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Research information only. PrecisePep is an educational library. It is not medical advice and is not intended to assist, encourage or enable self-administration. The compounds documented here are research chemicals — most are not approved for human use. Read the full disclaimer.

PrecisePep/Peptide Library/Thymosin Alpha-1

Immune & Anti-Inflammatory

Thymosin Alpha-1

Tα1 · thymalfasin · Zadaxin® · Ta1

A thymic peptide approved as a medicine in more than thirty countries for hepatitis B and C — one of the few compounds in this library with a genuine international regulatory footprint, just not a Western one.

T-cellTLRImmune modulationApproved abroadTwice weeklyHashimoto interest

00 Overview

Thymosin Alpha-1 has a real drug identity outside the West. It is a 28-residue peptide originally isolated from thymic tissue, marketed as thymalfasin (Zadaxin), and approved in more than thirty countries — principally for chronic hepatitis B and C, and used in some jurisdictions as an adjuvant in sepsis, immunodeficiency and vaccine response.

Its mechanism is immunomodulatory rather than immunostimulant, and the distinction matters. It promotes maturation of naive T cells, augments dendritic cell function through TLR2 and TLR9 signalling, and shifts Th1/Th2 balance toward cell-mediated immunity — but it is also reported to restrain excessive inflammatory responses, which is why it attracted attention in sepsis and in severe respiratory infection.[1][2]

It is the compound in the 15-Compound Matrix immune pillar, and in the research community it is used largely for general immune support, post-viral recovery and as an accompaniment to aggressive protocols. That is well outside its approved indications, which are specific infectious diseases in specific populations.

Approved — somewhere else

Thymosin Alpha-1 has a label, a manufacturer and post-marketing experience in dozens of countries. It is not FDA-approved. That combination is unusual in this library and worth reading carefully: the safety record is real, and it was generated in hepatitis patients on a defined regimen, not in healthy adults taking it indefinitely for wellness.

// Mechanism of action

T-cell maturation. Promotes differentiation of thymocytes and naive T cells into functional mature T cells, and increases CD4+ and CD8+ counts and activity — the original thymic-hormone rationale.

TLR signalling. Acts through Toll-like receptors 2 and 9 on dendritic cells and monocytes, augmenting antigen presentation and driving Th1-weighted responses.

Bidirectional immune modulation. Enhances antimicrobial and antiviral response while reported to attenuate excessive inflammatory signalling — the property that made it a sepsis candidate. A modulator rather than a simple activator.

Natural killer cell and cytokine effects. Increases NK cell activity and modulates IL-2, interferon-gamma and other cytokines.

Thymic involution context. The thymus involutes with age, and declining thymic output is a central feature of immunosenescence. That is the basis of the longevity and immune-ageing interest, and it is a rationale rather than a demonstrated outcome.

01 Reported benefits

Effects that have been reported. A study-tier entry means a result was published — not that the effect is established, reproducible, or transferable from a rodent to a person.

Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.

Approved for chronic hepatitis B and C [1]

Registered in more than thirty countries as thymalfasin, with trial evidence supporting antiviral response, alone and in combination with interferon.

Human clinical · registered

Sepsis mortality signal [2]

Randomised work in severe sepsis reported improved outcomes, and the compound has been studied as an immunomodulatory adjunct in critical care.

RCT · human

T-cell reconstitution and immune restoration [1]

Demonstrated increases in T-cell counts and function in immunocompromised populations — the core mechanistic finding.

Human clinical

Vaccine response augmentation [3]

Studied as an adjuvant to improve antibody response to influenza and hepatitis B vaccination in poor responders including elderly and dialysis patients.

RCT · human

Investigated in severe respiratory infection [4]

Evaluated during COVID-19 for immune restoration in patients with lymphopenia, with mixed and largely observational results.

Observational + trials

Oncology adjuvant investigation [1]

Studied as an adjunct in melanoma, hepatocellular carcinoma and non-small-cell lung cancer, with orphan designations granted in some settings.

Human clinical

02 Adverse effects & risks

Adverse effects, contraindications and unknowns. The grey-market tier is where under-reporting is worst: uncontrolled use produces no systematic safety surveillance at all, so absence of a reported harm is not evidence of safety.

Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.

Favourable safety profile across clinical use [1]

Injection-site reactions are the principal adverse effect; systemic events are uncommon. Backed by decades of marketed use in multiple countries.

Human clinical · post-marketing

Transient injection-site erythema and discomfort [1]

The most frequently reported adverse effect in trials.

Human clinical

Safety data is from disease populations on defined regimens

The record is real but was generated in hepatitis, sepsis and oncology patients over defined courses — not in healthy adults dosing indefinitely.

