Thymosin Alpha-1

Thymosin alpha-1 is a chain of 28 amino acids. It was isolated from calf thymus tissue and sequenced in 1977 by Allan Goldstein's group, as one of several peptides in a thymus extract called thymosin fraction 5 (Goldstein 1977). The drug version is called thymalfasin; in most of the trials below it was given by injection under the skin.

It was developed commercially by SciClone Pharmaceuticals under the brand name Zadaxin. In its annual report for 2016, filed with the US Securities and Exchange Commission in 2017, the company stated that Zadaxin was approved in over 30 countries, mainly China and countries in the Pacific Rim, Latin America, Eastern Europe and the Middle East, chiefly for hepatitis B and as an immune enhancer. China accounted for most of its sales. It has not been approved in the US: a US phase 3 trial in hepatitis B did not confirm the benefit seen in other studies (Mutchnick 1999).

Clinical research has been done mainly in China and other Asian countries, with some trials in Europe and the US, in hepatitis B and C, cancer, sepsis and, more recently, COVID-19. Results have been mixed, and the two largest recent placebo-controlled trials, in sepsis and in severe pancreatitis, found no benefit on their main outcomes (Wu 2025; Ke 2022). Products sold online as "TA1" are not the approved drug.

• Type: peptide, 28 amino acids, originally isolated from the thymus.
• Studied for: chronic hepatitis B and C, melanoma, sepsis, severe pancreatitis and COVID-19.
• Strongest evidence: several randomised trials, with mixed results; the largest, in 1,106 adults with sepsis, found no effect on deaths.
• Legal status: approved as thymalfasin in a number of countries outside the US and EU; not FDA-approved.

At a glance: 10 studies report a dose (9 in people, 1 in animals).

Doses used in human studies

• Rost KL 1999: 900 µg/m2, single dose and once daily for 5 days, in three formulations (Subcutaneous; 5 days)
• Chien RN 1998: 1.6 mg twice weekly for 26 weeks or 52 weeks; control group untreated (Subcutaneous, twice weekly; 26 or 52 weeks of treatment; 18 months of follow-up)
• Mutchnick MG 1999: 1.6 mg twice weekly, or placebo (6 months of treatment and 6 months of follow-up)
• Sherman KE 1998: 1.6 mg twice weekly with interferon 3 MU three times weekly, compared with interferon plus placebo, or double placebo (Subcutaneous; 26 weeks)
• Maio M 2010: 1.6 mg, 3.2 mg or 6.4 mg with dacarbazine and interferon alfa, or 3.2 mg with dacarbazine alone; control group dacarbazine plus interferon alfa (Up to 24 months of follow-up)
• Wu J 2025: Every 12 hours for up to 7 days; amount per dose not given in the abstract; see the paper (Subcutaneous, every 12 hours; Up to 7 days of treatment; 28-day follow-up)
• Ke L 2022: 1.6 mg every 12 hours for 7 days, then 1.6 mg once daily for 7 days, or saline placebo (Subcutaneous; 14 days of treatment)

Every study

Thymosin alpha-1 is thought to act on the immune system, especially T cells, but the trials above measured clinical outcomes more than mechanisms. The supporting observations:

• Thymus origin: it is one of the peptides in a thymus extract that was being studied for its role in the development and function of T lymphocytes (Goldstein 1977).
• Immune markers in sepsis: patients given it had a larger rise in mHLA-DR, a marker of monocyte immune activity, than controls (Wu 2013).
• Effector T cells: it is described as enhancing effector T-cell responses, which was the rationale for testing it with chemotherapy in melanoma (Maio 2010).

1. Wash your hands and work on a clean, uncluttered surface. Let a refrigerated vial reach room temperature so the stopper is easier to pierce.
2. Wipe the rubber stopper of the peptide vial and of the bacteriostatic water with a fresh alcohol swab, and let them air-dry.
3. Draw the chosen volume of bacteriostatic water into a sterile syringe. With 2 mL, a 5 mg vial ends up at 2,500 mcg/mL, or 25 mcg per U-100 unit.
4. Insert the needle through the stopper and let the water run slowly down the inside wall of the vial, not straight onto the powder.
5. Swirl or roll the vial gently until the powder dissolves. Do not shake it: foaming can damage some peptides.
6. Check the solution against the light. It should be clear; cloudiness or particles mean something is wrong with the vial or the water.
7. Write the date and the volume of water on the label. Every unit calculation later depends on that volume.
8. Store the reconstituted Thymosin Alpha-1 vial in the refrigerator, away from light.

• A U-100 insulin syringe holds 1 mL in 100 units, so each unit is 0.01 mL. The marks measure volume, not peptide.
• Syringes come in 0.3 mL (30 units), 0.5 mL (50 units) and 1 mL (100 units) sizes. The smaller ones have finer marks and are easier to read for small volumes.
• Read the volume at the top edge of the plunger's rubber seal, at eye level.
• Tap out air bubbles before reading: a bubble takes up volume and makes the reading wrong.
• Use a new sterile syringe and needle every time, and dispose of them in a sharps container.

• The peptide vial, with its certificate of analysis (COA) for that batch. See how to read a COA.
• Bacteriostatic water (water with 0.9% benzyl alcohol), which keeps a multi-use vial from growing bacteria. Sterile water has no preservative.
• Sterile syringes to add the water, and U-100 insulin syringes to measure.
• Alcohol swabs for the stoppers.
• A sharps container for used needles.
• A label or marker to write the date and the volume of water on the vial.

In clinical trials, thymalfasin has generally been reported as well tolerated. Trials in hepatitis B reported no significant side effects (Chien 1998), adding it to chemotherapy in melanoma did not add toxicity (Maio 2010), and no safety outcome differed from placebo in the large sepsis trial (Wu 2025).

• Possible harm in a subgroup: in the large sepsis trial, patients under 60 had a higher risk of death on thymosin alpha-1 than on placebo in a prespecified subgroup analysis. This may be a chance finding, but it means benefit cannot be assumed (Wu 2025).
• Product quality: the approved drug is made under regulated conditions. Products sold online as "TA1" or "thymosin alpha-1" are not checked by any regulator for identity, purity, dose or sterility, and trial results do not automatically apply to them.
• Manufacturer funding: several trials were funded by SciClone or had authors who received fees from it (Wu 2025; Ke 2022), which is worth keeping in mind for positive results.
• Injection risks: any injected product that is not sterile can cause infection.

Before mixing

• Freeze-dried (lyophilised) peptide is the most stable form. It is usually kept refrigerated, or frozen for long storage, sealed and away from light.
• Heat, moisture and light speed up degradation. Keep the vial in its box and avoid leaving it in a car or by a window.

After mixing

• Keep the reconstituted vial refrigerated and away from light. Do not freeze it again: freezing and thawing a solution can break the peptide down.
• How long a mixed vial stays good depends on the peptide and the diluent, and for most research peptides there is no published stability data. Follow the supplier's guidance and discard any vial that turns cloudy.
• Pierce the stopper as few times as possible, and always with a new sterile needle after wiping it with alcohol.
• Write the volume of water on the label (for example "2 mL"). Without it, the unit calculations cannot be checked later.