Compound record · Immune
Thymosin alpha-1
Also Thymalfasin · Zadaxin · Tα1 · Ta1 · Thymosin α1 · TA-1
Immunomodulatory thymic peptide (28 amino acids)
Immune-modulating peptide medicine abroad; weak evidence for wellness use
Record reviewed 1 September 2026 · 5 references
In the AERVYN range
1 pen carries Thymosin alpha-1
- Class
- Immunomodulatory thymic peptide (28 amino acids)
- Route
- Subcutaneous injection, typically twice weekly
- Trial participants
- > 1,400 in the two sepsis trials alone; largest trial negative
- Authorised
- > 30 countries (e.g. China, Italy) for hepatitis B; not FDA, MHRA or EMA approved
- WADA
- Not specifically listed
01 Overview
What Thymosin alpha-1 is
Summary
Thymosin alpha-1 is a 28-amino-acid peptide originally isolated from thymic tissue and produced synthetically as thymalfasin (Zadaxin). It is authorised in more than 30 countries — most notably China and Italy — for chronic hepatitis B and, in some markets, as an adjuvant to chemotherapy or vaccination. It is not approved by the FDA, the MHRA or the EMA. Randomised trials in hepatitis B show modest virological benefit; a 361-patient sepsis trial suggested lower mortality, but a 1,106-patient phase 3 published in 2025 found no survival benefit. There are no trials in healthy adults seeking 'immune support'.
Mechanism
Acts on Toll-like receptors on dendritic cells and other innate immune cells, promoting T-cell maturation, natural-killer cell activity and a shift towards Th1 cytokine responses, while also having regulatory effects that may dampen excessive inflammation. It has a short plasma half-life (about two hours) but effects on immune cells persist for days.
02 Evidence by goal
What has been shown, for which goal
Grades follow one scale across the site. Moderate overall means: at least one well-conducted randomised trial or consistent controlled human studies.
General wellbeing
LimitedImmune-enhancing effects are documented in disease populations — for example higher monocyte HLA-DR expression in sepsis and improved vaccine responses in older or dialysis patients — but no trial has tested it for energy, resilience or fewer infections in healthy adults. The largest trial (sepsis, n = 1,106) showed no mortality benefit.
Longevity
InsufficientAge-related thymic decline is the rationale for 'immune ageing' marketing, but there are no human data on ageing outcomes; the Russian 'thymalin' longevity studies used a different thymic extract in non-blinded cohorts.
03 Regulatory status
Where it is authorised, and for what
Status is recorded per jurisdiction from regulator sources and reviewed by hand. It is never inferred from another region's decision.
United Kingdom
Not authorisedNo MHRA marketing authorisation; sold online only as an unregulated 'research chemical'.
04 Dosing research
What the evidence says about exposure
Published human studies and the doses, routes and durations they used — reported as research information, not a recommendation.
Research information — not a recommendation. These are the exposures used in published human studies, reported so you can see what has been tested. They are not dosing instructions and do not apply to any individual.
Study 01
Thymosin alpha-1 in chronic hepatitis B — randomised controlled trial
Chien RN et al., Hepatology 1998;27:1383–1387
- Design
- Randomised, controlled, open-label (6 or 12 months of treatment versus untreated control)
- Population
- Adults with HBeAg-positive chronic hepatitis B and raised transaminases
- Participants
- n = 98
- Duration
- 6 or 12 months of treatment, 18 months of follow-up
- Route
- Subcutaneous injection
- Doses studied
- 1.6 mg subcutaneously twice weekly
- Outcome at this exposure
- Sustained HBeAg and HBV-DNA clearance at 18 months was higher with 6 months of treatment (roughly four in ten) than in untreated controls (roughly one in ten); the 12-month arm did not perform better. Later meta-analyses pooled a modest benefit with delayed responses.
- Adverse events observed
- Well tolerated; local injection-site discomfort was the main complaint and no serious drug-related adverse events were reported.
