Thymosin Alpha-1

Typical use cases

Dosing guidelines

Titration

Clinical regimens generally use a fixed dose (1.6 mg twice weekly) rather than titration; body-weight dosing (~40 µg/kg) has been reported for individuals under 40 kg.

Reconstitution

Lyophilized powder reconstituted with sterile water for injection (label: 1.0 mL diluent per 1.6 mg vial, yielding 1.6 mg/mL); the reconstituted Zadaxin product is labeled for immediate use.

Injection sites

Subcutaneous injection, typically into the abdomen or thigh.

Storage & handling

Store refrigerated at 2-8°C (36-46°F). Reconstituted Zadaxin is labeled for immediate use; compounded/research reconstituted peptide is commonly refrigerated and used within a limited window.

Side effects

• Injection-site redness, discomfort, or irritation Mild · Common
• Joint pain or muscle aches Mild · Uncommon
• Fatigue Mild · Uncommon
• Rash or local swelling Mild · Uncommon
• Fever or flu-like symptoms (more often when combined with interferon) Moderate · Uncommon
• Transient immune over-activation in autoimmune-prone individuals Moderate · Rare

Research summary

Thymosin Alpha-1 (Tα1) is among the most clinically studied immunomodulatory peptides, with an evidence base spanning decades and dozens of randomized trials, primarily outside the United States. As the synthetic drug thymalfasin (Zadaxin), it is approved in numerous countries for chronic hepatitis B and C, where trials reported virological response rates around 40% as monotherapy and improved outcomes in combination with interferon — though these indications have been largely superseded by direct-acting antivirals. Mechanistically it acts as an agonist of Toll-like receptors 2 and 9 on myeloid and dendritic cells, promoting T-cell maturation, NK-cell activation, and balanced cytokine production, which underlies its study as a vaccine adjuvant (notably improving influenza response in elderly and immunocompromised populations) and as adjunctive cancer therapy intended to reduce chemotherapy toxicity. A large Chinese randomized trial in severe sepsis suggested a modest mortality reduction, and retrospective COVID-19 reports described restoration of lymphocyte counts in severely lymphopenic patients, but prospective COVID data remained limited and reviews reached conflicting conclusions. Overall the peptide is consistently described in the literature as well tolerated with mostly mild, local adverse effects. Key limitations include heterogeneous study designs, many older trials predating modern standards of care, small sample sizes in oncology studies, and a lack of head-to-head comparisons with contemporary immunotherapies.

Key references

• https://pmc.ncbi.nlm.nih.gov/articles/PMC7747025/
• https://en.wikipedia.org/wiki/Thymosin_%CE%B11
• https://www.rxlist.com/zadaxin-drug.htm
• https://pubmed.ncbi.nlm.nih.gov/10027483/
• https://pmc.ncbi.nlm.nih.gov/articles/PMC10144173/

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