Thymosin Alpha-1
TA-1 — 28-amino-acid immunomodulator (Zadaxin)
Thymosin alpha-1 is a 28-amino-acid peptide, first isolated from the thymus, that helps regulate immune responses, especially T-cell function. A synthetic version, thymalfasin (Zadaxin), is approved in a number of countries outside the US, mainly for chronic hepatitis B; it is not FDA-approved. Off-label use for post-viral recovery or immune aging is not supported by strong trial evidence.
Quick reference
How Thymosin Alpha-1 is dosed in practice
The established regimen is 1.6 mg of thymosin alpha-1 injected SubQ twice a week — the dose and schedule of thymalfasin (Zadaxin) in the countries where it's licensed. There's no titration; every dose is 1.6 mg.
For chronic hepatitis B, the course is about 6 months. Off-label courses for immune support commonly run 3–6 months, sometimes repeated seasonally. Daily dosing is not part of the approved regimen.
Where the numbers come from: the thymalfasin regimen used in hepatitis B trials. Thymosin alpha-1 is not FDA-approved, so there is no US label.
Work out the units to draw with the reconstitution calculator and how long a vial lasts with the vial duration calculator.
How Thymosin Alpha-1 works
Thymosin alpha-1 was first isolated from thymus tissue and is now made synthetically as a 28-amino-acid peptide. It supports T-cell maturation and function (particularly Th1 responses), activates natural killer (NK) cells, and acts on dendritic cells, which present antigens to the immune system.
It is described as an immune modulator rather than a simple stimulant, which is why it has been studied in chronic viral infections, as a vaccine booster in people with weak immune responses, and alongside cancer treatment.
Its main approved use is chronic hepatitis B, where studies found it helped some patients clear the virus, with mixed results across trials. Use for long COVID, post-viral fatigue or immune aging is off-label and has not been established in trials.
In the DoseCraft framework, thymosin alpha-1 is filed under Inflammation (immune balance) and, indirectly, ATP Shortage (post-viral recovery) — a framework placement, not a tested outcome.
Reconstitution math
- Remove the flip-off cap from the 1.6 mg or 5 mg vial.
- Draw 1 mL of bacteriostatic water into a sterile syringe.
- Inject slowly down the vial wall.
- Swirl gently. Do not shake.
- Refrigerate. Stable approximately 30 days at 2–8°C.
Dose math
5 mg vial + 1 mL bac water → 5 mg per mL (5,000 mcg/mL).
On a 100-unit insulin syringe (1 IU = 0.01 mL):
- • 32 IU = 1.6 mg (1,600 mcg) — the standard dose
- • A 5 mg vial holds three 1.6 mg doses
- • Single-dose 1.6 mg vials: reconstitute with 1 mL and inject the whole amount
Safety + side-effect profile
Thymalfasin has been used as a prescription drug in several countries for many years, and side effects in trials were uncommon and mild.
Not reported in trials: liver, hormonal or heart problems — though long-term off-label use in healthy people hasn't been studied. Avoid with: immunosuppressive treatment, including organ-transplant rejection prophylaxis (it works against the intent of those drugs), pregnancy and breastfeeding (not enough data).
Interaction notes: don't combine with immunosuppressive biologics (TNF blockers, JAK inhibitors) without your specialist. In autoimmune disease, an immune-enhancing drug could in theory worsen some conditions; the clinical evidence is limited, so talk to your specialist first.
- • Injection-site soreness or redness
- • Occasional brief flu-like feeling
- • Rare allergic reactions
Frequently asked
What is Thymosin Alpha-1?
Thymosin alpha-1 (TA-1) is a 28-amino-acid peptide first isolated from the thymus that supports T-cell function and NK-cell activity. A synthetic version, thymalfasin (Zadaxin), is approved in a number of countries outside the US, mainly for chronic hepatitis B. It is not FDA-approved.
What is the typical TA-1 dose?
1.6 mg SubQ twice a week — the regimen of thymalfasin (Zadaxin), the approved drug outside the US. For hepatitis B the course is about 6 months; off-label immune-support courses commonly run 3–6 months. Daily dosing is not part of the approved regimen.
How do I reconstitute TA-1?
5 mg vial + 1 mL bacteriostatic water → 5 mg/mL. On a 100-unit insulin syringe, 32 IU = 1.6 mg. Single-dose 1.6 mg vials are reconstituted with 1 mL and injected in full. Refrigerate after reconstitution; use within about 30 days.
Is TA-1 effective for long COVID?
Not established. Thymosin alpha-1 was studied in hospitalized COVID-19 patients with mixed results, and there are no completed trials showing benefit for long COVID. Practitioners who use it typically follow the standard 1.6 mg twice-weekly regimen.
Can TA-1 trigger autoimmune flares?
It's possible in theory, since thymosin alpha-1 enhances some immune responses, and evidence in autoimmune disease is limited. If you have an autoimmune condition, involve your specialist before using it and track symptoms and inflammatory markers.
Is TA-1 safe long-term?
Thymalfasin has been used for years as a prescription drug outside the US, and side effects in trials were mild and uncommon. Long-term off-label use in healthy people hasn't been studied. The approved schedule is 1.6 mg twice a week in courses (about 6 months for hepatitis B), not open-ended daily use.
Should I cycle TA-1?
Use it in courses. The hepatitis B course is about 6 months; off-label immune-support courses commonly run 3–6 months, with breaks or seasonal repeats — all at 1.6 mg twice a week.
Related compounds
Often researched, stacked, or compared with Thymosin Alpha-1.
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