Research information only, not medical advice. Thymosin alpha-1 (thymalfasin) is a 28-amino-acid synthetic peptide identical to the naturally occurring thymic peptide. It acts as an immunomodulator (biological response modifier) rather than as a direct antiviral. It is not FDA-approved for any indication in the United States; the branded product Zadaxin (thymalfasin, SciClone) is approved for chronic hepatitis B and C in roughly 35 other countries, primarily in Asia and South America. At its December 4, 2024 Pharmacy Compounding Advisory Committee meeting, the FDA evaluated thymosin alpha-1 and proposed that thymosin alpha-1 acetate not be placed on the Section 503A bulk drug substances list.
Thymosin Alpha-1 at a glance
The clinical evidence base consists of randomized controlled trials and meta-analyses, concentrated in two areas: chronic hepatitis B and severe sepsis. Mechanistically, thymosin alpha-1 promotes dendritic-cell maturation and T-cell differentiation and primes Th1 responses via Toll-like receptor (TLR9/TLR2) signaling. In chronic hepatitis B, meta-analyses of RCTs indicate that monotherapy roughly doubles the sustained/delayed virological response rate versus control, though responses are often delayed and end-of-treatment effects are not statistically significant; major clinical practice guidelines for chronic HBV do not include thymosin alpha-1 as a recommended treatment. In severe sepsis the evidence is mixed: the single-blind ETASS trial suggested a mortality benefit, but the larger double-blind TESTS trial (1,106 patients) found no overall mortality reduction.
See how we grade evidence for the methodology behind this page.
Evidence profile
73 studies- Human RCT 7 · 10%
- Human trial 30 · 41%
- Review 20 · 27%
- Animal 5 · 7%
- In-vitro 3 · 4%
- Unknown 8 · 11%
The longer the green, the stronger the human evidence. For most research peptides the bar is dominated by animal and in-vitro work, which is a signal to read every claim carefully.
Regulatory status
Clinical trials
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The Safety and Effectiveness of a Type of Interleukin-2 Plus Zidovudine Plus Thymosin in HIV-Positive Patients With and Without Symptoms of Infection
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Thymosin Plus PEG-Interferon in Hepatitis C Patients With Cirrhosis Who Did Not Respond to Interferon or Interferon Plus Ribavirin
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Thymosin Plus PEG-Interferon in Non-Cirrhotic Hepatitis C Patients Who Did Not Respond to Interferon or Interferon Plus Ribavirin
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A Trial of Thymalfasin in Adult Patients With Hepatocellular Carcinoma
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Dendritic Cell Based Therapy of Renal Cell Carcinoma
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Efficacy Study of Thymosin alpha1 & Pegylated Interferon-alpha2a to Treat Chronic Hepatitis B
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Thymosin Alfa 1 in Recipients of Allogeneic Hematopoietic Transplantation for Hematological Malignancies
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Efficacy of Thymosin alpha1 for Severe Sepsis
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Thymosin Alpha 1, Interferon Alpha, or Both, in Combination With Dacarbazine in Patients With Malignant Melanoma
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Dendritic Cell Based Therapy for Breast Cancer Patients
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A Pilot Study to Evaluate ZADAXIN's® (Thymalfasin) Ability to Enhance Immune Response to the H1N1sw Influenza Vaccine
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Thymosin Alpha-1 in Combination With Peg-Interferon Alfa- 2a and Ribavirin for the Therapy of Chronic Hepatitis C Nonresponsive to the Combination of IFN and Ribavirin.
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Optimized Treatment and Regression of HBV-induced Early Cirrhosis
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Optimized Treatment and Regression of HBV-induced Compensated Liver Cirrhosis
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Thymalfasin Adjuvant Therapy in Hepatitis B Virus (HBV)-Related Hepatocellular Carcinoma (HCC) After Curative Resection
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Phase II Trial for Combination Treatment of PEG-Tα1 and Adefovir for HBeAg Positive Chronic Hepatitis B
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Phase Ⅲ Trial for Combination Treatment of PEG-Tα1 and Adefovir for HBeAg-positive Chronic Hepatitis B
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Thymosin Alpha 1 in the Prevention of Pancreatic Infection Following Acute Necrotizing Pancreatitis
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Abscopal Effect for Metastatic Colorectal Cancer
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Abscopal Effect for Metastatic Small Cell Lung Cancer
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Abscopal Effect for Metastatic Non-small Cell Lung Cancer.
