Thymosin Alpha-1 (Ta1)
Thymosin alpha-1 is a 28-amino-acid peptide originally isolated from the thymus gland that plays a fundamental role in immune system regulation. It is approved in over 30 countries under the brand name Zadaxin for the treatment of hepatitis B and C, and as an immune adjuvant in cancer therapy. Thymosin alpha-1 enhances both innate and adaptive immunity by activating dendritic cells, natural killer cells, and T lymphocytes, making it one of the most clinically validated immune peptides available.
FormBlends Peptide Context
Reviewed May 14, 2026Use Thymosin Alpha 1 peptide guide as a decision-support page, not a shortcut. Its job is to frame benefits, dosing, evidence strength, sourcing, and safety boundaries in one place, especially where the search overlaps with peptide therapy. A useful reader should leave with better questions about clinician oversight, evidence quality, safety limits, cost, pharmacy path, and what changes for their own health history.
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Clinical decision snapshot
Thymosin Alpha-1 authority snapshot
Thymosin Alpha-1 is evaluated by mechanism, evidence quality, regulatory status, practical access, and safety questions a licensed clinician would need to review before use.
Evidence signal
Strong human evidence
Regulatory reality
Reinstated for compounding (Feb 2026)
Safety screen
Injection site discomfort, Mild erythema at injection site, Rare flu-like symptoms during initial dosing should be reviewed in context.
This page currently connects to 6 source-backed evidence items through visible references or structured citation data.
Decision path
What is the supervised-review path for Thymosin Alpha-1?
Thymosin Alpha-1 should be evaluated by evidence quality, safety status, source quality, dosing context, and whether the goal fits a legitimate clinical pathway. This page is a research and decision aid, not a self-prescribing guide.
- Peptide
- Thymosin Alpha-1
- Category
- Immune
- Evidence
- Strong human evidence
- FDA status
- Not FDA approved
Step 1
Check evidence level
Thymosin alpha-1 is one of the best-studied peptides in existence. It's FDA-approved in over 35 countries (though not the US) under the brand name Zadaxin. Large-scale clinical trials in hepatitis B (N=548) and hepatitis C have been published. It's also been studied in COVID-19 treatment. The evidence base is genuinely strong.
Review evidenceStep 2
Screen safety context
Injection site discomfort, Mild erythema at injection site, Rare flu-like symptoms during initial dosing should be discussed in light of history, dose, and source.
Check side effectsStep 3
Confirm access route
If FormBlends offers access, review the product page and provider pathway before deciding.
Review product accessLast updated: April 3, 2026
Typical Dosage
1.6 mg injected subcutaneously, 2-3 times per week. Some acute protocols use daily dosing for the first 2 weeks.
Administration
Subcutaneous injection
Typical Cost
$200-400/month
FDA Status
Not FDA Approved
Half-Life
Approximately 2 hours after subcutaneous injection
Onset of Action
Immune marker changes detectable within days. Clinical improvement in hepatitis trials took 6-12 months.
Bioavailability
Well-absorbed subcutaneously. Not orally bioavailable.
About Thymosin Alpha-1
Thymosin alpha-1 (Ta1) is a 28-amino-acid peptide naturally produced by the thymus gland. Molecular weight: 3,108 Da. CAS number: 62304-98-7. The synthetic version, sold internationally as Zadaxin (thymalfasin), is manufactured by SciClone Pharmaceuticals and is approved in over 35 countries for treating hepatitis B and boosting immune function.
The thymus is the organ responsible for maturing T cells, the immune system's primary adaptive defense. The thymus reaches peak size during adolescence and then gradually shrinks (a process called involution). By age 50-60, most of the thymus has been replaced by fatty tissue. Thymosin alpha-1 is one of the key signaling molecules the thymus produces, and its levels decline along with thymic function.
The evidence base for thymosin alpha-1 is stronger than most peptides. A Phase 3 clinical trial published in Hepatology in 1998 (PMID: 9755232) enrolled 548 patients with chronic hepatitis B and showed that combining thymosin alpha-1 with interferon alpha produced higher viral clearance rates than interferon alone. A 2013 meta-analysis in the World Journal of Hepatology (PMID: 23646230) pooled data from 8 clinical trials and confirmed the benefit.
During the COVID-19 pandemic, thymosin alpha-1 gained additional attention. A retrospective study published in Expert Opinion on Biological Therapy in 2021 (PMID: 33550879) found that critically ill COVID-19 patients treated with thymosin alpha-1 had a 28-day mortality rate of 11% compared to 30% in the control group. While retrospective studies have limitations, the magnitude of the difference was noteworthy.
