Thymosin Alpha-1 Dosing and Reconstitution

Last updated: July 2026

The most studied thymosin alpha-1 dose is 1.6 mg per injection, and the single-dose clinical vial is reconstituted with 1 mL of diluent to give 1.6 mg/mL — so one full 1.6 mg dose is exactly 1 mL, which reads as 100 units on a U-100 syringe. Research-grade vials arrive as a larger lyophilised powder (commonly 5 mg or 10 mg) that you reconstitute yourself, and then the number of units you draw depends entirely on how much bacteriostatic water you added — not on the peptide.

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TL;DR — key takeaways

Standard clinical dose is 1.6 mg. Approved use (thymalfasin / Zadaxin) for chronic hepatitis B is 1.6 mg subcutaneously twice weekly; COVID-19 trials used 1.6 mg daily.
Not FDA-approved in the US. Thymosin alpha-1 is approved in 30+ countries but is investigational / research-use here. This page is dosing maths, not a recommendation to use it.
Units follow concentration. A 1.6 mg dose is 100 units at 1.6 mg/mL, 80 units at 2 mg/mL, or 64 units at 2.5 mg/mL — same milligrams, different draw.
The rule never changes: units = (dose ÷ concentration) × 100, because a U-100 syringe holds 100 units per mL.

What thymosin alpha-1 is

Thymosin alpha-1 (Tα1; generic name thymalfasin, trade name Zadaxin) is a 28-amino-acid peptide first isolated from thymus tissue. It behaves as an immunomodulator rather than a hormone in the testosterone sense: it acts through Toll-like receptors on dendritic cells and supports T-cell maturation and cytokine signalling. Its serum half-life is short — roughly two hours — yet the approved hepatitis-B schedule doses it only twice weekly, because the downstream immune effect outlasts the peptide in the blood. That mismatch is worth flagging: the dosing interval is set by clinical trials, not by the half-life, so do not try to reason your own frequency from the pharmacokinetics.

Because thymosin alpha-1 is largely a research or off-label compound outside its approved markets, product quality and vial labelling vary. Confirm the stated milligrams against a certificate of analysis before you calculate anything — the maths below is only as accurate as the number printed on the vial.

The one formula behind every draw

Reconstitution turns a dry powder into a known concentration. You choose the volume of bacteriostatic water; that choice sets the mg/mL, and the mg/mL sets your units. Two facts do all the work:

Concentration = vial mg ÷ water mL. A 10 mg vial in 5 mL is 2 mg/mL.
Units = (dose mg ÷ concentration mg/mL) × 100. A U-100 syringe has 100 units in 1 mL.

There is no thymosin-specific constant. The identical arithmetic works for BPC-157, tesamorelin, or any vialled peptide — only the numbers on your label change.

Reconstitution & dose chart

Units shown are for a single 1.6 mg dose. Pick the row that matches your vial and the water you plan to add; always confirm against your own vial label.

Vial	BAC water	Concentration	1.6 mg dose	Doses / vial
1.6 mg	1 mL	1.6 mg/mL	100 units (1 mL)	1
5 mg	2 mL	2.5 mg/mL	64 units	3
5 mg	2.5 mL	2 mg/mL	80 units	3
10 mg	4 mL	2.5 mg/mL	64 units	6
10 mg	5 mL	2 mg/mL	80 units	6

Notice the 1.6 mg clinical vial is the only one where a dose fills the whole syringe. Dilute a research vial too little and the 1.6 mg draw would exceed 1 mL — e.g. a 10 mg vial in 5 mL is fine at 0.8 mL, but the same vial in only 3 mL (3.33 mg/mL) needs 0.48 mL, still under a millilitre, whereas over-diluting to 1 mg/mL would push a 1.6 mg dose to 1.6 mL, more than one syringe holds.

Units at a fixed 1.6 mg dose, visualised

Same 1.6 mg dose, three common concentrations. The stronger the vial, the fewer the units — the drug is unchanged.

Worked examples

Each uses units = (dose ÷ concentration) × 100. Change only the label numbers.

Example 1 — the clinical single-dose vial

A 1.6 mg vial reconstituted with 1 mL diluent = 1.6 mg/mL.

1.6 mg ÷ 1.6 mg/mL = 1 mL. 1 mL × 100 = 100 units — the entire U-100 syringe.

Example 2 — a 5 mg research vial

Vial 5 mg + 2.5 mL BAC water = 5 ÷ 2.5 = 2 mg/mL.

1.6 mg ÷ 2 mg/mL = 0.8 mL. 0.8 mL × 100 = 80 units.

Draw 80 units for each 1.6 mg dose.

Example 3 — a 10 mg vial, more water

Vial 10 mg + 5 mL = 2 mg/mL. Same concentration as Example 2, so the same 80 units per 1.6 mg dose — but the bigger vial holds more doses.

Example 4 — same vial, less water

Vial 10 mg + 4 mL = 2.5 mg/mL.

1.6 mg ÷ 2.5 = 0.64 mL. 0.64 mL × 100 = 64 units.

Less water, higher concentration, fewer units — for the identical 1.6 mg dose.

Example 5 — a smaller 0.8 mg dose

From a 2 mg/mL vial, if a protocol calls for 0.8 mg: 0.8 ÷ 2 = 0.4 mL × 100 = 40 units — exactly half of Example 2, as expected.

Example 6 — doses per vial

A 10 mg vial ÷ a 1.6 mg dose = 6.25, so 6 full doses per vial. The discard-after-reconstitution window still caps how long it can be used, whatever the maths says.

How this is calculated

Every figure here rests on two facts only: a U-100 syringe holds 100 units per millilitre, and concentration is milligrams divided by the water you added. We compute concentration from your vial and diluent, divide the dose by it for the volume, then multiply by 100 for units, rounding only to the graduations your syringe actually offers. No medical judgement is embedded — this is arithmetic. Thymosin alpha-1 is an education and maths example here, not a treatment we endorse; whether to use it, and at what dose, is a decision for a qualified prescriber, and in the US it remains investigational.

Frequently asked questions

Is thymosin alpha-1 FDA-approved?

No. It is approved as thymalfasin (Zadaxin) in more than 30 countries, mainly for chronic hepatitis B and as a vaccine adjuvant, but it is not FDA-approved in the United States, where it is used investigationally or off-label. Nothing here is a recommendation to use it.

Why is the standard dose 1.6 mg?

Because that is the amount studied in the pivotal hepatitis-B trials and supplied in the clinical single-dose vial. Doses in the literature cluster around 1.45–1.75 mg per injection; 1.6 mg is the reference point.

How much bacteriostatic water should I add?

Enough to make a concentration whose 1.6 mg draw is a readable number of units and under 1 mL. A 5 mg vial in 2–2.5 mL or a 10 mg vial in 4–5 mL both land in the practical 64–80 unit range.

Does a stronger vial mean I inject more drug?

No. Units measure volume, not milligrams. A 1.6 mg dose is 1.6 mg whether it reads 64 or 100 units — the stronger vial simply packs it into less liquid.

Sources

This guide is for general educational purposes only and does not constitute medical advice. Always follow your prescriber’s specific instructions and consult a qualified clinician before changing any protocol.