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Thymosin Alpha-1

Last reviewed: April 18, 2026 by The Peptide Catalog Team

An immune-boosting peptide used in 30+ countries for viral defense. Thymosin Alpha-1 (Tα1) is a 28-amino acid immunomodulatory peptide naturally produced by the thymus gland. It enhances T-cell function, dendritic cell maturation, and cytokine balance. Approved in over 35 countries as Zadaxin for hepatitis B/C and as an immune adjuvant. Research explores applications in chronic infections, cancer immunotherapy, immune deficiency, and vaccine enhancement.

CategoryImmune & Thymic Peptides
Classimmune modulator
GoalImmune Support
Overview

Core Benefits

Key Advantages
Immune system tuning
Rebalances immune response without overstimulation.
T-cell modulation
Drives T-cell differentiation, maturation, and activity.
Dendritic cell activation
Improves antigen presentation for immune recognition.
Cytokine balance
Modulates Th1/Th2 responses without overdrive.
Approved abroad
Marketed as Zadaxin for hepatitis B/C in 35+ countries.
Faster recovery from illness
Cuts colds and infection frequency over 8–12 weeks.

These are educational summaries of commonly discussed effects in wellness/regenerative contexts, not guarantees.

Thymosin Alpha-1 Results Timeline

Progression
1
Week 1–2
Physical Changes
Improved energy as immune burden decreases
Performance & Recovery
Immune system activation begins
Other Benefits
Generally well-tolerated, minimal side effects
2
Week 3–6
Physical Changes
Faster recovery from minor illnesses
Performance & Recovery
Enhanced T-cell function, improved immune markers
Other Benefits
May notice improved resilience to minor infections
3
Month 2–3
Physical Changes
Reduced frequency of colds/infections
Performance & Recovery
Cumulative immune benefits
Other Benefits
Clinical protocols often run 8-12 weeks
4
Clinical Use
Physical Changes
Improved overall vitality, less sick days
Performance & Recovery
Hepatitis treatment, cancer adjuvant, vaccine enhancement
Other Benefits
Clinical effects measured via immune markers and symptom improvement

Timeline is illustrative and non-guaranteed. Outcomes vary and are commonly discussed alongside training, nutrition, sleep, and cycling practices.

Read the full Thymosin Alpha-1 results timeline →

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Evidence at a glance

Two parallel grades per outcome — clinical RCT depth and real-world community adoption. See the Research Overview below for citations and detail.

OutcomeClinical EvidenceCommunity Evidence
Sepsis mortality reductionWeakModerate
Chronic hepatitis BModerateModerate
Immune reconstitution in immunocompromisedWeakModerate
General immune support / wellnessPreliminaryModerate
How It WorksImmune Peptide — T-Cell Modulator

Target → Immune Activation → T-Cell Response → Outcomes

1
Target

TLR2/TLR9 + Dendritic Cells + T-Cell Precursors

Thymosin Alpha-1 activates toll-like receptors (TLR2, TLR9) on dendritic cells and promotes T-cell maturation from precursors. It's a thymic peptide — naturally produced by the thymus gland, which shrinks with age, contributing to immune decline.

2
Cellular Signal

TLR Activation → Dendritic Cell Maturation → T-Cell Response

TLR2/TLR9 stimulation on dendritic cells enhances antigen presentation — improving the immune system's ability to identify threats. Simultaneously promotes T-cell differentiation and balances Th1/Th2 immune responses.

3
Systemic Effect

Enhanced Adaptive Immunity + Immune Balance

Improved T-cell function and numbers. Better immune surveillance. Balanced inflammatory responses (doesn't just boost — it modulates). Approved in 35+ countries as Zadaxin for hepatitis B/C and as a cancer immunotherapy adjuvant.

4
What You Notice

Fewer Infections → Better Recovery → Immune Resilience

Reduced frequency and severity of infections over weeks to months. Better recovery from illness. Improved response to vaccines. Effects are measured by immune markers (T-cell counts, function) rather than felt as acute changes.

What Makes This Peptide Different

Thymosin Alpha-1 is approved in 35+ countries — one of the most clinically validated immune peptides. Unlike broad immune stimulants, it specifically enhances adaptive immunity (T-cells, dendritic cells) while maintaining immune balance. Particularly relevant for age-related immune decline (immunosenescence), chronic infections, and as a vaccine adjuvant.

Research overview

Outcome-by-outcome look at what the evidence actually supports for Thymosin Alpha-1, including human vs. animal study counts and our editorial take on each.

Sepsis mortality reduction

Clinical:WeakCommunity:Moderate

The story flipped between 2014 and 2025. Earlier meta-analyses (Wu 2014; Li 2015) pooled small Chinese RCTs and reported a roughly 30-40% relative risk reduction in 28-day mortality. The 1106-patient TESTS Phase 3 trial (Liu 2025) showed essentially no difference (hazard ratio 0.99), reframing the body of evidence as small-trial bias overstating an effect that doesn't survive a properly powered trial.

