Thymosin Alpha-1 dosage

What Thymosin Alpha-1 is

Thymosin alpha-1 is a 28-amino-acid thymic peptide, and its synthetic form thymalfasin is approved in a number of countries outside the United States. It has been studied in hepatitis, sepsis, and as a vaccine adjunct, with mixed trial findings. It is not FDA-approved.

Thymosin alpha 1 is a peptide naturally occurring in the thymus that has been studied for modifying and restoring immune function ^1. A historical review describes it as a biological response modifier that activates and regulates various cells of the immune system ^2. Immune markers in trials In the ETASS trial in severe sepsis, greater improvement in monocyte HLA-DR was observed on days 3 and 7 in the thymosin… How it works →

What the human evidence shows

• The TESTS trial, a multicentre, double-blinded, placebo-controlled phase 3 trial at 22 centres in China between September 2016 and December 2020, randomized 1106 adults aged 18 to 85 with sepsis (sepsis-3 criteria) 1:1 to subcutaneous thymosin alpha 1 or placebo stratified by age and centre; 1089 were analysed, and 28-day all-cause mortality was 23.4% with thymosin alpha 1 versus 24.1% with placebo (hazard ratio 0.99, 95% CI 0.77 to 1.27; p = 0.93) (NCT02867267) ^3.
• The ETASS trial, a multicentre, single-blind randomized controlled trial in six tertiary teaching hospitals in China between May 2008 and December 2010, allocated 361 patients with severe sepsis 1:1 to subcutaneous thymosin alpha 1 (ZADAXIN) or control; 28-day all-cause mortality was 26.0% versus 35.0% (log rank p = 0.049) and monocyte HLA-DR improvement was greater in the treated group on days 3 and 7 (NCT00711620) ^4.
• A multicentre, double-blind, randomised, placebo-controlled trial in patients with predicted severe acute necrotising pancreatitis (APACHE II score 8 or more and CT severity score 5 or more, admitted within 7 days of symptom onset) randomized 508 patients to subcutaneous thymosin alpha 1 or saline placebo; infected pancreatic necrosis developed in 15.7% versus 18.1% (difference -2.4%, 95% CI -7.4 to 5.1; p = 0.48) ^7.
• An open-label randomized controlled trial in 120 patients with hepatitis B virus-related acute-on-chronic liver failure enrolled from 2017 to 2019 (NCT03082885) compared standard medical therapy alone (n = 58) with standard therapy plus subcutaneous thymosin alpha 1 (n = 56); the 90-day liver-transplantation-free survival rate was 75.0% versus 53.4% (p = 0.030) ^8.
• A large randomized study in metastatic melanoma assigned 488 patients to five treatment groups combining dacarbazine and interferon alfa with thymosin alpha 1 at three dose levels, dacarbazine plus thymosin alpha 1, or dacarbazine plus interferon alfa as control, with best overall response at 12 months as the primary endpoint and follow-up to 24 months; median overall survival was 9.4 months with thymosin alpha 1 versus 6.6 months in the control group (hazard ratio 0.80; p = 0.08) ^9.
• A randomized clinical trial in Japan randomized 316 patients with chronic hepatitis B, positive HBV-DNA and raised alanine aminotransferase to one of two thymalfasin monotherapy dose levels for 24 weeks, with a 72-week observation period; at 72 weeks 36.4% of the higher-dose group achieved ALT normalization and 22.8% cleared HBe antigen, with similar rates in the lower-dose group ^10.

How long did human studies run?

• The TESTS sepsis trial administered study drug for seven days unless stopped early for ICU discharge, death or withdrawal of consent, with 28-day all-cause mortality as the primary outcome ^3.
• The ETASS trial dosed for seven consecutive days (twice daily for five days, then once daily for two days) and assessed mortality at 28 days ^4.
• The acute necrotising pancreatitis trial dosed for 14 days (twice daily for the first 7 days, once daily for the following 7 days), with infected pancreatic necrosis during the index admission as the primary outcome ^7.
• The acute-on-chronic liver failure trial dosed once daily for the first week and then twice weekly from week 2 to week 12, with 90-day transplantation-free survival as the endpoint ^8.
• The Japanese chronic hepatitis B trial treated for 24 weeks and observed participants for a total of 72 weeks, that is 12 months after therapy stopped ^10.

Who was excluded from the studies

• The TESTS trial excluded, among others, people with an infection that could not be managed by surgery or drainage, an underlying disease estimated to cause death within 28 days, or where the family wished life-sustaining treatment to be discontinued; the full criteria are in the trial's supplementary appendix ^3.
• The acute necrotising pancreatitis trial enrolled only patients with an APACHE II score of 8 or more and a CT severity score of 5 or more admitted within 7 days of symptom onset, and 94.3% of participants required intensive care ^7.

