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Thymosin Alpha 128 residuesSDAAVDTSSEITTKDLKEKKEVVEEAENEach bubble = one amino acid. Size = residue mass. Color = chemical class.Also known as: Tα1, Ta1, Thymalfasin
Approved in 35 countries, studied in over 11,000 patients across 30+ clinical trials. Thymosin Alpha 1 (Tα1) is a 28-amino-acid peptide your thymus gland produces to prime T-cell and NK cell immunity. The Zadaxin label established 1.6 mg subcutaneously twice weekly as the clinical standard for hepatitis B, with HBeAg seroconversion rates reaching 30 to 40% versus 18% on placebo (PMC4688733). The FDA restricted US compounding access in 2023, though a 2024 review [1] covering the full trial evidence base challenged that decision directly. Community use now centers on immune support, long COVID recovery, and longevity protocols.
Thymosin Alpha 1 (Tα1, CAS 62304-98-7, molecular weight 3108 Da) is a 28-amino-acid acetylated peptide naturally produced by the thymus gland, approved in 35 countries under the brand name Zadaxin. The US restricted it from compounding pharmacies, creating a regulatory contradiction that defines its story. It binds Toll-like receptors TLR2 and TLR9 on dendritic cells, triggering downstream T-cell differentiation and NK cell activation through MyD88-dependent signaling. The clinical dose is 1.6 mg (1600 mcg) subcutaneously twice weekly, established by decades of Zadaxin prescribing data. The hepatitis B trials built the evidence base. A Phase III RCT (PMC4688733) showed HBeAg seroconversion at 30 to 40% versus 18% on placebo at 12 months. The Dinetz and Lee 2024 review [1] pulled together 30+ trials enrolling 11,000+ subjects and found consistent immune activation across indications. A separate 2024 meta-analysis [2] of 39 RCTs in acute COPD exacerbations (3,329 patients) confirmed improved FEV1, oxygenation, and reduced hospital stay. Community use has expanded well past hepatitis. Longevity practitioners, long COVID patients, and ME/CFS communities use the same 1600 mcg twice-weekly protocol for T-cell restoration. The practical limitation: Tα1 produces no subjective "feel." Bloodwork (CBC with differential, CD4/CD8 ratio) is the only way to confirm it's working. The TESTS Phase 3 sepsis trial (n=1,106)[3] missed its primary mortality endpoint (HR 0.99, p=0.93). That null result is worth knowing. It didn't undermine the hepatitis or immune-support evidence, but it set a boundary on what Tα1 can do in acute critical care.
Tα1 binds TLR2 and TLR9 on dendritic cells. That initial contact triggers MyD88-dependent signaling cascades that upregulate MHC class I and class II expression, improving how dendritic cells present antigens to T cells. Downstream effects split across two immune arms. On the adaptive side, Tα1 drives maturation of CD4+ helper T cells and CD8+ cytotoxic T cells from immature thymic precursors. Even in aged or immunocompromised individuals, it partially restores thymic output of mature T-cell subsets from CD4-/CD8- progenitors. NK cell cytotoxicity increases in parallel. The p38 MAPK and NF-κB pathways carry the cytokine signal. Tα1 pushes Th1-type cytokine production (IL-2, IL-12, IFN-γ) while dampening excessive Th2 responses. This is the immune-balancing property that separates Tα1 from pure immune stimulants. It upregulates regulatory T cells and modulates IDO (indoleamine 2,3-dioxygenase) expression, which helps prevent autoimmune overshoot. At the cellular level, Tα1 boosts oxidative killing in macrophages and neutrophils by stimulating NADPH oxidase activity. Pathogens get cleared faster. A single injection triggers signaling cascades on dendritic cells that activate T-cell differentiation responses lasting days to weeks, which explains why twice-weekly dosing works despite the 2-hour plasma half-life.
Well-established immunomodulator with 40+ years of clinical data. 1.6 mg SC 2x/week for hepatitis B is the gold standard (Zadaxin label; approved in 35+ countries). Cancer adjuvant data emerging (NSCLC Phase II, HCC retrospective 2024–2025). TESTS Phase 3 sepsis trial (n=1,106)[3] failed primary 28-day mortality endpoint. COVID-19 benefit limited to severe/elderly subgroups in meta-analyses; highly heterogeneous (I²=90%). Long COVID evidence is ex vivo only (PMC10030336, n=10).
