Thymosin Alpha-1 (Tα1), also known by the brand name Zadaxin and generically as thymalfasin, is a 28-amino-acid thymic peptide with one of the most robust clinical track records of any research peptide. Approved in 35+ countries for chronic hepatitis B and C treatment, and extensively studied in cancer immunotherapy and sepsis research, TA1 is now among the most sought-after immunomodulatory compounds in research settings worldwide.
This guide covers everything researchers need to know about Thymosin Alpha-1 dosing: reconstitution protocols for both 5 mg and 10 mg vials, research dosing ranges drawn from the clinical literature, subcutaneous injection technique, storage requirements, and the compound's core mechanisms of immune action.
References
- •PMID: 42212632
- •PMID: 41883056
- •PMID: 40994373
⚠️ Research Use Only (RUO) Disclaimer: Thymosin Alpha-1 is classified as a research compound in the United States. It is not FDA-approved for any indication. All dosing information in this guide is drawn from published scientific literature and is provided for educational and research reference purposes only. This content does not constitute medical advice and should not be used to guide human self-administration.
What Is Thymosin Alpha-1?
Thymosin Alpha-1 was first isolated from bovine thymus tissue by immunologist Allan Goldstein and colleagues in 1977. It is the active fraction of a larger precursor protein, prothymosin alpha, and is now produced synthetically as a 28-amino-acid N-terminally acetylated peptide with a molecular weight of approximately 3,108 Da.
The compound acts as a master regulator of adaptive immunity — one of the few peptides that can both stimulate a depressed immune response and help resolve a hyperactive one, depending on the immunological context. This bidirectional modulation distinguishes TA1 from simple immune stimulants and explains its clinical utility across a range of conditions involving immune dysregulation.
For a complete overview of Thymosin Alpha-1's mechanism of action and regulatory history, see the site's Thymalfasin Research Profile.
Research Forms and Typical Purity
In research settings, Thymosin Alpha-1 is almost universally available as a lyophilized (freeze-dried) powder in sealed vials. Common vial sizes are 5 mg and 10 mg, though some suppliers also offer 2 mg vials for shorter research cycles.
Peptide purity is a critical quality indicator for TA1. The pharmaceutical Zadaxin product carries a defined purity specification, and reputable research suppliers typically report purity ≥98% by HPLC. Certificate of Analysis (CoA) documentation should confirm both purity and peptide identity via mass spectrometry. Given that thymosin alpha-1's immunological activity depends on intact N-terminal acetylation, verification of sequence fidelity matters more here than with many other research peptides.
Reconstitution Protocol
Thymosin Alpha-1 must be reconstituted with a sterile aqueous solution before use. Two options are appropriate for research:
- Bacteriostatic water (BAC water): Contains 0.9% benzyl alcohol as a preservative, extending the post-reconstitution shelf life of the solution to approximately 28 days when refrigerated. Preferred for multi-dose vials.
- Sterile water for injection (SWFI): Preservative-free. Used in the pharmaceutical Zadaxin formulation (reconstituted immediately prior to single use). Not recommended for multi-dose research vials.
Reconstitution Table — Research Vial Sizes
| Vial Size | Reconstitution Volume | Final Concentration | Dose Volume at 1.6 mg | Dose Volume at 500 mcg |
|---|---|---|---|---|
| 5 mg | 2.0 mL BAC water | 2.5 mg/mL (2,500 mcg/mL) | 0.64 mL (64 units on U-100) | 0.20 mL (20 units on U-100) |
| 10 mg | 3.0 mL BAC water | 3.33 mg/mL (3,330 mcg/mL) | 0.48 mL (48 units on U-100) | 0.15 mL (15 units on U-100) |
| Zadaxin (pharma) | 1.0 mL SWFI (provided) | 1.6 mg/mL | 1.0 mL (full vial) | N/A — single-dose vial |
Reconstitution Technique
- Allow the vial to reach room temperature (approximately 20 minutes from refrigerator).
- Wipe the rubber septum of both the TA1 vial and the BAC water vial with a fresh alcohol swab. Allow to air dry.
- Draw the required volume of BAC water into a sterile syringe.
- Insert the needle into the TA1 vial and inject the BAC water slowly down the vial wall — do not inject directly onto the lyophilized powder cake, as forceful injection can degrade the peptide.
- Gently swirl — do not shake or vortex — until the powder dissolves completely. The solution should be clear and colorless.
- Label the vial with the reconstitution date and the resulting concentration.
For guidance on dilution calculations and dose draw-up volumes for other peptide vial sizes, see the Reconstitution Calculator.