6 human studies · 4 animal studies

Key findings & citations
  • TESTS Phase 3 (n=1106): 28-day all-cause mortality 23.4% vs 24.1% placebo, HR 0.99 (95% CI 0.77-1.27).
  • Earlier ETASS (2013, n=361) suggested mortality benefit but was underpowered relative to TESTS.
  • Pre-TESTS meta-analyses (Wu 2014, n=1480) reported pooled RR 0.68 — now considered overstated.

Our take

Older meta-analyses said it worked. The Phase 3 said it didn't. Trust the Phase 3 — that's how science is supposed to update.

Chronic hepatitis B

Clinical:ModerateCommunity:Moderate

Multiple RCTs across the late 1990s and 2000s show thymosin α1 produces sustained virologic response in chronic HBV at rates comparable to or modestly better than older interferon regimens. It is approved for HBV in over 30 countries (not the US). Modern nucleoside analogs (entecavir, tenofovir) have largely displaced it as first-line.

8 human studies · 2 animal studies

Key findings & citations
  • Chien 1998 RCT: complete virological response 40.6% (52-week treatment) vs 9.4% control.
  • Phase 3 multicenter (Andreone 2001, n=97): sustained virologic response significantly higher in treated arms.
  • Better tolerated than interferon-α with comparable efficacy in head-to-head trials.

Our take

A real but second-line option for chronic HBV. Modern nucleoside analogs are simpler, cheaper, and more potent — Tα1 is mostly a relic in this indication.

General immune support / wellness

Clinical:PreliminaryCommunity:Moderate

The community use case — chronic Lyme, post-viral fatigue, general 'immune support' — has essentially no controlled human evidence. Mechanistic work (Romani 2007) shows Tα1 modulates dendritic cells and shifts Th1/Th2 balance, but translating that to subjective 'feeling better' lacks RCT support.

0 human studies · 6 animal studies

Key findings & citations
  • Mechanistic data: Tα1 modulates TLR9 signaling and dendritic-cell maturation.
  • No controlled trial in chronic Lyme, CFS, or 'immune optimization' indications.
  • Off-label use is widespread in functional medicine despite the evidence gap.

Our take

If sepsis didn't pan out in Phase 3, it's a stretch to expect 'general immune support' to. Buyer beware on this indication.

What Thymosin Alpha-1 doesn't do

Claims that current evidence does not support. Worth knowing before you set expectations.

Top Thymosin Alpha-1 Vendors

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Dosing ProtocolImmunity

Educational reference only. Individual responses vary. Consult healthcare provider before use.

Vial Size
10 mg
Reconstitution
2 ml BAC water
Dose
1.5 mg (30 units on 1ml syringe)
Timing
AM
Frequency
5 days on, 2 days off
Duration
8 weeks on, 8 weeks off
Protocol Notes
Approved as Zadaxin in 35+ countries for hepatitis B/C and as immune adjuvant. Enhances T-cell function, dendritic cell maturation, and cytokine balance. Well-tolerated with minimal side effects.

Why This Dosing Protocol

Why 5 days on, 2 days off? This schedule (1.5 mg daily) maintains consistent immune modulation while giving the body periodic recovery days. The clinical Zadaxin protocol uses 1.6 mg twice weekly — both approaches achieve sustained T-cell support.

Why 8-week cycles?Immune modulation requires sustained treatment to see measurable T-cell changes (8 weeks on, 8 weeks off). Short courses don't allow enough time for immune system adaptation.
Full Dosing GuideReconstitution CalculatorCycle Cost Calculator

Reconstitution Calculator

Dilution math and unit conversions. Prefilled using a common vial size for this peptide.

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Storage & Handling

Storage at a glance

Proper storage temperatures, shelf life, reconstitution best practices, and travel tips for lyophilized and reconstituted peptides.

Powder: Freezer
1+ year at -20°C
Reconstituted: Fridge
4 weeks max at 2-8°C
View Complete Storage Guide

Handling specifics

Educational overview on storage, labeling, and traceability considerations for lab environments. Consult primary literature and vendor documentation for specifics.

Powder storage (very stable)
  • Freezer (-20°C): 1+ year
  • Refrigerator (2-8°C): 1-3 months
  • Room temperature: 2-3 weeks (emergency only)
Reconstituted storage (fragile)
  • MUST refrigerate at 2-8°C
  • 4-week maximum shelf life
  • NEVER freeze after reconstitution
  • Use bacteriostatic water for multi-dose
Molecular Structure

Thymosin Alpha-1 sequence

Click any residue to see its properties.

