Overview
Overview
Thymosin Alpha-1 (Tα1) is a 28–amino acid peptide originally isolated from the thymus gland, recognized for its broad immunomodulatory properties[1]. It has been investigated as an immune enhancer in chronic viral infections (hepatitis B/C, HIV/AIDS) and critical illness (sepsis, COVID-19)[2][3]. This educational protocol presents a once‑daily subcutaneous approach using a practical dilution for clear insulin‑syringe measurements. Reconstitute: Add 3.0 mL bacteriostatic water → ~1.67 mg/mL conc
- Category
- Immune
- Routes
- subcutaneous
Mechanism
Thymosin Alpha-1
Mechanism of action
Mechanism of action
TA1 is a signaling peptide. It does not kill viruses or cancer cells directly. Instead, it tunes the immune system so the body's existing defenses work more effectively. The pathway is well-mapped. TA1 binds two pattern-recognition receptors on antigen-presenting cells - Toll-like receptor 2 (TLR2) and Toll-like receptor 9 (TLR9) - which are the same receptors the immune system uses to detect bacterial and viral DNA. Activating them mimics the signal of a real pathogen and primes the rest of the immune response. Downstream of TLR2 and TLR9, three things happen: dendritic cells mature into effective antigen presenters, T cells differentiate into helper (CD4+) and cytotoxic (CD8+) populations, and the immune balance shifts toward Th1 , which is the side of immunity that handles intracellular infections (like hepatitis viruses) and tumor surveillance. Importantly, TA1 is described in the literature as a modulator rather than a pure stimulator. Across decades of clinical use it does not appear to produce the cytokine-storm-style overactivation seen with some other immune therapies, which is one reason its safety profile has held up across so many indications.
Key research findings
- 01
Identity / origin (animal-model foundation): Thymosin alpha-1 (Tα1; also called thymalfasin) is a 28-amino-acid peptide originally isolated from thymic tissue (thymosin fraction 5) and identified as the factor that restored immune function in thymectomized animals (reviewed by King & Tuthill, 2016).
- 02
Mechanism (in vitro / cell-based): Characterized as a pleiotropic immune-response modifier that signals through Toll-like receptors (e.g., TLR2/TLR9) on myeloid and plasmacytoid dendritic cells, influencing T-cell maturation and Th1-type cytokine production.
- 03
Animal models: Studied for effects on immune-cell subsets, dendritic-cell activation, responses to infection, and as a vaccine adjuvant; reported activity is framed as immunomodulatory rather than directly antimicrobial.
- 04
Human studies: Evaluated in clinical trials in immune-suppression and chronic viral-infection contexts and marketed as thymalfasin in several countries; the consistency and quality of controlled human efficacy data vary by context.
- 05
Human (observational, COVID-19): In a retrospective, non-randomized analysis of hospitalized severe COVID-19 patients (Liu et al., 2020), Tα1 administration was associated with changes in circulating CD4+/CD8+ T-cell counts and T-cell exhaustion markers (PD-1, Tim-3); interpretation is limited by the observational design.
