Pinc PeptideThe girly peptide research blog

Thymosin alpha-1 · Dose evidence · updated 8 October 2026

Thymosin alpha-1 dosage: what studies actually used

The short answer

In its 2024 review, FDA said it had approved no drug product containing thymosin alpha-1, so there is no US label dose4. Abroad, Italy’s Zadaxin label gives one 1.6 mg vial twice a week for 4 weeks, repeated from week 8 to week 12, as an add-on to flu vaccination in people with weakened immune systems1. Most trials used 1.6 mg under the skin, from every 12 hours for 7 days in sepsis to twice a week for 48 weeks in hepatitis C, and the largest found no benefit on their main goals4567. No dose is established for the immune-support uses promoted online, and FDA found the evidence did not support effectiveness for any of the 12 uses it examined4.

Not dosing advice. This page reports doses that studies and approved labels used, with their sources. It does not recommend a dose, and we do not give mixing, injection or unit-conversion instructions. Gray-market vials often do not contain what their label says. How we report doses.

Every dose studied in people

StudyWhoPeopleDose and routeWhat happened
TESTS (Wu 2025), double-blind randomized Phase 3 trial Adults with sepsis at 22 hospitals in China 1,106 1.6 mg every 12 hours
Injection under the skin · 7 days		 28-day death rates were 23.4% with thymosin alpha-1 and 24.1% with placebo, and no secondary or safety outcome differed5.
Ciancio 2012, double-blind randomized Phase 3 trial Adults with chronic hepatitis C not cured by earlier interferon and ribavirin 552 1.6 mg twice a week, added to peginterferon alfa-2a and ribavirin
Injection under the skin · 48 weeks		 Lasting cure rates (sustained viral response) were 12.7% with thymosin alpha-1 and 10.5% with placebo, not a significant difference; among the 182 who finished all 48 weeks they were 41.0% and 26.3%7.
TRACE (Ke 2022), double-blind randomized trial Adults 18 to 70 with predicted severe acute pancreatitis at 16 hospitals in China 508 1.6 mg every 12 hours, then 1.6 mg once a day
Injection under the skin · 7 days, then 7 more days		 Infection of the damaged pancreas occurred in 15.7% versus 18.1% on placebo, not a significant difference, and 90-day death rates were 9.1% in both groups6.
Maio 2010, open-label randomized Phase 2 trial People with stage IV melanoma on dacarbazine chemotherapy, with or without interferon alfa 488 1.6, 3.2 or 6.4 mg on days 8 to 11 and 15 to 18 of each 28-day cycle
Injection under the skin · Up to 6 cycles		 There were 10 and 12 tumor responses in the two 3.2 mg groups versus 4 in the control group, and median survival of 9.4 versus 6.6 months was not a statistically significant gain8. The schedule shown comes from the trial’s registry record2.
ETASS (Wu 2013), randomized trial, patients blinded Adults with severe sepsis at 6 hospitals in China 361 1.6 mg twice a day, then 1.6 mg once a day
Injection under the skin · 5 days, then 2 more days		 28-day death rates were 26.0% versus 35.0% in the control group, a borderline result (P = 0.062), and no serious drug-related adverse event was recorded9.
Iino 2005, randomized comparison of two doses, no untreated group Japanese patients with chronic hepatitis B (HBeAg positive) 316 0.8 or 1.6 mg six times a week for 2 weeks, then twice a week for 22 weeks