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SBRT Combined With Thymalfasin for Metastatic Esophageal Cancer
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Therapeutic Safety and Efficacy of REP 2139 (REP 9AC') in HBV Infected Patients
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Radiotherapy Combined With Thymosin for Metastatic NSCLC Patients Who Showed Stable Disease After First Line TKI Therapy
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The Efficacy and Safety of Ta1 for Sepsis
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Efficacy of Thymosin Alpha 1 on Improving Monocyte Function for Sepsis
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Thymosin Alpha 1 Plus Maintenance Therapy With the Standard of Care (SoC) in Patients With Metastatic Non-Small Cell Lung Cancer (NSCLC), EGFR Wild Type
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First Line Bio-immunotherapy With Thymosin Alpha 1 in Patients With Sensitizing EGFR Mutation Positive Non Small Cell Lung Cancer Who Are Taking Standard of Care Therapy
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SBRT Combination With rhGM-CSF and Tα1 for Stage IV NSCLC Patients Who Failed in Second-line Chemotherapy
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The Efficacy and Safety of Thymosin-α1 in Patients With HBV-related ACLF
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Efficacy and Safety of Combination Therapy of Thymalfasin and Entecavir in HBeAg-positive ETV-experienced Patients
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Study of Thymosin α1 to Reduce Acute Pneumonia For Bulky None-small Cell Lung Cancer
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Experimental Trial of rhIFNα Nasal Drops to Prevent 2019-nCOV in Medical Staff
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Thymosin Alpha 1 to Prevent COVID-19 Infection in Renal Dialysis Patients
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Thymalfasin (Thymosin Alpha 1) to Treat COVID-19 Infection
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Immunotherapy for Elderly Patients With Chronic Osteoporotic Pain
- NCT04901104 NOT_YET_RECRUITING
Long-term Prognosis of Patients With Sepsis After Immunotherapy
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Zadaxin and HIV-positive Patients With Immune Reconstitution Disorder
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Thymosin-alpha 1 for Adjuvant Treatment After Radical Resection of High-risk Stage II and III Colorectal Cancer
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Protective Effect of Thymosin Α1 Against Negative Immune Dysregulation and Organ Dysfunction After Acute Aortic Dissection Surgery (PANDA II)
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Thymosin α1 Use in Rheumatic Heart Disease Patients Undergoing Cardiac Surgery on Cardiopulmonary Bypass
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Platform Adaptive Embedded Trial for Acute Respiratory Distress Syndrome
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Thymalfasin-based PRaG Mode for Advanced Refractory Solid Tumors
- NCT06024356 COMPLETED
Neoadjuvant Chemoradiotherapy Combined With PD-1 Inhibitor and Thymalfasin for Locally Advanced Mid-low Rectal Cancer
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Neoadjuvant Chemoradiotherapy Combined With PD-1 Inhibitor and Thymalfasin for pMMR/MSS Locally Advanced Mid-low Rectal Cancer
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The Impact of Thymosin α-1 on the Efficacy of Concurrent Chemoradiotherapy Followed by Immunotherpay Consolidation for Locally Advanced NSCLC
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Thymosin Alpha-1 for irAE Secondary to ICIs
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TPF Concurrent Chemo-radiotherapy Plus Immunotherapy for Local Advanced Esophageal Squamous Cell Carcinoma
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Efficacy and Safety of Anti-PD-1, Thymalfasin, and SOX in Neoadjuvant Treatment of cStage III Gastric/Gastroesophageal Junction Adenocarcinoma
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The Safety, Tolerability, and Efficacy of KD01 in Gynecologic Malignancies
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Radiotherapy With Sequential Chemotherapy Combined With PD-1 Inhibitor and Thymalfasin for BRPC
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Thymalfasin and Recombinant Human IL-2 Injections in Treating Lymphocytopenia for Patients With Malignant Hematological Tumors
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Immuno-effect of Tα1 for Stage I NSCLC
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Neoadjuvant With Tα1 Plus Immuno-chemotherapy for Resectable NSCLC
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Thymalfasin (Thymosin Alpha 1; Ta1) as an Enhancer of Vaccine Response Among Older Adults Receiving Booster Doses of COVID-19 Vaccine
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"Thymalfasin Immunotherapy Study with Triple Regimen in Advanced MSS/pMMR Colorectal Cancer"
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Protective Effect of Ulinastatin and Thymosin α1 Against Negative Immune Dysregulation and Organ Dysfunction After Acute Aortic Dissection Surgery (PANDA XI)
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A Study Evaluating Neoadjuvant Chemotherapy, Concurrent Chemoradiotherapy Combined With Dual Immune Checkpoint Blockade in Patients With Locally Advanced Non-Small Cell Lung Cancer
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A Study Evaluating Concurrent Chemoradiotherapy Combined With Dual Immune Checkpoint Blockade for Limited-stage Small Cell Lung Cancer
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Phase II Trial of Neoadjuvant Thymalfasin, PD-1 Inhibitor, and Chemoradiotherapy for cStage III GEJ Adenocarcinoma
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AI-assisted Subtyping-directed Precision Treatment in Acute Aortic Dissection
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Thymosin Alpha 1 Combined With Anti-PD-1 Monoclonal Antibody in Elderly Patients With Advanced Melanoma
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Thymosin-α1 for Recurrent Implantation Failure
Indexed research
Sorted by evidence level, strongest first.
