Thymosin Alpha-1
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Thymus-derived immunomodulatory peptide; dual-action Th1 stimulator and Treg inducer approved in 35+ countries as ZADAXIN for hepatitis B
Quick Facts
| Property | Value |
|---|---|
| Also Known As | Tα1, ZADAXIN, Thymalfasin |
| Category | Immune Modulation / Anti-Aging |
| Sequence | 28-amino acid polypeptide (N-acetylated) |
| Molecular Weight | 3108 Da |
| Molecular Formula | C₁₂₉H₂₁₅N₃₃O₅₅ |
| PubChem CID | 16129620 |
| Administration | SubQ |
| Typical Dose Range | 1.6 mg SubQ 2x/week (standard); up to 1.6 mg 2x/day (critical care) |
| Half-Life | ~2 hours |
| Storage | Lyophilized: -20°C, 2 years; Reconstituted: 2–8°C, use within 1–2 weeks |
| FDA Status | Not FDA-approved in USA; approved in 35+ countries as ZADAXIN for chronic HBV |
| WADA Status | Prohibited under S0 (Non-Approved Substances) |
Mechanism of Action
Thymosin Alpha-1 is an endogenous 28-amino acid peptide naturally secreted by the thymus gland. Its unique therapeutic value lies in its dual immunomodulatory action: it simultaneously stimulates Th1 immune responses against pathogens while inducing regulatory T-cells (Tregs) to prevent autoimmunity (PMID-27450734).
Th1 stimulation occurs via upregulation of IL-2, IFN-γ, and TNF-α, enhancing NK cell cytotoxicity, CD8+ T-cell activity, and dendritic cell maturation for improved antigen presentation. Tα1 also acts as a TLR9 agonist, activating innate immune pathogen sensing (PMID-11381492).
The Treg induction arm operates through the IDO (indoleamine 2,3-dioxygenase) pathway — activating tryptophan catabolism that drives Treg differentiation and immune tolerance. This prevents excessive immune activation while maintaining pathogen clearance. In clinical use, this balance enables Tα1 to fight infections and enhance anti-tumor immunity while calming autoimmune overactivity (PMID-36812669).
Tα1 also supports thymopoiesis (thymic T-cell production), which is particularly relevant in aging and immunocompromised states where thymic involution reduces adaptive immune capacity (PMID-41373628).
Key Research Areas
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Hepatitis B (ZADAXIN Indication) — Two meta-analyses demonstrate superiority of combination therapy (Tα1 + antiviral) over antiviral monotherapy. IFN + Tα1 achieved higher HBV-DNA negativity and HBeAg loss in 535 patients across 7 RCTs (PMID-21272455). Entecavir + Tα1 improved clinical response in 1,144 patients across 7 RCTs (PMID-33076834).
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Sepsis and Critical Care — The definitive 2025 TESTS Phase 3 RCT (n=1,089, BMJ) found Tα1 did NOT reduce 28-day mortality in sepsis vs. placebo (23.4% vs. 24.1%), contradicting earlier positive meta-analyses (PMID-39814420). An earlier meta-analysis (2016) had shown mortality benefit for Tα1 alone (28-day) and Tα1 + ulinastatin combination (28+90-day) (PMID-26517783).
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COVID-19 — Systematic review of 8 studies showed Tα1 significantly reduced mortality in moderate-to-critical COVID-19 patients (PMID-37845598). A pilot RCT (n=49) demonstrated accelerated CD4+ T-cell recovery by day 5 (PMID-36056913).
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Cancer Immunotherapy Adjunct — Review of Tα1 as immunotherapy adjunct covers melanoma, lung, and hepatocellular carcinoma applications, enhancing ADCC and tumor antigen recognition (PMID-36812669).
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Aging and Immune Senescence — Tα1 restores thymic output in aged individuals and supports adaptive immune function during immunosenescence (PMID-41373628).
Evidence Level Summary
| Evidence Type | Count | Notes |
|---|---|---|
| Phase 3 RCT | 1 | TESTS sepsis trial (n=1,089) — negative primary endpoint |
| Systematic reviews / meta-analyses | 4 | 2 HBV, 1 COVID-19, 1 sepsis — all Level I |
| Phase 2 RCT | 1 | COVID-19 pilot (n=49) |
| Narrative reviews | 5 | Immune modulation, cancer, aging, HBV |
| Total vault studies | 11 |
The evidence base for Thymosin Alpha-1 is the strongest of any research peptide in the vault, with 5 Level I studies and 2 human RCTs. It is approved in 35+ countries (ZADAXIN) for chronic HBV, providing real-world clinical validation. However, the 2025 TESTS Phase 3 RCT (BMJ) was negative for sepsis mortality, requiring honest qualification of the sepsis evidence. The HBV and COVID-19 data remain positive. Tα1 has an excellent established clinical safety profile from millions of patients globally.
Clinical Applications
- Immune Support — Th1 stimulation and Treg induction for balanced immunity
- Autoimmune Conditions — Treg induction via IDO pathway for immune tolerance
- Cancer Adjunct Therapy — Enhanced ADCC, tumor antigen recognition, immunotherapy synergy
- Anti-Aging — Thymopoiesis restoration, immune senescence reversal
Protocols Using This Peptide
- Immune Restoration Protocol — Core immunomodulatory peptide
Ageless Peps Products
- AP-TA1-Vial — Thymosin Alpha-1 Vial, $72-$86 retail
- AP-TA1-500MCG-Capsules — Thymosin Alpha-1 Capsules, 500mcg x 60 caps, $184 retail
Dosing Reference
Research Dosing Ranges
| Route | Dose Range | Frequency | Duration | Source | ||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SubQ | 1.6 mg | 2x/week | 6–12 months (chronic); 4–8 weeks (acute) | ZADAXIN label; PMID-28422855); OS HR 0.308 in propensity-matched analysis (PMID-34011034). Synergizes with checkpoint inhibitors by turning "cold" tumors "hot" (PMID-31555601). Safety confirmed across 11,000+ subjects (PMID-38308608). Action: Consider as immunotherapy adjunct under oncologist supervision.
Synergistic Combinations
Related Research
Related#peptide #immune #anti-aging #subq |