Immune · 503A · Subcutaneous
Thymosin Alpha-1: the immune modulator with three decades of clinical data.
Thymosin Alpha-1 (Tα1, brand name Zadaxin) is a 28-amino-acid peptide naturally produced by the thymus gland. It is approved in 35+ countries for hepatitis B, hepatitis C, and as an adjuvant in cancer therapy. In the U.S., it is used off-label as an immune-modulation adjunct under physician supervision.
What Thymosin Alpha-1 is
Thymosin Alpha-1 is a 28-amino-acid peptide first isolated by Allan Goldstein in 1972 from bovine thymus. It is the active immune-modulating fraction of thymosin fraction 5. Synthetic Tα1 is biochemically identical to the endogenous peptide.
Marketed as Zadaxin by SciClone Pharmaceuticals, Tα1 is approved in over 35 countries for chronic hepatitis B and C, as a vaccine adjuvant, and as an adjunct in certain cancer immunotherapies. It is not FDA-approved in the United States — though it has held orphan-drug status for several indications.
In the U.S., compounded Tα1 from licensed 503A pharmacies is used off-label as an immune-modulation adjunct: in patients with recurrent infections, chronic viral reactivation, post-acute infection syndromes, or as a supportive layer alongside oncology care directed by their oncologist.
How it works
Tα1 binds toll-like receptor 9 (TLR9) and acts on plasmacytoid dendritic cells and myeloid dendritic cells, increasing their maturation and ability to present antigen. It also supports T-helper cell maturation and pushes a more balanced Th1/Th2 response.
Mechanistically, Tα1 is a modulator — not a stimulator. It tunes the immune system toward more effective response without producing the cytokine-storm risk of broad immune stimulators. This is why it is used in both viral infection (to enhance response) and autoimmune-adjacent settings (to rebalance).
The peptide is small, biocompatible, and rapidly cleared. The relevant effects are downstream and accumulate with a course of therapy rather than appearing acutely after a single dose.
What patients use it for
Immune modulation
Tα1's defining effect — tuning T-cell, NK-cell, and dendritic-cell function. Used in protocols for recurrent infection, chronic viral activity, and post-infection recovery.
T-cell maturation support
Tα1 supports the maturation of naïve T cells in the thymus and periphery. Particularly relevant after age 40 when thymic function declines.
Vaccine adjuvant
Tα1 has been studied as an adjuvant to improve vaccine response in older or immunosuppressed adults — including influenza and hepatitis B vaccines.
Adjunct in oncology care
Has been used internationally as an adjunct in melanoma, hepatocellular carcinoma, and non-small-cell lung cancer protocols — always in coordination with the patient's oncologist.
Evidence summary
Tα1 has the most extensive clinical trial base of any peptide in the kindr longevity catalog outside of FDA-approved GLP-1s. Multiple Phase III trials for hepatitis B and C established efficacy and safety at the doses used clinically.
Costantini et al. (Frontiers in Immunology, 2020) reviewed Tα1's mechanism and use in viral and oncologic settings. Garaci et al. have published extensively on its role in CD4 reconstitution and vaccine adjuvancy.
Off-label use for general immune support in healthy adults is less rigorously studied. The mechanistic rationale and tolerability profile are strong, but outcome data in healthy populations is limited — discuss honestly with your physician.
Dosing and clinical context
General clinical context only. Kindr Health physicians determine the appropriate dose and protocol for each patient based on history and labs. This is not a prescription or dosing recommendation.
Standard hepatitis-protocol dose is 1.6 mg subcutaneously twice weekly. Off-label immune-support protocols often use 1.6 mg twice weekly for 4–12 weeks, sometimes longer, depending on the indication.
Administered as a subcutaneous injection — abdomen or thigh — with simple supplies. Most patients self-administer after initial instruction.
Course length and re-treatment are individualized. A typical first course is 8–12 weeks with reassessment.