Evidence scope

03 Dosing ranges

Figures below are documented, not recommended. Study ranges come from published protocols in the stated model; grey-market ranges are what the research community reports using and carry no safety validation of any kind.

Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.

Approved regimen: 1.6 mg twice weekly, subcutaneous [1]

The standard thymalfasin regimen for chronic hepatitis — 1.6 mg twice weekly, typically over six to twelve months. This is a genuine labelled dose, unusual for this library.

Registered product

Higher or daily dosing in critical care [2]

Sepsis and critical-care protocols have used more frequent administration over short courses.

RCT · human
SettingDoseFrequencyDuration
Chronic hepatitis B/C (approved)1.6 mgTwice weekly6–12 months
Sepsis / critical careTrial-definedDaily or more frequentShort course
Vaccine adjuvantTrial-definedAround vaccinationShort course

04 Synergy & interactions

Combination effects. Almost no peptide combination has been studied as a combination in humans; stack logic is overwhelmingly mechanistic inference and community practice. Each linked compound has its own page.

Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.

With interferon in hepatitis [1]

The best-studied combination — thymalfasin plus interferon in chronic hepatitis, with trial evidence for combined antiviral response.

RCT · human

With vaccination [3]

Studied as an adjuvant to improve antibody response in poor responders.

RCT · human

05 Protocols

Whole schedules — dosing, titration, cycle length, and off-time — as documented in trials, as proposed from mechanism, and as circulated in the research community. Reproduced for study and comparison only.

Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.

Registered hepatitis regimen [1]

1.6 mg subcutaneously twice weekly over six to twelve months, alone or with interferon, with virological endpoints.

Registered product

05b Condition-specific interest

Thymosin Alpha-1 has genuine approvals in a number of countries and a real clinical trial literature, which puts it in a small group within this library. The organising problem is not whether it does something — it is that every approved use exploits its ability to enhance immune response, while most community use is for conditions where the immune system is already overactive.

No approval, no trial

Approved as Zadaxin in a number of countries for chronic hepatitis B, and used as a vaccine adjuvant. Not approved in the United States. Every other use on this page is off-label or investigational. The compound is an immune modulator with a directional effect, and the direction matters more here than anywhere else in this library.

Study — approved, randomised

Chronic hepatitis B — the approved indication

Pathophysiology
Chronic hepatitis B persists because the immune response fails to clear infected hepatocytes. The therapeutic problem is an immune system that is not doing enough, which is the mirror image of an autoimmune condition.

Mechanistic rationale
Ta1 promotes T-cell maturation and Th1-weighted immunity, which is exactly what is wanted here. Randomised trials, generally in combination with interferon, supported approval in a number of countries. This is the evidence base that every other claim about this compound is borrowed from, and it is worth noticing what kind of problem it solves.

Community reports
Not a self-directed use. Hepatitis B is suppressible with tenofovir or entecavir, which are oral, effective and widely available.

Components carrying the argument: T-cell maturation, Th1 polarisation, dendritic cell effects

Study — real, and comprehensively superseded

Chronic hepatitis C

Pathophysiology
Chronic HCV infection with progressive fibrosis. Historically difficult to treat and requiring prolonged interferon-based therapy with severe adverse effects.

Mechanistic rationale
Ta1 was studied in combination with interferon and ribavirin and had a genuine role in that era. Hepatitis C is now curable in the great majority of cases with 8 to 12 weeks of direct-acting antivirals, at cure rates above 95% with mild side effects. This entry exists to make clear that the historical evidence is real and that citing it today would be decades out of date.

Community reports
No meaningful community use for this indication, appropriately.

Components carrying the argument: Historical adjunct to interferon-based therapy

Study — genuine trials, unresolved answer

Sepsis and critical illness

Pathophysiology
Sepsis involves an early hyperinflammatory phase followed in many patients by immunoparalysis — a state of profound immune suppression that predisposes to secondary infection and is associated with late mortality.

Mechanistic rationale
Immunoparalysis is a rational target for an immune-restoring agent, and Ta1 has been tested in randomised trials in sepsis, including a substantial Chinese multicentre programme. Results have been promising rather than definitive, and this is genuinely the most interesting unresolved question about the compound. It is also a hospital-based intensive care intervention, which is the opposite of the setting it is used in commercially.

Community reports
No community use, and none is possible. Included because it is where the serious research is.

Components carrying the argument: Reversal of immunoparalysis

Study — the most defensible off-label rationale

Vaccine response and immunosenescence

Pathophysiology
Thymic involution reduces naive T-cell output with age, and vaccine responses in older adults are correspondingly blunted — which is a real, measurable and clinically consequential problem.

