What Thymosin Alpha-1 is, where its 1.6 mg twice-weekly dosage actually comes from, what the controlled hepatitis trials found (including where they were negative), half-life and storage — educational use only, not medical advice.
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Foundational Guide: Available Now
Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.
Thymosin Alpha-1 at a glance
What it is
Thymosin Alpha-1 (Ta1; the synthetic form is thymalfasin, marketed as Zadaxin) — a 28-amino-acid peptide identical to a naturally occurring thymic immune-signalling peptide.
Researched for
Chronic hepatitis B and C, immune adjuvant use, and — in the current trial record — as an adjuvant in oncology and critical care.
Plasma half-life
Approximately 2 hours, with peak serum concentration within 2 hours and levels back to baseline within 24 hours (Ancell et al., 2001).
Regulatory status
Not FDA-approved — the FDA drug-label database returns no thymalfasin label. Marketed internationally as Zadaxin; research/educational use only domestically.
Educational reference. This page does not publish dose ranges or reconstitution arithmetic.
What it is / mechanism
Thymosin Alpha-1 is an immune modulator rather than a general stimulant, and the distinction matters for how it is studied. It engages Toll-like receptors TLR2 and TLR9 on myeloid and plasmacytoid dendritic cells, driving dendritic-cell maturation and downstream T-cell activation and differentiation, with reported effects on Th1/Th2 balance and cytokine output including interferon-gamma and interleukin-2. It is thought to act on thymocytes by promoting their differentiation into active T cells. That recalibrating mechanism is why it has been investigated as an adjunct in chronic viral infection, as a vaccine adjuvant, and — in the trials running today — alongside chemotherapy and checkpoint inhibitors in oncology, rather than as a standalone agent.
Researched effects
The most substantial controlled evidence is in chronic hepatitis B, and reading it carefully gives a more interesting picture than the summary usually offered. A meta-analysis comparing thymosin alpha-1 against interferon alfa (Yang et al., Antiviral Research 2008) pooled four randomised controlled trials in 199 patients. At the end of six months of treatment, thymosin alpha-1 was not superior to interferon on any endpoint — the odds ratios for virological, biochemical and complete response were 0.62, 0.60 and 0.54, the last favouring interferon with a confidence interval excluding 1. At the six-month follow-up after treatment ended, the position reversed decisively: odds ratios of 3.71, 3.12 and 2.69, all favouring thymosin alpha-1. The pattern is a delayed but more durable response, which fits an immune-modulating mechanism better than a directly antiviral one, and it means any single-timepoint comparison can make the drug look either worse or better than interferon depending on when you measure. Individual trials reported HBV DNA clearance at six months in 9 of 17 patients on Ta1 versus 10 of 16 on interferon and 4 of 15 historical controls, and in a separate randomised trial 40.6% at six months against 9.4% in untreated controls. In hepatitis C the record is weaker and includes an outright negative result: one trial found no significant difference from placebo in the number of patients reaching a normal serum ALT.
Evidence & regulatory status
Evidence: moderate and specific rather than broad. The controlled hepatitis B literature is real but small — the principal meta-analysis pooled four randomised trials in 199 patients, not the thousands sometimes claimed. Its most robust finding is a delayed response pattern: no advantage over interferon at end of treatment, a clear advantage six months later.
Where it is negative: in chronic hepatitis C, one controlled trial found no significant difference from placebo in ALT normalisation. Combination trials with interferon alfa-2b reported better results than interferon alone, but the monotherapy signal in hepatitis C is not comparable to hepatitis B.
Regulatory: not FDA-approved. A search of the FDA drug-label database returns no thymalfasin or thymosin alpha-1 label. It is marketed internationally as Zadaxin; domestic research-grade material is sold for research and educational use only.
Current trials: unlike most compounds in this library, thymosin alpha-1 has an active registered trial programme. It includes a phase 3 study of 2,500 participants as adjuvant treatment after radical resection of high-risk stage II and stage III colorectal cancer (NCT05086614), recruiting with primary completion scheduled for March 2027, alongside phase 1 and phase 2 work in vaccine enhancement, chemoradiotherapy and immune-related adverse events.