Injection under the skin · 24 weeks		 Twelve months after treatment ended, 36.4% of the 1.6 mg group had normal levels of the liver enzyme ALT and 22.8% had cleared HBeAg, a blood marker of an active virus, with similar rates at 0.8 mg410. ALT flared temporarily in 22 people, and treatment was interrupted in 164.
Tuthill 2023 and registry results (NCT04428008), open-label randomized pilot trial Dialysis patients at five centers in Kansas City, to prevent COVID-19 189 1.6 mg twice a week, after dialysis
Injection under the skin · 8 weeks		 Within 6 months, COVID-19 occurred in 5 of 91 treated and 7 of 98 untreated people, and 3 versus 7 died; no statistical tests were posted1112.
Shetty 2022, double-blind randomized Phase 3 trial Adults in hospital with moderate or severe COVID-19 in India 105 1.6 mg two times a day (moderate group) or three times a day (severe group), as FDA describes it
Injection under the skin · 7 days		 In the severe group, 11.1% died on thymosin alpha-1 versus 38.5% on placebo; FDA noted that the paper gave no death figures for the moderate group or the trial as a whole413.
Carraro 2012, open-label randomized pilot study Dialysis patients given a pandemic H1N1 flu vaccine 99 3.2 or 6.4 mg, given 7 days before and on the day of vaccination
Injection under the skin · Two dosing days, 7 days apart		 Antibody levels at 3 weeks were higher than with the vaccine alone but then fell faster, and FDA saw no lasting benefit414.
Chien 1998, randomized trial with an untreated group People with chronic hepatitis B 98 1.6 mg twice a week
Injection under the skin · 26 or 52 weeks		 Eighteen months after entry, blood markers of the virus (HBV DNA and HBeAg) had cleared in 40.6% of the 26-week group, 26.5% of the 52-week group and 9.4% of untreated people, though rates were similar when treatment ended15.
Mutchnick 1999, double-blind randomized Phase 3 trial People with chronic hepatitis B (HBeAg positive) 97 1.6 mg twice a week
Injection under the skin · 6 months, then 6 months of follow-up		 Complete responses, with virus markers cleared and staying cleared, occurred in 14% versus 4% on placebo, which missed statistical significance (P = 0.084)416. The authors said the results did not confirm benefits reported in other studies16.
Gravenstein 1989, double-blind randomized trial Male veterans aged 65 to 99 given the 1986 flu vaccine 90 900 µg/m² of body surface twice a week (8 doses), starting right after the vaccine
Injection under the skin · 4 weeks		 Of 85 men analyzed, 69% on thymosin alpha-1 and 52% on placebo had a fourfold antibody rise; FDA said response rates were similar until 6 weeks after vaccination and called the study’s usefulness questionable417.
Shehadeh 2023, open-label randomized pilot trial US adults in hospital with COVID-19, low blood oxygen and low lymphocyte counts 49 1.6 mg once a day
Injection under the skin · 7 days		 Clinical recovery was not significantly faster than with standard care alone, and FDA found no difference in deaths or in the need for a ventilator418.
Dillman 1982, Phase 1 dose-finding study, as described by FDA People with advanced cancer 14 One dose of 0.6, 1.2, 2.4, 4.8 or 9.6 mg/m² of body surface
Injection into muscle · Single dose		 It was well tolerated: one person had a fever at 2.4 mg/m² and two had mild nausea after 4.8 and 9.6 mg/m²4. Dose increases stopped at 9.6 mg/m² without a dose-limiting toxicity, partly because no link between dose and immune response was evident4.