PMID 38308608: Dinetz/Lee 2024 narrative review, 30+ trials, 11,000+ subjects; PMC4688733: Hepatitis B Phase III RCT (Zadaxin vs placebo); PMID 39648386: AECOPD meta-analysis, 39 RCTs, 3,329 patients
TESTS Phase 3 sepsis trial (PMID 39814420) null result: HR 0.99, p=0.93. COVID-19 meta-analyses: I²=90% heterogeneity: conflicting results driven by study design differences. Long COVID dosing extrapolated from hepatitis B trials. No human longevity RCT. PMID 38308608 is a narrative review from a pro-compounding advocacy position, not a formal systematic meta-analysis.
Trusted immune primer for post-viral recovery, longevity, and seasonal immune support. No subjective "feel" limits enthusiasm but does not undermine trust among informed users. Widely used in long COVID/ME-CFS communities with anecdotal reports of T-cell exhaustion reversal.
Community dose (1600 mcg 2x/week) matches clinical standard well. However, community cycling (8–12 weeks on / 4 weeks off) has no clinical trial basis: all trials ran continuous protocols for 6–52 weeks without break periods. Community primary use cases (longevity, long COVID) lack RCT evidence and rely on mechanistic extrapolation from hepatitis B and immunology data.
| Level | Dose / Injection | Frequency |
|---|---|---|
| Beginner | 1,600mcg | 2x/week |
| Moderate | 1,600mcg | 2x/week |
| Aggressive | 1,600mcg | 3x/week |
Reconstitution math for a 10 mg vial with 2.0 mL bacteriostatic water: concentration is 5000 mcg/mL. Total volume is 200 units on a 100-unit insulin syringe (you'll need to refill). Each unit delivers 50 mcg. So 1600 mcg is 32 units, 750 mcg is 15 units. For a 5 mg vial with 2.0 mL bacteriostatic water: concentration is 2500 mcg/mL. Each unit delivers 25 mcg. So 1600 mcg is 64 units, 750 mcg is 30 units. The 10 mg vial is your better value. At 1600 mcg twice weekly, one vial covers just over 3 injections. Budget about $29/month from research-chemical sources ($45 per 10 mg vial). Zinc matters. Tα1 requires zinc as a cofactor for T-cell and NK cell activation. Test RBC zinc before your protocol and supplement 15 to 30 mg zinc glycinate daily if deficient. Skipping this step is probably the most common beginner mistake. Don't judge efficacy by how you feel. Tα1 produces no acute subjective signal. Get bloodwork (CBC with differential, CD4+/CD8+ counts) at baseline and week 8. That's the confirmation window.
In hepatitis B clinical trials, Tα1 was administered at 1.6 mg subcutaneously twice weekly for 6-12 months. For general immune support, shorter courses of 8-12 weeks with a 4-week break are commonly used. Some protocols use continuous low-frequency dosing (1-2x/week) without cycling for chronic immune deficiency. No desensitization or tachyphylaxis has been documented in clinical use.
No receptor desensitization, tachyphylaxis, or antibody formation has been documented with TA1 in clinical trials, which ran continuous protocols for 6–52 weeks without break periods. Community cycling (8–12 weeks on / 4 weeks off) is cost-management-driven and community-derived, not pharmacologically required. Some ME-CFS patients report symptom return within 2–3 days of stopping, suggesting continuous dosing may be more appropriate for post-viral indications than cycling.
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Expected: ALT normalization, HBV viral load reduction, HBeAg seroconversion ~30–40% vs ~18% placebo at 12 months (PMC4688733)
Monitor: HBV viral load, HBeAg/anti-HBe, ALT/AST at 3-month intervals; CBC with differential at baseline and month 3
Add 2.0 mL bacteriostatic water to a 10 mg vial (yields 5000 mcg/mL) or a 5 mg vial (yields 2500 mcg/mL). Swirl gently. Do not shake. Allow bubbles to settle before drawing.
For 1600 mcg from a 10 mg vial: draw 32 units on a 100-unit insulin syringe. From a 5 mg vial: draw 64 units. For 750 mcg (beginner tier): draw 15 units from a 10 mg vial or 30 units from a 5 mg vial.
