Human RCT
Mensch
Chien RN. et al. 2001
Improvement of seroconversion rates in chronic hepatitis B observed in some randomised trials
What does NOT follow: Data are heterogeneous; later meta-analyses showed varying effect sizes.
Peptide entry · Healing
Thymosin Alpha-1
TA1 · Tα1 · Zadaxin
Highest evidence
Human RCT
Studies recorded
4· 4 in humans
Legal status · US
UnapprovedScientific context only. Not medical advice, not a recommendation to use.
At a glance
Synthetic 28-amino-acid peptide identical to a naturally occurring thymus peptide. Approved as Zadaxin in more than 30 countries (not US/EU) for hepatitis B treatment and as an immunomodulator.
Researched for
Chronic hepatitis BSepsis (adjunctive)Immune modulation in immunosuppressionCOVID-19 (early-pandemic studies)
Official status
US: Unapproved
No FDA approval. In 2020 the FDA removed thymosin alpha-1 from the 503A compounding list — pharmacies may no longer routinely compound it.
Overview
What is it?
Synthetic 28-amino-acid peptide identical to a naturally occurring thymus peptide. Approved as Zadaxin in more than 30 countries (not US/EU) for hepatitis B treatment and as an immunomodulator.
How is it meant to work? →
Thymosin Alpha-1 is an N-terminally acetylated peptide originally isolated from the thymus. It modulates T-lymphocyte maturation and function and acts on dendritic cells via Toll-like receptors (TLR9 / TLR2). In preclinical and …
What do studies show? →
Human RCTImprovement of seroconversion rates in chronic hepatitis B observed in some randomised trials
What do users report? →
Thymosin alpha-1 is regarded as one of the most clinically studied peptides of all (over 30 trials, more than 11,000 participants) and is approved as thymalfasin (Zadaxin) in more than 35 countries.⚠ anecdotal – not scientific evidence
01
Mechanism of action
Thymosin Alpha-1 is an N-terminally acetylated peptide originally isolated from the thymus. It modulates T-lymphocyte maturation and function and acts on dendritic cells via Toll-like receptors (TLR9 / TLR2). In preclinical and some clinical studies, increased interferon-gamma responses and altered T-cell subpopulations have been reported.
02
Evidence at a glance
Reading note. The distribution shows on which evidence tier each observation sits. Strong colours mark stronger evidence — weaker tiers are deliberately visible, not hidden.
03
What the studies show
Human RCT
Mensch
Wu J. et al. 2013
Reduction in 28-day mortality in severe sepsis reported in a Chinese multicentre trial (ETASS)
What does NOT follow: Single trial, no consistent replication in Western sepsis cohorts.
Human trial
Mensch
Modulation of T-cell subpopulations in immunocompromised patients documented in preclinical and small clinical studies
What does NOT follow: Mechanistic findings; clinical endpoint relevance not consistently demonstrated.
04
Where studies disagree
Open question
Is thymosin alpha-1 efficacy in sepsis reproducible in Western cohorts?
POSITION A
ETASS (China) reported significant 28-day mortality reduction.
POSITION B
Later smaller trials outside China could not consistently replicate the effect.
CURRENT STATE · A larger multicentre replication trial (TESCEX) was planned in 2020; results pending.
05
Pharmacokinetics
Theoretical concentration curve at a half-life of 2 h. Pure pharmacokinetic model — not a dosing recommendation.
Open in PK tool →Start time: t₀ = 0h
Repeat interval: off (single dose)
06
Routes of administration in the literature
Which routes of administration the available studies describe — neutral reporting, not a usage guide.
Subcutaneous
In the hepatitis B trials administered twice weekly subcutaneously; once daily in ETASS.
06b
Amounts reported in sources
Which amounts were reported in which source — ordered by context (approval, trial, animal model, secondary literature, community).
06d
Safer use & risks
Risk notes for harm reduction — descriptive, not a usage or dosing guide.
This substance is approved (in at least one country) — use belongs in medical hands, within the approved indication and a physician-set dose.
Online numbers are not a benchmark
Amounts from TikTok, YouTube and forums are mostly imitation rather than data — and are often wrongly derived from animal studies (µg/kg). Not a reliable benchmark for humans.
Sterility & infection risk
Injection solutions prepared or stored non-sterile carry an infection and abscess risk. Contamination is common with grey-market product.
Unknown product quality
Research-/grey-market product is not quality-tested: identity, purity and actual content are often unknown, and counterfeits occur.
Mind interactions
Combinations with medications or pre-existing conditions can carry risks (see the Interactions section). Clarify with a doctor beforehand.
Warning signs — seek medical help
With persistent pain, redness/swelling at the injection site, fever, shortness of breath, racing heart, chest pain or allergic reactions, seek medical help immediately.
