Skip to content

Tissue Repair & Anti-Inflammatory

Thymosin Alpha-1

Thymic peptide that boosts T-cell and dendritic-cell function; approved abroad (Zadaxin) for hepatitis B, not FDA-approved.

InvestigationalEvidence level 4 of 5: Human RCTs or approved abroadAlso: Tα1, Thymalfasin, Zadaxin

Overview

Thymosin alpha-1 (thymalfasin) is a 28-amino-acid peptide originally isolated from the thymus, the organ where T cells mature. It acts on dendritic cells through Toll-like receptors, promoting T-cell maturation, Th1-type responses, natural killer activity and antigen presentation, while helping restrain excessive inflammation. Marketed as Zadaxin, it is approved in more than 30 countries for chronic hepatitis B and C and as an adjunct to vaccines and cancer therapy. It is used off-label for immune support in chronic infection, immunosenescence and post-viral fatigue. Its safety record across decades of clinical use is very good. Efficacy is more variable: benefits appear in some infection and oncology settings, but a large 2025 sepsis trial found no mortality benefit.

Classification
Synthetic 28-amino-acid N-acetylated thymic peptide (thymalfasin)
Route
Subcutaneous
Half-life
~2 hours (SC)

Mechanism of action

Primary targetToll-like receptors (TLR2/TLR9) on dendritic cells; T-cell maturation
  1. Subcutaneous injectionTypically given twice weekly; peaks within about 2 hours.
  2. Dendritic cell TLR signalingActivates TLR9 and TLR2 pathways on antigen-presenting cells.
  3. T-cell maturationPromotes thymocyte differentiation and CD4+/CD8+ T-cell function.
  4. Th1 and NK enhancementIncreases IL-2, interferon-γ and natural killer cell activity.
  5. Balanced immune responseImproves pathogen and vaccine responses while modulating excessive inflammation.
Downstream effects
  • Improved viral clearance
  • Better vaccine response
  • Immune rebalancing

Researched for

  • Chronic hepatitis B and C
  • Sepsis
  • Vaccine adjuvant in older or immunocompromised adults
  • Cancer immunotherapy adjunct
  • COVID-19 and post-viral illness

Research notes

  • Meta-analyses of hepatitis B RCTs show improved virologic response versus no treatment, comparable to interferon in some analyses.
  • TESTS trial (Wu et al., BMJ 2025, ~1,100 patients): no significant reduction in 28-day sepsis mortality.
  • Improves antibody response to influenza and hepatitis B vaccines in elderly and dialysis patients in small trials.
  • Excellent tolerability across decades of use; long-term data in healthy 'immune optimization' use are lacking.

Reported side effects

  • Injection-site redness or discomfort
  • Transient flu-like symptoms
  • Mild fatigue
  • Rare rash

Contraindications & cautions

  • Organ transplant recipients on immunosuppression
  • Active autoimmune flare (theoretical Th1 activation)
  • Pregnancy and breastfeeding (limited data)
  • Hypersensitivity to thymalfasin

Lab monitoring

  • CBC with differential (lymphocyte subsets if available)
  • CMP
  • CRP, ESR, hsCRP
  • Vitamin D, zinc
  • Quantitative immunoglobulins; viral titers if indicated

Dosing and pricing for Thymosin Alpha-1

Dosing references and compound pricing are available to established patients in the secure portal after a medical evaluation.

Ready to take control of your health?

Start with a 60-minute physician evaluation, virtually in seven states or in person in Reston, Virginia.

Request a consultation 703-400-5314

Cash-pay. HSA and FSA accepted. Monday–Friday, 10 AM – 2 PM (virtual and in person).