Subcutaneous injection in the abdomen (2 inches from navel), thigh, or upper arm. Use a 29 to 31 gauge insulin syringe, 0.5-inch needle. Rotate sites between injections.
Pinch a fold of skin, insert the needle at a 45-degree angle, push the plunger slowly, and hold for 5 seconds before withdrawing.
Inject twice weekly, spaced 3 to 4 days apart (Monday and Thursday is standard). Morning is preferred. No food or fasting requirements.
Refrigerate at 2 to 8 degrees Celsius. Use reconstituted research-grade peptide within 7 days; pharmaceutical-grade (Zadaxin) is stable longer.
No published SC vs. IM pharmacokinetic comparison: COVID-19 protocols (PMC7747025) used the same mcg doses IM as the SC standard
IM is not the community or clinical standard for self-administration. SC is preferred for accessibility, reproducibility, and patient tolerance. No head-to-head bioavailability comparison exists.
Complementary mechanisms: TA1 modulates adaptive immunity (T-cells, NK cells); BPC-157 addresses tissue repair, gut integrity, and local anti-inflammation. Combined for post-illness or post-surgery recovery.
BPC-157 250–500 mcg SC or IM daily + TA1 1600 mcg SC 2x/week; inject at separate sites
Different thymosin family with no immune pathway overlap: TB-500 = tissue repair via actin regulation; TA1 = adaptive immunity via T-cells. Stacked for post-illness recovery addressing both immune restoration and tissue healing. Naming confusion common: these are entirely distinct peptides.
TB-500 2–5 mg SC 2x/week + TA1 1600 mcg SC 2x/week; may share injection days or stagger
Acute infection stack: LL-37 provides direct antimicrobial/biofilm activity (innate immunity); TA1 rebuilds adaptive immune capacity (T-cells, NK cells). Used in long COVID protocols targeting both pathogen clearance and immune restoration. Monitor for additive immune activation: start LL-37 at low dose (50 mcg) when combining.
LL-37 50–100 mcg SC 2x/week + TA1 1600 mcg SC 2x/week; inject at separate sites on separate days
Longevity stack: Epithalon provides telomere-protective/epigenetic effects via pineal modulation; TA1 addresses age-related immune decline (immunosenescence). Common in anti-aging longevity protocols.
Epithalon 5–10 mg SC daily x10 days (annual course) timed before or concurrent with TA1 1600 mcg SC 2x/week
Direct pharmacological antagonism: TA1 activates T-cell signaling pathways that calcineurin inhibitors suppress. In transplant recipients, TA1 immune activation risks acute graft rejection. Absolute contraindication in that population.
Do not combineBroad suppression of the immune pathways TA1 activates: co-administration negates TA1 efficacy. Concurrent systemic steroid use also typically indicates an underlying condition (autoimmune flare) where TA1 is itself contraindicated.
Do not combineTheoretical immune amplification risk outside oncologist-supervised settings. Note: emerging 2024–2025 oncology data (PMID 36871535, ASCO JCO 2024 e16226) suggests potential synergy in cancer + reduced ICI-induced colitis: interaction is nuanced and context-dependent. Not for self-research concurrent use.