Primary source: Chronic hepatitis B (strongest evidence): Pooled analysis of three RCTs in the Zadaxin label found sustained virologic response advantages over placebo with 1.6 mg twice weekly for 6 months, especially when measured 12 months after the end of therapy. This is the foundation of TA1's international approval. Chronic hepatitis C with interferon (moderate): Pooled analysis of 2 RCTs and 1 historical-controlled trial showed sustained ALT normalization in 22.4% of TA1 + interferon patients versus 9.3% with interferon alone. Newer DAA-based hepatitis C regimens have largely replaced interferon, so the practical relevance has narrowed. Cancer chemotherapy adjunct (moderate, fragmented): Smaller RCTs and observational studies report reduced infection rates and better immune-cell preservation during chemotherapy in hepatocellular carcinoma, NSCLC, and melanoma cohorts. Trials are inconsistent in design, and a single landmark RCT does not yet exist. Severe sepsis (mixed - read carefully): The 2025 BMJ TESTS trial (1,106 adults, 22 Chinese centers, double-blinded, placebo-controlled) was the largest TA1 sepsis study ever conducted. The primary endpoint - 28-day all-cause mortality - was not significantly different (hazard ratio 0.94, 95% CI 0.76-1.16, p=0.54). A 2025 Frontiers meta-analysis of 11 RCTs (n=1,927) reported a pooled odds ratio of 0.73 for 28-day mortality, but the authors flagged heterogeneity and credibility caveats. Many secondary write-ups oversimplify this. Post-COVID and long COVID (early): A 2023 meta-analysis of COVID-19 trials found mortality reduction in some patient subgroups but no consistent length-of-stay improvement. Dedicated long COVID trials are limited. General immune support / anti-aging (mechanism, not trials): Thymic involution with age is real, and TA1 is mechanistically a thymic peptide, but dedicated trials in healthy adults using TA1 for anti-aging endpoints are limited. Most community use rests on the chronic-disease trial base. Read the BMJ 2025 sepsis paper carefully
Pharmacokinetic profile
Single-dose plasma curve over 24h. Shaded band = commonly-cited therapeutic window. Illustrative only.
Researched Effects
Researched benefits
Areas of active research and investigation. Results may vary and are based on preclinical or early clinical data.
Supports enhanced T‑cell function and overall immune competence[1][2].
Demonstrates an excellent safety profile; doses up to 1.6 mg twice weekly for 6–12 months have been well-tolerated[4][7].
Even at experimental doses up to 16 mg SC over 12 months, no significant Tα1‑specific toxicity has been observed[7].
Protocol Reference
Protocol reference
Commonly cited research range: 300–500 mcg, daily.
Reference figures reported in the research literature — not a dosing recommendation. For interactive vial math and scheduling, see the Calculator and Schedule tabs.
Cited protocol & reconstitution guide
Source-backed reference fields by phase, including any volume fields authored in the cited guide.
Standard adult (≥40 kg)
1.6 mg per injection
Adult under 40 kg — 30 kg body weight
1.2 mg
Adult under 40 kg — 35 kg body weight
1.4 mg
| Phase | Reference amount | Units / volume |
|---|---|---|
| Standard adult (≥40 kg) | 1.6 mg per injection | 32 units (0.32 mL) |
| Adult under 40 kg — 30 kg body weight | 1.2 mg | 24 units (0.24 mL) |
| Adult under 40 kg — 35 kg body weight | 1.4 mg | 28 units (0.28 mL) |
Titration protocol
- Standard adultStart1.6 mg per injection
Subcutaneous. Twice weekly, injections spaced 3-4 days apart (e.g., Monday and Thursday). Rotate sites — abdomen, thigh, or upper arm. A twice-weekly dose missed by 1-2 days is typically resumed on schedule without doubling up.
- Adult under 40 kg — weight-adjustedBuild40 mcg/kg
Body-weight-adjusted rule for adults weighing under 40 kg (88 lb). Same twice-weekly subcutaneous schedule. At 5 mg/mL this works out to 0.008 mL (0.8 units) per kg of body weight.
- Adult under 40 kg — 30 kg body weightBuild1.2 mg
Twice weekly. Labeled an approximate dose in the source table.
- Adult under 40 kg — 35 kg body weightBuild1.4 mg
Twice weekly. Labeled an approximate dose in the source table.
- Adult ≥40 kg body weightBuild1.6 mg
Standard adult. Twice weekly.
- Cycle reference — 6 monthsBuild1.6 mg
Twice weekly across the full run.
- Cycle reference — 6-12 monthsBuild1.6 mg
Twice weekly across an extended-duration run.
- Cycle reference — 7 days continuousBuildNot stated as a mg value
Every 12 hours for 7 days. The source table gives the schedule only, with no mg value.
- Cycle reference — 4-12 weeksMaintenanceNot stated as a mg value
Community-derived pattern, not drawn from a controlled trial. A separately noted community pattern is 1 mg daily for 10-30 days, also not from controlled trials.
Storage & Handling
Storage requirements(typical for most peptides)
Can be stored for extended periods. Protect from moisture.
