Your immune system's master switch
A 28-residue peptide that modulates T-cell maturation and innate immune signaling.
Educational content. This page describes Thymosin Alpha-1 for informational purposes only and is not medical advice, diagnosis, or treatment. Consult a licensed provider before starting, stopping, or modifying any therapy.
Meta-analysis of 19 RCTs in 1,557 patients showed significantly reduced 28-day all-cause mortality in sepsis.[4]
Enhances anti-tumor immunity when combined with chemotherapy or immunotherapy, with preclinical and clinical evidence of improved outcomes.[7]
Thymosin alpha-1 (thymalfasin, marketed as Zadaxin) is a naturally occurring 28-amino acid peptide originally isolated from the thymus gland by Dr. Allan Goldstein in the 1970s. The thymus is responsible for T cell maturation, and thymosin alpha-1 is one of its key hormonal products regulating immune development and function.
Thymalfasin has been approved in more than 35 countries for hepatitis B, as a vaccine adjuvant, and as an immunomodulatory agent. It is one of the most extensively studied peptide therapeutics, with over 70 clinical trials involving thousands of patients. It demonstrates unique bidirectional immunomodulation, enhancing weakened responses while regulating excessive inflammation.
Thymosin alpha-1 functions primarily as a toll-like receptor (TLR) agonist, binding TLR-9 and TLR-2 on dendritic cells and macrophages. This activates MyD88-dependent signaling, triggering IKK and p38 MAPK phosphorylation, driving NF-kappaB and AP-1 to produce IL-6, IL-10, IL-12, and type I interferons.
It promotes dendritic cell maturation by upregulating CD40, CD80, and MHC class I/II, enhancing antigen presentation. It also directly promotes T cell maturation from precursors to functional helper and cytotoxic T cells.
A distinctive feature is bidirectional immunomodulation: in immunosuppression it upregulates effector functions; in hyperinflammation it promotes regulatory T cells and IL-10 to dampen excess. This makes it safer than unidirectional stimulants.
Your immune system's master switch
Thymosin alpha-1 activates innate immunity through TLR-9/TLR-2 agonism, triggering MyD88/IKK/MAPK cascades that drive cytokine production and upregulate antigen-presenting molecules. It promotes T cell maturation, enhances NK cell activity, and uniquely demonstrates bidirectional immunomodulation, boosting suppressed immunity while dampening hyperinflammation.
Key studies supporting the therapeutic use of this peptide.
Thymalfasin 1.6 mg SC twice weekly for 6 months produced significantly higher sustained virological response vs placebo.
Mutchnick MG, Lindsay KL, Schiff ER, et al. — J Viral Hepat, 6(5):397-403 (1999) · PubMed
Significantly reduced 28-day all-cause mortality with acceptable safety, strongest in severe sepsis subgroups.
Li C, Bo L, Liu Q, Jin F — Int J Infect Dis, 33:90-6 (2015) · PubMed
Significantly reduced mortality, restored CD4+/CD8+ T cells, reversed T cell exhaustion markers (PD-1, Tim-3).
Liu Y, Pan Y, Hu Z, et al. — Clin Infect Dis, 71(16):2150-2157 (2020) · PubMed
Complete virological response: 40.6% (26-week) and 26.5% (52-week) vs 9.4% untreated controls.
Chien RN, Liaw YF, Chen TC, et al. — Hepatology, 27(5):1383-7 (1998) · PubMed
Typical protocols used in clinical practice. Always consult a licensed provider for personalized dosing.
Subcutaneous (standard)
Subcutaneous (acute/critical)
Subcutaneous (standard): Standard approved dosing for viral hepatitis
Subcutaneous (acute/critical): Sepsis/critical illness protocol
The standard 1.6 mg twice-weekly dose is the most extensively studied and represents approved dosing in 35+ countries.
For patients under 40 kg, adjust to 40 mcg/kg twice weekly.
Peak plasma levels at 1-2 hours post-injection, half-life ~2 hours. Immunological effects persist for days due to downstream cellular activation.
One of the best-characterized peptide therapeutics, with data from 70+ clinical trials and decades of commercial use in 35+ countries. Safety profile superior to interferons and interleukins.
Bidirectional immunomodulation contributes to safety: it does not typically cause cytokine storm or uncontrolled activation.
Regular CBC monitoring recommended. In hepatitis B, ALT flares may indicate beneficial immune-mediated clearance.
See how Thymosin Alpha-1 compares to peptides with overlapping benefits.
| Peptide | Primary Use | Administration | Cycle Length | Key Differentiator |
|---|---|---|---|---|
| Thymosin Alpha-1 | Immune Support | Injection | 6–12 months (chronic) / 1–4 weeks (acute) | Only peptide with bidirectional immunomodulation, enhancing suppressed immunity while regulating hyperinflammation, approved in 35+ countries |
| Glutathione | Antioxidant & Detoxification | IV, Oral, Sublingual | Ongoing supplementation | The body's own master antioxidant, with clinical data supporting oral bioavailability (challenging earlier assumptions) and dramatic immune cell activation at high doses |
| KPV | Anti-Inflammatory & Wound Healing | Injection, Oral, Topical | 4 to 8 weeks | Smallest known anti-inflammatory peptide that directly blocks NF-kB nuclear import without melanocortin receptor binding, cAMP elevation, or pigmentation effects |
| Cathelicidin LL-37 | Chronic Wound Healing & Antimicrobial | Topical | 4 weeks (twice weekly application) | The only human cathelicidin. A single endogenous peptide that combines wound-healing, angiogenic, and broad-spectrum antimicrobial activity through overlapping FPR2/ALX and EGFR pathways. |
Current FDA classification and compounding eligibility.
The FDA placed this substance in Category 2 of the 503A bulk drug substances evaluation, flagging significant safety risks. 503A compounding carries FDA enforcement risk, so most pharmacies decline to prepare it and many physicians hesitate to prescribe it.
Nomination withdrawn September 2024, then reviewed by PCAC on December 4, 2024. PCAC voted against inclusion on the 503A bulks list. FDA cited inadequate safety data and immunogenicity concerns. Remains ineligible for 503A compounding despite the procedural removal from the formal Category 2 list. Not among the 12 peptides HHS withdrew from Category 2 in April 2026.
PCAC reviewed and recommended against inclusion on 503A bulks list
Removed from Category 2 (nomination withdrawn); remains listed under 'other significant safety risks'
Placed in 503A Category 2 with significant safety risks identified
Last verified April 12, 2026. PepHookup tracks public FDA actions. This is not legal or medical advice.
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Find a ProviderA tripeptide antioxidant central to cellular redox, detoxification, and immune function.
Produced endogenously and supplemented via IV, injection, or oral routes; clinical evidence remains mixed.
A 3-residue α-MSH fragment with selective anti-inflammatory activity.
Studied for IBD, colitis, and wound healing; acts independently of melanocortin receptor binding.
A 37-residue antimicrobial peptide from the human cathelicidin family.
Broad roles in innate immunity and wound healing; named in the April 2026 HHS Category 2 withdrawal for PCAC re-evaluation.