Pricing updated 2026-04-09
Organ transplant recipients on immunosuppressive therapy face the most serious risk. Tα1 activates the T-cell signaling pathways that calcineurin inhibitors (cyclosporine, tacrolimus) suppress. In that population, immune activation can trigger acute graft rejection. This is an absolute contraindication. Autoimmune flare acceleration is documented in community and clinic reports. Hashimoto's patients have reported thyroid antibody titer spikes after starting Tα1. MS patients have reported flare acceleration. Lupus patients carrying antinuclear antibodies should check inflammatory markers (CRP, ESR, ANA) before starting and should not use Tα1 during active flare. The confusing part: autoimmune patients actually have lower serum thymosin alpha-1 levels [4]. That makes supplementation seem logical, but Tα1's immune-priming action feeds the same T-cell pathways driving the flare. Published trial safety data across 11,000+ subjects shows a mild profile in non-autoimmune populations. Injection site redness and soreness occur in 5 to 18% of patients across trials. Transient fatigue occurs in 3 to 8%. Flu-like symptoms are rare and resolve within 24 to 48 hours. Myalgia reached 5% in one oncology loading-dose study. ME/CFS and post-viral patients should know about the first-dose immune reaction. A subset experiences 24 to 48 hours of symptom exacerbation after the initial injection. This is an immune activation event, not an allergic reaction. Starting at 750 to 1000 mcg for the first two injections before escalating to 1600 mcg reduces this risk. Interferon-alpha combinations (common in hepatitis protocols) can amplify flu-like side effects through additive immune stimulation. Stacking with other immune-stimulating peptides (LL-37, KPV) carries the same additive activation risk; space injections and start at low doses. Contraindications: pregnancy or breastfeeding (insufficient safety data), known hypersensitivity to Tα1 or formulation components, organ transplant recipients on immunosuppression, active autoimmune diseases in flare, and children under 18. When to seek medical attention: any autoimmune flare symptoms (joint pain, antibody titer rise, sustained fatigue spike), signs of graft rejection in transplant patients, high-grade fever, or allergic reaction (rash, difficulty breathing).
Verify Thymosin Alpha 1 dosing and safety with a second opinion
FDA compounding restriction (Category II, Sept 2023; removed Sept 2024; final 503A determination pending April 2026: PCAC Dec 2024 recommended against 503A approval) has shifted most US users to research-chemical grade sources. FDA cited manufacturing impurity concerns and theoretical immunogenicity at high doses. Research-chemical TA1 lacks pharmaceutical-grade purity verification.
| Test | When | Target |
|---|---|---|
| CBC with differential (lymphocyte count) | Baseline and week 8 | Lymphocyte count: 1.0–4.8 × 10⁹/L; improvement from depleted baseline expected |
| CD4+ and CD8+ T-cell counts, CD4/CD8 ratio | Baseline and week 8 (specialty lab add-on) | CD4/CD8 ratio: 1.0–3.5; CD4+ >500/µL; improvement from depleted baseline expected |
| NK cell activity | Baseline and week 8 (specialized immunology lab) | — |
| RBC zinc | Baseline (recommended pre-protocol) | 9.0–14.7 mg/L (RBC zinc reference range) |
| ALT / AST | Baseline and month 3 (hepatitis B patients) | ALT normalization target: <40 U/L |
| HBV viral load + HBeAg / anti-HBe | Baseline and every 3 months (hepatitis B patients only) | — |
| Inflammatory markers (CRP, ESR, antinuclear antibodies) | Baseline in patients with personal or family history of autoimmune conditions | — |
| T-cell exhaustion markers (PD-1, TIM-3 expression) | Baseline and week 8 (post-viral / long COVID use; requires specialized immunology lab) | — |
Primary practical marker for immune activation; lymphocyte increase is the accessible proxy for T-cell modulation
Direct measure of T-cell modulation: the primary mechanism of TA1 action and primary endpoint in hepatitis B trials
NK cell cytotoxicity is a key TA1 efficacy endpoint in clinical immunology trials
TA1 requires zinc as a cofactor for T-cell and NK cell activation; deficiency may blunt response
Primary clinical endpoint for hepatitis B response monitoring
Primary efficacy endpoints for the Zadaxin-approved hepatitis B indication
Rule out active autoimmune flare before starting; monitor for worsening in Hashimoto's, MS, or lupus patients during cycle
Gold standard for confirming T-cell exhaustion reversal in post-viral/PASC context (PMC10030336)
Treatment initiation. TA1 begins activating dendritic cells and priming T-cell responses. No noticeable clinical changes yet. Injection site irritation is possible but uncommon.
Early immune activation. T-cell subsets (CD4+, CD8+) begin to increase. NK cell activity starts to rise. Some users report improved energy and reduced frequency of minor infections.
Peak immune modulation. Measurable improvements in T-cell counts and function on bloodwork. Patients with hepatitis B may see ALT normalization and viral load reduction. Improved response to vaccinations if co-administered.
Sustained immune balancing. Continued improvements in immune markers. In hepatitis B trials, HBeAg seroconversion rates increased with extended treatment. Effects persist for weeks after discontinuation due to immune memory.
