Thymosin Alpha-1
Tα1 · Thymalfasin · Zadaxin
Thymic peptide that modulates innate and adaptive immunity; used clinically in some viral hepatitis settings.
Key takeaways
- Thymic immunomodulator (Zadaxin), approved in dozens of countries but not the US or EU.
- Standard clinical schedule is 1.6 mg SubQ twice weekly for 6–12 months.
- Decades of hepatitis and immune-adjunct trials; consistently well tolerated.
- Off-label anti-aging and immune-boost use lacks matching trial populations.
Overview
What it is
Thymosin alpha-1 (thymalfasin) is a 28-amino-acid thymic peptide that modulates innate and adaptive immunity: it promotes T-cell maturation, activates dendritic and natural killer cells, and pushes responses toward a Th1 profile.
Pharmacokinetics
Half-life is roughly two to three hours with around 50% bioavailability, given subcutaneously. The labeled Zadaxin schedule is twice-weekly injection, since the immune effects it triggers outlast the plasma levels.
What the evidence says
Thymosin alpha-1 has a real international evidence base: approved in dozens of countries for chronic hepatitis B and C and as an immune adjunct, with decades of trials behind it, though not FDA or EMA approval. Recent reviews find it consistently well tolerated. Off-label wellness use borrows that immunology without matching the trial populations.
Reported dosing protocols
Protocols reported in research literature and clinic/community use — informational context, not a dosing recommendation.
| Use case | Dose | Route | Frequency | Duration |
|---|---|---|---|---|
| Chronic hepatitis B (Zadaxin label) | 1.6 mg | SubQ | 2× weekly | 6–12 months |
| Immune support (off-label) | 1.6 mg | SubQ | 2× weekly | 4–12 weeks |
Pharmacokinetic summary
- Model tier
- Simple (t½ + F, Tmax estimated)
- Half-life
- 2.9 hours
- Bioavailability
- 50%
- Typical dose
- 0.8–3.2 mg
Frequently asked questions
Is thymosin alpha-1 the same as TB-500?
No. They're different thymic peptides with different biology. Thymosin alpha-1 modulates T-cell and dendritic-cell immunity, while thymosin beta-4 (TB-500) is an actin-binding repair peptide. The shared thymosin name causes constant confusion.
Why is thymosin alpha-1 dosed only twice weekly?
The peptide clears in two to three hours, but the immune effects it triggers, like T-cell maturation and cytokine shifts, persist for days. Clinical trials settled on twice-weekly subcutaneous dosing and it worked, so that schedule became the labeled regimen.
Is thymosin alpha-1 available in the US?
Not as an approved drug. It's marketed in dozens of countries as Zadaxin for hepatitis and immune support, and US access runs through compounding or grey-market research peptides. The trial data is real but largely from Asian and European hepatitis populations.
References
- Estimated — Thymic peptide; ~2–3 hour half-life, immunomodulatory.
- Dominari et al., 2020 — comprehensive review of the thymosin alpha-1 literature — Background pharmacology and current clinical uses.
- Dinetz et al., 2024 — safety and efficacy of thymosin alpha-1 in human clinical trials — Review across the human trial base; finds it well tolerated.
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Protocols featuring Thymosin Alpha-1
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