Store in refrigerator door. Never freeze after reconstitution.
Label vials with reconstitution date. Discard if cloudy.
Reconstitution steps
- 01🌡️01 Inspect the vial — Confirm the label, vial size, lot number, and that the powder pellet looks intact and dry.
- 02🧴02 Choose your concentration — Match a row from the reconstitution table above to the vial size you have and the syringe size you plan to use.
- 03💉03 Prep the surfaces — Wipe the rubber stopper of both the BAC water vial and the TA1 vial with a fresh alcohol swab. Let them dry.
- 04💧Draw 1 mL bacteriostatic water into a sterile syringe — this 5 mg vial yields 5 mg/mL.
- 05🔄05 Inject the BAC water — Insert the needle into the TA1 vial and push the BAC water down the inside wall of the vial, not directly onto the powder pellet.
- 06🏷️06 Mix gently — Swirl the vial slowly until the powder dissolves. Do not shake. The solution should be clear with no visible particles.
- 07❄️07 Label and refrigerate — Write the reconstitution date on the vial and store at 2-8°C (35.6-46.4°F). Use within 30 days.
- 08💉Important: This guide is for educational purposes only and is not medical advice. For research use only. Not for human consumption.
Additional storage notes
35.6-46.4°F (2-8°C) long-term — Short-term room temperature is acceptable per the Zadaxin label, but refrigeration extends shelf life. Use the manufacturer's expiration date as the long-term reference.
35.6-46.4°F (2-8°C) — Use within 30 days. Avoid freezing - freeze-thaw cycles degrade the peptide.
Protect from direct light — Store in original packaging or a closed compartment.
Insulated cooler with cold pack — Avoid letting the vial sit at room temperature for extended travel periods. Do not freeze.
Clinical Evidence
Clinical evidence
Investigated in immunology research and clinical studies for immune modulation in infection and vaccine-adjuvant contexts.
Chronic hepatitis B (strongest evidence): Pooled analysis of three RCTs in the Zadaxin label found sustained virologic response advantages over placebo with 1.6 mg twice weekly for 6 months, especially when measured 12 months after the end of therapy. This is the foundation of TA1's international approval. Chronic hepatitis C with interferon (moderate): Pooled analysis of 2 RCTs and 1 historical-controlled trial showed sustained ALT normalization in 22.4% of TA1 + interferon patients versus 9.3% with interferon alone. Newer DAA-based hepatitis C regimens have largely replaced interferon, so the practical relevance has narrowed. Cancer chemotherapy adjunct (moderate, fragmented): Smaller RCTs and observational studies report reduced infection rates and better immune-cell preservation during chemotherapy in hepatocellular carcinoma, NSCLC, and melanoma cohorts. Trials are inconsistent in design, and a single landmark RCT does not yet exist. Severe sepsis (mixed - read carefully): The 2025 BMJ TESTS trial (1,106 adults, 22 Chinese centers, double-blinded, placebo-controlled) was the largest TA1 sepsis study ever conducted. The primary endpoint - 28-day all-cause mortality - was not significantly different (hazard ratio 0.94, 95% CI 0.76-1.16, p=0.54). A 2025 Frontiers meta-analysis of 11 RCTs (n=1,927) reported a pooled odds ratio of 0.73 for 28-day mortality, but the authors flagged heterogeneity and credibility caveats. Many secondary write-ups oversimplify this. Post-COVID and long COVID (early): A 2023 meta-analysis of COVID-19 trials found mortality reduction in some patient subgroups but no consistent length-of-stay improvement. Dedicated long COVID trials are limited. General immune support / anti-aging (mechanism, not trials): Thymic involution with age is real, and TA1 is mechanistically a thymic peptide, but dedicated trials in healthy adults using TA1 for anti-aging endpoints are limited. Most community use rests on the chronic-disease trial base. Read the BMJ 2025 sepsis paper carefully
- 01Identity / origin (animal-model foundation): Thymosin alpha-1 (Tα1; also called thymalfasin) is a 28-amino-acid peptide originally isolated from thymic tissue (thymosin fraction 5) and identified as the factor that restored immune function in thymectomized animals (reviewed by King & Tuthill, 2016).
