA data (openFDA drugsfda endpoint) searched for the active ingredient thymalfasin, October 28, 2026: no matching application. api.fda.gov ↩
  28. U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (“Thymosin-alpha 1 (Ta1)” under “Bulk drug substances nominated but withdrawn”). Updated April 22, 2026; checked October 28, 2026. fda.gov ↩
  29. U.S. Food and Drug Administration. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A: Categories 1–3 (updated May 14, 2026; thymosin alpha-1 not listed). Checked October 28, 2026. fda.gov/media/94155 ↩
  30. U.S. Food and Drug Administration. Minutes of the December 4, 2024 Pharmacy Compounding Advisory Committee meeting (separate votes: thymosin alpha-1 free base, majority against, tally not printed; thymosin alpha-1 acetate 4 yes, 17 no). Checked October 28, 2026. fda.gov/media/185642 ↩
  31. World Anti-Doping Agency. The 2027 Prohibited List (in force January 1, 2027): thymosin alpha-1 is not named; “Thymosin-ß4 and its derivatives e.g. TB-500” are prohibited under S2. Checked October 28, 2026. wada-ama.org ↩
  32. ClinicalTrials.gov NCT07675980. Thymosin-α1 for Recurrent Implantation Failure (Fakih IVF Fertility Center, Abu Dhabi; randomised, double-blind; recruiting). Checked October 28, 2026. clinicaltrials.gov ↩
  33. Low TL, Hu SK, Goldstein AL. Complete amino acid sequence of bovine thymosin beta 4: a thymic hormone that induces terminal deoxynucleotidyl transferase activity in thymocyte populations. Proc Natl Acad Sci U S A. 1981;78(2):1162-1166. doi: 10.1073/pnas.78.2.1162 · PMID: 6940133 ↩

For catalog details, see the Genovare Thymosin Alpha-1 25mg AQ pen. For editorial standards, continue to the editorial policy.

Research products mentioned in this article

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