Side effects reported in studies

• Any adverse event
  66.4% vs 67.6% placebo · TESTS trial, adults with sepsis ³
• Serious adverse events
  26.8% vs 29.3% placebo · TESTS trial, adults with sepsis ³
• Anaemia
  10.7% (overall across arms) · TESTS trial, adults with sepsis ³

Thymosin Alpha-1 draw calculator

Pick the vial strength and the water added, enter an amount, and see the concentration, the units to draw and how many draws the vial holds. Arithmetic only.

1 · Vial strength

sizes on the market

5 mg10 mg20 mg

2 · Water added

1 mL2 mL3 mL5 mL

3 · Amount per draw

mcgmg

4 · Syringe

30u50u100u

Your mix

10 mg + 2 mL water = 5 mg/mL

10 units holds 0.5 mg (500 mcg)

Draw toEnter an amount in step 3

U-100 syringe · 100 units = 1 mL

Computed from your inputs. Not a dose or a recommendation.

Compare water volumes for this vialShow

More water = lower concentration = a larger, easier-to-measure draw. Tap a row to use it.

Water	mg/mL	Draw
0.5 mL	20	—
1 mL	10	—
1.5 mL	6.667	—
2 mL	5	—
2.5 mL	4	—
3 mL	3.333	—
5 mL	2	—

Supplies and handling

• Lyophilized vial
  Sealed vial with the freeze-dried cake. Check the label, lot and the certificate of analysis before opening.
• Sterile diluent
  The diluent named on the product documentation. Bacteriostatic water contains benzyl alcohol; sterile water does not.
• Graduated syringes
  Sized to the volume being measured. U-100 insulin syringes are graduated in units where 100 units = 1 mL.
• Alcohol prep pads
  For wiping vial stoppers before each puncture.
• Nitrile gloves
  Clean gloves for aseptic handling.
• Sharps container
  Puncture-resistant container for used needles.

Storage

Handle according to the supplier's documentation for the specific lot; do not assume that storage conditions for approved products elsewhere apply to research material.

• Lyophilized (unmixed) vials: typically stored cold and dry, away from light, as the documentation directs. Many are stable longer frozen.
• Reconstituted vials: typically refrigerated (about 2–8 °C), protected from light and not frozen.
• Bacteriostatic water contains benzyl alcohol, which inhibits bacterial growth in multi-use vials; sterile water has no preservative.

Handling mistakes and troubleshooting

Added the wrong volume of diluent

The concentration changes, not the amount of compound in the vial. Recalculate with the volume actually added and relabel the vial.

Shook the vial and it foamed

Let it settle in the refrigerator. Foam is a sign of agitation; some peptides aggregate when shaken. Note it on the label.

The solution is cloudy or has particles

Do not use it. Cloudiness can indicate incomplete dissolution, contamination or degradation. Record the lot and contact the supplier with the certificate of analysis.

The powder cake looks melted or shrunken before reconstitution

This can indicate the vial was exposed to heat or moisture. Record the lot and condition on arrival.

Liquid sprayed back when the needle was removed

Pressure built up in the vial. Withdraw a small volume of air while adding diluent to keep pressure neutral.

Regulatory status

Status

The synthetic form, thymalfasin (Zadaxin), is described in a 2020 review as approved in more than 35 countries for hepatitis B and C and as an immune enhancer in other conditions ^1. No FDA-approved label was found in a DailyMed search, so it is not FDA-approved ^5.

United States (FDA)

No FDA-approved label for thymalfasin (Zadaxin) was found in DailyMed; it is described as approved in more than 35 other countries ^1,5.

Sport (WADA)

Thymosin alpha 1 is not named in the 2026 WADA Prohibited List text reviewed; the list names thymosin-beta-4 and its derivatives (e.g. TB-500) in S2.3, which is a different peptide ^6.

Status varies by country and changes over time. How we describe regulatory status.

Thymosin Alpha-1 compared with related compounds

Frequently asked questions

References

1. Thymosin alpha 1: A comprehensive review of the literature World J Virol. 2020
2. Historical review of thymosin α 1 in infectious diseases Expert Opin Biol Ther. 2015
3. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial BMJ. 2025
4. The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial Crit Care. 2013
5. DailyMed search for thymalfasin / Zadaxin (no FDA-approved label found on search) DailyMed (NLM). 2026
6. WADA 2026 Prohibited List World Anti-Doping Agency. 2026
7. Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial Intensive Care Med. 2022
8. Safety and efficacy of Thymosin alpha1 in the treatment of hepatitis B virus-related acute-on-chronic liver failure: a randomized controlled trial Hepatol Int. 2022
9. Large randomized study of thymosin alpha 1, interferon alfa, or both in combination with dacarbazine in patients with metastatic melanoma J Clin Oncol. 2010
10. 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