- 02Mechanism (in vitro / cell-based): Characterized as a pleiotropic immune-response modifier that signals through Toll-like receptors (e.g., TLR2/TLR9) on myeloid and plasmacytoid dendritic cells, influencing T-cell maturation and Th1-type cytokine production.
- 03Animal models: Studied for effects on immune-cell subsets, dendritic-cell activation, responses to infection, and as a vaccine adjuvant; reported activity is framed as immunomodulatory rather than directly antimicrobial.
- 04Human studies: Evaluated in clinical trials in immune-suppression and chronic viral-infection contexts and marketed as thymalfasin in several countries; the consistency and quality of controlled human efficacy data vary by context.
- 05Human (observational, COVID-19): In a retrospective, non-randomized analysis of hospitalized severe COVID-19 patients (Liu et al., 2020), Tα1 administration was associated with changes in circulating CD4+/CD8+ T-cell counts and T-cell exhaustion markers (PD-1, Tim-3); interpretation is limited by the observational design.
Evidence maturity varies by compound; much peptide research is preclinical (in vitro or animal-model). Where human data are limited, findings should be read as research observations, not clinical conclusions.
References
Literature references
Published research articles and sources related to Thymosin Alpha-1.
- 01Wu J, Pei F, Zhou L, et al. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ (2025)et al. (2025)
- 02Gu B, Zhou Y, Nie Y, et al. Efficacy of thymosin α1 for sepsis: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Cellular and Infection Microbiology (2025)et al. (2025)
- 03Dominari A, et al. Thymosin alpha 1: A comprehensive review of the literature. World Journal of Virology (2020)et al. (2020)
- 04Tao N, et al. Thymosin α1 and Its Role in Viral Infectious Diseases: The Mechanism and Clinical Application. Molecules (MDPI) (2023)et al. (2023)
- 05Dinetz E, Lee E. Comprehensive Review of the Safety and Efficacy of Thymosin Alpha 1 in Human Clinical Trials. Alternative Therapies in Health and Medicine (2024)et al. (2024)
- 06SciClone Pharmaceuticals Zadaxin (thymalfasin) Professional Monograph - dosing, indications, and pregnancy category. SciClone / peptidesociety.org archive (2018)et al. (2018)
- 07Rost K, Wierich W, Masayuki F, Tuthill C, Horwitz D, Herrmann W. Pharmacokinetics of thymosin alpha 1 after subcutaneous injection of three different formulations in healthy volunteers. International Journal of Clinical Pharmacology and Therapeutics (1999)et al. (1999)
- 08U.S. Food and Drug Administration Bulk Drug Substances Nominated for Use in Compounding Under Section 503A - 503A bulks list updates and Category 2 status. FDA (2024)et al. (2024)
- 09U.S. Food and Drug Administration PCAC Topic 1: thymosin alpha-1-related bulk drug substances - December 4, 2024 transcript. FDA Pharmacy Compounding Advisory Committee (2024)et al. (2024)
- 10Lexology / Hyman Phelps & McNamara FDA removes certain peptide bulk drug substances from Category 2 of interim 503A bulks list and sets dates for PCAC review. Lexology (2024)et al. (2024)
- 11Tian Y, et al. Thymosin alpha 1 alleviates inflammation and prevents infection in patients with severe acute pancreatitis through immune regulation: a systematic review and meta-analysis. Frontiers in Immunology (2025)et al. (2025)
- 12Zadaxin Drug Description / RxList compilation ZADAXIN thymosin alpha 1 (thymalfasin) - indications, dosing, and ALT flare label note. RxList / SciClone label compilation (2024)et al. (2024)
Observed Effects
Observed effects in cited research
Reported observations
- Injection-site reaction — Common — Mild redness, soreness, or swelling that resolves within hours. Rotate sites.