Mechanistic rationale
Ta1 has been used as a vaccine adjuvant, particularly in older adults and in dialysis patients responding poorly to hepatitis B vaccination. This is the off-label use with the most coherent supporting logic: a T-cell maturing agent in a population whose limitation is T-cell maturation.

Community reports
Used in longevity and immune-support contexts, generally without any measurement of whether immune function was impaired to begin with. Lymphocyte subsets and vaccine titres are measurable.

Components carrying the argument: Naive T-cell maturation

Theorized to study — old literature, active question

Cancer immunotherapy adjunct

Pathophysiology
Tumours evade immune clearance, and augmenting anti-tumour immunity is the principle behind the checkpoint inhibitors that transformed several cancers.

Mechanistic rationale
Ta1 has been studied as an adjunct in melanoma and hepatocellular carcinoma, with a literature that is older and smaller than the modern immunotherapy field. It is mechanistically in the right family. Anyone with cancer should be discussing immune-modulating agents with their oncology team, because interactions with checkpoint inhibitors and with chemotherapy are real and are not characterised for this compound.

Community reports
Used in cancer contexts, often alongside conventional treatment and often without the oncologist knowing.

Components carrying the argument: Anti-tumour immune augmentation

Study — investigated, not established

COVID-19 and acute viral illness

Pathophysiology
Severe COVID-19 involves both hyperinflammation and lymphopenia, and the lymphopenia is associated with worse outcomes.

Mechanistic rationale
Ta1 was investigated during the pandemic on the lymphopenia rationale, with observational and small trial data reporting mixed results. It did not become part of standard care anywhere, which is the informative outcome.

Community reports
Community use for acute illness prophylaxis is common and untested.

Components carrying the argument: Lymphocyte restoration

Theorized — and the direction is the whole issue

Hashimoto thyroiditis — direction contested

Pathophysiology
Autoimmune destruction of thyroid follicular cells driven by a self-directed T-cell response, with TPO and thyroglobulin antibodies as markers. The immune system is over-active against thyroid tissue.

Mechanistic rationale
Ta1 is described as a modulator rather than a simple stimulant, and is proposed to restore tolerance through dendritic cell maturation and regulatory T-cell activity. The counter-argument is not subtle: every approved use exploits its ability to mature naive T-cells and drive Th1-weighted immunity, which is the opposite of what an autoimmune condition needs. Whether the regulatory arm dominates the T-cell-maturing arm in this specific disease is exactly what has never been tested.

Community reports
Clinics and users report dampened flares, reduced fatigue and falling TPOAb and TgAb titres. Antibody titres are the most cited outcome and the weakest one — see below.

Components carrying the argument: Ta1 alone; sometimes alongside BPC-157 for the gut arm

Important caveat

Why falling antibody titres may mean little

Pathophysiology
TPOAb and TgAb are diagnostic markers of autoimmune thyroiditis. They correlate poorly with symptom burden, with rate of progression to overt hypothyroidism, and with levothyroxine requirement.

Mechanistic rationale
Selenium supplementation reliably lowers TPOAb in randomised trials — and has never been shown to change the clinical course, thyroid function or symptoms. That is the cautionary precedent: a compound can move the number everyone measures without changing the disease.

Community reports
Because titres are cheap to measure and visibly change, they dominate self-reported outcomes. A falling titre is a satisfying result that may be clinically inert.

Components carrying the argument: Applies to any intervention marketed on antibody reduction

Actionable

The direction problem, stated once for all autoimmune use

Pathophysiology
Autoimmune conditions are treated by suppressing or redirecting immune activity. Inflammatory bowel disease, rheumatoid arthritis, lupus and multiple sclerosis are all managed with immunosuppression or targeted biologics.

Mechanistic rationale
Ta1 is used across autoimmune conditions in community settings on the "modulator, not stimulant" framing. That framing is doing a great deal of work for a compound whose approvals all depend on enhancing immune response. Pushing immune tone in an unspecified direction in someone with an autoimmune disease is not obviously the goal, and anyone on immunosuppressive therapy should treat this as an interaction question for their specialist.

Community reports
Widely used in autoimmune contexts. Prescribers are rarely told.

Components carrying the argument: Immune direction — the unresolved question

ConditionImmune problemStatusThe thing to know
Chronic hepatitis BToo little responseApproved in several countriesTenofovir/entecavir suppress it orally
Hepatitis CToo little responseHistoricalNow curable in 8–12 weeks
SepsisImmunoparalysisRandomised trials, unresolvedAn ICU intervention
Vaccine responseBlunted with ageStudiedMost coherent off-label rationale
Cancer adjunctImmune evasionOlder literatureInteraction question for oncology
Hashimoto / autoimmunityToo much responseNoneThe direction is the whole problem
Antibody titresSelenium lowers them and changes nothing
What actually has evidence for these conditions

For hepatitis B: tenofovir or entecavir suppress the virus, are oral, and are widely available. Vaccination prevents it entirely. For hepatitis C: direct-acting antivirals cure the great majority of cases in 8 to 12 weeks — among the most effective treatments in all of medicine.

