Thymosin Alpha-1: what it is, what the studies show and where it stands
Thymosin alpha-1 (thymalfasin) is a 28-amino-acid peptide given by injection to modify immune responses. It is authorised as Zadaxin in Italy; no approved product was found in the US or Canada.
At a glance
US Not approved
Canada Not authorized
Group Immune
Sources 17
Checked 10 Oct 2026What is Thymosin Alpha-1?
Thymosin alpha-1 (thymalfasin) is a 28-amino-acid peptide given by injection to modify immune responses. It is authorised as Zadaxin in Italy; no approved product was found in the US or Canada. [6]
Other names: thymalfasin, thymosin alpha 1, Ta1, TA1, timosina alfa-1, Zadaxin.
How it has been given to people: Injection under the skin or into muscle (Italian label). Under the skin in the trials found.
Looking for doses? Thymosin Alpha-1 dosage chart and vial math
Is Thymosin Alpha-1 approved in the US and Canada?
United States: Not FDA approved. FDA lists thymosin alpha-1 among bulk substances that were in compounding category 2 until the nominations were withdrawn, and calls the safety information inadequate. [13]
Canada: Not authorized in Canada. No thymalfasin, thymosin or Zadaxin product is in the Drug Product Database, and Health Canada advisories list thymosin alpha among seized unauthorized injectable peptide drugs. [16]
Both were checked on 10 Oct 2026 against the regulators' own product databases.
Which approved products contain Thymosin Alpha-1?
| Product | Country | Approved for | Label |
|---|---|---|---|
| Zadaxin | Italy | Add-on (adjuvant) to influenza vaccination in immunocompromised people. That is the only indication on the Italian label. | Label |
What human studies of Thymosin Alpha-1 exist?
The 8 findings listed here: 7 from randomized human trials and 1 from smaller or observational human studies.
In 98 patients with chronic hepatitis B, the complete virological response rate 18 months after entry was 40.6% after 26 weeks of treatment and 26.5% after 52 weeks, against 9.4% in untreated controls. Rates were similar across groups at the end of treatment. [4]
A placebo-controlled, double-blind Phase 3 trial in 97 patients with chronic hepatitis B did not confirm that benefit: complete response in 14% on thymosin alpha-1 and 4% on placebo (P = 0.084). [5]
In 316 Japanese patients with chronic hepatitis B randomized between 0.8 mg and 1.6 mg for 24 weeks, 36.4% of the 1.6 mg group had normal ALT 12 months after stopping. The two doses gave similar results. The abstract describes no placebo group. [6]
In the largest trial found (TESTS, 1089 adults with sepsis analysed, double-blind), death from any cause by day 28 was 23.4% with thymosin alpha-1 and 24.1% with placebo: no clear benefit. [7]
An earlier single-blind trial in 361 patients with severe sepsis (ETASS) reported 28-day mortality of 26.0% with thymosin alpha-1 and 35.0% in controls, with a borderline P value. [9]
In 488 patients with metastatic melanoma, median overall survival was 9.4 months in those given thymosin alpha-1 with chemotherapy and 6.6 months in the control group, a difference that did not reach statistical significance (P = .08). [11]
A randomized pilot in 194 dialysis patients had reported only preliminary counts when published: 3 deaths in the treated group and 7 in the control group, with efficacy analysis still to come. [12]
After injection under the skin in 9 healthy volunteers, peak blood levels came at 1 to 2 hours and there was no build-up between single and repeated dosing. [3]
What are the side effects of Thymosin Alpha-1?
Reported in human studies or on a label:
- Italian label: no clinically notable side effects apart from occasional mild, short-lived pain at the injection site. [1]
- In the Japanese hepatitis B trial all adverse drug reactions were mild; most were changes in liver enzymes. [6]
- In the 1089-patient sepsis trial no safety outcome differed significantly between thymosin alpha-1 and placebo. [7]
- In the 98-patient hepatitis B trial no significant side effects were observed. [4]
- In the melanoma trial, adding thymosin alpha-1 to dacarbazine and interferon alfa did not add toxicity. [11]
- FDA says compounded thymosin alpha-1 may carry a significant risk of immune reactions for some routes of administration. [13]
Warnings on the label
- Italian label: contraindicated in pregnancy and while breastfeeding, and in people hypersensitive to the active substance or any excipient. [1]
- Italian label: use with caution in people with atopy or a history of allergic reactions. [1]
- Italian label: in people with autoimmune disease, use must be assessed case by case. [1]
- Italian label, interactions: caution when given together with other immune-modifying medicines. [1]
- Italian label: not to be used in children. [1]
- Italian label: do not mix with other medicines. [1]
What is the half-life of Thymosin Alpha-1?
