Thymosin alpha-1 (Ta1) is a clinically proven, 28-amino-acid peptide (MW ~3,108 g/mol, Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH) naturally produced by the thymus gland. A synthetic version (thymalfasin, marketed as Zadaxin) is approved in over 35 countries for treating hepatitis B and C and as an immune adjuvant. It modulates rather than simply boosts immunity, making it unique among immune therapies. Clinical trials involving thousands of patients show robust safety data, with an FDA orphan drug designation for hepatitis B in the US. A 2024 study showed potential in restoring T-cell counts in immunological non-responder HIV patients.
Category: Immune Modulator. Evidence rating: C (early/mixed human evidence).
Clinical status: Approved in 35+ countries (Zadaxin); FDA orphan drug designation; not FDA-approved in the US
Ta1 (C129H215N33O55) activates Toll-like Receptors TLR2 and TLR9 on immune cells, triggering the MyD88 and NF-kB signaling pathways to put the immune system on alert without destructive inflammation. Key mechanism: increases MHC Class I expression, unmasking hidden viruses and cancer cells for…
Research base: 41 registered clinical trials and 65 indexed publications reference Thymosin Alpha-1.
Safety considerations: One of the safest immune therapies available; well-tolerated even at doses 100x higher than therapeutic standard; Most common complaint: temporary redness or stinging at injection site (10-15% of users), similar to a mosquito bite, lasting 30-60 seconds; Mild "immune flu" possible: low-grade fatigue, body aches from cytokine circulation (sign of immune activation, not infection).
Reviewed by the PeptideAtlas Editorial Team. Last reviewed: 2026-08-12.
Related peptides: Thymulin, IM862.
Compare: Thymosin Alpha-1 vs Thymulin, Thymosin Alpha-1 vs IM862.
No. Despite being approved in over 35 countries as Zadaxin and having FDA orphan drug designation for hepatitis B, it has not received full FDA approval. It is available through compounding pharmacies in the US.
They are different peptides with different functions. Thymosin alpha-1 (28 amino acids) primarily modulates immune function via TLR2/TLR9. Thymosin beta-4 (43 amino acids) is involved in tissue repair and cell migration. Different genes, different receptors, different applications.
The Zadaxin protocol uses 1.6 mg SC twice weekly. For general immune support, 1.6 mg twice weekly for 4-8 weeks. For acute illness, 1.6 mg daily for 7-14 days. Even at much higher doses, Ta1 shows no toxicity -- the body simply breaks down excess peptide into amino acids.
Transplant patients take immunosuppressants to prevent rejection. Ta1's immune-boosting properties can overcome this suppression and trigger fatal organ rejection. This is the only absolute contraindication.
No. Ta1 is a modulator, not just a booster. If immunity is too low (cancer, HIV, aging), it turns it up. If the immune system is overactive (some autoimmune conditions), it helps balance it down. This bidirectional modulation distinguishes it from simple immune boosters.