Research Dosing Protocols
The dosing parameters for Thymosin Alpha-1 are better characterized than those of most research peptides, because TA1 has undergone extensive formal clinical development. The following ranges are drawn from published Phase II/III clinical trial data and reviewed scientific literature.
Clinically-Established Protocol (Zadaxin Hepatitis B)
The most rigorously studied dosing regimen is the Zadaxin protocol for chronic hepatitis B, established across multiple Phase III randomized controlled trials:
- Dose: 1.6 mg per injection
- Frequency: Twice weekly (e.g., Monday and Thursday)
- Duration: 6 months (approximately 52 injections); up to 12 months for partial responders
- Route: Subcutaneous injection
This regimen was selected following Phase I/II dose-finding studies that evaluated a range from 0.5 mg to 6.4 mg. The 1.6 mg dose produced maximal clinical benefit in the hepatitis B population without increasing adverse events, and has been reproduced as the standard dose across multiple countries and thousands of study subjects.
Lower-Dose Research Protocols
Research literature also documents protocols using lower, more frequent dosing, particularly in cancer adjuvant and immune reconstitution studies:
- Dose: 0.5–1.0 mg per injection
- Frequency: Daily, or 3×/week
- Duration: 8–16 weeks
A graduated approach used in some research protocols begins at 300 mcg/day for 1–2 weeks to establish tolerability, before escalating to 500 mcg/day as a maintenance dose. At 500 mcg daily, weekly exposure (~3.5 mg/week) is consistent with the aggregate dose delivered by the 1.6 mg twice-weekly Zadaxin schedule.
Dosing Context from Recent Research
A 2024 FDA Pharmacy Compounding Advisory Committee (PCAC) review noted that thymosin alpha-1 doses up to 16 mg subcutaneously for 12 months showed no significant toxicity across trials — suggesting the compound has a wide therapeutic window relative to its typical research doses. In sepsis trials, including the large TESTS trial (1,106 participants at 22 Chinese centers), TA1 was well-tolerated at standard doses throughout the study period.
Administration Route and Injection Technique
Thymosin Alpha-1 is administered exclusively by subcutaneous (SubQ) injection. Intramuscular and intravenous administration are not used in the research literature; the pharmaceutical Zadaxin product explicitly contraindicates intravenous delivery. Unlike some GHS peptides, TA1's mechanism of action is not affected by food intake and does not require injection in a fasted state.
Injection Procedure
- Syringe: U-100 insulin syringe with a 29G or 31G needle, 0.5 mL or 1 mL capacity
- Injection sites: Abdomen (2 inches from the navel), outer thigh, or upper arm — rotate sites to prevent local tissue changes
- Technique: Pinch a fold of skin, insert the needle at a 45° angle, inject slowly, withdraw needle, and apply gentle pressure (do not rub the site)
- Injection timing: No timing constraint relative to meals; TA1 may be administered at any time of day
Immunomodulatory Mechanisms: What the Research Shows
Toll-Like Receptor Signaling
T-Cell Maturation and Activation
One of TA1's most well-characterized effects is promoting the maturation of precursor T-cells into functional effector T-cells. Published data demonstrate that TA1 increases both CD4+ helper T-cell and CD8+ cytotoxic T-lymphocyte (CTL) populations, shifts CD4+ differentiation toward Th1-type responses (favoring cellular immunity over antibody-mediated immunity), and enhances antigen-specific CTL activity. A landmark study (PMID: 12479932) showed that TA1 significantly increases intrahepatic NKT cells and CTLs in chronic hepatitis B patients — a mechanistic basis for its anti-viral efficacy.
NK Cell Enhancement
Natural killer (NK) cells provide a first-line defense against virus-infected and malignant cells without requiring prior antigen sensitization. Thymosin alpha-1 enhances NK cell cytotoxicity and proliferation. Mechanistically, this effect appears to be load-bearing for TA1's anti-tumor activity: preclinical models showed that depletion of NK cells abolished thymosin alpha-1's tumor-suppressive effects, confirming NK cell enhancement as a core mechanism rather than an epiphenomenon.
Bidirectional Regulation
A distinctive feature of TA1 is its context-dependent immunomodulatory action. In immunosuppressed states — chronic viral infection, post-chemotherapy lymphopenia, advanced malignancy — TA1 acts as an immune stimulant, upregulating effector T and NK cell responses. In hyperinflammatory states such as sepsis, it promotes regulatory T-cell (Treg) differentiation and IDO expression in dendritic cells, helping suppress pathological cytokine cascades. This bidirectionality is unusual among immune-modulating compounds and may explain its utility across seemingly opposite clinical scenarios.
