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What is thymosin alpha-1?

Thymosin alpha-1 explained in plain English: what it is, what the research shows, side effects, legal status and dosage, plus a calculator for syringe units. Doses shown come only from the label or published trials, each with its source. Also called Ta1, Thymalfasin, Zadaxin.

Thymosin alpha-1 is approved as Zadaxin in over 30 countries, but not by the FDA. This page is educational; talk with a qualified healthcare professional before using any substance.

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= 5,000 mcg

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Syringe, no result yetU-100, 1 mL syringe holding up to 100 units. Enter your dose.0102030405060708090100

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What is thymosin alpha-1?

Thymosin alpha-1 (Ta1) is a natural peptide of 28 amino acids first found in the thymus, the gland where immune T cells mature. A lab-made version, thymalfasin, is sold as the medicine Zadaxin.

Zadaxin is approved in more than 30 countries, including China and Italy, but not in the US.

What does thymosin alpha-1 do?

Thymosin alpha-1 helps T cells mature and work, and boosts signals that help the body fight viruses and tumors. That’s why it is called an immune modulator.

What is thymosin alpha-1 used for?

Where approved, it is used for chronic hepatitis B, sometimes with other antiviral drugs, and as an immune booster with some vaccines and in people with weakened immunity. In the US it is used off-label by wellness clinics for “immune support,” which isn’t an approved use.

What does the research on thymosin alpha-1 show?

Thymosin alpha-1 has more human research than most peptides: dozens of clinical trials with thousands of patients, mostly in hepatitis B and C, cancer and severe infections. Results have been mixed, with some trials showing benefit and others not.

There is little evidence for its use in healthy people.

Thymosin alpha-1 side effects and risks

In clinical trials it was generally well tolerated; the most common side effect was discomfort or redness where it was injected. The FDA has noted a possible risk of immune reactions to compounded versions.

Because it stimulates the immune system, people with autoimmune disease or organ transplants should not use it without specialist advice. Products sold online aren’t checked for purity or strength.

Thymosin alpha-1 is not approved by the FDA. In 2024 it moved off the FDA’s list of compounding substances with safety concerns after its nomination was withdrawn, which is not an approval.

How do you reconstitute thymosin alpha-1?

Thymosin alpha-1 comes as a powder that is mixed with bacteriostatic water or the diluent supplied. The calculator above turns the vial size, the water and a dose into syringe units, and the reconstitution guide explains each step.

See the dosage section below for what is known about doses, with sources.

Thymosin alpha-1 dosage

Thymosin alpha-1 is not FDA-approved, but its label outside the US (Zadaxin) gives a dose for chronic hepatitis B. There is no approved dose for other uses.

From the official prescribing information (label). Your prescriber decides your dose and when to change it.

Thymosin alpha-1 doses, with sources
WhenDoseHow often
Zadaxin, chronic hepatitis B (outside the US)1.6 mg[1]Twice a week, 3–4 days apart, for 6 months
  1. RxList, Zadaxin (thymalfasin) label information

Medical disclaimer: this dosage information is for education only and comes from the source shown for each row. It is not medical advice and not a recommendation for you. Only a licensed prescriber who knows your health can decide whether Thymosin alpha-1 is right for you and at what dose. Don't start, change or stop a medicine based on this page, and don't use research peptides or unapproved drugs based on trial doses.

Thymosin alpha-1 concentration chart

The concentration of a Thymosin alpha-1 vial depends only on its size and the water you add. Each unit on a U-100 syringe holds one hundredth of a mL.

Thymosin alpha-1 concentration by vial size and water
Vial + waterConcentrationPer unit (U-100)
5 mg + 1 mL5,000 mcg/mL (5 mg/mL)50 mcg per unit (0.05 mg per unit)
5 mg + 2 mL2,500 mcg/mL (2.5 mg/mL)25 mcg per unit (0.025 mg per unit)
5 mg + 3 mL1,666.67 mcg/mL (1.66667 mg/mL)16.67 mcg per unit (0.01667 mg per unit)
10 mg + 1 mL10,000 mcg/mL (10 mg/mL)100 mcg per unit (0.1 mg per unit)
10 mg + 2 mL5,000 mcg/mL (5 mg/mL)50 mcg per unit (0.05 mg per unit)
10 mg + 3 mL3,333.33 mcg/mL (3.33333 mg/mL)33.33 mcg per unit (0.03333 mg per unit)

Frequently asked questions

What is thymosin alpha-1 used for?

Outside the US it is approved for chronic hepatitis B and as an immune booster in some conditions. In the US it is used off-label for immune support, which isn't approved.

Is thymosin alpha-1 the same as TB-500?

No. Both come from the thymus gland family of peptides, but thymosin alpha-1 acts on the immune system, while TB-500 is a fragment of thymosin beta-4 studied for tissue repair.

Is thymosin alpha-1 FDA approved?

No. It has been tested in US trials and holds orphan designations, but it has never been approved by the FDA.

Sources

  1. Wikipedia, Thymosin α1 (with cited studies)
  2. ClinicalTrials.gov, Thymosin alpha1 and pegylated interferon for chronic hepatitis B
  3. FDA, Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks

Last updated .

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