Thymosin Alpha-1 (Thymalfasin)

Brand names: Zadaxin® (international)

Mechanism of action: Enhances T-cell differentiation and maturation; Activates dendritic cells; Improves natural killer (NK) cell function; Modulates innate and adaptive immunity; May reduce excessive inflammatory responses while supporting host defense

Approved indications: Chronic hepatitis B (varies by country); Chronic hepatitis C (historically, varies by country); Immune dysfunction in selected conditions (varies by country)

Proposed indications: Sepsis adjunct therapy; COVID-19 (selected populations); Cancer immunotherapy adjunct; Vaccine response enhancement; Recurrent infections; Autoimmune diseases

Reported dosing range*: 1.6 mg subcutaneous, twice weekly

Where approved outside the U.S. (as Zadaxin), the recognized regimen is 1.6 mg subcutaneously twice weekly (Garaci E et al. (2012). Thymosin alpha1: from bench to bedside. Annals of the New York Academy of Sciences). This applies only where the drug is actually approved and prescribed -- verify current approval status by country independently, as it varies and changes.

*General range reported in available research or other sources -- not an individualized recommendation. Actual use should be supervised by a qualified provider.

Typical clinical dosing schedule: Administered by subcutaneous injection under physician supervision. Dosing depends on the approved indication and regional prescribing information.

Administration: Subcutaneous injection — Per physician-directed, indication-specific schedule

Compare with: TB-500 (Thymosin β4 Fragment)BPC-157GHK-Cu (Copper Tripeptide-1)

Evidence rating: ⭐⭐⭐⭐☆ — Well-studied with hundreds of publications, though indications differ by country.

Landmark trials: Chronic hepatitis B trials — Multiple randomized trials demonstrated improved virologic outcomes when combined with antiviral therapy.; Critically ill population meta-analyses — Suggested reduced mortality in selected critically ill populations, though results remain heterogeneous.

Common side effects: Injection-site pain, Fatigue, Mild fever, Headache

Serious risks: Generally well tolerated. Potential concern for exacerbating immune activity in susceptible individuals.

Drug interactions: Immunosuppressants; Checkpoint inhibitors (potential additive immune effects)

Monitoring: CBC, Liver function (when indicated), Clinical response, Infection status

Legal status: Not FDA-approved in the United States, though approved in some other countries. Not legally available by prescription in the U.S. — any use should only occur under the direction of a licensed healthcare provider, after independently verifying current legal status.

Regulatory status: Approved in multiple countries • Not FDA approved

Contraindications: Hypersensitivity; Use caution in organ transplant recipients due to immune stimulation; Autoimmune disorders (individual risk assessment)

Pregnancy & breastfeeding: Insufficient data; avoid unless benefits clearly outweigh risks.

Garaci E. (2007). Thymosin Alpha-1: A historical overview. Annals of the New York Academy of Sciences. Romani L., et al. (2021). Reviews on Thymosin Alpha-1 and COVID-19. King R, et al. (2021). Systematic review of Thymosin Alpha-1 in infectious disease.