For immune support in ageing: vaccination — influenza, pneumococcal, shingles, COVID boosters — has by an enormous margin the largest effect on infectious outcomes in older adults. Alongside it: correcting vitamin D deficiency, adequate protein, resistance training and sleep.

For Hashimoto: levothyroxine treats the hypothyroidism, titrated to TSH. There is no disease-modifying therapy for the autoimmune process in routine use, which is exactly why the space attracts interest — and why claims should be held to a higher standard rather than a lower one. Selenium has randomised evidence for lowering TPOAb, with the caveat above about what that endpoint means. Coeliac disease is meaningfully more common in Hashimoto and is worth excluding, since it impairs levothyroxine absorption directly.

06 Handling, reconstitution & storage

Physical-chemistry reference for laboratory handling of the lyophilised material. Reproduced so that stability and concentration mathematics can be studied — see the calculator for the arithmetic and the reconstitution guide for sterile technique.

Reconstitution

The approved product ships with defined reconstitution instructions. Research supply is lyophilised, commonly 10 mg per vial. At 1.6 mg twice weekly a 10 mg vial is about three weeks.

Storage

Lyophilised: refrigerated or frozen. Reconstituted: 2–8 °C.

Common vial sizes

Commonly 10 mg lyophilised vials; approved product supplied at 1.6 mg per vial.

Stability notes

A 28-residue acetylated peptide with ordinary handling requirements.

07 Legal & regulatory status

Regulatory status changes and differs by country. This is a summary for orientation, not legal advice — check your own jurisdiction.

Approved in more than thirty countries as thymalfasin (Zadaxin) for chronic hepatitis B and C, with additional approved or investigational uses varying by jurisdiction.

Not FDA-approved. It has held US orphan drug designations for specific indications, which is a development incentive rather than an approval. Material sold as research-grade Tα1 is not the licensed product.

Regulatory update — current as at August 2026

On 4 December 2024 the FDA's Pharmacy Compounding Advisory Committee voted 4–17 against including Thymosin Alpha-1 on the Section 503A Bulks List. The committee cited a lack of evidence for clinical effectiveness and safety in the uses under review.

This was an earlier and separate round from the July 2026 meeting, and it is the part of the story that the coverage of that meeting almost entirely omits. Across two sittings in October and December 2024, PCAC considered seven substances — including ipamorelin, kisspeptin-10, AOD-9604, CJC-1295 and thymosin alpha-1 — and rejected every one of them. In July 2026 the same committee recommended six of the seven it looked at. What changed between the two rounds was the FDA's April 2026 restructuring of the Category 2 list and the set of substances nominated, not the arrival of new efficacy trials for anything on this page.

A negative advisory vote is not a ban and is not binding. It does mean there is no current 503A compounding pathway for this substance, and that a committee reviewing the evidence was not persuaded by it.

Regulatory and trial claims re-checked against primary sources on 16 August 2026. Checked: PCAC rejected it 4-17 on 4 December 2024; approvals abroad unchanged. Approvals, trial readouts and compounding decisions move faster than anything else on this page — a date here means someone looked, not that nothing has changed since.

Anti-doping

Athletes subject to WADA, USADA, UKAD, NCAA or military testing should assume any peptide is prohibited unless they have verified otherwise against the current WADA Prohibited List. Several classes here (growth-hormone secretagogues, TB-4 analogues, metabolic modulators) are explicitly named. Check the current list — it is republished annually.

§ Sources & further reading

Links resolve to PubMed records, trial registries, publisher pages or primary documents. Where a body of work rather than a single paper is cited, the link opens a PubMed query so the full result set — including newer papers than this page — can be reviewed. Verify every claim against the primary source before relying on it.

  1. PubMed: thymalfasin / thymosin alpha-1 in chronic hepatitis B and C (live query)Database or literature search
  2. PubMed: thymosin alpha-1 in sepsis and critical care (live query)Database or literature search
  3. PubMed: thymosin alpha-1 as a vaccine adjuvant in poor responders (live query)Database or literature search
  4. PubMed: thymosin alpha-1 in COVID-19 and severe respiratory infection (live query)Database or literature search
Reminder

For educational and research reference only. Nothing on this site is medical advice, a recommendation, or an instruction to administer any substance to a human being. Every figure on this page is a record of what has been reported, not a recommendation. Full disclaimer.