Safety and contraindications
Among the best-tolerated peptides in clinical use. Most common side effect is mild injection-site reaction. Serious adverse events are rare across decades of international use.
Contraindications: pregnancy, active autoimmune disease (relative — discuss with physician), organ transplant on immunosuppression, known hypersensitivity.
Compounded Tα1 in the U.S. is not FDA-approved. Use under physician supervision through a licensed 503A pharmacy.
Who it's typically considered for
- Adults with recurrent infections or chronic viral reactivation patterns
- Patients in post-acute infection recovery (where appropriate)
- Patients on long courses of immunosuppressive medication where a modulator is being considered (with prescriber coordination)
- Patients seeking immune-axis support as part of a broader longevity protocol
Frequently asked questions
Is Thymosin Alpha-1 FDA-approved?
Not in the United States. Tα1 (Zadaxin) is approved in over 35 countries for hepatitis B, hepatitis C, and as a vaccine / cancer adjuvant. U.S. use is via compounded Tα1 from licensed 503A pharmacies under physician prescription.
Is Thymosin Alpha-1 the same as Thymosin Beta-4 (TB-500)?
No. Despite the similar name, they are different peptides with different functions. Thymosin Alpha-1 is immune-modulating. Thymosin Beta-4 (TB-500) is a tissue-repair peptide. Both come from the thymus but they are distinct molecules.
How long until I notice changes?
Tα1's effects are immunologic and cumulative. Many patients notice fewer / shorter infections by the second month of a course. Energy and recovery changes — when they occur — usually follow at 4–8 weeks.
Can I take Tα1 with HRT?
Yes. Tα1 and HRT address different systems and are commonly layered. Your kindr physician reviews your full medication list before prescribing.
Is Tα1 safe in autoimmune disease?
It depends on the autoimmune condition and severity. Tα1 is a modulator, not a stimulator, so the risk profile is different from typical immune stimulants — but in active autoimmune disease the decision should be individualized with your physician.
Can Tα1 be used as a vaccine adjuvant?
Internationally, yes — Tα1 has trial data improving response to influenza and hepatitis B vaccines in older or immunosuppressed adults. Off-label use for this purpose is uncommon in U.S. retail practice but is part of the published evidence base.
How much does Thymosin Alpha-1 cost?
Compounded Tα1 protocols typically run $200–$450 per month depending on dose and duration. The initial kindr physician review is free; a transparent quote is provided before any prescription is filled.
Sources
- Costantini C et al. A reappraisal of thymosin alpha 1 in cancer therapy. Frontiers in Immunology (2020). — www.frontiersin.org/articles/10.3389/fimmu.2020.00748/full
- Garaci E et al. Thymosin alpha 1 in the treatment of cancer: from basic research to clinical application. International Immunopharmacology (2003). — pubmed.ncbi.nlm.nih.gov/14592598
- Iino S et al. The efficacy and safety of thymosin alpha-1 in Japanese patients with chronic hepatitis B. Hepatology Research (2005). — pubmed.ncbi.nlm.nih.gov/15914092
- Goldstein AL. From lab to bedside: emerging clinical applications of thymosin alpha 1. Expert Opinion on Biological Therapy (2009). — pubmed.ncbi.nlm.nih.gov/19566479
Considering Thymosin Alpha-1?
A Kindr Health physician reviews every longevity intake — peptides are prescribed only when medically indicated based on your history and labs. There is no charge for the initial review.
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Medically reviewed by Dr. Ana Lisa Carr, MD, MBA
Board-Certified Family Medicine Physician · Lead Provider / Medical Reviewer
NPI 1689841744 · Last reviewed: May 10, 2026
Last reviewed May 10, 2026. Compounded medications are prepared by FDA-registered 503A pharmacies and are not FDA-approved drug products. Prescriptions require a clinical evaluation; a Kindr Health physician determines eligibility. Not for use in pregnancy. This page provides educational information and is not medical advice.