- Human RCT 2025The Synergistic and Attenuated Mechanism of Action of the Xihuang Pill in Dual Immunotherapy After Stenting for Advanced Cholangiocarcinoma: A Controlled Clinical Trial
This controlled clinical trial compared Xihuang pill combined with dual immunotherapy versus immunotherapy alone in 120 advanced cholangiocarcinoma patients after stenting, finding improved anti-tumor efficacy and reduced toxicity.
- Human RCT 2024A Prospective and Randomized Control Study on Effects of Thymalfasin for Injection on Perioperative Immune Function and Long-term Prognosis of Patients with Colorectal Cancer
- Human RCT 2024Immune-Enhancing Treatment among Acute Necrotizing Pancreatitis Patients with Metabolic Abnormalities: A Post Hoc Analysis of a Randomized Clinical Trial
- Human RCT 2023A pilot trial of Thymalfasin (Ta1) to prevent covid-19 infection and morbidities in renal dialysis patients: Preliminary report
- Human RCT 2026A prospective clinical study on the effectiveness of Phellinus igniarius decoction in treating immune dysfunction in colorectal cancer patients following chemfotherapy
This prospective randomized controlled trial found that Phellinus igniarius decoction improved immune function and quality of life in colorectal cancer patients after chemotherapy.
- Human RCT 2016Thymosin α1 for injection dilution effects on the oral ulcer nursing in the patients with oral endotracheal intubation
A randomized controlled trial in 100 ICU patients found that Thymosin α1 for injection dilution was more effective than compound chlorhexidine gargle in treating oral ulcers caused by oral endotracheal intubation, with faster healing.
- Human RCT 2011Effect of the zadaxin dilution on oral ulcer after chemotherapy
This randomized controlled trial compared zadaxin dilution with Xileisan for treating oral ulcers after chemotherapy, finding that zadaxin dilution resulted in shorter healing time and lower pain index.
- Human trial 2026Preliminary results from a phase II trial of spatially fractionated radiotherapy combined with immunotherapy and anti-angiogenic therapy in patients with bulky solid tumors: early evidence of promising efficacy and favorable safety
- Human trial 2026Thymalfasin combined with immune checkpoint inhibitors in the treatment of non-small cell lung cancer: A retrospective study on efficacy, safety, and immunological function
This retrospective study evaluated thymalfasin combined with immune checkpoint inhibitors and chemotherapy in 120 advanced NSCLC patients, finding that platinum-based doublet regimens with thymalfasin may prolong survival and improve immune function without increasing toxicity.
- Human trial 2026Neoadjuvant immunochemotherapy plus thymalfasin in locally advanced gastric cancer: a prospective clinical trial
+ 63 more studies indexed for Thymosin Alpha-1.
Frequently asked questions
- Is Thymosin Alpha-1 approved for human use?
- Thymosin alpha-1 (thymalfasin) is a 28-amino-acid synthetic peptide identical to the naturally occurring thymic peptide. It acts as an immunomodulator (biological response modifier) rather than as a direct antiviral. It is not FDA-approved for any indication in the United States; the branded product Zadaxin (thymalfasin, SciClone) is approved for chronic hepatitis B and C in roughly 35 other countries, primarily in Asia and South America. At its December 4, 2024 Pharmacy Compounding Advisory Committee meeting, the FDA evaluated thymosin alpha-1 and proposed that thymosin alpha-1 acetate not be placed on the Section 503A bulk drug substances list.
- What does the research on Thymosin Alpha-1 show?
- The clinical evidence base consists of randomized controlled trials and meta-analyses, concentrated in two areas: chronic hepatitis B and severe sepsis. Mechanistically, thymosin alpha-1 promotes dendritic-cell maturation and T-cell differentiation and primes Th1 responses via Toll-like receptor (TLR9/TLR2) signaling. In chronic hepatitis B, meta-analyses of RCTs indicate that monotherapy roughly doubles the sustained/delayed virological response rate versus control, though responses are often delayed and end-of-treatment effects are not statistically significant; major clinical practice guidelines for chronic HBV do not include thymosin alpha-1 as a recommended treatment. In severe sepsis the evidence is mixed: the single-blind ETASS trial suggested a mortality benefit, but the larger double-blind TESTS trial (1,106 patients) found no overall mortality reduction.