Thymosin Alpha-1
Thymosin alpha-1 is a naturally occurring thymic peptide with immune-modulating properties, marketed outside the United States under the brand name Zadaxin.
Regulatory status: Approved in a number of countries outside the US (as Zadaxin) for uses including chronic hepatitis B and C and as an immune adjunct, but not FDA-approved. In the US it is available only as a compounded or research peptide.
Default vial
10 mg
Default mix
2 mL
Reported range
1.6 mg (label dose)
Draw (U-100)
32 u
Zadaxin labelling: 1.6 mg twice weekly (e.g. Mon and Thu) for six months. Approved outside the US, not by the FDA.
Where these numbers come from
Thymalfasin (Zadaxin) product labelling for chronic hepatitis B: 1.6 mg subcutaneously twice weekly for six months. Not FDA-approved in the United States.
- Singapore National Drug Formulary — thymalfasin (Zadaxin) 1.6 mg
- Thymalfasin in chronic hepatitis B — trial report (PubMed 15482167)
Reviewed August 2026
What it is
- A 28-amino-acid peptide fragment derived from prothymosin alpha, originally isolated from thymic tissue.
- Made synthetically today rather than extracted, and sold internationally as Zadaxin.
- Typically given by subcutaneous injection.
- Has a longer international clinical history than most compounds in this library.
How it is described to act
- 1
Absorbed into systemic circulation after subcutaneous injection.
- 2
Proposed to interact with receptors on immune cells including T-lymphocytes and dendritic cells, per the pharmacology accompanying its international labelling.
- 3
Reported downstream effects include modulation of Toll-like receptor signalling and cytokine production.
- 4
Studied clinically outside the US in chronic viral hepatitis, as a vaccine adjuvant, and in some sepsis and immunocompromised-patient settings.
What the research has looked at
Chronic viral hepatitis
- Non-US clinical trials and regulatory filings supporting Zadaxin approval reported improved viral response markers in chronic hepatitis B and C patients in some, though not all, trials.
Immune modulation
- PubMed-indexed publications from 2025–2026 continue to study thymosin alpha-1 in infectious-disease and immune-modulation contexts, showing ongoing research interest without a US regulatory filing.
Strength of evidence: Limited human evidence
There is genuine human trial and marketing history abroad, but no FDA approval and no pivotal-trial evidence accepted by US regulators.
Some human data exist, but they are small, short, or not designed to answer the questions people ask online.
Reported cautions and unknowns
- International labelling and published trials describe it as generally well tolerated, with injection-site reactions the most common adverse event. No FDA-reviewed US safety dataset exists.
- Compounded material in the US is not FDA-approved, so purity, dosing and sterility are not verified the way an approved drug's are.
References
Handling this vial
- Lyophilized vials are generally stored at 2–8 °C and kept out of light; once reconstituted with bacteriostatic water they are refrigerated and commonly discarded after 28 days.
- Mix by aiming water down the vial wall and rolling gently — do not shake — and never re-freeze a reconstituted vial.
- Pep-Tidy cannot verify what is in your vial. Ask your supplier for a current Certificate of Analysis (HPLC/MS).
Thymosin Alpha-1 questions people ask
How do you reconstitute Thymosin Alpha-1?
A common starting point for a 10 mg vial of Thymosin Alpha-1 is 2 mL of bacteriostatic water, which gives 5 mg per mL. Aim the water down the inside wall of the vial, let it dissolve on its own, and roll gently instead of shaking. Pep-Tidy's reconstitution calculator will recalculate the numbers for any other vial size or water volume you use.
How many units of Thymosin Alpha-1 is one dose?
At 5 mg per mL, that works out to about 32 units on a U-100 insulin syringe for a 1600 mcg dose. Change the vial size, water volume, or target dose in the calculator and the syringe reading updates with it. This is arithmetic, not a dosing recommendation.
What dosing schedule is reported for Thymosin Alpha-1?
Published and community sources describe 1.6 mg (label dose), subcutaneous, twice weekly, typically run 26 weeks on. These figures describe what has been reported, not what anyone should take — talk to a licensed clinician first.
How should Thymosin Alpha-1 be stored?
Lyophilized Thymosin Alpha-1 vials are generally kept at 2–8 °C and out of light. Once reconstituted with bacteriostatic water they are refrigerated and commonly discarded after about 28 days. Never re-freeze a reconstituted vial and never shake it.
Read this before you act on anything above
Everything on this page is a summary of what other people have published — it is not medical advice, not a recommendation, and not a dosing instruction. Reported dose ranges describe what appears in the literature or in community protocols, not what anyone should take. Talk to a licensed clinician before using any peptide.