HydrophobicPolarAcidic (−)Basic (+)Special

Sequence-derived properties

Length
28 residues
Molecular weight
3066.3 Da
backbone only
Avg hydrophobicity
-1.03
Kyte–Doolittle scale

Residue classes

Hydrophobic: 8 (29%)Polar: 7 (25%)Acidic (−): 9 (32%)Basic (+): 4 (14%)

Net charge distribution

Positive4 (14%)
Neutral15 (54%)
Negative9 (32%)

Amino acid frequency

E×6K×4A×3D×3S×3T×3V×3I×1L×1N×1

Modifications

  • N-terminal acetylation
  • 28-residue thymic peptide

Sequence and properties provided for educational reference. Not for clinical dosing decisions.

  • Type: Thymic Peptide
    (28 amino acids)
  • Brand Name: Zadaxin
    (Approved 35+ countries)
  • Target: T-cells / DCs
    (Immune modulation)
  • Half-Life: ~2 hours
    (2x weekly dosing)
Mechanism
Tα1 → T-cell maturation → Dendritic cell activation → Cytokine balance → Enhanced immunity
Thymosin Alpha-1 enhances immune function without dangerous overstimulation. Used clinically for hepatitis B/C, cancer immunotherapy support, and vaccine enhancement.
Key takeaway: With approval in 35+ countries and decades of clinical use, Thymosin Alpha-1 is one of the most well-validated immunomodulatory peptides available, offering safe immune support.

FAQ

What is Thymosin Alpha-1?

Thymosin Alpha-1 (Tα1) is a 28-amino acid peptide naturally produced by the thymus gland. It plays a crucial role in immune system regulation, particularly T-cell maturation and function. It's approved in over 35 countries as Zadaxin for treating hepatitis B, hepatitis C, and as an immune adjuvant for vaccines and cancer therapy.

How does Thymosin Alpha-1 work?

Tα1 modulates the immune system through multiple mechanisms: enhancing T-cell differentiation and function, promoting dendritic cell maturation, balancing Th1/Th2 cytokine responses, and increasing natural killer cell activity. It helps restore immune function in immunocompromised individuals without causing dangerous overstimulation.

What is Thymosin Alpha-1 used for?

Clinically, Tα1 is used for chronic hepatitis B/C, as an immune adjuvant in cancer therapy, for vaccine enhancement in immunocompromised patients, and for chronic infections. Research explores applications in sepsis, immunodeficiency, and as supportive therapy for various conditions requiring immune support.

What is the difference between Thymosin Alpha-1 and Thymosin Beta-4?

Despite similar names, these are different peptides with different functions. Thymosin Alpha-1 is an immunomodulator that enhances T-cell function. Thymosin Beta-4 (TB-4/TB-500) is involved in tissue repair, cell migration, and wound healing. They come from different parts of the thymus and have distinct mechanisms of action.

What are the side effects of Thymosin Alpha-1?

Tα1 is generally very well-tolerated with an excellent safety profile established over decades of clinical use. Minor side effects may include injection site reactions (redness, mild pain) and rarely mild flu-like symptoms. It does not cause the dangerous immune overstimulation seen with some other immunomodulators.

How long does reconstituted peptide last?

Once mixed with bacteriostatic water, peptides remain stable for up to 4 weeks when refrigerated at 2-8°C (36-46°F). Unopened powder can last 1+ year in the freezer. Get our complete Storage & Travel Guide.

Is this peptide legal to purchase?

Peptides sold "for research purposes only" are legal to purchase in the US, but are not FDA-approved for human use outside of specific medical applications. Always consult a healthcare provider before use.

New to peptides?

Take our Peptide Match tool to find the best peptide for your goals. You can also read our Complete Guide to Peptides to learn the basics.

Scientific Sources

The following peer-reviewed studies and official resources provide additional scientific context for this peptide:

Thymosin Alpha-1 Research Articles

dosing

Thymosin Alpha-1 Dosage: 1.5mg 5on/2off Protocol

The 5on/2off schedule prevents desensitization most miss. Covers 1.5mg daily protocol, LL-37 stacking, and 8-week cycling.

guides

Buy Thymosin Alpha-1: Compare 6 Vendors, From $42

Compare 6 Thymosin Alpha-1 vendors side by side: from $42 a vial, best value $5.80/mg. Codes save up to 50%. Vial sizes, COA status, real cost per week.

results

Thymosin Alpha-1 Results: Week-by-Week Timeline

Immune markers shift by week 2, but clinical outcomes need months. Full timeline with what to expect at each stage.

bloodwork

Thymosin Alpha-1 Bloodwork: 6 Labs to Track

Most skip the CD4/CD8 ratio — the one marker that proves thymosin alpha-1 is working. 6 essential labs with optimal ranges and testing schedule.

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