A doctor, not a forum
Concrete questions about use and amount belong in a conversation with a doctor — not in a comment thread.
07
Known adverse events from studies
Factual reporting of what studies observed. Not a safety statement for individual use.
Human RCT
Local injection-site reactions
From aggregated trials; in clinical datasets mostly mild and transient.
gelegentlich
07b
Interactions & combinations
Documented interactions and contraindications from studies, prescribing information and guidelines. Where no data exists, this is stated.
Reporting of risks, NOT a combination guide. The absence of an entry does not mean „safe to combine“ but „not sufficiently studied“.
No documented interactions recorded
We have not yet found robustly documented interactions for this peptide. This does NOT mean none exist — the data is limited.
09
Regulatory voices
Direct statements from official assessment documents — paraphrased with date and source link.
FDAU.S. Food and Drug Administration
2020-08-01FDA decision on the 503A bulk drug list, 2020.
The agency has determined that this substance does not meet the criteria for inclusion.
10
Anecdotal observations
Weakest evidence tier — not supported by studies
Reading note. This section gathers popular claims from communities and forums. They are explicitly marked as weakest-tier evidence. Unblinded self-reports are particularly prone to placebo, recall and confirmation biases.
Why no amounts or protocols are listed here. We deliberately show only WHAT communities report — not in what amount or how it is used. Anecdotal "doses" or "biohacker protocols" are neither verified nor standardised nor safe; publishing them would be a usage guide, which we do not provide on principle. Specific amounts belong in a conversation with a doctor, not in a forum.
Thymosin alpha-1 is regarded as one of the most clinically studied peptides of all (over 30 trials, more than 11,000 participants) and is approved as thymalfasin (Zadaxin) in more than 35 countries.
often cited as the 'most-tested peptide'
Not supported by studies: Despite this volume of data it is not FDA-approved. The most convincing data concern hepatitis B; for other indications the picture is mixed.
Thymosin alpha-1 is frequently promoted as a broad 'immune booster' (infection defense, long covid, sepsis).
common wellness framing
Not supported by studies: A large randomized sepsis trial (TESTS, 2025, over 1,000 patients) missed its primary endpoint — an important check on blanket 'immune booster' claims. Effect is indication-dependent and not generally proven.
11
Legal status by country
12
Reconstitution calculator
Pure mg/mL maths — works like a calculator. Not a usage recommendation.
Peptides ship as a dry powder. Once dissolved in a liquid (reconstitution), this calculator answers a single question: how much substance is in one millilitre of solution afterwards?
- 1Enter the vial's substance amount (printed on the label).
- 2Enter how much solvent you add.
- 3Result = concentration in mg per mL.
Printed on the label
/
Liquid you add
=
2.50
mg / mL
5 mg in 2 mL gives 2.50 mg/mL — each millilitre contains 2.50 mg of substance.
14
Study register
Human RCTRandomised controlled trial
Chien RN. et al. · 2001
Thymosin alpha-1 in the treatment of chronic hepatitis B
Human RCTRandomised controlled trialn = 361
Wu J. et al. · 2013
Effect of thymosin alpha-1 on the 28-day mortality of severe sepsis (ETASS)
Concrete results
28-day mortality (absolute)
26.0% vs 35.0%
vs Kontroll-Arm · 28 Tage
Human RCTRandomised controlled trialn = 1106
Wu J, et al. · 2025
The efficacy and safety of thymosin alpha1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial
SampleAdults (18–85 y) with sepsis; 22 centres in China.
Endpoint28-day all-cause mortality.
Concrete results
28-day mortality
23,4% vs 24,1%
vs Placebo (HR 0,99) · 28 Tage
Findings:No difference: 23.4% vs. 24.1% mortality (HR 0.99; P=0.93). No secondary or safety endpoint was significant. Subgroup signals (age, diabetes) are hypothesis-generating only.
Limitations:Primary endpoint missed; subgroup analyses exploratory; single-country (China).
Human RCTRandomised controlled trial
· 2005
A randomized, controlled, clinical study of thymosin alpha-1 versus interferon-alpha in patients with chronic hepatitis B lacking HBeAg in China
SamplePatients with chronic hepatitis B lacking HBeAg (China).
EndpointVirological/biochemical response.
Concrete results
Complete response
42,3% vs 3,3%
vs Kontrolle · Nachbeobachtung
Findings:Complete response 42.3% vs. 3.3% in controls; among responders, HBV DNA remained undetectable in 83.3% even 6 months after treatment.
Limitations:Limited sample size; hepatitis-B-specific; older study.
15
Sources & method
Reviewed by
editor-placeholder
Last reviewed
2026-05-22
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