Thymosin Alpha-1
Thymosin Alpha-1
An immune peptide studied for its effects on T-cell function
Thymosin Alpha-1 (TA1) is a naturally occurring peptide hormone produced by the thymus gland, a vital organ for immune cell development. Lab and clinical studies link it to the maturation and function of T-cells. The synthetic version, thymalfasin (Zadaxin), is approved in over 30 countries (manufacturer figure) for chronic hepatitis B and C, but as of October 2026 not in the US or EU. A 2025 Phase 3 trial (TESTS) in 1,106 adults with sepsis found no mortality benefit.
Read the research profile for mechanisms, citations, and safety context before comparing vendors. View the Thymosin Alpha-1 research profile.
Key Benefits
Mechanism of Action
In lab studies, TA1 binds to Toll-like receptors (TLRs) on immune cells, which triggers a signaling cascade that enhances the adaptive immune response. It promotes the differentiation of T-helper 1 (Th1) cells and increases the production of key cytokines like Interleukin-2 (IL-2) and Interferon-gamma (IFN-gamma). This is thought to help cytotoxic T-cells and Natural Killer (NK) cells identify virally infected or malignant cells, although the TESTS sepsis trial found no survival benefit.
Dosing Guidelines
Typical Dose
600 mcg - 1.6 mg
Frequency
2-7x per week
Duration
4-12 weeks
Note: These figures come from user and vendor reports of subcutaneous injection. Users commonly report 0.5-1.5 mg 2-3 times a week, and daily injections during acute illness. The hepatitis B label dose abroad is 1.6 mg twice a week for 6-12 months, and the TESTS sepsis trial used 1.6 mg every 12 hours for 7 days. The label lists deliberate immunosuppression, such as after organ transplant, as a contraindication.
Research & Studies
TA1's mechanism, reported benefits and side effects, dosing context and legal notes.
Read Full ResearchSide effects, safety signals and contraindications reported across common research peptides.
Read Full ResearchWhat the research-use-only label means, plus sport restrictions and import rules for peptides.
Read Full ResearchPotential Side Effects
Reported side effects may include:
- - Well tolerated in trials (manufacturer data; TESTS sepsis trial)
- - Injection-site discomfort or redness (user and vendor reports)
- - Flu-like symptoms, fatigue or poor sleep after a dose (user reports)
- - ALT flares can occur in hepatitis B treatment (label)
This information is for research purposes only. Always consult with a healthcare professional.
Popular Stacking Options
Thymosin Alpha-1 + BPC-157
Users combine systemic immune modulation from TA1 with BPC-157 for gut-related goals. BPC-157's gut data come mostly from rodents, and no study has tested the combination.
Shop this stackThymosin Alpha-1 + TB-500
Users describe this as a healing and recovery stack. TA1 has human trial data, but the TB-500 fragment has none, and the pairing hasn't been studied.
Shop this stackThymosin Alpha-1 + GHK-Cu
Some users combine the two for wellness and anti-aging goals. GHK-Cu's human evidence is limited to small topical studies, and no study has tested them together.
Shop this stackFrequently Asked Questions
Is Thymosin Alpha-1 a steroid?
No, it is not a steroid. TA1 is a peptide, a short chain of amino acids naturally produced by your thymus gland to regulate immune cells. It works by modulating your immune system, not through the hormonal pathways associated with anabolic steroids.
How is TA1 different from TB-500?
Both were first isolated from thymus extracts, but they have different jobs. TA1 is studied as an immune modulator, mainly for T-cell function, and is approved abroad for hepatitis B and C. TB-500 (a fragment of Thymosin Beta-4) is studied for tissue repair in animals; as of October 2026 the fragment has no human data.
Can I use TA1 when I'm sick?
Users describe taking TA1 daily during illnesses like the flu, but no trial has shown that it shortens duration or severity. In the TESTS trial (2025, 1,106 adults with sepsis, 1.6 mg every 12 hours for 7 days), 28-day mortality was 23.4% with TA1 and 24.1% with placebo. Anyone who is ill should talk to a healthcare professional.
How long does it take for Thymosin Alpha-1 to work?
You don't typically 'feel' TA1 like a stimulant, and no study has measured how soon users notice anything. Users describe timelines from a few days during an illness to several weeks for chronic conditions. In the hepatitis B trials, responses often appeared 12 months or more after treatment ended (label).
Is Thymosin Alpha-1 safe?
TA1 has been well tolerated in trials, and it is an approved medication in over 30 countries, though not in the US or EU. TESTS found no difference in safety outcomes versus placebo. Users report injection-site redness, flu-like symptoms, fatigue or poor sleep. The hepatitis B label notes that ALT flares can occur and lists deliberate immunosuppression as a contraindication. Products sold for research use are not the approved medicine.
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