WhatPeptide

Thymosin Alpha-1

An immunomodulatory peptide approved in over 35 countries (as Zadaxin) for hepatitis B/C and as an immune adjunct. Not FDA-approved in the US. Was placed on FDA Category 2 list (September 2023 – September 2024) before being removed when the nominator withdrew. Current regulatory status is in flux; FDA continues to flag safety concerns.

Moderate evidence Unregulated Immune

Written by WhatPeptide Editorial Team · Last updated 2026-03-17

Half-life

About 2 hours

Dosage range

1.6 mg subcutaneous two times weekly (protocol-dependent)

Administration

Subcutaneous injection

Research level

Moderate

How Thymosin Alpha-1 works

Thymosin Alpha-1 modulates innate and adaptive immune responses including dendritic-cell function and T-cell signaling. It has been investigated across viral, oncologic adjunct, and immunodeficiency contexts. Effect sizes vary by disease model and co-therapy context.

Also known as: Ta1, Thymalfasin, Zadaxin

Research relevance

Immune Support
Strong research relevance 90
Anti-Aging & Longevity
Some relevance 40
Recovery & Healing
Some relevance 30
Sleep & Relaxation
Some relevance 20
Cognition & Focus
Some relevance 20
Injury Rehab
Some relevance 20

Side effects & safety

Injection-site redness Fatigue Mild fever-like symptoms

Contraindications

Autoimmune disease may require caution
Pregnancy

Consult a healthcare provider before use if any of these apply to you.

Key studies

FAQ

What is Thymosin Alpha-1? +
An immunomodulatory peptide approved in over 35 countries (as Zadaxin) for hepatitis B/C and as an immune adjunct. Not FDA-approved in the US. Was placed on FDA Category 2 list (September 2023 – September 2024) before being removed when the nominator withdrew. Current regulatory status is in flux; FDA continues to flag safety concerns. Its mechanism of action is supported by moderate clinical and preclinical evidence.
What is Thymosin Alpha-1 researched for? +
Thymosin Alpha-1 has the strongest research relevance for Immune Support, Anti-Aging & Longevity, Recovery & Healing. Evidence is supported by moderate clinical and preclinical evidence.
What are the side effects of Thymosin Alpha-1? +
Reported side effects include Injection-site redness, Fatigue, Mild fever-like symptoms. Key contraindications: Autoimmune disease may require caution; Pregnancy.
Is Thymosin Alpha-1 FDA approved? +
Thymosin Alpha-1 is not FDA-approved. It is available as a research compound or through compounding pharmacies in some jurisdictions.
How is Thymosin Alpha-1 administered? +
Thymosin Alpha-1 is typically administered via subcutaneous route. Researched dosage range: 1.6 mg subcutaneous two times weekly (protocol-dependent). Half-life: About 2 hours.

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