PeptideCalculations
thymic immune-modulating peptide, 28 amino acids

Thymosin Alpha-1 dosage

Thymosin alpha-1 is thymalfasin, sold as Zadaxin in more than 30 countries (not the US). The labeled dose is 1.6 mg subcutaneous twice a week for 6 to 12 months, the same regimen as the 1998 hepatitis B trial that supports it. Community use copies that exactly, 1.6 mg twice weekly, with some people doing 1.6 mg daily for a week during an illness. Over 2,000 patients in trials and under 1% had a drug-related side effect.

By the Peptide Calculations editors · Updated 2026-10-19 · Studied for chronic hepatitis B and C, immune support during chemotherapy, sepsis and severe infection trials

Dose
1.6 mg twice weekly
per dose · FDA label
How often
twice weekly
any time of day
How long
label: 6 to 12 months
community: 4 to 12 weeks, repeated as needed
Route
subcutaneous only
the label says never intravenous

1Dose ranges by source

RangePerBasisNote
1.6 mg twice weeklydoseFDA label
clinical trial (Chien et al. 1998, Hepatology, 98 chronic hepatitis B patients, randomized; same dose as the Zadaxin label, 900 mcg/m2)
26 or 52 weeks; no significant side effects
1.6 mg once or twice weeklydoseCommonly reported
commonly reported
maintenance; some do 1.6 mg daily for 5 to 7 days during acute illness, and a few report 3 to 6.4 mg, which is above any label

2Dose to units chart

10 mg vial + 2 mL bacteriostatic water = 5 mg/mL, so each unit on a U-100 insulin syringe holds 50 mcg.

DoseDraw (mL)UnitsDoses in vial
1.6 mg0.32326
2 mg0.4405
Open in the Thymosin Alpha-1 calculatorFull 10 mg + 2 mL table

10 mg + 2 mL = 5 mg/mL, so 1.6 mg = 0.32 mL = 32 units. A 5 mg vial + 1 mL gives the same 32 units. The Zadaxin vial is 1.6 mg in 1 mL, one dose per vial.

3Side effects

injection site discomfort or rednessrash (rare)joint pain with hand swelling (rare)transient muscle soreness (rare)ALT flare during hepatitis treatment (expected on the label)
Before you start. Not FDA approved; the FDA has flagged it for compounding restrictions. People on immunosuppressants after a transplant should not use an immune stimulant. The hepatitis data is the strongest evidence and the daily high-dose community protocols have no trial behind them. Not medical advice. Talk to a clinician and start low.

Storage: lyophilized: fridge (label 2 to 8 C); reconstituted: use immediately on the label, within 4 weeks refrigerated by common practice

4Thymosin Alpha-1 dosage questions

Thymosin alpha 1 dosage?

1.6 mg subcutaneously twice a week. That is the Zadaxin label dose, the dose in the 1998 hepatitis B trial and what most people copy. The label runs it 6 to 12 months; community cycles are usually 4 to 12 weeks.

How many units is 1.6 mg of thymosin alpha 1?

With 10 mg in 2 mL (5 mg/mL) 1.6 mg is 32 units. With 5 mg in 1 mL it is also 32 units. With 5 mg in 2 mL it is 64 units.

Can you take thymosin alpha 1 daily?

Some ICU trials gave 1.6 mg every 12 hours for a week, and community users sometimes do 1.6 mg daily for 5 to 7 days when sick. The chronic data is all twice weekly. Daily use is a short-term choice, not a maintenance plan.

Is thymosin alpha 1 FDA approved?

No. It is approved in over 30 countries under the name Zadaxin, mainly for hepatitis B, and has US orphan designations, but no US approval. The FDA has also restricted compounding of it.

5Sources

  1. Chien RN et al., Hepatology 1998, Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial (PubMed 9581695)
  2. RxList, Zadaxin (thymalfasin) prescribing summary: 1.6 mg subcutaneous twice weekly, how supplied, adverse reactions
  3. Peptide Protocol Wiki, Thymosin alpha-1 dosing (community protocols)

Educational summary of published labels, trials and commonly reported use. Not medical advice.

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