Distinct cadence: the studied regimen is twice weekly, not daily — worth flagging because most peptides in this library are dosed daily and the schedules are not interchangeable.
Research timeline
Dated milestones taken from the primary records: the molecule's discovery, its first registered human study, the trials that shaped the evidence and the regulatory decisions. Each entry links to the record it comes from.
Allan Goldstein's group isolates thymosin alpha-1 from calf thymus and sequences it: a heat-stable, strongly acidic peptide of 28 amino acids, one of several in the thymus extract called thymosin fraction 5. PMID 265536
A randomised trial in 33 patients with HBeAg-negative chronic hepatitis B compares six months of thymosin alpha-1 with interferon alfa: complete response at the end of treatment was 29.4% against 43.8%, and 41.2% against 25% six months later; neither difference was significant. PMID 8855175
A randomised trial in 98 patients with chronic hepatitis B, against untreated controls, finds the same response rates at the end of therapy but more complete virological responses 18 months after entry with the 26-week course (40.6% against 9.4%). PMID 9581695
ETASS, a single-blind trial in 361 patients with severe sepsis in China, reports 28-day mortality of 26.0% with thymosin alpha-1 against 35.0% with standard care, a borderline result (P = 0.062 unstratified). PMID 23327199
A retrospective multicentre cohort of 2,282 hospitalised COVID-19 patients in China finds thymosin alpha-1 use associated with a higher rate of non-recovery after adjustment, most of all in the sickest patients; the study was observational, not randomised. PMID 34408744
FDA's Pharmacy Compounding Advisory Committee votes 4 in favour and 17 against adding thymosin alpha-1 (free base and acetate, voted separately with the same result) to the pharmacy-compounding (503A) list; the majority cited no compelling evidence of effectiveness and safety for the uses reviewed. FDA · PCAC minutes, Dec 4, 2024
TESTS, the double-blind phase 3 sepsis trial (1,106 adults in China), is published in The BMJ: 28-day mortality was 23.4% with thymosin alpha-1 and 24.1% with placebo, no meaningful difference, and no secondary or safety outcome differed. PMID 39814420
Records checked Oct 3, 2026
Claims at a glance
The claims most often made about this compound, each with the strongest kind of evidence we found for it. The grade says what was studied, not whether the claim is true; the line beside it says what that study showed.
Improves survival in sepsisHuman, randomised trial. In a placebo-controlled phase 3 trial of 1,106 adults, 28-day mortality was 23.4% on the peptide and 24.1% on placebo: no clear difference. PMID 39814420
Treats chronic hepatitis BHuman, randomised trial. Four pooled trials against interferon alfa: no better at the end of six months' treatment, better six months after it; three of the four enrolled HBeAg-negative patients. PMID 18078676
Prevents infections in critically ill patientsHuman, randomised trial. In a double-blind trial of 508 patients with predicted severe acute pancreatitis, infected necrosis occurred in 15.7% against 18.1% on placebo, not a significant difference. PMID 35713670
Strengthens the response to vaccinesHuman, non-randomised. A small pilot in haemodialysis patients found higher flu-vaccine antibody titres at day 21 but a faster fall by day 42. PMID 22178096
Fights cancerHuman, randomised trial. In 488 patients with metastatic melanoma, survival gains against the control regimen did not reach statistical significance; a large colorectal trial has not reported. PMID 20194853
Boosts the immune systemCell or tissue studies only. In human dendritic cells it raised responses to viral signals and sharply lowered responses to bacterial ones, so the direction depends on the trigger. PMID 26096650
Reverses immune ageingNo study found. None of the 64 registry records under its name tests an ageing, longevity or thymic-restoration endpoint (checked 5 October 2026); the literature here is reviews and mechanism work. ClinicalTrials.gov search, 2026-10-05
The reasoning behind each grade, study by study, is in this guide's Benefit & Outcome Review.
Grades checked Oct 5, 2026
A printable reference sheet with the compound's key facts, storage guidance and a vial record comes with All-Access Lifetime.