Week 1: Protocol initiation. Tα1 activates TLR2/TLR9 signaling on dendritic cells and the T-cell differentiation cascade begins. Nothing changes clinically. Injection site redness hits 5 to 18% of users across trials; transient fatigue runs 3 to 8%. ME/CFS patients may notice a minor energy fluctuation in the first 24 to 48 hours from first-dose immune activation. Weeks 2 to 4: Early immune activation. CD4+ and CD8+ T-cell subsets begin maturation. NK cell cytotoxic activity starts climbing. Some users report reduced severity of minor infections in this window. ME/CFS responders may notice energy gains. Most people report nothing subjective. Transient flu-like symptoms are rare and resolve within 24 to 48 hours; myalgia reached 5% in one oncology loading-dose study. Weeks 4 to 8: Peak immune modulation. Bloodwork starts showing measurable T-cell count and CD4/CD8 ratio improvements. Hepatitis B patients may see ALT normalization and viral load reduction. AECOPD data (39 RCTs, 3,329 patients)[2] confirmed improved FEV1 and oxygenation in this window. Vaccine co-administration shows improved antibody titers in elderly populations. Week 8 bloodwork is the confirmation point. Weeks 8 to 12+: Sustained immune balancing. T-cell subset improvements continue. Hepatitis B patients see HBeAg seroconversion rates increase with extended treatment, peaking at 12 months post-treatment. Effects persist for weeks after stopping because of immune memory; no tachyphylaxis has been documented. Community cycles typically end here. ME/CFS users may notice symptom return within days of stopping, pointing toward continuous dosing for that population rather than cycling.
TLR2/TLR9 (and TLR3/TLR4) signaling activation on dendritic cells. Downstream T-cell differentiation cascade begins. No measurable clinical changes yet.
No acute subjective signal. Mild injection site redness possible. ME-CFS subset may note minor 24–48h energy fluctuation (first-dose immune activation).
CD4+ and CD8+ T-cell subsets begin maturation and differentiation. NK cell cytotoxic activity increasing. No clinical-level immune response detectable without specialized labs.
Some users report reduced severity of minor infections. ME-CFS responders may note energy improvement in this window. Most report nothing subjective.
Measurable improvements in T-cell counts and CD4/CD8 ratio on bloodwork. Hepatitis B patients: ALT normalization and HBV viral load reduction. Vaccine co-administration: enhanced antibody titers in elderly. AECOPD: ↑FEV1, ↑pO2, ↓hospital stay (PMID 39648386, 39 RCTs).
Reduced infection frequency becoming noticeable. Bloodwork showing improved lymphocyte count. Post-viral patients reporting sustained energy improvements. Week 8 bloodwork is the key confirmation window.
Continued T-cell subset improvements. Hepatitis B: HBeAg seroconversion increases with extended treatment; peak response at 12 months post-treatment. Effects persist weeks after discontinuation due to immune memory: no tachyphylaxis documented.
Community cycles typically end here. Infection frequency measurably reduced over cycle. ME-CFS users may report symptom return within days of stopping, suggesting continuous dosing requirement.
Source: Approximately 2 hours following subcutaneous injection, with blood levels returning to baseline within 24 hours (PMID 10027483)
Loading the interactive decay curve.
Thymosin Alpha 1 is marketed as Zadaxin (SciClone Pharmaceuticals) and is approved as a prescription drug in over 35 countries for hepatitis B treatment and as an immune adjuvant. It is not FDA-approved in the United States. The FDA designated TA1 as Category II under 503A/503B compounding rules in September 2023, restricting US compounding pharmacy access. That designation was removed in September 2024, but the final 503A determination remains pending. The PCAC committee in December 2024 recommended against 503A approval. The final ruling is expected by April 2026. TA1 is currently available in the US as a research chemical. It is not scheduled as a controlled substance. Athletes should note that immunomodulatory peptides may fall under WADA prohibited substance categories depending on interpretation; check current WADA guidelines before use in tested competition. This content is for informational purposes only. Thymosin Alpha 1 is not approved by the FDA for any indication in the United States. Nothing on this page constitutes medical advice. Consult a licensed healthcare provider before starting any peptide protocol.
Peptide Schedule Research TeamReviewed Apr 202614 Citations
