Thymic peptide researched for immune modulation, T-cell activation, and antiviral response. Approved in over 35 countries as Zadaxin® for hepatitis B.
Last Updated: May 2026
Thymosin Alpha-1 (Tα1) is a synthetic 28-amino-acid thymic peptide approved in 35+ countries as Zadaxin for the treatment of hepatitis B and hepatitis C, with additional approved indications in some markets for cancer chemotherapy support and severe immunodeficiency. It is not currently FDA-approved in the United States, though it has approval pathways in most major non-US markets. Research-grade Thymosin Alpha-1 is also sold by third-party laboratories for laboratory use only.
Thymosin Alpha-1 is a synthetic 28-amino-acid peptide originally isolated from thymus tissue, functioning as a key immune modulator through Toll-like receptor 9 (TLR9) activation, dendritic cell maturation, and T-cell differentiation toward Th1 responses. Unlike the Khavinson Thymalin extract (which contains multiple peptides), Thymosin Alpha-1 is a defined single-sequence peptide with characterized receptor-binding mechanisms. It enhances cell-mediated immune responses, particularly against viral infections and tumors. Evidence level: Human RCT (Phase 3 for hepatitis B/C); approved in 35+ countries.
In Phase 3 trials for chronic hepatitis B, Thymosin Alpha-1 produced sustained virological response rates of 25–40% as monotherapy and higher rates in combination with interferon — leading to approval as Zadaxin in 35+ countries. Additional clinical research has explored cancer chemotherapy support (improving immune recovery), severe combined immunodeficiency adjunctive therapy, and septic shock immune modulation. The clinical evidence base is among the strongest for any thymic peptide. Evidence level: Human RCT (Phase 3, multiple indications); regulatory approval in 35+ countries.
Thymosin Alpha-1 is the most clinically-developed immune-modulating peptide, with Phase 3 evidence and broad international approval distinguishing it from research-stage compounds in the same therapeutic space.
| Compound | Mechanism | Clinical evidence | Regulatory status |
|---|---|---|---|
| Thymosin Alpha-1 | TLR9, T-cell Th1 differentiation | Phase 3 (HBV, HCV) | Approved in 35+ countries (Zadaxin) |
| Thymalin | Proposed bioregulatory (extract) | Russian clinical | Approved Russia/CIS |
| LL-37 | Cathelicidin antimicrobial | Preclinical + early clinical | Not approved |
| VIP | VPAC1/2 receptor | Phase 2 (multiple) | Not approved |
Thymosin Alpha-1's safety profile in Zadaxin clinical use is favorable — the most common side effects are mild injection-site reactions, occasional transient lymphocyte changes, and mild headache. Serious adverse events are rare. Long-term safety data from approved clinical use in 35+ countries provides one of the more robust safety bases for any immune-modulating peptide. Evidence level: Phase 3 clinical safety; post-market surveillance in 35+ countries.
Thymosin Alpha-1 (Zadaxin) is approved in 35+ countries for hepatitis B, hepatitis C, and related immune indications, but is not currently FDA-approved in the United States. In the FDA context, Thymosin Alpha-1 was withdrawn from Category 2 of the 503A bulks list in September 2024, opening a potential pathway for compounding pharmacy access — though formal Category 1 inclusion remains pending PCAC review. Current US regulatory status in FDA peptide regulation 2025–2026 timeline.
Because the international approvals apply to Zadaxin specifically — not to research-grade Thymosin Alpha-1 sold by third-party laboratories. Research-grade material is subject to wider purity variance, occasional underdosing, and inconsistent endotoxin control. Independent HPLC purity testing and mass spectrometry identity confirmation (expected MW 3,108.3 Da) are essential. Guidance in how-to-test-peptides hub.
Peptigrity purchases Thymosin Alpha-1 vials anonymously at standard customer pricing, sends them to ISO-accredited third-party labs for HPLC, mass spectrometry, and endotoxin analysis, and publishes the unedited certificate of analysis. The lab test table above this section shows the cross-shop dataset. Methodology in how we calculate trust scores.
No, not currently in the United States, though it is approved in 35+ countries as Zadaxin. In April 2024, the FDA's position on Thymosin Alpha-1 began shifting — the compound was withdrawn from Category 2 of the 503A bulks list in September 2024. Formal PCAC review for potential Category 1 inclusion remains pending.
Thymosin Alpha-1 is legal to purchase as a research chemical for laboratory use in most jurisdictions and is available by prescription as Zadaxin in countries where approved. The September 2024 Category 2 withdrawal opens a potential compounding pharmacy pathway in the US, though formal authorization remains pending. Country breakdown in peptide legal status guide.
Thymosin Alpha-1 is a defined single 28-amino-acid synthetic peptide with characterized receptor binding (TLR9, T-cell differentiation pathways); Thymalin is a multi-component polypeptide extract from bovine thymus tissue. Thymosin Alpha-1 has Phase 3 clinical evidence and international approval; Thymalin operates within the Khavinson bioregulator framework with Russian/CIS approval.
Independent third-party HPLC certificate of analysis from a lab the vendor does not own or pay, with mass spectrometry identity confirmation (expected MW 3,108.3 Da) and endotoxin testing. COA interpretation in red flags in peptide certificates of analysis.
No. Peptigrity is an independent review platform, not a medical authority. The approved Zadaxin dose for hepatitis B is 1.6 mg subcutaneously twice weekly under physician supervision. Anyone considering Thymosin Alpha-1 should consult a licensed physician.
Thymosin Alpha-1 is not specifically prohibited by WADA but related immune-modulating peptides may face scrutiny in competitive sport. For drug-testing context across the peptide class, see do peptides show up on drug tests.
This section is for educational and informational purposes only and does not constitute medical advice. Thymosin Alpha-1 is approved in 35+ countries as Zadaxin but is not currently FDA-approved in the United States. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.
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