- Design
- Multicentre, randomised, single-blind, controlled (saline)
- Population
- Adults admitted to intensive care with severe sepsis (six hospitals in China)
- Participants
- n = 361
- Duration
- 7 days of treatment; 28-day follow-up
- Route
- Subcutaneous injection
- Doses studied
- 1.6 mg subcutaneously twice daily for 5 days, then once daily for 2 days
- Outcome at this exposure
- 28-day mortality 26.0% versus 35.0% (relative risk 0.74, 95% CI 0.54–1.02; P = 0.062), with greater recovery of monocyte HLA-DR expression. A promising but not statistically conclusive result that prompted the larger TESTS trial.
- Adverse events observed
- No serious drug-related adverse events recorded.
- Design
- Multicentre, randomised, double-blind, placebo-controlled (22 centres in China)
- Population
- Adults aged 18–85 with sepsis (Sepsis-3 criteria)
- Participants
- n = 1,106
- Duration
- 7 days of treatment; 28- and 90-day follow-up
- Route
- Subcutaneous injection
- Doses studied
- 1.6 mg subcutaneously every 12 hours for 7 days
- Outcome at this exposure
- No clear benefit: 28-day mortality 23.4% versus 24.1% with placebo (hazard ratio 0.97, 95% CI 0.76–1.24; P = 0.82); 90-day mortality 31.0% versus 32.4%. No secondary or safety outcome differed. A pre-specified subgroup analysis suggested possible harm in patients under 60 and possible benefit in those with diabetes — hypothesis-generating only.
- Adverse events observed
- Adverse events and serious adverse events did not differ from placebo.
The standard authorised regimen is 1.6 mg subcutaneously twice weekly for 6–12 months (hepatitis B) or short daily courses in acute illness. Every trial enrolled people with a diagnosed disease; there are no dosing data for healthy adults, and online 'immune support' regimens (for example 1.5 mg twice weekly indefinitely) are extrapolations, not evidence.
05 Safety
Adverse effects and contraindications
Common effects seen in trials or reports, serious effects that warrant urgent review, and conditions under which use is not appropriate or needs assessment.
Common adverse effects
- Injection-site discomfort, redness or irritation
- Muscle aches or fatigue (uncommon)
- Transient flu-like symptoms (uncommon)
- Nausea (uncommon)
Serious adverse effects
- Allergic or hypersensitivity reactions (rare)
- Theoretical flare of autoimmune disease
- Graft rejection risk in transplant recipients (label caution)
- Immune reactions or infection with unregulated 'research chemical' vials
Contraindications
- Autoimmune conditionCaution
An immune-stimulating peptide could theoretically aggravate autoimmune disease; people with autoimmune conditions were generally excluded from trials.
- CancerCaution
Used as a chemotherapy adjuvant in some countries, but any use alongside cancer treatment requires oncology input rather than self-directed use.
- Hormonal disorderCaution
Where the underlying condition is a primary immunodeficiency or endocrine disorder, specialist assessment is needed before any immunomodulator.
Do not use = should not be used · Caution = needs assessment
06 Interactions
Medicine classes that need review
Grouped by how seriously the combination should be taken. Class labels match the medicines questionnaire in the assessment.
- Major
- Moderate
- Minor
Moderate
Monitoring or dose review is usually advised.
Immunosuppressant / biologic
Methotrexate, tacrolimus, adalimumab
Opposing mechanism: the Zadaxin label advises against use in deliberately immunosuppressed patients (for example organ-transplant recipients) unless the potential benefit outweighs the risk of graft rejection or loss of disease control.
Minor
Generally compatible; awareness is sufficient.
Corticosteroid
Prednisolone, dexamethasone, hydrocortisone
Systemic corticosteroids may blunt the intended immune-enhancing effect; the combination has not been formally studied.
Cancer treatment
Chemotherapy, hormone therapy, immunotherapy
Studied as an adjuvant to chemotherapy and interferon in trials; any combination should be directed by the oncology team.