Studies, animals and users: kept apart

Doses below are what studies used or what a label says. They are not advice, and gray-market products may not contain what their label says.

In human studies

Approved labels abroad: 1.6 mg under the skin twice weekly, 3 or 4 days apart, for 6 months (52 doses) for chronic hepatitis B (Indonesia); and one 1.6 mg vial, into muscle or under the skin, twice weekly for 4 weeks from the first flu shot, repeated from week 8 to week 12 (Italy)4. The most common trial dose was 1.6 mg under the skin, usually twice weekly, for up to 12 months4716. Sepsis and pancreatitis trials gave 1.6 mg every 12 hours for 7 days (followed in the pancreatitis trial by once daily for 7 more days), or twice daily for 5 days and then once daily for 2 days569. COVID-19 trials gave 1.6 mg once daily, or 2 to 3 times daily, for 7 days4. Other studies used 0.8 mg six times a week for 2 weeks and then twice weekly in hepatitis B, 900 µg/m² twice weekly with a flu shot in older men, 3.2 or 6.4 mg with a pandemic flu vaccine, and up to 6.4 mg in melanoma48101417. Across trials, doses ranged from about 1 to 16 mg4. We found no human study of nasal sprays or of the 300 to 500 µg daily schedules common online.

In animal studies

Mice: 10 mg/kg under the skin twice daily for 7 days slowed lung tumor growth; 0.02 to 6 mg/kg twice daily for 7 days shrank melanoma tumors by 45 to 50% at every dose, with no dose-response; 6 mg/kg twice daily in a sepsis model gave only non-significant trends; 200 µg/kg a day into the abdominal cavity for 7 or 14 days lowered virus levels in a cytomegalovirus model; and 0.05 or 0.5 µg/kg daily for 4 days after a tetanus vaccine raised antibody levels by about 25 to 35%4. Rats: single IV doses of about 0.175 mg/kg in two blood-level studies4. These are animal research doses, not human doses.

What users report Anecdotal · not validated · not a recommendation

A peptide dosing website (published 1 March 2026, updated 28 September 2026) lists 300 to 500 µg injected under the skin once a day19.

Half-life and how it is taken

Half-life
About 2 hours (means 1.8 to 2.6 hours)20Elimination half-life in 9 healthy volunteers after an under-the-skin dose of 900 µg/m² (1.6 to 2.2 mg), comparing Zadaxin with two other makers’ products. Blood levels peaked within about 2 hours, and 5 daily doses did not build up420. In rats given about 0.175 mg/kg IV, two studies found 1.9 and 3.0 hours4.
Routes
  • Subcutaneous injection (the approved route abroad; nearly all human data)
  • Intramuscular injection (allowed on the Italian label; used in early cancer trials)
  • Nasal spray (sold by some US clinics as 3 mg and 10 mg sprays; no human data found)
  • Intravenous injection (rat blood-level studies only)
  • Injection into the abdominal cavity (mouse studies only)

What the Zadaxin labels abroad say

FDA has approved no thymosin alpha-1 product, so these doses come from labels abroad, for the uses and people those labels name4. Neither label’s use is general immune support or long COVID, two of the uses promoted online14.

  • Italy (prescription only): one 1.6 mg vial, into muscle or under the skin, twice a week for 4 weeks from the first flu shot, then again from the second shot in week 8 to week 12121. The label’s only use is as an add-on to flu vaccination in people with weakened immune systems, and its dose is for adults1.
  • The Italian label also gives a weekly dose of 900 µg per square meter of body surface, worked out from height and weight, without saying how that fits with one vial twice a week1.
  • The Italian label says not to use it in children or during pregnancy or breastfeeding, to take care in people prone to allergies, and to decide case by case in autoimmune disease1.
  • Indonesia, as FDA described the registered label in 2024: 1.6 mg under the skin twice a week, 3 or 4 days apart, for 6 months (52 doses) without a break, for chronic hepatitis B in adults 18 or older whose liver still copes (compensated disease) and who have active virus in the blood4.
  • The Indonesian label warns that liver enzymes can flare during treatment, and counts the drug as contraindicated in people whose immune system is suppressed on purpose, such as transplant patients, unless the benefits clearly outweigh the risks4.

The Italian label text is the version AIFA made available on 26 February 20261. SciClone said in 2014 that Zadaxin was approved in over 30 countries, but FDA said it could not independently verify those approval claims, so other countries’ labels are not covered here422.

Why no dose is established for other uses

FDA’s 2024 review found that the evidence did not support effectiveness for any of the 12 uses it examined4. FDA said that without a well-defined link between dose and response, it is hard to know the smallest dose that has any effect4. It also said the vaccine studies varied too much to establish a best dose or schedule for boosting flu-shot responses4.

As of 5 October 2026, we found no independent lab tests of gray-market thymosin alpha-1, so what the vials hold is unknown23.

Trials left out of the table

  • Hepatitis B with early (compensated) cirrhosis, Wu 2018 (690 people, open-label): with thymosin alpha-1 added to entecavir for 52 weeks, the combined rate of worsening liver disease, liver cancer or death was similar to entecavir alone over a median follow-up of 38.2 months, but the abstract gives no dose24.
  • COVID-19 boosters in older adults (NCT06821100, Phase 1, 75 people planned): 4.8 mg on day 0, or on days 0 and 3, followed by the booster, compared with no thymosin alpha-125. It was still recruiting at its 16 July 2026 registry update, with completion estimated for 1 December 202625.
  • Colorectal cancer after surgery (NCT05086614, Phase 3, 2,500 people planned, Fudan University): 1.6 mg under the skin twice a week for 6 months, compared with observation3. The record has not been updated since it was posted on 21 October 2021, when it said ‘recruiting’ and estimated that its main data collection would end on 31 March 20273.