- Transient ALT flare (liver enzyme bump) — Common in HBV/HCV use — An ALT rise to >2x baseline can occur during therapy; per the Zadaxin label, treatment is generally continued unless signs of liver failure appear.
- Mild transient fatigue — Occasional — Usually first few injections as immune activation begins.
- Mild flu-like symptoms — Occasional — Reflects immune-system activation, not infection.
- Headache — Rare — Mild and transient; resolves with hydration.
- GI discomfort — Rare — Mild stomach upset reported in a minority of users.
- Polyarthralgia with hand edema — Very rare — Joint pain with hand swelling reported in isolated cases.
- Hypersensitivity / allergic reaction — Very rare — Limited to individuals with known peptide sensitivities.
Drug-interaction profile
- TA1 has a notably clean drug-interaction profile. The Zadaxin label reports no clinically significant interactions in published trials and notes compatibility with antiretroviral therapy, conventional hepatitis treatments, and most antimicrobial regimens. Never mix TA1 with other drugs in the same syringe - always inject separately.
- The one place to slow down is when TA1 is being considered alongside other immune-modulating drugs (immunosuppressants, biologics, or other immune enhancers). Additive effects are theoretically possible and warrant clinician oversight.
Quality-control risk
- TA1 is a research-use product in the US. Vial-to-vial purity and content can vary across suppliers. A current Certificate of Analysis (COA) and a clear product label are the minimum quality signals to look for.
Research Considerations
Research considerations
Research Use Only - not for human or veterinary therapeutic use. Has been studied in clinical research; on this platform it is handled strictly as a research material. Consult a licensed healthcare professional for any clinical decisions.
- TA1 has a benign safety record across more than three decades of international clinical use, but the same immune-activating mechanism that makes it useful also creates clear groups of people who should not use it without specialist oversight.
- Organ transplant recipients on immunosuppressive therapy. TA1 enhances cell-mediated immunity, which is the exact arm of immunity that anti-rejection drugs are trying to suppress. Combining the two could undermine transplant medication or trigger rejection.
- Adults with active autoimmune flares. Because TA1 amplifies T-cell activity, it could in theory worsen an active autoimmune attack. Some clinical reports suggest stable, well-controlled autoimmune patients tolerate TA1, but starting the peptide during a flare is not supported by the evidence base.
- Pregnant or breastfeeding women. Human safety data in pregnancy and lactation is limited. Animal studies have not shown fetal harm, but the Zadaxin label categorizes the drug as Category C and recommends use only when benefits clearly outweigh risks.
- Adults under 18. Pediatric safety has not been established in published trials.
- Anyone with known hypersensitivity to TA1, thymalfasin, or any vial component.
Factors noted in the research literature; not patient-specific medical advice.
Regulatory Status
Regulatory status
RUO
Comparisons
Comparisons
| Compound | Mechanism | Route | Status |
|---|---|---|---|
| Thymosin Alpha-1this | A 28-amino-acid thymic peptide that modulates immune function, studied for enhancement of T-cell maturation, dendritic-cell function, and Toll-like-receptor signaling. | subcutaneous | Investigational / RUO |
| Tirzepatide | Activates both GIP and GLP-1 receptors, providing synergistic effects on insulin secretion, glucose control, and appetite regulation. | subcutaneous | Investigational / RUO |
| Vesugen (Lys-Glu-Asp) | A synthetic tripeptide bioregulator (Lys-Glu-Asp) studied for gene-regulatory support of vascular endothelial tissue. | subcutaneous | Investigational / RUO |
| Vilon | A synthetic immunoregulatory dipeptide (Lys-Glu) studied for gene-regulatory and immunomodulatory activity, including effects on lymphocyte markers and chromatin structure. | subcutaneous | Investigational / RUO |
| 5-Amino-1MQ | Inhibits nicotinamide N-methyltransferase (NNMT), increasing NAD+ availability and enhancing mitochondrial metabolism. | oral, subcutaneous | Investigational / RUO |
| Adipotide | A peptidomimetic that targets prohibitin on the vasculature of white adipose tissue and delivers a pro-apoptotic sequence, studied for selective reduction of fat-tissue blood supply. | subcutaneous | Investigational / RUO |
| AICAR | A cell-permeable nucleoside phosphorylated intracellularly to ZMP, an AMP-mimetic that activates AMP-activated protein kinase (AMPK), shifting cells toward oxidative metabolism. | subcutaneous | Investigational / RUO |
Attributes shown for research comparison only; not a statement of efficacy or therapeutic equivalence.
