What Is Thymosin Alpha-1? Dosage, Half-Life & How to Track It
Also known as: Zadaxin · Tα1 · Thymalfasin
Thymosin Alpha-1 (Tα1) is a 28-amino-acid peptide, generic name thymalfasin, originally isolated from the thymus gland and studied for its broad immunomodulatory effects. Under the brand name Zadaxin, it is approved in roughly 35 countries — not including the US — for chronic hepatitis B and C and as an immune adjunct in serious infection. A common protocol starts at 300 mcg subcutaneously daily for a week, then steps to 500 mcg daily for several more weeks, with a half-life of roughly 2 hours. Educational information only.
What Thymosin Alpha-1 is and how it works
Thymosin Alpha-1 is a naturally occurring 28-amino-acid peptide fragment produced by the thymus gland, the organ responsible for training T-cells early in immune development. Its synthetic version, thymalfasin, reproduces that fragment and is used to support and modulate immune function, particularly where the immune system is struggling to clear a persistent threat.
The clinical use case is specific: it is studied, and outside the US approved, as an adjunct treatment for chronic hepatitis B and C, helping the immune system respond to a virus that has otherwise evaded clearance, and it has been investigated in sepsis and other critical illness, including COVID-19, as a way of supporting an immune system under severe stress. It is marketed as Zadaxin in roughly 35 countries; it does not have FDA approval in the United States, where its use is off-label or research.
Unlike a lot of compounds in this library, Thymosin Alpha-1 has real regulatory approval history and decades of clinical use elsewhere — the evidence base here is meaningfully stronger than for most research peptides, even without a US indication.
Typical dosing & reconstitution
Thymosin Alpha-1 ships as a lyophilized powder reconstituted with bacteriostatic water. A common protocol begins at 300 mcg once daily for the first week to assess tolerance, then steps up to a 500 mcg daily maintenance dose — about 3.5 mg per week, in the same range used clinically.
| Vial | BAC water | Concentration | 1 unit (U-100) ≈ |
|---|---|---|---|
| 5 mg | 3 mL | 1.67 mg/mL | 16.7 mcg |
| 10 mg | 3 mL | 3.33 mg/mL | 33.3 mcg |
At 1.67 mg/mL, the Week 1 dose (300 mcg) is 18 units and the maintenance dose (500 mcg) is 30 units. From the 10 mg vial at 3.33 mg/mL, those same doses are 9 and 15 units respectively — for doses under about 10 units, a 30- or 50-unit syringe reads more accurately, which the calculator flags automatically.
Half-life & what it means for frequency
Thymosin Alpha-1’s serum half-life is roughly 2 hours after a subcutaneous dose — short enough that, like the GHRPs, it clears well within a day and does not build a long-term depot. That is the basis for the once-daily schedule used in both clinical and research protocols.
The short half-life means daily consistency is what actually drives the protocol’s effect — there is no accumulating reserve to fall back on if a day is missed, which matters over the 8–16 week durations commonly used in published protocols.
What to track & common side effects
Given its clinical history, Thymosin Alpha-1’s side-effect profile is better characterized than most peptides in this library: it is generally well tolerated, with injection-site reactions the most common complaint and no consistent pattern of serious adverse effects in the populations it has been studied in.
What is worth tracking over an 8–16 week course is straightforward: the daily streak, since protocols this long are where doses quietly start slipping, and whatever the underlying reason for running it is — an infection marker, energy levels, or a lab value your prescriber is following.
How to track Thymosin Alpha-1 in Stackeddd
Log the daily dose across an 8–16 week course and let the streak keep a long protocol from quietly losing days — Thymosin Alpha-1’s short half-life means consistency is what actually drives the effect. Nail the reconstitution once and every day’s dose is already calculated, whether you are on the 5 mg or 10 mg vial.
Model it yourself · free, no account
Reconstitution Calculator
Model it yourself: enter your vial size and BAC water and the Peptides tab returns concentration and exact insulin-syringe units for both the Week 1 and maintenance dose — the same math built into the Stackeddd app.
Related compounds
Related reading: Peptide reconstitution math: how much BAC water to add
Frequently asked questions
What is Thymosin Alpha-1 used for?
It is a 28-amino-acid immunomodulatory peptide, marketed as Zadaxin, approved in roughly 35 countries (not the US) as an adjunct treatment for chronic hepatitis B and C. It has also been studied in sepsis and other critical illness as immune support.
What is the half-life of Thymosin Alpha-1?
Roughly 2 hours after a subcutaneous dose, which is why it is dosed once daily rather than less frequently — there is no long-lasting depot to carry the effect between doses.
How is Thymosin Alpha-1 dosed?
A common protocol starts at 300 mcg subcutaneously once daily for the first week, then steps to a 500 mcg daily maintenance dose, about 3.5 mg/week, for the remainder of an 8–16 week course.
Is Thymosin Alpha-1 FDA-approved?
Not in the United States. It is approved under the brand name Zadaxin in roughly 35 other countries for chronic hepatitis B/C and related immune support, giving it more real-world clinical history than most research peptides, even without a US indication.
This is educational information, not medical advice. Doses and protocols above reflect published references and community practice — protocol decisions belong with your prescribing physician. Generic names used throughout. How this reference is built & how the AI is tested →
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