Questions people ask

How much thymosin alpha-1 should I take?

No dose is established for the uses promoted online, and FDA found the evidence did not support effectiveness for any of the 12 uses it examined4. Most trials used 1.6 mg under the skin, and Italy’s label gives one 1.6 mg vial twice a week only as an add-on to flu shots in adults with weakened immune systems14. Thymosin alpha-1 is not approved in the US, and US pharmacies may not compound it4262728.

What is the dose of Zadaxin?

Italy’s label gives one 1.6 mg vial, into muscle or under the skin, twice a week for 4 weeks from the first flu shot, repeated from week 8 to week 12, for adults with weakened immune systems1. Indonesia’s label, as FDA described it, gives 1.6 mg under the skin twice a week for 6 months in adults with chronic hepatitis B4.

Can you take thymosin alpha-1 every day?

In the trials on this page, daily doses were given only in short courses, such as 1.6 mg every 12 hours for 7 days in sepsis, or for 7 days followed by once a day for 7 days in pancreatitis56. Longer courses, such as 48 weeks in hepatitis C, were given twice a week7. We found no trial of daily use for months, and FDA found no published animal studies of repeated doses; the maker’s summaries report no safety signals but do not include the data4.

How long do you take thymosin alpha-1?

By FDA’s count, trial courses ran from 1 day to 12 months, and one hepatitis B trial gave 1.6 mg twice a week for 52 weeks415. The Italian label’s course is 4 weeks from the first flu shot, repeated from week 8 to week 121. No course length has been shown to help for the immune-support uses promoted online4.