Half-life & pharmacokinetics
Thymosin Alpha-1's serum half-life is approximately 2 hours, and unlike many figures in this library that one is traceable: a clinical pharmacology review (Ancell et al., American Journal of Health-System Pharmacy, 2001) reports rapid absorption with peak serum concentrations within two hours and blood levels returning to baseline within 24 hours. The obvious question follows immediately — how does a peptide cleared within a day get dosed twice a week? The answer is that the dosing interval tracks the immune response rather than the molecule. Thymosin alpha-1 acts by driving dendritic-cell maturation and downstream T-cell differentiation, and those cellular changes persist long after the peptide itself is gone. This is why the compound is a poor candidate for the reasoning that works elsewhere in this library, where a short half-life implies frequent dosing; here the entire published regimen is built on a twice-weekly schedule despite a two-hour half-life, and research into long-acting formulations exists precisely because the native molecule's persistence is not what determines the effect.
Reported side effects & toxicology
Across the international trial base thymosin alpha-1 is generally reported as well tolerated, with mild injection-site reactions the most commonly cited effect — a profile that compares favourably with interferon alfa, its main comparator in the hepatitis literature, and one reason the combination trials were pursued. Because it modulates immune signalling rather than suppressing it, general caution around autoimmune conditions and interactions with immunosuppressant therapy is commonly discussed, and it is a specific consideration in the transplant setting. It is not FDA-approved and domestic research-grade material is not for human consumption as sold. This summarises published tolerability reporting; the current oncology trials exist precisely because its risk-benefit profile in those settings is not yet established.
Storage & handling
Lyophilised (unmixed): store cold; long-term storage is typically at -20°C, and it is reported as stable refrigerated for shorter periods. Keep sealed and protected from light and moisture.
Reconstituted: refrigerate at roughly 2-8°C, use within a commonly reported window of about 2-4 weeks, keep away from light and do not freeze once mixed.
References
Built from primary sources: Ancell, Phipps and Young, American Journal of Health-System Pharmacy 2001 (PMID 11381492) for pharmacokinetics — peak within 2 hours, baseline within 24 hours, serum half-life approximately 2 hours — and for the trial-by-trial hepatitis B and C efficacy figures including the negative hepatitis C ALT result; Yang et al., Antiviral Research 2008 (PMID 18078676) for the meta-analysis of four randomised trials in 199 patients comparing thymosin alpha-1 with interferon alfa; ClinicalTrials.gov record NCT05086614 for the 1.6 mg twice-weekly six-month regimen and the current phase 3 programme; and the FDA drug-label database, which returns no thymalfasin label. Verified 12 August 2026. Two figures previously published on this page — a claim of 30-plus randomised trials in 11,000-plus subjects, and a 36% versus 19.5% sustained-response comparison — could not be traced to any indexed study and have been replaced with the sourced figures above.
Evidence File
The Thymosin Alpha-1 Evidence File: Four Large Trials, One Corrected Result
Thymosin alpha-1 has one of the largest randomised evidence bases in this library and one of the least accurately summarised. Four trials of more than 480 patients each have reported, three of them placebo-controlled and two masked at four separate levels. This file works through the ClinicalTrials.gov record term by term, names every search string used, traces the dose figure the whole market repeats back to its origin in 2001, and states exactly what each registry field does and does not permit anyone to claim.
Four trade and generic names return one identical 66-record set
One primary result revised by a post-publication correction
Sevenfold spread in weekly exposure across registered protocols
Four records withdrawn at zero enrolment: nothing was tested in them
How the registry was searched, and why no single term is complete
TESTS: the largest trial ever run on this compound, and the number that changed after publication
ETASS: the 361-patient predecessor that generated a decade of copy
The other two large randomised trials: hepatitis C and necrotising pancreatitis
The one dose-ranging study, and what a posted results table shows
Where 1.6 mg comes from, and why the interval is the variable that moves
COVID-19: one retrospective headline, two randomised trials that did not reproduce it
Named absences, and exactly what each registry field permits anyone to say
8 more sections in the Evidence File for Thymosin Alpha-1
Unlock the Evidence File, Sourcing File and Benefit & Outcome Review for Thymosin Alpha-1 for $14 — or every compound in the library, plus the printable reference sheets, for $99.
The sections above this one stay free to read without an account.