The standard dosing protocol is 1.6 mg injected subcutaneously twice per week. This is the dose used in most clinical trials and in the Zadaxin prescribing information. Some practitioners use higher doses (3.2 mg twice weekly) for acute infections or immune challenges, then step down to the standard maintenance dose.
Thymosin alpha-1 works through multiple immune pathways. It activates Toll-like receptors (TLR2 and TLR9) on dendritic cells, which are the immune system's sentinel cells. It promotes the maturation of T cells from precursor cells. And it enhances the function of natural killer (NK) cells, the immune system's first line of defense against infected or abnormal cells.
The peptide was restricted from US compounding during the 2023 FDA actions but was one of the 14 compounds reinstated in February 2026. Its long track record of safety across international clinical trials and its approved status in dozens of countries made it one of the more controversial compounds on the restricted list.
Store lyophilized thymosin alpha-1 at -20C before reconstitution. Reconstitute with sterile water or bacteriostatic water. Once reconstituted, store at 2-8C and use within 14 days.
How Thymosin Alpha-1 Works
Thymosin alpha-1 activates toll-like receptors (TLR2 and TLR9) on dendritic cells, which are the immune system's primary antigen-presenting cells. This activation triggers a cascade that increases T cell maturation, enhances natural killer cell cytotoxicity, and promotes the production of cytokines like interferon-alpha and interleukin-2. It also helps restore immune balance in immunocompromised patients by shifting the immune response from Th2 (antibody-dominant) toward Th1 (cell-mediated) immunity.
Receptor targets:
Benefits
- Enhances T cell function and maturation
- Activates natural killer cells and dendritic cells
- Approved in 30+ countries for chronic hepatitis B and C
- Used as immune adjuvant alongside cancer therapies
- Restores immune function in immunocompromised patients
- Improves vaccine response rates in elderly and immunodeficient populations
- Well-established safety profile from decades of clinical use
What Does the Research Say?
Thymosin alpha-1 is one of the best-studied peptides in existence. It's FDA-approved in over 35 countries (though not the US) under the brand name Zadaxin. Large-scale clinical trials in hepatitis B (N=548) and hepatitis C have been published. It's also been studied in COVID-19 treatment. The evidence base is genuinely strong.
A phase III study of thymalfasin and interferon alpha-2a for chronic hepatitis B
Hepatology, 1998 · DOI · PubMed
Large Phase 3 trial (N=548) showed thymosin alpha-1 combined with interferon achieved higher viral clearance rates than interferon alone in chronic hepatitis B
PubMed evidence trail
Research sources used to frame this page
For Thymosin Alpha-1, FormBlends checks the page topic against primary trials, systematic reviews, guidelines, and current PubMed-indexed literature where available. These citations are context, not a claim that every study applies to every patient.
Emerging pharmacotherapies for obesity: A systematic review
Broad context for new and established obesity-drug categories.
PubMed
Glucagon-like receptor agonists and next-generation incretin-based medications
Current review for incretin-based obesity medications and cardiometabolic effects.
PubMed
Potential Side Effects
- Injection site discomfort
- Mild erythema at injection site
- Rare flu-like symptoms during initial dosing
- Fatigue
Drug Interactions
| Compound | Interaction | Severity |
|---|---|---|
| Immunosuppressants (tacrolimus, cyclosporine) | Thymosin alpha-1 stimulates immune function, which directly counteracts the purpose of immunosuppressive drugs. Contraindicated in transplant patients. | major |
| Interferon alpha | These are commonly used together. The Phase 3 hepatitis B trial specifically combined thymosin alpha-1 with interferon and showed improved outcomes. | minor |
Who Is Thymosin Alpha-1 For?
Women
No sex-specific contraindications. Used similarly in men and women for immune support. Some practitioners incorporate it into perimenopausal immune support protocols.
Adults Over 50
Thymic output declines noticeableally with age (the thymus largely involutes by age 50-60). Thymosin alpha-1 may help compensate for this age-related immune decline. The hepatitis trials included patients across age ranges.
Athletes
Not currently on WADA's prohibited list. Used by some athletes for immune support during heavy training periods when infection risk is elevated.
Regulatory Status
FDA Approved
No
Approved for:
Compounding Legal
Yes
2026 HHS Status
Reinstated for compounding (Feb 2026)
Not FDA-approved in the US but approved in 35+ countries as Zadaxin for hepatitis B and as an immune adjuvant. Was reinstated for US compounding in February 2026.
Last verified: 2026-04-06
Stacking Options
Thymosin Alpha-1 is commonly stacked with the following peptides for enhanced results:
Conditions Addressed
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