Less than 3 hours after injection under the skin in healthy volunteers, with the peak blood level at 1 to 2 hours and no build-up over 5 days of dosing. [3]
How does Thymosin Alpha-1 compare with others in its group?
These are the peptides filed under immune. The last column says whether a randomized human trial is on record for each.
| Peptide | US | Canada | Half-life | Randomized human trial |
|---|---|---|---|---|
| Thymosin Alpha-1 | Not approved | Not authorized | Less than 3 hours after injection under the skin in healthy volunteers, with the peak blood level at 1 to 2 hours and no build-up over 5 days of dosing. | Yes |
| LL-37 | Not approved | Not authorized | Not found | Yes |
| Vilon | Not approved | Not authorized | Not found | No |
What could not be found
These were searched for and did not turn up. They are listed so a missing number is not mistaken for a hidden one.
- A label for hepatitis B or any other use outside Italy. The commonly quoted approval in other countries for hepatitis B at 1.6 mg twice weekly was not verified: no other regulator label was fetched. The hepatitis B regimen recorded here comes from trials [4], [5], [6], not from a label.
- Any US label: openFDA has none.
- FDA orphan-drug designation status: the FDA orphan designation database returned a bot challenge page to curl and could not be read.
- The dose and schedule used in the TESTS sepsis trial are not in the PubMed abstract [7]; they are taken from the registry record [8]. The same applies to ETASS [9], [10].
- How often the dose was given in the Japanese hepatitis B trial [6] and in the melanoma trial [11]: not stated in the abstracts.
- Thymosin alpha-1 is not named on the WADA 2026 Prohibited List [15]. The list was searched for thymalfasin and thymosin; the only thymosin entry is thymosin beta-4.
- A missed-dose rule: the Italian label does not give one.
Thymosin Alpha-1 questions
Is Thymosin Alpha-1 approved in the US?
Not FDA approved. FDA lists thymosin alpha-1 among bulk substances that were in compounding category 2 until the nominations were withdrawn, and calls the safety information inadequate.
Is Thymosin Alpha-1 authorized in Canada?
Not authorized in Canada. No thymalfasin, thymosin or Zadaxin product is in the Drug Product Database, and Health Canada advisories list thymosin alpha among seized unauthorized injectable peptide drugs.
What is the half-life of Thymosin Alpha-1?
Less than 3 hours after injection under the skin in healthy volunteers, with the peak blood level at 1 to 2 hours and no build-up over 5 days of dosing.
Has Thymosin Alpha-1 been tested in a randomized human trial?
Yes. At least one randomized human trial is listed on this page.
Sources
Each one was opened on 10 Oct 2026 and matched to the line it supports.
- ZADAXIN 1,6 mg/ml polvere e solvente per soluzione iniettabile: Riassunto delle caratteristiche del prodotto Agenzia Italiana del Farmaco (AIFA) 2026. api.aifa.gov.it.
- AIFA medicines database record for ZADAXIN, AIC 028364 Agenzia Italiana del Farmaco (AIFA) 2026. api.aifa.gov.it.
- Rost KL et al. Pharmacokinetics of thymosin alpha1 after subcutaneous injection of three different formulations in healthy volunteers. Int J Clin Pharmacol Ther 1999. PubMed 10027483.
- Chien RN et al. Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial. Hepatology 1998. PubMed 9581695.
- Mutchnick MG 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. PubMed 10607256.
- 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. PubMed 15850471.
- Wu J et al. The efficacy and safety of thymosin alpha1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ 2025. PubMed 39814420. Trial NCT02867267.
- The Efficacy and Safety of Ta1 for Sepsis ClinicalTrials.gov 2016. clinicaltrials.gov. Trial NCT02867267.
- Wu J et al. The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial. Crit Care 2013. PubMed 23327199. Trial NCT00711620.
- Efficacy of Thymosin alpha1 for Severe Sepsis ClinicalTrials.gov 2008. clinicaltrials.gov. Trial NCT00711620.
- Maio M 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. PubMed 20194853.
- Tuthill CW et al. A pilot trial of Thymalfasin (Ta1) to prevent covid-19 infection and morbidities in renal dialysis patients: Preliminary report. Int Immunopharmacol 2023. PubMed 36881981.
- Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks US Food and Drug Administration 2026. fda.gov.
- Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act US Food and Drug Administration 2026. fda.gov.
- World Anti-Doping Code International Standard Prohibited List 2026 World Anti-Doping Agency 2026. wada-ama.org.
- Unauthorized injectable peptide drugs seized and sold by Canada Peptide may pose serious health risks Health Canada 2025. recalls-rappels.canada.ca.
- Unauthorized injectable peptide drugs seized from Optimum Wellness Centre in Calgary, Alberta may pose serious health risks Health Canada 2025. recalls-rappels.canada.ca.
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