Thymosin Alpha-1 (Zadaxin): Hepatitis B Research, PH Status

Abstract still life: a frosted glass shield-shaped form catching warm light, on grey stone — **Thymosin Alpha-1.** Illustration, not a product photo.

Research compound. Not approved by FDA Philippines for human use unless stated. Nothing here is a dosing recommendation or medical advice.

What it is

Thymosin alpha-1 is a 28 amino acid peptide originally isolated from thymus tissue and later made synthetically. It is one of the few compounds in this library sold as an actual registered medicine: SciClone Pharmaceuticals markets it as Zadaxin, chemical name thymalfasin, and it is used clinically in a number of countries.

Its main approved indications are chronic hepatitis B and chronic hepatitis C, either alone or alongside interferon-based therapy. Beyond hepatitis, it has been studied as an immune adjuvant, meaning something given alongside another treatment or vaccine to strengthen the immune response, in areas such as vaccination in people with a weaker immune response and as a supportive therapy in serious infection. Those broader uses sit in the research literature and are not the same as an approved-label indication in every country where the drug is sold.

How it works

Thymosin alpha-1 acts on the immune system rather than on a single organ or pathogen. It influences T-cell maturation and activity and modulates the production of cytokines, the signalling proteins immune cells use to coordinate a response. The practical goal in hepatitis treatment is to help the immune system clear virus-infected liver cells more effectively, which is why it is often paired with antiviral drugs rather than used alone.

What the research found

Approval and use in countries outside the Philippines

A 2009 review by Goldstein and colleagues, one of the researchers involved in the peptide's original characterisation, described thymosin alpha-1 as approved in more than 35 countries for the treatment of hepatitis B and C. An earlier 2002 review of the drug's development documented specific approval milestones, including registration in Sri Lanka and Brunei in 1999 and an added hepatitis C indication in Peru and Sri Lanka by 2000. It has never been approved by the US FDA or the European Medicines Agency; its regulatory footprint is concentrated in Asia, Latin America and parts of Europe and the Middle East where SciClone and its licensing partners pursued approval.

Hepatitis B evidence

The hepatitis B evidence base is old enough that it has been formally re-examined more than once. A 2008 meta-analysis by Yang and colleagues compared thymosin alpha-1 against interferon-alpha in chronic hepatitis B. A 2026 Cochrane systematic review pooled the published randomized trials, which the review notes were published between 1991 and 2018, to give an updated verdict on efficacy. Readers who want a bottom-line answer on whether it works for hepatitis B should read that Cochrane review's conclusions directly rather than rely on any single older trial, since Cochrane reviews are specifically designed to correct for the limitations of the individual studies feeding into them.

Immune adjuvant and other uses

Thymosin alpha-1 has also been studied as an adjunct in settings outside hepatitis, including vaccine response in people with reduced immunity and as supportive therapy in serious infection. Those applications are part of the broader research and off-label literature around the drug rather than confirmed here as approved indications in any specific country, and they should not be read as evidence the drug is approved for those uses everywhere it is sold.

Side effects reported in studies

As an approved drug with decades of clinical use abroad, thymosin alpha-1 has a published safety record in the countries where it is registered, generally described as well tolerated with injection-site reactions as the most common complaint. This page does not reproduce a specific adverse-event rate because no single verified source for that figure was opened while researching it; anyone considering the drug should read the product label used in the country where it is registered.

Status in the Philippines

Whether a thymalfasin or Zadaxin product is currently registered with FDA Philippines could not be confirmed. The agency's online verification portal accepts interactive searches by product or establishment name rather than serving a static, linkable results page, and that search could not be completed for this article. Do not treat the absence of a confirmed answer here as evidence either that it is or is not registered locally; if that matters for a decision, search the FDA Philippines verification portal directly or ask a licensed Philippine physician or pharmacist. It is not a scheduled controlled substance under RA 9165. As with any medicine, prescribing and use belong with a licensed Philippine physician.

Storage

Zadaxin is supplied as a lyophilised powder for reconstitution and, like most peptide products, needs refrigeration before and after mixing, with protection from heat and light. Anyone handling a product obtained outside a licensed pharmacy channel should follow the manufacturer's insert rather than general peptide-storage advice, since a registered pharmaceutical product may have different stability data from a research-chemical vial. See the beginner guide for general handling basics.

Common questions

What is thymosin alpha-1?

It is a 28 amino acid peptide first isolated from thymus tissue and now made synthetically. It modulates immune activity, particularly T-cell function, and is sold under the brand name Zadaxin, chemical name thymalfasin.

Is Zadaxin approved anywhere?

Yes. Published research describes it as approved in more than 35 countries for chronic hepatitis B and C, with specific approvals documented in countries including Sri Lanka, Brunei and Peru. It has never been approved by the US FDA or the European Medicines Agency.

Does thymosin alpha-1 actually work for hepatitis B?

A 2026 Cochrane systematic review pooled trials published between 1991 and 2018 to assess this question. Older meta-analyses have compared it against interferon-alpha. Readers should check a current systematic review rather than a single older trial, since the evidence base has been re-evaluated over time.

Is thymosin alpha-1 registered with FDA Philippines?

This could not be confirmed. FDA Philippines runs an online verification portal for registered products, but it requires submitting an interactive search rather than loading a static page, which this research could not complete. Treat the registration status as unconfirmed rather than assuming either way.

Is thymosin alpha-1 legal in the Philippines?

It is not a scheduled controlled substance under RA 9165. Whether a specific Zadaxin or thymalfasin product carries an active FDA Philippines registration is unconfirmed; buying or importing an unregistered pharmaceutical product carries separate legal exposure from buying a research chemical.