Thymosin Alpha-1
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Thymosin Alpha-1 dosage
No dose of Thymosin Alpha-1 is approved in the US, because FDA has approved no drug that contains it.1 Published doses come from foreign labels for the brand Zadaxin and from clinical trials under medical care, most often 1.6 mg under the skin.2 FDA notes that the smallest dose needed for a response is hard to determine.12
This page summarizes published sources for information only. It is not medical advice and does not tell anyone to use a product. Questions about your own health belong with a licensed clinician. For questions about an order or a product, contact us.
Why there is no approved dose
FDA has approved no drug containing thymosin alpha-1, so there is no FDA-approved dose for any use.1 The doses on this page come from foreign labels for the brand Zadaxin, as summarized in FDA's 2024 review, and from published clinical trials in which patients received the drug under medical care.2 FDA adds that, without well-defined dose-response studies, the smallest dose that produces a pharmacological response is hard to determine.12 None of these figures is guidance for any person.
Foreign label schedules for Zadaxin
Zadaxin is a finished drug product, a 1.6 mg powder for injection, and FDA notes it cannot be used interchangeably with Ta1 as a substance.2 Its labels abroad, as FDA summarizes them, give these schedules. Neither is an FDA-approved dose.
| Label | Approved use | Schedule |
|---|---|---|
| Indonesia | Chronic hepatitis B in adults 18 or older with compensated liver disease and active viral replication | 1.6 mg under the skin twice weekly, 3 or 4 days apart, for six months (52 doses) without interruption2 |
| Italy | Adjuvant to flu vaccination in immunocompromised people | One 1.6 mg vial into the muscle or under the skin twice weekly for four weeks from the first vaccination, repeated from week 8 (second vaccination) to week 122 |
Doses used in clinical trials
Most trials used the same 1.6 mg amount as the Zadaxin vial, under the skin, and varied how often and how long it was given.2 The table lists each study's population, schedule and duration.
| Study | People | Dose, route and schedule | Duration |
|---|---|---|---|
| TESTS phase 3, China (2025) | 1,106 adults with sepsis | 1.6 mg in 1 mL under the skin every 12 hours, plus or minus 2 hours | Up to 7 days86 |
| ETASS, China (2013) | 361 adults with severe sepsis | 1.6 mg under the skin twice a day, then once a day | 5 days, then 2 days2 |
| Hepatitis B trial (1998) | 98 patients | 1.6 mg under the skin twice weekly | 26 or 52 weeks4 |
| Hepatitis B phase 3 trial (1999) | 97 patients | 1.6 mg under the skin twice weekly | 6 months51 |
| Flu vaccine trial (1989) | 90 men aged 65 to 99 | 900 micrograms/m2 under the skin twice weekly, first dose right after vaccination | 8 doses92 |
| Metastatic melanoma (2010) | 488 patients | 1.6, 3.2 or 6.4 mg with dacarbazine and interferon alfa, or 3.2 mg with dacarbazine alone | 4-week cycles, up to 6 cycles71 |
| COVID-19 trials, US and India (2022) | 49 and 105 hospitalized adults | 1.6 mg under the skin once daily (US) or two to three times daily (India) | 7 days2 |
| Stem cell transplant studies (2010, 2011) | 14 and 30 transplant recipients | 1.6 mg under the skin daily | 16 weeks1 |
| Pharmacokinetic study (1999) | 9 healthy volunteers | 900 micrograms/m2 under the skin (actual doses 1.6 to 2.2 mg) | Single and repeated doses within 7-day periods32 |
Across all the clinical studies FDA reviewed, doses ran from about 1 to 16 mg per day (0.6 to 9.6 mg/m2), usually under the skin, for 1 day to 12 months.21 A dose in a trial is not evidence that the dose works. The 1,106-patient TESTS trial, for example, found no mortality benefit with its twice-daily schedule.6 The highest strength FDA found in clinical studies was a 2 mg/mL solution, and it said a more concentrated solution could raise the risk of immune reactions.1
How long a dose stays in the blood
In 9 healthy volunteers given Ta1 under the skin, blood levels peaked in 1 to 2 hours, and the elimination half-life was under 3 hours.3 FDA summarizes the half-life as about 2 hours and notes that levels did not build up over 5 days of daily dosing.2
Doses used in animal studies
A mouse melanoma study gave 0.02 to 6 mg/kg under the skin twice daily for 7 days, and a mouse sepsis model used 6 mg/kg under the skin twice daily.21 FDA notes that these animal doses are markedly higher, by body surface area, than the doses used in most human studies.2 They describe mouse experiments and cannot be read as doses for people.
No dose for a research vial
The schedules above describe what patients received under medical care, and they are not guidance for any person.12 A research vial is not Zadaxin, and the vial sold on this site carries the label: For research use only. Not for human or veterinary use. No human dose is established outside those labeled and supervised settings, so this page gives no dose for personal use.
