Question 1

What is Thymosin Alpha-1 used for?

Accepted Answer

TA1 (Zadaxin / thymalfasin) is approved internationally for chronic hepatitis B, chronic hepatitis C, and as an immune adjunct in cancer care, and has been studied in severe sepsis, post-viral recovery, and general immune support. It is not FDA-approved in the United States.

Question 2

What is the standard Thymosin Alpha-1 dose?

Accepted Answer

The Zadaxin-anchored protocol is 1.6 mg subcutaneously twice weekly, with injections spaced 3-4 days apart. Adults under 40 kg use 40 mcg/kg twice weekly. This is research-context dosing, not a personal-use recommendation.

Question 3

How is Thymosin Alpha-1 reconstituted?

Accepted Answer

A 10 mg vial reconstituted with 2 mL bacteriostatic water yields 5 mg/mL. At that concentration, a 1.6 mg dose equals 0.32 mL or 32 units on a U-100 insulin syringe. Other vial sizes (5 mg, 20 mg) are covered in the reconstitution guide .

Question 4

Is Thymosin Alpha-1 FDA-approved?

Accepted Answer

No. TA1 is approved as Zadaxin in 35+ countries for chronic hepatitis B, chronic hepatitis C, and cancer adjunct use, but it has never received FDA approval. As of June 2026, its US 503A compounding status is unsettled - FDA placed it in Category 2 in September 2023, removed it from Category 2 in September 2024 after the nominators withdrew their nominations, and the PCAC reviewed it on December 4, 2024 with a final determination still pending.

Question 5

Did the 2025 BMJ TESTS trial prove TA1 works for sepsis?

Accepted Answer

No - the trial's primary endpoint was negative. The TESTS trial enrolled 1,106 adults with sepsis at 22 Chinese centers and reported a 28-day all-cause mortality hazard ratio of 0.94 (95% CI 0.76-1.16, p=0.54), which is not statistically significant. A 2025 Frontiers meta-analysis of 11 RCTs reported a pooled odds ratio of 0.73, but the authors flagged heterogeneity. Sepsis is an active research question, not a settled TA1 application.

Question 6

What are the observed effects of Thymosin Alpha-1?

Accepted Answer

Reported observed effects are mild and uncommon: injection-site reactions, transient fatigue, and mild flu-like symptoms. A transient ALT rise to more than twice baseline is documented during HBV therapy and is generally not a reason to stop treatment. Joint pain with hand swelling has been reported in isolated cases. See the observed effects table for full detail.

Question 7

Who should not use Thymosin Alpha-1?

Accepted Answer

Organ transplant recipients on immunosuppressive therapy, adults with active autoimmune flares, pregnant or breastfeeding women (Zadaxin is Category C), adults under 18, and anyone with known hypersensitivity. Adults on stable immune-modulating drugs should only consider TA1 with clinician oversight because of theoretical additive effects.

Question 8

Is Thymosin Alpha-1 the same as TB-500?

Accepted Answer

No. TA1 (28 amino acids) and TB-500 / thymosin beta-4 fragment (43 amino acids) are different peptides from the same thymosin family. TA1 acts on TLR2/TLR9 and immune T-cell pathways; TB-500 binds actin and acts on cell migration and tissue repair. They are sometimes used in the same research context but they do different things. See the TB-500 protocol for the comparison.

Question 9

How long until Thymosin Alpha-1 starts working?

Accepted Answer

Pharmacokinetics: peak blood level at 1-2 hours, half-life 2-3 hours, no accumulation between twice-weekly doses. Immune-cell-level changes typically build over 4-8 weeks of repeated dosing. Endpoints in HBV trials (viral load reduction, sustained virologic response) are usually measured at 6-12 months.

Question 10

Can Thymosin Alpha-1 be stacked with other peptides?

Accepted Answer

Common research stacks include TA1 with BPC-157 for combined immune and tissue-repair contexts. TA1 should never be mixed with another drug in the same syringe and should not be combined with systemic immunosuppressants without clinician oversight. Stacking is research context, not a treatment recommendation.

Question 11

Where can I read the original Zadaxin label?

Accepted Answer

Zadaxin/thymalfasin label data is available from SciClone Pharmaceuticals' historical materials and from international regulatory filings. The professional monograph published through the peptide research community summarizes the labeled HBV/HCV indications, the under-40-kg dosing adjustment, and the Category C pregnancy classification.

Phase	Daily reference amount	Units / volume
Week 1	300 mcg (0.3 mg)	18 units (0.18 mL)
Weeks 2–8	500 mcg (0.5 mg)	30 units (0.30 mL)

Phase	5 mg 3 mL water	10 mg 3 mL water
Week 1	18 u 0.18 mL	9 u 0.09 mL
Weeks 2–8	30 u 0.30 mL	15 u 0.15 mL

Thymosin Alpha-1.

Calculated volume reference

Cited protocol & reconstitution guide

Reconstitution by vial size