FAQ
Frequently asked questions
TA1 (Zadaxin / thymalfasin) is approved internationally for chronic hepatitis B, chronic hepatitis C, and as an immune adjunct in cancer care, and has been studied in severe sepsis, post-viral recovery, and general immune support. It is not FDA-approved in the United States.
The Zadaxin-anchored protocol is 1.6 mg subcutaneously twice weekly, with injections spaced 3-4 days apart. Adults under 40 kg use 40 mcg/kg twice weekly. This is research-context dosing, not a personal-use recommendation.
A 10 mg vial reconstituted with 2 mL bacteriostatic water yields 5 mg/mL. At that concentration, a 1.6 mg dose equals 0.32 mL or 32 units on a U-100 insulin syringe. Other vial sizes (5 mg, 20 mg) are covered in the reconstitution guide .
No. TA1 is approved as Zadaxin in 35+ countries for chronic hepatitis B, chronic hepatitis C, and cancer adjunct use, but it has never received FDA approval. As of June 2026, its US 503A compounding status is unsettled - FDA placed it in Category 2 in September 2023, removed it from Category 2 in September 2024 after the nominators withdrew their nominations, and the PCAC reviewed it on December 4, 2024 with a final determination still pending.
No - the trial's primary endpoint was negative. The TESTS trial enrolled 1,106 adults with sepsis at 22 Chinese centers and reported a 28-day all-cause mortality hazard ratio of 0.94 (95% CI 0.76-1.16, p=0.54), which is not statistically significant. A 2025 Frontiers meta-analysis of 11 RCTs reported a pooled odds ratio of 0.73, but the authors flagged heterogeneity. Sepsis is an active research question, not a settled TA1 application.
Reported observed effects are mild and uncommon: injection-site reactions, transient fatigue, and mild flu-like symptoms. A transient ALT rise to more than twice baseline is documented during HBV therapy and is generally not a reason to stop treatment. Joint pain with hand swelling has been reported in isolated cases. See the observed effects table for full detail.
Organ transplant recipients on immunosuppressive therapy, adults with active autoimmune flares, pregnant or breastfeeding women (Zadaxin is Category C), adults under 18, and anyone with known hypersensitivity. Adults on stable immune-modulating drugs should only consider TA1 with clinician oversight because of theoretical additive effects.
No. TA1 (28 amino acids) and TB-500 / thymosin beta-4 fragment (43 amino acids) are different peptides from the same thymosin family. TA1 acts on TLR2/TLR9 and immune T-cell pathways; TB-500 binds actin and acts on cell migration and tissue repair. They are sometimes used in the same research context but they do different things. See the TB-500 protocol for the comparison.
Pharmacokinetics: peak blood level at 1-2 hours, half-life 2-3 hours, no accumulation between twice-weekly doses. Immune-cell-level changes typically build over 4-8 weeks of repeated dosing. Endpoints in HBV trials (viral load reduction, sustained virologic response) are usually measured at 6-12 months.
Common research stacks include TA1 with BPC-157 for combined immune and tissue-repair contexts. TA1 should never be mixed with another drug in the same syringe and should not be combined with systemic immunosuppressants without clinician oversight. Stacking is research context, not a treatment recommendation.
Zadaxin/thymalfasin label data is available from SciClone Pharmaceuticals' historical materials and from international regulatory filings. The professional monograph published through the peptide research community summarizes the labeled HBV/HCV indications, the under-40-kg dosing adjustment, and the Category C pregnancy classification.
Research-use notice
Research Use Only. This educational content and calculation support is intended for private research documentation. It does not provide medical advice, human-use directions, or claims of safety or effectiveness.