Thymosin Alpha-1 benefits and uses

Where it is approved, and for what

Outside the US, Ta1 is sold as the brand Zadaxin for a few specific uses.² FDA's 2024 review reports approval in Italy as an adjuvant to flu vaccination in immunocompromised people, in India for chronic hepatitis B in adults with compensated liver disease, and in Hong Kong, plus a registration in Indonesia for chronic hepatitis B.² EMA gave thymalfasin an orphan designation for liver cancer in 2002, which is not a marketing approval.¹¹

Treatment guidelines have not taken it up. FDA notes that Ta1 is not mentioned in the 2016 and 2018 AASLD hepatitis B guidance, the 2017 EASL guidelines or the 2024 WHO guidelines, and that no clinical practice guideline for US health professionals recommends it.²¹

Findings in people, by condition

Hepatitis B

• In a 1998 randomized, open-label trial of 98 patients, complete virological response at 18 months was 40.6% after a 26-week course and 26.5% after a 52-week course, against 9.4% untreated. Rates were similar at the end of therapy, and FDA noted the lack of blinding and HBV DNA tests far less sensitive than today's.³²¹
• In a 1999 double-blind phase 3 trial of 97 patients, complete response was 14% on Ta1 and 4% on placebo (P = 0.084), and undetectable HBV DNA at 12 months was 20% against 21%. The authors said the results did not confirm earlier reports, and FDA calls it the only double-blind trial of Ta1 alone against placebo.⁴²¹
• A 2001 meta-analysis of 5 trials found no clear effect at the end of treatment or 6 months after, but an odds ratio of 2.67 (95% CI 1.25 to 5.68) for response 12 months after treatment. FDA noted large differences between the pooled trials.²
• In randomized open-label and retrospective studies, adding Ta1 to entecavir or peginterferon gave results similar to the antiviral alone. With entecavir, undetectable HBV DNA at week 52 was 69.6% with Ta1 and 64.6% without it.¹

Hepatitis C

In a randomized double-blind trial, adding Ta1 to peginterferon and ribavirin gave a sustained response of 12.7%, against 10.5% with placebo, and the authors said it did not increase the on-treatment viral response.¹ A small placebo-controlled pilot of Ta1 alone cleared the virus in no one.¹

Sepsis

• ETASS (2013), a single-blind randomized trial of 361 adults with severe sepsis in China, reported 28-day mortality of 26.0% on Ta1 and 35.0% on saline (P = 0.062; log rank P = 0.049). ICU mortality, ICU stay and ventilation time did not differ.⁵²
• In ETASS, a blood marker of immune function (monocyte HLA-DR) rose more with Ta1 on days 3 and 7, though FDA noted it started lower in the Ta1 group. FDA said most sepsis trials do not show meaningful clinical benefit.²¹
• TESTS (2025), a double-blind phase 3 trial of 1,106 adults aged 18 to 85 at 22 centers in China, found 28-day mortality of 23.4% on Ta1 and 24.1% on placebo (hazard ratio 0.99, 95% CI 0.77 to 1.27). No secondary or safety outcome differed significantly.⁶

COVID-19

A 2020 retrospective review of 76 severe cases reported lower mortality with Ta1 (11.11% against 30.00%), but it was not randomized.⁷ In randomized trials, a US open-label study of 49 hospitalized adults found no difference in recovery time, mortality or ventilation. A 105-patient double-blind trial from India reported lower mortality in its severe group, but FDA noted its small size and unreported details, such as when the data were collected.² Three of four meta-analyses from 2022 to 2023 found no decrease in mortality, and FDA judged the evidence insufficient.¹

Cancer

In a randomized open-label trial of 488 patients with stage IV melanoma, median overall survival was 9.4 months when Ta1 was added to chemotherapy and 6.6 months without it (hazard ratio 0.80; P = .08, not significant).⁸ FDA said response rates did not differ significantly and that the comparison regimens are outdated.¹ In liver cancer, one randomized trial reported no difference in one-year recurrence after surgery plus chemoembolization, and a 25-patient randomized pilot found no difference in response or median survival with chemoembolization.¹

Vaccine response

In a 1989 double-blind trial of 90 men aged 65 to 99 given a flu vaccine, 69% on Ta1 and 52% on placebo reached a fourfold antibody rise, with the difference in men 77 and older.⁹² In a 2012 trial of 99 dialysis patients given an H1N1 vaccine, Ta1 raised antibody levels only at day 21, and later responses were higher without it. FDA concluded the evidence is not sufficient to reach any conclusion on Ta1 as a vaccine adjuvant.²¹

Other uses FDA reviewed

• Stem cell transplant: small studies suggested better immune recovery, but a case series found more infections with Ta1, and FDA found no evidence that it reduces infections after transplant.¹
• COPD flare-ups: two studies of 84 and 122 patients reported better lung function with few details, and FDA found a lack of evidence.¹
• FDA found no clinical studies at all in chronic fatigue syndrome, and insufficient evidence in HIV and non-small cell lung cancer.¹

Lab and animal findings

In mice with melanoma, Ta1 under the skin twice daily for 7 days reduced tumor size by 45 to 50% at every dose tested, with no dose response, while a mouse sepsis model showed only trends that were not statistically significant.² In lab and animal work, Ta1 activated dendritic cells and induced the enzyme IDO, which the authors linked to immune tolerance and protection from allergic inflammation in animals.¹⁰ These findings come from cells and animals, not from people.

What has not been studied

No study reviewed for this page tested Ta1 in healthy people for wellness, fitness or anti-aging goals.¹² It is an immune peptide, and none of the 12 uses FDA reviewed involved tissue repair, wound healing or muscle.¹ Readers comparing peptides by goal can see Peptides and healing and recovery and Peptides and muscle growth, and the different molecule in What is TB-500?.

How to read these results

Many Ta1 trials were small, unblinded or compared against treatments now outdated, and the later double-blind trials did not confirm the earlier signals.²¹ In December 2024, members of FDA's compounding advisory committee who voted against Ta1 cited a lack of convincing effectiveness data.¹² A reported benefit in one trial is a finding to test again, not a promise of any effect.

Related pages

Read the full Thymosin Alpha-1 profile, the doses those trials used in Thymosin Alpha-1 dosage, and the reactions they reported in Thymosin Alpha-1 side effects.