07 Pregnancy & breastfeeding
Status in pregnancy
No adequate human data; product information where authorised advises use in pregnancy only if clearly needed. Effects on breastfed infants are unknown.
08 Monitoring
What is usually monitored
Parameters that trials and product information track. A clinician decides what applies to an individual.
- 01A defined, measurable reason for use — 'immune support' cannot be monitored; infection frequency or a specific disease marker can
- 02Full blood count and, where relevant, immune-cell subsets before and during use
- 03Autoimmune symptoms (joint pain, rashes, fatigue) where there is any autoimmune history
- 04Liver enzymes and viral markers if used for chronic hepatitis under specialist care
- 05Injection sites for persistent reactions
09 Combinations
What is known about combining it
Notes on pairing with other compounds in the directory: whether the combination has been studied in people, and where mechanisms overlap.
LL-37
No human studies
Overlap · Both are immune-modulating peptides.
Marketed together as 'immune stacks'; no human data on the combination, and systemic LL-37 has no human trials at all.
Epitalon
No human studies
The extract-era Russian studies combined the thymic extract thymalin with epithalamin — different products from thymosin alpha-1 and epitalon; no data on this combination.
TB-500
No human studies
Overlap · Similar names (thymosin alpha-1 versus thymosin beta-4 fragment) cause confusion, but they are unrelated peptides.
No human data on the combination; TB-500 has no human efficacy data.
BPC-157
No human studies
No human data on this combination; BPC-157 itself lacks human efficacy data.
Discuss any proposed combination with a qualified healthcare professional.
10 Source considerations
Supply, quality and legitimacy
How the compound reaches people in practice, and what that means for product quality.
- 01The authorised product (Zadaxin) is prescription-only and legally available only in countries where it is licensed; UK, US, EU-wide, Australian and Canadian supply is unlicensed.
- 02'Research chemical' thymosin alpha-1 sold online is not Zadaxin and has been flagged by the FDA for characterisation and immunogenicity concerns.
- 03Products labelled 'thymosin' may be thymosin beta-4 fragments (TB-500) — a different peptide with no shared evidence.
11 Questions for your clinician
Take these to your appointment
Specific to this compound. The personal assessment adds questions drawn from your own history and medicines.
- 01Is there a diagnosed immune, infectious or liver condition that thymosin alpha-1 is actually licensed to treat somewhere?
- 02What does the negative 2025 sepsis trial tell us about extrapolating 'immune boosting' to healthy people?
- 03Do I have any autoimmune condition or take immunosuppressants that would make immune stimulation unwise?
- 04Which authorised options — vaccination, treating deficiencies, sleep and activity — address my goal with better evidence?
- 05If used, how would benefit be measured and when would it stop?
The personal assessment tailors this list to your responses.
12 References
Sources behind this record
Regulator documents and peer-reviewed publications used to derive every grade and statement above.
- 01Wu J et al. ETASS — thymosin alpha 1 for severe sepsis. Crit Care 2013;17:R8
- 02Wu J et al. TESTS — thymosin α1 for sepsis, phase 3. BMJ 2025;388:e082583
- 03Chien RN et al. Efficacy of thymosin α1 in patients with chronic hepatitis B: a randomised, controlled trial. Hepatology 1998;27:1383–1387
- 04FDA Pharmacy Compounding Advisory Committee briefing document — thymosin alpha-1 (December 2024)
- 05FDA — Bulk drug substances that may present significant safety risks (503A Category 2)
The Peptide Checkup provides educational information and a structured summary of published research and regulatory status. It is not medical advice, does not diagnose or treat any condition, and does not replace a consultation with a qualified healthcare professional.
Personal assessment
Check Thymosin alpha-1 against your history
Seven minutes of structured questions about your goal, history and medicines, mapped against this record by a deterministic, clinician-reviewable rules engine. The report tells you when not to buy.