Sourcing File
The Thymosin Alpha-1 Sourcing File: An Acidic Peptide and an Invisible Impurity
Most peptide sourcing guidance generalises, and for thymalfasin several of the generalisations fail. It is a 28-residue peptide that begins with an acetylated serine followed by an aspartate-alanine pair and ends in an asparagine, and those three structural facts produce compound-specific failure modes, one of which a mass spectrometer cannot detect at all. This file works through the verified identity block, the salt arithmetic recomputed from the molecular formula, the failure modes, the single FDA record that does exist, and a certificate read line by line.
Two different mass fields returned for one compound by one database
Acetate salt penalty under 8 percent, well below the generic rule of thumb
The likeliest impurity here is invisible to mass spectrometry
One FDA record exists, and its finished flag reads false
The identity block, and the two masses one database returns
Why the counter-ion penalty here is smaller than the rule of thumb, and the water is not
Four failure modes derived from this sequence, one of them invisible to a mass spectrum
Three thymic names that resolve to three different molecules
The FDA record that does exist, and the field that says what it is
What a certificate has to show for this compound specifically
A certificate read line by line
7 more sections in the Sourcing File for Thymosin Alpha-1
Unlock the Evidence File, Sourcing File and Benefit & Outcome Review for Thymosin Alpha-1 for $14 — or every compound in the library, plus the printable reference sheets, for $99.
The sections above this one stay free to read without an account.
Benefit & Outcome Review
The Thymosin Alpha-1 Benefit Review: Twelve Claims, Each Read Against Its Own Comparator
Most benefit reviews grade claims as strong, moderate or weak. For this compound that scale hides the variable that decides everything, which is what each trial compared the peptide against. The comparators in this file are not interchangeable: matched placebo on top of standard care in some, an active drug in another, a historical benchmark rather than the trial's own control arm in a third, no intervention at all in a fourth, and in one case no concurrent comparison group whatsoever. Grading them on one scale produces a false ranking. This review states the tier and the comparator first, every time, and then says what each design can and cannot support.
Twelve marketed claims, each graded against the comparator actually used
Over 2,500 randomised participants behind the tolerability record
Two heavily marketed uses with no trial in either database
One mechanism whose direction of effect reverses by receptor family
The reading key: tier first, comparator second
The mechanism claim, and the published result that reverses its sign
Sepsis and critical illness: the most human data of any claim, and no clinical benefit
Hepatitis B and hepatitis C: one delayed signal against interferon, one clean negative
Cancer adjuvant: unresolved rather than established
Infection prevention and vaccine response
The two claims with no record, and the one claim that is genuinely well supported
7 more sections in the Benefit & Outcome Review for Thymosin Alpha-1
Unlock the Evidence File, Sourcing File and Benefit & Outcome Review for Thymosin Alpha-1 for $14 — or every compound in the library, plus the printable reference sheets, for $99.
Quick answers about guide scope, access, and educational use context.
What is the reported Thymosin Alpha-1 dosage?
1.6 mg subcutaneously twice weekly. That figure is stated in the registry record of a currently recruiting phase 3 trial (NCT05086614), which specifies thymosin alpha-1 1.6 mg by subcutaneous injection twice a week for six months, and it matches the regimen used in the international hepatitis programme. It describes a studied protocol, not a recommendation — there is no FDA-approved dose because there is no FDA-approved product.
Is Thymosin Alpha-1 FDA-approved?
No. A search of the FDA drug-label database returns no label for thymalfasin or thymosin alpha-1, which means there is no approved US product, no approved indication and no approved dose. It is marketed internationally as Zadaxin for chronic hepatitis B and C and as an immune adjuvant. Domestic research-grade material is sold for research and educational use only.
Why is Thymosin Alpha-1 dosed twice weekly when its half-life is only two hours?
Because the dosing interval follows the immune response rather than the molecule. Serum levels peak within two hours and return to baseline within 24 hours, but the mechanism is dendritic-cell maturation and downstream T-cell differentiation, and those cellular effects persist well beyond the peptide's clearance. This is the clearest example in this library of a compound where the usual 'short half-life means frequent dosing' reasoning gives the wrong answer.
How well does Thymosin Alpha-1 work for hepatitis B?