Go deeper

Sources

  1. 1ZADAXIN 1.6 mg/ml powder and solvent for solution for injection: summary of product characteristics (Riassunto delle caratteristiche del prodotto), AIC 028364026 Agenzia Italiana del Farmaco (AIFA), 26 Feb 2026. api.aifa.gov.it
  2. 2NCT00911443: Thymosin Alpha 1, Interferon Alpha, or Both, in Combination With Dacarbazine in Patients With Malignant Melanoma ClinicalTrials.gov, 9 Jul 2009. clinicaltrials.gov
  3. 3NCT05086614: Thymosin-alpha 1 for Adjuvant Treatment After Radical Resection of High-risk Stage II and III Colorectal Cancer ClinicalTrials.gov, 21 Oct 2021. clinicaltrials.gov
  4. 4FDA Evaluation of Thymosin Alpha-1 (Ta1)-Related Bulk Drug Substances (Ta1 free base and Ta1 acetate), briefing document for the Pharmacy Compounding Advisory Committee meeting of December 4, 2024 U.S. Food and Drug Administration, 15 Nov 2024. fda.gov
  5. 5The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial BMJ, 15 Jan 2025. pubmed.ncbi.nlm.nih.gov
  6. 6Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial Intensive Care Medicine, Jul 2022. pubmed.ncbi.nlm.nih.gov
  7. 7Thymosin alpha-1 with peginterferon alfa-2a/ribavirin for chronic hepatitis C not responsive to IFN/ribavirin: an adjuvant role? Journal of Viral Hepatitis, Jan 2012. pubmed.ncbi.nlm.nih.gov
  8. 8Large randomized study of thymosin alpha 1, interferon alfa, or both in combination with dacarbazine in patients with metastatic melanoma Journal of Clinical Oncology, 1 Apr 2010. pubmed.ncbi.nlm.nih.gov
  9. 9The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial Critical Care, 17 Jan 2013. pubmed.ncbi.nlm.nih.gov
  10. 10The efficacy and safety of thymosin alpha-1 in Japanese patients with chronic hepatitis B; results from a randomized clinical trial Journal of Viral Hepatitis, May 2005. pubmed.ncbi.nlm.nih.gov
  11. 11NCT04428008: Thymosin Alpha 1 to Prevent COVID-19 Infection in Renal Dialysis Patients (results posted 21 April 2026) ClinicalTrials.gov, 21 Apr 2026. clinicaltrials.gov
  12. 12A pilot trial of Thymalfasin (Ta1) to prevent covid-19 infection and morbidities in renal dialysis patients: Preliminary report International Immunopharmacology, Apr 2023. pubmed.ncbi.nlm.nih.gov
  13. 13A Double-blind Multicenter Two-arm Randomized Placebo-controlled Phase-III Clinical Study to Evaluate the Effectiveness and Safety of Thymosin α1 as an Add-on Treatment to Existing Standard of Care Treatment in Moderate-to-severe COVID-19 Patients Indian Journal of Critical Care Medicine, Aug 2022. pubmed.ncbi.nlm.nih.gov
  14. 14Thymosin-alpha 1 (Zadaxin) enhances the immunogenicity of an adjuvated pandemic H1N1v influenza vaccine (Focetria) in hemodialyzed patients: a pilot study Vaccine, 1 Feb 2012. pubmed.ncbi.nlm.nih.gov
  15. 15Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial Hepatology, May 1998. pubmed.ncbi.nlm.nih.gov
  16. 16Thymosin alpha1 treatment of chronic hepatitis B: results of a phase III multicentre, randomized, double-blind and placebo-controlled study Journal of Viral Hepatitis, Sep 1999. pubmed.ncbi.nlm.nih.gov
  17. 17Augmentation of influenza antibody response in elderly men by thymosin alpha one. A double-blind placebo-controlled clinical study Journal of the American Geriatrics Society, Jan 1989. pubmed.ncbi.nlm.nih.gov
  18. 18A Pilot Trial of Thymalfasin (Thymosin-α-1) to Treat Hospitalized Patients With Hypoxemia and Lymphocytopenia Due to Coronavirus Disease 2019 Infection Journal of Infectious Diseases, 11 Jan 2023. pubmed.ncbi.nlm.nih.gov
  19. 19Thymosin Alpha-1 Dosage: 5 mg Vial (published 1 March 2026, updated 28 September 2026) PeptideDosages, 28 Sep 2026. peptidedosages.com
  20. 20Pharmacokinetics of thymosin alpha1 after subcutaneous injection of three different formulations in healthy volunteers International Journal of Clinical Pharmacology and Therapeutics, Jan 1999. pubmed.ncbi.nlm.nih.gov
  21. 21Banca Dati Farmaci: ZADAXIN (timosina alfa 1) 1.6 mg/ml powder and solvent for solution for injection, AIC 028364026 Agenzia Italiana del Farmaco (AIFA), accessed 5 Oct 2026. medicinali.aifa.gov.it
  22. 22SciClone Pharmaceuticals 2014 Annual Report (Form 10-K for fiscal 2014) SciClone Pharmaceuticals, Inc., 12 Mar 2015. annualreports.com
  23. 23Thymosin Alpha 1: safety testing results and vendor ratings Finnrick, accessed 5 Oct 2026. finnrick.com
  24. 24Combination of entecavir with thymosin alpha-1 in HBV-related compensated cirrhosis: a prospective multicenter randomized open-label study Expert Opinion on Biological Therapy, Jul 2018. pubmed.ncbi.nlm.nih.gov
  25. 25NCT06821100: Thymalfasin (Thymosin Alpha 1; Ta1) as an Enhancer of Vaccine Response Among Older Adults Receiving Booster Doses of COVID-19 Vaccine ClinicalTrials.gov, 16 Jul 2026. clinicaltrials.gov
  26. 26Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks U.S. Food and Drug Administration, 22 Apr 2026. fda.gov
  27. 27Final Summary Minutes of the Pharmacy Compounding Advisory Committee Meeting, December 4, 2024 U.S. Food and Drug Administration, 21 Feb 2025. fda.gov
  28. 28Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act (categories list) U.S. Food and Drug Administration, 14 May 2026. fda.gov

Not medical advice. Talk to a licensed clinician before using any drug. Report an error.