Thymosin Alpha-1
Also called Tα1; TA1; thymalfasin (Zadaxin)
An immune-regulating peptide studied in people with specific illnesses. A large sepsis trial showed no clear survival benefit, and hepatitis B evidence is very uncertain. It is not a general immune booster.
Overview
What it is
A 28-amino-acid peptide originally from the thymus. Thymalfasin is its synthetic form, approved in some countries outside the US.
How it works
It influences T cells and antigen presentation, how immune cells show pieces of a threat to other immune cells. "Immune modulation" means changing parts of the response, not turning everything up.
What the research shows
The 2025 TESTS trial of 1,106 adults with sepsis found 28-day death rates of 23.4% with thymosin alpha-1 versus 24.1% with placebo, no clear benefit. A September 2026 Cochrane review of ten hepatitis B trials (1,349 adults) rated most evidence very low certainty.
Studied for
- Sepsislarge trial, no clear survival benefit
- Chronic hepatitis Bvery low certainty
- Approved uses in some other countries
Safety and regulatory status
Safety and side effects
Reported effects include injection-site discomfort and less common redness or rash. The FDA notes product quality, aggregation and impurity concerns and says information on compounded products is inadequate to fully characterize risk. Discuss with your clinician if you have an autoimmune condition, a transplant, are pregnant or take immune-suppressing drugs.
Regulatory status
No FDA-approved product. On FDA's list of compounding substances with potential safety risks. Approved in some other countries for specific uses.
Mixing and dosing reference
Reference information only. Read before using this section.
Thymosin Alpha-1 (5 mg Vial) Dosage Protocol
- Vial
- 5 mg Thymosin Alpha-1
- Add diluent
- 3 mL
- Concentration
- 1.67 mg/mL
- 1 unit (U-100)
- 16.67 mcg in 0.01 mL
- Route
- Subcutaneous
- Typical range
- 300–500 mcg once daily (gradual titration).
Standard / Gradual Approach
| Week | Daily Dose (mcg) | Units (per injection) (mL) |
|---|---|---|
| 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) |
How to mix
- Draw 3.0 mL bacteriostatic water with a sterile syringe.
- Inject slowly down the vial wall; avoid foaming.
- Gently swirl/roll until dissolved (do not shake).
- Label with reconstitution date and refrigerate at 2–8 °C (35.6–46.4 °F), protected from light.
Protocol source: PeptideDosages.com
Common questions
How does it make you feel?
There is no validated "working" sensation; how you feel says little about immune function.
Is it approved in the US?
No. Approval elsewhere is not US approval.
Should I stop my hepatitis B medicine to try it?
No. Never stop prescribed treatment to try a peptide.
Related in Immune Health
Sources and further reading (5)
- National Cancer Institute. Thymalfasin drug dictionary.
- Wu J, et al. Thymosin α1 for sepsis (TESTS). BMJ, 2025 (with correction).
- Naing C, et al. Thymosin-α1 for chronic hepatitis B. Cochrane Database Syst Rev, Sept 2026.
- FDA. Thymosin alpha-1 bulk drug substances: advisory briefing, Dec 2024.
- Source summary: PeptideDosages.com research overview (rewritten for NVO).
Laboratory research material: TA-1 (Thymosin Alpha-1) Research Use Only