The best controlled evidence is a meta-analysis of four randomised trials in 199 patients comparing it against interferon alfa. At the end of six months of treatment it was not superior to interferon on any endpoint, and on complete response interferon was favoured. Six months after treatment ended the result reversed strongly in thymosin alpha-1's favour, with odds ratios of 3.71 for virological, 3.12 for biochemical and 2.69 for complete response. The honest summary is a slower but more durable response, and a smaller evidence base than most commercial pages imply.
Are there any negative trials of Thymosin Alpha-1?
Yes, and they are worth knowing. In chronic hepatitis C, one controlled trial found no significant difference from placebo in the number of patients achieving a normal serum ALT level. The hepatitis C results that are usually quoted come from combination trials with interferon alfa-2b, where the combination outperformed interferon alone — a different claim from monotherapy efficacy. The head-to-head comparisons against interferon in hepatitis B also showed no advantage at the end of the treatment period.
Is Thymosin Alpha-1 still being studied?
Actively, which is unusual for a compound in this library. The registry includes a phase 3 trial of 2,500 participants as adjuvant treatment after radical resection of high-risk stage II and stage III colorectal cancer, recruiting with primary completion scheduled for March 2027, plus phase 1 and phase 2 studies in vaccine enhancement, concurrent chemoradiotherapy and immune-related adverse events from checkpoint inhibitors. The centre of gravity has moved from hepatitis to oncology adjuvant use.
What is Thymosin Alpha-1's half-life?
Approximately 2 hours in serum, with peak concentrations reached within two hours of administration and levels back to baseline within 24 hours, per a clinical pharmacology review published in the American Journal of Health-System Pharmacy in 2001. That is a sourced figure rather than a circulating estimate.
Is Thymosin Alpha-1 the same as Thymalin or Thymosin Beta-4?
No, and the three are routinely confused. Thymosin Alpha-1 is a defined 28-amino-acid peptide whose synthetic form is thymalfasin. Thymalin is a different preparation entirely — a thymic peptide extract from the Khavinson research line, not a single characterised molecule. Thymosin Beta-4 is an unrelated 43-amino-acid actin-binding peptide, the parent molecule of the TB-500 fragment, with a completely different mechanism and research literature.
Compliance and trust notes
Educational content only; no personalized health or outcome claims.
No personalized use recommendation outputs.
Use this material for general learning and research-context literacy.
Reading a Thymosin Alpha-1 certificate of analysis
A certificate of analysis (COA) is a laboratory’s report on one sample of one batch. The single most useful thing to know about it is that purity and identity are two separate results that fail in different ways. A high purity figure says the sample was mostly one substance; it does not say that substance was Thymosin Alpha-1. Identity — normally a mass-spectrometry result matching the expected molecular weight — is what establishes what the material actually is, and a certificate reporting purity alone has not answered that question.
Two further limits are worth holding onto. Mass per vial is its own test: a vial can be 99% pure and still contain less material than the label claims. And sterility, endotoxin, heavy metals and residual solvent screening are separately commissioned tests, usually priced individually — so a “third-party tested” badge asserts none of them unless the certificate names them. Check that the batch or lot number on the document matches the vial in front of you; an unmatched certificate describes someone else’s material.
Medibact does not test, endorse or resell peptides, and publishes no rating of any laboratory. How to read a peptide certificate of analysis walks through the document section by section, and what each COA field establishes covers the field-by-field detail and the laboratories that publish their methods.
You’ll need bacteriostatic water
The diluent for reconstituting Thymosin Alpha-1
Reconstitution is volume arithmetic — it assumes a lyophilized vial is dissolved in bacteriostatic water, which is sterile water preserved with 0.9% benzyl alcohol. The preservative is what allows a vial to be entered more than once; plain sterile water carries none and is single-entry by design. Medibact supplies USP-grade Bacteriostatic Water for Injection in a 30 mL multi-dose vial, produced in an FDA-registered U.S. facility and shipped from the United States, for research use only. One 30 mL vial covers 30 reconstitutions at 1 mL each, 15 at 2 mL, or 10 at 3 mL — division only, not a dosing recommendation.
Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.
