# Thymosin alpha-1 FAQ: Mechanism, Approval, Dosing, Comparisons > Thymosin alpha-1 FAQ: what it is, what it does, FDA status, dosing protocols, half-life, side effects, autoimmune contraindications, WADA status, comparison to TB-500. Twenty-four questions, direct answers, every quantitative claim cited to a verified trial. ## What is Thymosin alpha-1? A naturally occurring 28-amino-acid acetylated peptide first isolated from calf thymus in 1977; the synthetic form (thymalfasin) is marketed as the branded product Zadaxin and is approved outside the US in 30+ countries for hepatitis B and C [1][20]. ## What does Thymosin alpha-1 do? Modulates innate and adaptive immunity by activating TLR-9 and TLR-2 on dendritic cells, promoting T-cell maturation, raising IFN-γ and IL-2 output, and shifting cytokine balance toward a Th1 antiviral profile [4][5]. ## What is Thymosin alpha-1 used for? Studied in chronic hepatitis B and C (approved indications in 30+ countries), severe sepsis (ETASS RCT and pooled meta-analysis), non-small-cell lung cancer adjuvant therapy, severe COVID-19 (observational cohorts and 2023 meta-analyses), and as a vaccine adjuvant in immunocompromised patients [6][8][12][15][18]. ## Is Thymosin alpha-1 FDA-approved? Not FDA-approved in the United States. The branded synthetic form (thymalfasin) is approved in 30+ countries for hepatitis B and C. The FDA's December 2024 Pharmacy Compounding Advisory Committee reviewed Tα1 and Tα1-acetate for inclusion on the Section 503A compounding bulks list [21]. ## Who is excluded from Thymosin alpha-1 trials? Clinical trials typically exclude pregnant or breastfeeding individuals, organ-transplant recipients on immunosuppressants, and patients with active autoimmune disease — the immunostimulatory mechanism is the contraindication, not direct drug toxicity [20]. ## How does Thymosin alpha-1 make you feel? Trials report it is generally well-tolerated; transient injection-site reactions and mild erythema are the most commonly documented effects [20]. Subjective 'energy' or wellbeing claims circulate outside the trial literature and are clinician anecdote rather than measured trial endpoints. ## Does Thymosin alpha-1 give you energy? No randomized trial uses 'energy' as a primary endpoint. Fatigue improvement is sometimes a secondary outcome in hepatitis and oncology adjuvant studies, attributed to reduced infection burden or preserved T-cell function rather than a direct stimulant effect. ## Does Thymosin affect aging? Thymic involution drives age-related T-cell decline; the Gravenstein influenza-adjuvant trial in elderly subjects and the Perruccio post-transplant reconstitution work establish a precedent for Tα1's role in restoring immune competence in depleted populations [18][19]. Indication-specific RCTs in healthy older adults are not yet published. ## How long does it take for Thymosin alpha-1 to work? Hepatitis B and C trials measured virological response at 6 months [12][14]. Sepsis trials measured 28-day mortality [6]. There is no validated short-window onset for healthy-adult immune use. ## How long should you take Thymosin alpha-1? Hepatitis trials typically dosed for 6 months [12][14]. The ETASS sepsis protocol ran 7 days [6]. Vaccine-adjuvant protocols ran 4 weeks [18]. No consensus protocol exists for non-trial outpatient use. ## What is the dosing protocol for Thymosin alpha-1? The standard regimen in hepatitis trials is 1.6 mg subcutaneously twice weekly for 6 months [20]. The ETASS sepsis trial used 1.6 mg subcutaneously twice daily for 5 days then once daily for 2 days [6]. ## How much Thymosin alpha-1 should I take? Trial doses range from 900 μg to 16 mg subcutaneously, with 1.6 mg twice weekly the most commonly studied unit dose [20]. Higher unit doses appear in early-phase oncology adjuvant studies. This is a research-context dose range, not a personal dosing recommendation. ## When is the best time to take Thymosin alpha-1? Most trials administered without regard to circadian timing; twice-weekly dosing was selected based on the peptide's pharmacokinetic half-life and the duration of downstream biological effect rather than on chronobiology [20]. The peptide has no known time-of-day-sensitive pharmacology in the published record. ## Thymosin alpha-1 vs TB-500 (Thymosin beta-4) Different proteins, different mechanisms. TB-500 is a synthetic fragment of Thymosin beta-4, an actin-binding peptide studied for tissue repair. Thymosin alpha-1 is a separate 28-amino-acid peptide studied for immune modulation. Both carry the 'thymosin' family name but their biology, indications, and trial records are entirely distinct. ## What are the side effects of Thymosin alpha-1? Across the published Zadaxin clinical program, the most commonly reported adverse events are injection-site discomfort and transient erythema. No dose-limiting toxicity has been documented up to 16 mg subcutaneous [20]. ## What is the half-life of Thymosin alpha-1? Plasma elimination half-life is approximately 2 hours after subcutaneous administration in healthy volunteers, though biological immunomodulatory effect persists 48–72 hours — the rationale for twice-weekly dosing in chronic indications [20]. ## How is Thymosin alpha-1 administered? Subcutaneous injection is the standard in every approved-indication trial [20]. Oral, intranasal, and IV routes appear only in early-phase exploratory work. Oral is not bioavailable — the peptide is hydrolyzed in the gastric environment. ## What is Zadaxin? Zadaxin is the SciClone Pharmaceuticals brand of thymalfasin (synthetic Thymosin alpha-1), approved in 30+ countries primarily for chronic hepatitis B and C and the basis for most published efficacy data [20]. ## Does Thymosin alpha-1 help with long COVID? Multiple 2020–2023 observational studies — notably Liu 2020 (Wuhan), Sun 2021 (multicenter retrospective), and Matteucci 2023 (PASC) — reported reduced mortality in severe COVID-19 and normalization of lymphocyte subsets in long-COVID patients [8][9][11]. Long-COVID data remains preliminary and lacks randomized controlled trials. ## Is Thymosin alpha-1 a steroid? No. It is a 28-amino-acid acetylated peptide hormone, structurally and pharmacologically unrelated to corticosteroids or anabolic steroids. The receptor mechanism (TLR-9 and TLR-2 on dendritic cells) is entirely distinct from steroid receptor pathways [4][5]. ## What is Thymosin alpha-1 used for in cancer? Studied as adjuvant to chemotherapy and immunotherapy in non-small-cell lung cancer, melanoma, and hepatocellular carcinoma. The mechanism is restoration of T-cell function suppressed by treatment or the malignancy itself [15][16][17]. ## Autoimmunity and Thymosin Alpha-1 Generally contraindicated by trial protocols. Because Thymosin alpha-1 amplifies T-cell activity, RCTs exclude patients with active autoimmune disease to avoid worsening immune-mediated tissue damage [20]. The exclusion is precautionary rather than driven by documented adverse events. ## WADA Status of Thymosin Alpha-1 Thymosin alpha-1 is not specifically named on the World Anti-Doping Agency Prohibited List as of 2025. Peptide hormones with immunomodulatory activity occupy a regulatory gray area; competing athletes should consult their sport-specific anti-doping authority before any use. ## What are Thymosin alpha-1 reviews from clinical trials? The Dominari 2020 comprehensive literature review in World Journal of Virology is the most-cited synthesis of the Thymosin alpha-1 corpus and covers hepatitis, sepsis, oncology, COVID-19, and immune reconstitution [2]. This site digests the same trial set as a chalked-out, indication-by-indication review. --- Chalked up, erased, and chalked back again — a classroom-style review of the published Thymosin alpha-1 literature, not a clinical recommendation.