Thymosin alpha-1

Also known as Thymalfasin, Zadaxin, Ta1

Human trials

Synthetic version of a 28 amino acid thymus peptide that modulates immune responses. Approved in some countries for hepatitis B and as an immune adjuvant, but not by the TGA, FDA or EMA (Not verified per country).

Not an approved medicine. Thymosin alpha-1 is not an approved medicine for this use in Australia or the United States. This page summarises published research for information only. It is not a recommendation to use Thymosin alpha-1, and VialOwl does not sell or supply it.

Background

28 amino acid peptide first isolated from calf thymus tissue (thymosin fraction 5) by Allan Goldstein's group in the 1970s. The synthetic version, thymalfasin (Zadaxin), is approved in some countries for hepatitis B and as an immune booster, but not by the TGA, FDA or EMA.

How it is thought to work

Acts on toll like receptors on dendritic cells, which then signal other immune cells, increasing T cell activity and cytokine production. It is described as an immune modulator rather than a simple stimulant.

What is claimed, and the evidence

Claim	Evidence	Notes
Treats chronic hepatitis B and C	Small human studies Mixed results	Approved in some countries (not TGA, FDA or EMA); trial results have been mixed and it is not a standard treatment in Australia.
Reduces death in sepsis	Human trials	The large TESTS phase 3 trial (1,106 adults) found no reduction in 28 day mortality versus placebo.
Improves vaccine response in older or immunocompromised people	Small human studies	Small studies reviewed; not established.
Add on treatment in cancer	Small human studies	Studied in combination therapies; no approval by TGA, FDA or EMA.
Prevents colds, boosts immunity or treats long COVID in healthy people	No published evidence	Common online claim with no controlled evidence.

Side effects

Effect	How often	Notes
Injection site discomfort	Frequency unknown	Reported in clinical use; the TESTS trial found no safety differences from placebo.
Immune reactions Serious	Frequency unknown	FDA flags a significant risk of immunogenicity for some routes and complexities with impurities in compounded products.

Warnings

Not approved by the TGA, FDA or EMA; the largest trial (sepsis) found no benefit.
FDA listed it among bulk substances that may present significant safety risks for compounding.
Unapproved products are not made to medicine standards and may be contaminated, underdosed, overdosed or contain a different substance from the label; the TGA warns that injected unapproved peptides carry risks including contamination, infection and local tissue damage.

Regulatory status

Australia: Not included on the ARTG (unapproved). Not specifically listed in the Poisons Standard (June 2026).
United States: Not FDA approved. Nomination withdrawn from 503A Category 2 (significant safety risks).

Sources

Also in Immune

From the VialOwl library, reviewed 26 September 2026. For education and general information. It is not medical advice and not a recommendation to use Thymosin alpha-1.