HomePeptide dosagesThymosin Alpha-1
Thymosin Alpha-1 dosage: chart, reported range and vial math
The range reported for thymosin alpha-1 is 1.5 to 1.6 mg twice a week. The Italian Zadaxin label gives one 1.6 mg vial twice a week for four weeks, as an add-on to flu vaccination. It is not approved in the US or Canada, and the largest trial, in sepsis, found no drop in deaths.
Thymosin Alpha-1 dosage chart
Reported range, not a label dosePick your vial size. Each row shows the dose in milligrams or micrograms, the volume to draw and the mark on a U-100 syringe.
| Source | Dose | Volume | Syringe units |
|---|---|---|---|
| Reported low end | 1.5 mg | 0.30 mL | 30 units |
| Zadaxin label (Italy) | 1.6 mg | 0.32 mL | 32 units |
Source The Italian Zadaxin label gives one 1.6 mg vial twice a week for four weeks. Reports describe 8 to 12 weeks. Not approved in the US or Canada. Vial math is arithmetic.
Which syringe fits each dose
For the 10 mg vial at 5 mg/mL.
| Dose | Volume | Units | 0.3 mL syringe | 0.5 mL syringe | 1 mL syringe |
|---|---|---|---|---|---|
| 1.5 mg | 0.30 mL | 30 units | Yes | Yes | Yes |
| 1.6 mg | 0.32 mL | 32 units | No | Yes | Yes |
How long a vial lasts
Whole doses in one vial. The row for the size picked above is marked.
| Vial | 1.5 mg | 1.6 mg |
|---|---|---|
| 10 mg vial | 6 doses | 6 doses |
How to mix a Thymosin Alpha-1 vial
These steps are for the 10 mg vial picked in the chart. Change the size there and the amounts here change with it.
- Wash your hands. Wipe the stopper of the peptide vial and the water vial with an alcohol swab.
- Draw 2 mL of bacteriostatic water into a syringe.
- Push the needle through the stopper of the peptide vial and let the water run slowly down the glass, not straight onto the powder.
- Swirl the vial gently until the powder is gone. Do not shake it.
- Write the date and 5 mg/mL on the vial, then put it in the fridge.
| Vial | Bacteriostatic water | Concentration |
|---|---|---|
| 10 mg vial | 2 mL | 5 mg/mL |
What Thymosin Alpha-1 is
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.
What to know before reading a dose
- Not approved in the US or Canada. The one label opened, from Italy, approves it only as an add-on to flu vaccination in immunocompromised people [1], not for hepatitis, sepsis, cancer or general immune support.
- The largest trial found, the double-blind placebo-controlled TESTS trial in 1089 adults with sepsis, showed no reduction in deaths [7]. An earlier smaller single-blind trial had suggested a benefit [9].
- For hepatitis B the trials disagree: a trial with untreated controls reported a benefit [4], while a placebo-controlled double-blind Phase 3 trial did not confirm it [5].
- The Italian label and the pharmacokinetic study differ on timing of the peak blood level: the label says the peak is reached at 6 hours, the volunteer study found 1 to 2 hours [1], [3].
- FDA no longer lists thymosin alpha-1 in category 2. Its page, current as of 22 April 2026, shows it under substances previously in category 2 whose nominations were withdrawn [13], and the 14 May 2026 category list does not contain it [14].
- Health Canada has listed thymosin alpha among seized unauthorized injectable peptide drugs [16], [17].
- The Italian label warns about use in people with autoimmune disease or allergies and contraindicates pregnancy and breastfeeding [1].
Doses on record for Thymosin Alpha-1
Every dose below was given in a human study or printed on an approved label, and each links to its source. Doses set by body weight are left that way.
| From | Where it was used | Dose | How often | For how long | Source |
|---|---|---|---|---|---|
| Label | Zadaxin, Italy: add-on to influenza vaccination in immunocompromised adults | one 1.6 mg vial per injection, into muscle or under the skin; the label says to adjust by its height and weight table (1.32 to 1.87 mg) | twice a week | four weeks from the first vaccination, repeated from week 8 to week 12 | [1] |
| Human study | Randomized trial in chronic hepatitis B with an untreated control group | 1.6 mg under the skin | twice a week | 26 weeks (a second group continued to 52 weeks) | [4] |
| Human study | Phase 3 placebo-controlled trial in chronic hepatitis B | 1.6 mg (route not stated in the abstract) | twice weekly | 6 months | [5] |
| Human study | Randomized comparison of two doses in Japanese patients with chronic hepatitis B, lower dose | 0.8 mg | not stated in the abstract | 24 weeks | [6] |
| Human study | Randomized comparison of two doses in Japanese patients with chronic hepatitis B, higher dose | 1.6 mg | not stated in the abstract | 24 weeks | [6] |
| Human study | Phase 3 TESTS trial in sepsis. Dose taken from the registry record; the registry gives the interval as 12 hours plus or minus 2. | 1.6 mg under the skin | every 12 hours | up to 7 days | [8] |
| Human study | ETASS single-blind trial in severe sepsis. Dose taken from the registry record. | 1.6 mg under the skin | twice a day for 5 days, then once a day for 2 days | 7 days | [10] |
| Human study | Randomized pilot in haemodialysis patients to prevent COVID-19, preliminary report | 1.6 mg under the skin | twice weekly | 8 weeks | [12] |
| Human study | Randomized trial in metastatic melanoma, given with dacarbazine and interferon alfa, lowest dose group | 1.6 mg | not stated in the abstract | not stated in the abstract | [11] |
| Human study | Same melanoma trial, given with dacarbazine with or without interferon alfa, middle dose groups | 3.2 mg | not stated in the abstract | not stated in the abstract | [11] |
| Human study | Same melanoma trial, given with dacarbazine and interferon alfa, highest dose group | 6.4 mg | not stated in the abstract | not stated in the abstract | [11] |
| Human study | Pharmacokinetic study in healthy volunteers comparing three formulations | 900 mcg per square metre of body surface, under the skin | single dose, then repeated dosing over 5 days | 5 days | [3] |
What the evidence shows
Each finding is tagged by the kind of study it comes from. Human trials are listed first.
Randomized human trial
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]
Randomized human trial
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]
Randomized human trial
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]
Randomized human trial
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]
Randomized human trial
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]
Randomized human trial
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]
Randomized human trial
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]
Small human study
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]
Side effects and warnings
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]
From 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]
Storage
Italian label: store in a refrigerator at 2 to 8 degrees C. Once reconstituted with the supplied solvent, use once and within 24 hours and discard what is left. [1]
Thymosin Alpha-1 dosage questions
How many units is 1.6 mg of Thymosin Alpha-1 from a 10 mg vial?
Mixed with 2 mL of bacteriostatic water, a 10 mg vial is 5 mg/mL. 1.6 mg is 0.32 mL, which is 32 units on a U-100 syringe.
How much water goes in a 10 mg Thymosin Alpha-1 vial?
2 mL gives 5 mg/mL. At that strength the doses in the chart sit at 30, 32 units on a U-100 syringe.
How many doses are in a 10 mg vial?
Whole doses in one vial: 6 at 1.5 mg, 6 at 1.6 mg.
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.
What does the Zadaxin label say about dose?
One 1.6 mg vial injected into muscle or under the skin twice a week for four weeks starting at the first vaccination, repeated from week 8 to week 12. The label adds that the dose is to be worked out from height and weight (900 mcg per square metre of body surface) using its table, which runs from 1.32 mg to 1.87 mg. Not for children.
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.
Looked for and not found
- 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.
Change log
10 Oct 2026Page published. 17 sources checked. Vial math added for the 10 mg vial.
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