Thymosin Alpha-1
Also known as: Tα1 · Talpha1 · Zadaxin · TA-1
Thymosin alpha-1 is a 28-amino-acid immune-modulating peptide derived from the thymus. Approved as Zadaxin in over 30 countries (not the US) for hepatitis B/C and as adjunctive chemotherapy support. Distinct from TB-500 (thymosin beta-4) in mechanism, indication, and evidence base.
Last reviewed · Panya.health editorial
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Not medical advice. Thymosin Alpha-1 is not approved for human medical use in most jurisdictions. The data below is what users do; it is not what regulators have validated. You decide your risk profile.
What it does, and how
Thymosin alpha-1 is the active fragment of prothymosin alpha, naturally produced by thymic epithelial cells. It modulates T-cell function, increases CD4+/CD8+ counts in immunocompromised patients, and enhances antigen presentation by dendritic cells. The mechanism is regulatory rather than directly cytotoxic or immunostimulatory. Tα1 nudges immune signaling toward a more competent state, which is why it has been studied for hepatitis B/C (where chronic infection reflects immune escape), as a chemotherapy adjuvant (where chemo-induced immunosuppression matters), and in sepsis (where immune dysregulation is the central problem). Sciclone Pharmaceuticals (now closer to a Chinese-affiliated structure) developed it as Zadaxin, registered in over 30 countries since the 1990s. Distinct from TB-500 (thymosin beta-4): TB-4 is a 43-amino-acid peptide involved in actin sequestration and tissue repair, with totally different downstream biology. The two compounds share a name root because both were isolated from thymus extracts decades ago, not because they have related function.
Typical practice
Approved Zadaxin protocol: 1.6 mg subcutaneous twice weekly for hepatitis B/C (typically 6 to 12 months), or 1.6 mg subcutaneous twice weekly during chemotherapy cycles for solid tumors. Off-label community practice for general immune support: 1.6 mg twice weekly in 8 to 12 week cycles. Reconstitution: lyophilized 1.6 mg vial in 1 mL bacteriostatic water for unit dosing; the calculator at panya.health/tools/reconstitution-calculator handles the math. Dosing is well-established because Zadaxin has been on the market for 30+ years; this is one of the few research-chem-space peptides with mature dosing literature from regulatory submissions rather than community guesswork.
The dosing above is community practice, not a regulator-validated protocol. Trial-validated dosing for Thymosin Alpha-1 in humans does not exist for most use cases listed.
Risks and contraindications
Phase 3 safety profile across thousands of Zadaxin-registered patients is unusually clean. Most common adverse event is injection site reaction (mild). Rare reports of fatigue or flu-like symptoms in the first few injections. No consistent hepatic, cardiovascular, or hematologic signals in the registry data. The regulatory-immune mechanism does not raise the same cancer-pathway concern as IGF-1-elevating peptides; in fact Tα1 is studied as a chemotherapy adjuvant. Pregnancy and breastfeeding off-limits by default. Active autoimmune disease under specialist care: consult before use because immune modulation cuts both ways. The cleanest off-label-research-chem use case is general immune support during a defined high-stress / high-illness-exposure period; the longevity-stack-as-life-extension framing is harder to defend on evidence grounds because Zadaxin's registry data is on disease populations, not healthy adults.
Where this stands legally
Not FDA-approved. Zadaxin (the brand name in markets where it's registered) is not available in the US. Sold legally as a research chemical. FDA orphan-drug designation exists for some indications (severe combined immunodeficiency).
Zadaxin is not licensed by the MHRA in the UK. Some private clinics import via specials licensing for hepatitis indications.
Zadaxin is registered in Italy (where SciClone's manufacturing partner Patheon is based) and several other EU countries for hepatitis B/C. Cross-border prescribing under EEA rules is possible.
Zadaxin is not registered with the TGA. Personal-import via the Personal Importation Scheme is permitted with a doctor's letter.
Zadaxin is registered with FDA Thailand for hepatitis B/C. Available by prescription at international hospitals (Bumrungrad, Bangkok Hospital). Off-label use under private clinic prescribing is widespread.
Zadaxin is registered with MOHAP. Available by prescription at major hospitals; off-label use through private clinics.
Where users say they source it
Names below are sourced from community discussion. None are currently scored against the Panya 11-signal rubric. Panya does not earn commission on any of these. You can search them yourself; treat the list as a starting point for your own diligence, not an endorsement.
- Zadaxin (SciClone Pharmaceuticals, the registered brand product)Pending Panya 11-signal audit
- Bumrungrad / Bangkok Hospital (Zadaxin Rx, Thailand)Pending Panya 11-signal audit
- Pure RawzPending Panya 11-signal audit
- Limitless LifePending Panya 11-signal audit
- AminolabsPending Panya 11-signal audit
Full vendor scorecards for Thymosin Alpha-1 land in a follow-up sprint after lawyer review and payment processor selection. We will not route users to any vendor that scores below 70 on the rubric.
Papers worth reading directly
- Garaci et al. — Thymosin alpha 1: a historical overview. Ann N Y Acad Sci, 2007 →
- Goldstein et al. — Thymosin alpha1 (Zadaxin): A peptide drug with multiple immunomodulatory activities. Vaccine, 2009 →
- Camerini, Garaci — Historical review on the discovery of thymosins and their functional roles. Front Biosci, 2011 →
- Romani et al. — Thymosin alpha1 activates dendritic cell tryptophan catabolism and establishes a regulatory environment. Blood, 2006 →
Panya blog posts
The phrase on every grey-market peptide site. What it actually means, what it does not mean, and why reading it wrong costs people money.
The clinic route costs more and takes longer. The research-chem route puts more on you. Neither is wrong. Here is how to choose.
Adjacent reading
Track Thymosin Alpha-1 in your peptide journal.
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