Related pages
Read the full Thymosin Alpha-1 profile, what trials reported in Thymosin Alpha-1 benefits and uses, and the reactions seen in those trials in Thymosin Alpha-1 side effects. For general background, see Peptide dosage basics.
More on Thymosin Alpha-1
Thymosin Alpha-1 benefits and uses
What published sources report about Thymosin Alpha-1 and its uses, with the evidence level of each finding. No promises.
Thymosin Alpha-1 side effects
Side effects of Thymosin Alpha-1 as reported in clinical trials and published studies, with links to the full profile. Reviewed by a qualified reviewer.
Thymosin Alpha-1 in the store
Thymosin Alpha-1 for sale: strengths, stock and shipping are on the product page.
For research use only. Not for human or veterinary use. Read the research use policy.
Frequently asked questions
How often can I take thymosin alpha 1?
No schedule can be given for any person, and no US dose exists because no Ta1 drug is FDA approved.1 For reference only, the Indonesian Zadaxin label used 1.6 mg twice weekly for six months in chronic hepatitis B, and hospital sepsis trials gave 1.6 mg once or twice daily for up to 7 days.28 FDA notes that the smallest dose needed for a response is hard to determine.1
Can I take thymosin alpha 1 every day?
Daily dosing appears only in studies under medical care: 1.6 mg daily for 16 weeks in small studies of stem cell transplant recipients, 1.6 mg once daily for 7 days in a US trial in hospitalized COVID-19 patients, and 1.6 mg once or twice daily for up to 7 days in sepsis trials.128 One of those transplant studies also reported serious harms, listed under Thymosin Alpha-1 side effects.1 The approved Zadaxin schedules abroad are twice weekly.2 None of this is guidance for personal use.
Can you take thymosin alpha 1 at night?
None of the labels or studies reviewed for this page addresses the time of day. What is known is that Ta1 clears quickly: after an injection under the skin, blood levels peaked in 1 to 2 hours, and FDA puts the half-life at about 2 hours.32 No dose of Ta1 is established for personal use at any time of day.1
Why were some thymosin alpha 1 doses given per square meter?
Some trials set the dose by body surface area, at 900 micrograms per square meter, instead of a fixed amount.2 In a 1999 pharmacokinetic study, that rule gave actual doses of 1.6 to 2.2 mg in 9 healthy volunteers.32 The most common dose across studies was a fixed 1.6 mg under the skin, and the Zadaxin labels use one 1.6 mg vial per dose.21
Written by D2C Peptides Editorial Team.
Pending qualified review.
Updated .
Sources
- Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances (FDA presentation slides, Pharmacy Compounding Advisory Committee Meeting, December 4, 2024). U.S. Food and Drug Administration, 2024.
- FDA Evaluation of Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances (Ta1 (free base) and Ta1 acetate), FDA Briefing Document, Pharmacy Compounding Advisory Committee, December 4, 2024 (memo dated 11/15/2024). U.S. Food and Drug Administration, 2024.
- Pharmacokinetics of thymosin alpha1 after subcutaneous injection of three different formulations in healthy volunteers (Rost KL et al.; PMID 10027483). International Journal of Clinical Pharmacology and Therapeutics (abstract via PubMed, NCBI E-utilities), 1999.
- Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial (Chien RN et al.; PMID 9581695). Hepatology (abstract via PubMed, NCBI E-utilities), 1998.
- Thymosin alpha1 treatment of chronic hepatitis B: results of a phase III multicentre, randomized, double-blind and placebo-controlled study (Mutchnick MG et al.; PMID 10607256). Journal of Viral Hepatitis (abstract via PubMed, NCBI E-utilities), 1999.
- TESTS trial: thymosin α1 in adults with sepsis, multicentre, double blinded, randomised, placebo controlled, phase 3 (Wu J et al.; PMID 39814420, PMCID PMC11780596, DOI 10.1136/bmj-2024-082583). BMJ (abstract via PubMed, NCBI E-utilities), 2025.
- Large randomized study of thymosin alpha 1, interferon alfa, or both in combination with dacarbazine in patients with metastatic melanoma (Maio M et al.; PMID 20194853). Journal of Clinical Oncology (abstract via PubMed, NCBI E-utilities), 2010.
- The Efficacy and Safety of Ta1 for Sepsis (TESTS), NCT02867267. ClinicalTrials.gov, U.S. National Library of Medicine, 2026.
- Augmentation of influenza antibody response in elderly men by thymosin alpha one. A double-blind placebo-controlled clinical study (Gravenstein S et al.; PMID 2642497). Journal of the American Geriatrics Society (abstract via PubMed, NCBI E-utilities), 1989.