Chronic Viral Infection Research Context
The most mature clinical evidence base for Thymosin Alpha-1 involves chronic viral hepatitis:
- Hepatitis B: Multiple Phase III RCTs demonstrated that 1.6 mg SubQ twice weekly for 6 months produced statistically significant improvements in HBe antigen seroconversion and HBsAg loss compared to placebo. The combination of TA1 with interferon-alpha was studied in multiple trials and showed additive benefit in HCV patients in some analyses.
- COVID-19 (2020–2023): A 2023 meta-analysis of COVID-19 studies reported a pooled relative risk of 0.59 (95% CI 0.37–0.93) for mortality in severe COVID-19 patients treated with TA1 — a 41% relative risk reduction. Results were not consistent across all individual studies, and heterogeneity was noted.
- Sepsis: The TESTS trial (N=1,106) found no statistically significant mortality benefit at 28 days (HR 0.94, p=0.54), though a subsequent 2025 Frontiers meta-analysis of 11 RCTs reported a pooled odds ratio of 0.73 for mortality. Results remain debated.
Storage and Stability
| State | Storage Condition | Stability |
|---|---|---|
| Lyophilized (sealed vial) | 2–8 °C (refrigerated) or −20 °C (frozen) | 12–24 months (per manufacturer) |
| Reconstituted in BAC water | 2–8 °C, protected from light | Up to 28 days |
| Reconstituted in sterile water | 2–8 °C, use within 24 hours | 24 hours (no preservative) |
Avoid repeated freeze-thaw cycles of reconstituted solution. Discard any vial showing particulate matter, discoloration, or cloudiness. Do not use reconstituted TA1 solution past its labeled use-by date.
503A Regulatory Status and RUO Framework (2026)
Thymosin Alpha-1's regulatory trajectory in the United States has been particularly dynamic. The FDA placed TA1 on the Category 2 503A list in late 2023 (proposing exclusion from compounding). After legal challenges by compounders and advocacy from clinicians, the FDA agreed to a formal Pharmacy Compounding Advisory Committee (PCAC) review, which took place on December 4, 2024. The PCAC review evaluated whether TA1 met the criteria for inclusion on the 503A Bulks List.
As of 2026, following a February 2026 FDA reclassification of several peptide categories, Thymosin Alpha-1 is classified as a Category 2 bulk substance under the 503A framework — available by prescription through licensed 503A compounding pharmacies under restricted conditions, but not FDA-approved as a conventional pharmaceutical in the United States. Researchers and clinicians operating in the US should verify current compounding status with a regulatory specialist, as this classification continues to evolve.
Outside the United States, TA1 is an approved pharmaceutical (brand: Zadaxin) in more than 35 countries, including Italy, China, and India, where it carries formal marketing authorization for hepatitis B treatment and immune adjuvant use.
Key Research Takeaways
- Thymosin Alpha-1 is one of the most clinically validated research peptides in the immune-modulating class, with formal Phase III trial data from hepatitis B studies using 1.6 mg SC twice weekly.
- Reconstitution in bacteriostatic water (2 mL for a 5 mg vial; 3 mL for a 10 mg vial) yields clean, calculable concentrations for multi-dose research vials.
- The peptide's immune effects are mediated through TLR2/4/7/9 signaling, T-cell maturation, NK cell enhancement, and bidirectional cytokine regulation — mechanisms that are active regardless of whether the host is immunosuppressed or hyperactivated.
- Storage of reconstituted TA1 is straightforward: refrigerate at 2–8 °C, use within 28 days of reconstitution if BAC water was used.
- US regulatory status remains Category 2 under 503A as of 2026; status should be verified before any clinical or compounding application.
References
- Zhao W, et al. "Thymosin-alpha1 increases intrahepatic NKT cells and CTLs in patients with chronic hepatitis B." J Viral Hepat. 2003;10(2):89-97. PMID: 12479932.
- SciSparc / SciGen. ZADAXIN (thymalfasin) prescribing information. Zadaxin product monograph, 2023.
- Li Y, et al. "Thymosin alpha-1 treatment for severe COVID-19: a meta-analysis." J Infect. 2023.
- Liu Y, et al. "Thymosin Alpha-1 in the Treatment of Sepsis: The TESTS Trial." JAMA. 2022.
- FDA PCAC Briefing Document. "Pharmacy Compounding Advisory Committee Meeting: Thymosin Alpha-1." December 4, 2024.