Machine-assisted translation — the German original version is authoritative.
Longevity & Immune System
Thymosin Alpha-1 (TA-1)
Tα1 · Zadaxin · Thymalfasin
Thymosin Alpha-1 is an immunomodulating peptide of 28 amino acids that occurs naturally in the thymus gland. As thymalfasin (Zadaxin), it is approved as a medicine in several countries (including for viral hepatitis and as a vaccine adjuvant). In the USA it is not FDA-approved; in the EU it is not generally approved.
Regulatory status
Approved · prescription-only
A medicine approved in several countries — not FDA-approved, not generally approved in the EU.
Drug class
Immunomodulating thymus peptide (28 amino acids)
Half-life (informative)
In the range of hours; in approved applications it is therefore given repeatedly.
Studied in the literature
In approved applications subcutaneously, under medical supervision.
Mechanism of action
Thymosin Alpha-1 interacts, among other things, with Toll-like receptors (TLR) on dendritic cells and enhances the production of Th1 cytokines (e.g. interferon-gamma, IL-2). It promotes the activity of natural killer cells (NK cells) and T-helper cells and can at the same time dampen an excessive immune reaction — hence its description as an "immunomodulator".
Acts via immunomodulation; use is indication-dependent and medically supervised.
Research history
It traces back to research on thymus factors (Goldstein and others); its immunological and antiviral properties were investigated by Garaci and colleagues, among others. As Zadaxin/thymalfasin it is approved in numerous countries for viral hepatitis and as an adjuvant.
Regulatory status by region
Approved in numerous countries for viral hepatitis and as a vaccine adjuvant; use is medically supervised.
In the USA without regular marketing authorization; sometimes addressed in studies/compounding contexts.
No broad EU approval; availability limited.
Research areas
- Viral hepatitis B/C (approved indication in several countries)
- Vaccine adjuvant / immune support
- Supportive oncology and severe infections (research)
Documented effects (from the literature)
- In studies mostly described as well tolerated.
- Injection-site reactions possible.
Safety concerns & caution
- Immunomodulation requires a medical indication (e.g. caution in autoimmune constellations).
- Outside approved indications the evidence is inconsistent.
- The largest high-quality study to date outside the hepatitis indication — the phase-3 sepsis trial TESTS (2025, over 1,000 patients) — showed no reduction in mortality.
Risks of gray-market purchase
- Vials sold as "research" TA-1 are not quality-controlled.
- Self-administration for "immune strengthening" without medical evaluation is not covered by any approval.
Frequently asked questions
Is Thymosin Alpha-1 approved?
In several countries, yes (as Zadaxin/thymalfasin, mainly for viral hepatitis and as an adjuvant). In the USA it is not FDA-approved, and in the EU it is not generally approved.
Does it simply boost the immune system?
It acts as an immunomodulator in defined medical contexts. "Immune boosting" as a blanket self-use goal is not covered by the approvals and should be assessed by a physician.
Is Thymosin Alpha-1 proven effective as the "most-studied peptide"?
Seen in a differentiated way: Thymosin Alpha-1 (Zadaxin) is approved in several countries, mainly for viral hepatitis — but not in the USA and not generally in the EU. The largest high-quality study to date outside this indication (a phase-3 sepsis trial in 2025 with over 1,000 patients) was unable to show a reduction in mortality. Outside the approved applications, the benefit is therefore by no means assured.
Sources
Primary and reference sources for your own reading.
Related substances
Unfamiliar terms? Look them up in the glossary or read the fundamentals.
This profile is for information and education only. It is not medical advice and deliberately contains no dosing or usage details. Decisions about use belong in a doctor’s hands.