Thymosin Alpha-1

01 · What it is

Thymosin alpha-1 has been given to thousands of people in randomised trials across four decades, and its two best trials point in different directions.

The larger and better-designed one was negative. In 2022, a multicentre, double-blind, placebo-controlled trial randomised 508 patients with predicted severe acute necrotising pancreatitis, 94.3% of whom needed intensive care, to thymosin alpha-1 or saline ¹⁶. Infected pancreatic necrosis developed in 15.7% of the treated group and 18.1% of the placebo group — a difference of −2.4%, 95% CI −7.4 to 5.1, p = 0.48. The result held across four predefined subgroups, and there was no difference in new-onset organ failure, bleeding or gastrointestinal fistula ¹⁶.

The earlier one was borderline. The ETASS trial randomised 361 patients with severe sepsis across six Chinese teaching hospitals, single-blind, with no placebo ⁷. Twenty-eight-day mortality was 26.0% with thymosin alpha-1 against 35.0% in controls — a relative risk of 0.74 whose confidence interval, 0.54 to 1.02, crosses 1. The unstratified p was 0.062 and the log-rank p was 0.049 ⁷.

The biomarker behaved better than the outcome. Monocyte HLA-DR expression, a measure of immune competence, improved significantly at day 3 and day 7 ⁷.

What it is. Thymosin alpha-1 is a genuine peptide: a highly conserved 28-amino-acid peptide that occurs naturally in the thymus and has roles in T-cell maturation and differentiation ¹⁷. It is a naturally occurring peptide hormone rather than a designed analogue ¹². Its international non-proprietary name is thymalfasin ⁸. This is not a research chemical; it is a medicine, sold and prescribed in a number of countries.

The indication list is very long, and that is itself worth noticing. Chronic hepatitis B ¹⁰ and C ^1,5, sepsis ^7,13, severe acute pancreatitis ^16,20, COVID-19 ¹⁸, acute exacerbations of COPD ¹⁹, HIV ¹¹, and cancer immunotherapy ¹⁷. An immunomodulator will plausibly show something in almost any condition where immune function is disturbed, which is most serious illness.

The evidence is abundant, largely Chinese, heavily meta-analysed, and thin on double-blind placebo control. The one trial in this file that had all three of those safeguards found nothing.

02 · Evidence at a glance

Evidence grade

Mixed Evidence — extensive randomised human data whose conclusions conflict by trial design

What it is

A naturally occurring 28-amino-acid thymic peptide ^12,17

International non-proprietary name

Thymalfasin ⁸

Largest double-blind placebo-controlled trial

508 patients, severe acute necrotising pancreatitis — NEGATIVE ¹⁶

Its primary outcome

Infected pancreatic necrosis 15.7% vs 18.1%; difference −2.4% (95% CI −7.4 to 5.1); p = 0.48 ¹⁶

Regimen used in that trial

1.6 mg subcutaneously every 12 h for 7 days, then 1.6 mg daily for 7 days, against saline ¹⁶

Largest sepsis trial

ETASS, 361 patients, single-blind, no placebo ⁷

Its primary outcome

28-day mortality 26.0% vs 35.0%; RR 0.74, 95% CI 0.54–1.02; p = 0.062 unstratified, 0.049 log-rank ⁷

Its biomarker outcome

Monocyte HLA-DR improved at day 3 (+3.9%, p = 0.037) and day 7 (+5.8%, p = 0.017) ⁷

Meta-analyses located

Hepatitis B ^3,4,6,14, COVID-19 ¹⁸, COPD ¹⁹, severe acute pancreatitis ²⁰

Indications with published human trials

At least seven ^{1,5,7,10,11,16,18,19}

Safety signal in the 508-patient trial

None; no difference in organ failure, bleeding or fistula ¹⁶

Serious drug-related adverse events, ETASS

None recorded ⁷

Approval status

Marketed in a number of countries. No regulatory record consulted for this guide — see Section 7

US approval

Not established here; a 2001 review describes it as then in phase III for hepatitis C ²

On the grade. Approved Pharma requires a marketing authorisation in at least one jurisdiction. Thymosin alpha-1 almost certainly holds one — it has an INN ⁸, it is prescribed clinically, and several trials cited here compare it against standard antivirals as an established option. But this guide has not consulted a regulatory record in any jurisdiction, and will not assert an approval it has not seen. Mixed Evidence is also the more informative grade, because the defining feature of this compound is that its human data conflict.

03 · Mechanism of action

An endogenous peptide, not a designed one

Thymosin alpha-1 occurs naturally in the thymus, is highly conserved, and participates in T-cell maturation and differentiation ¹⁷. Serum levels vary in normal and pathological conditions, and diseases marked by deregulated immune or inflammatory responses are associated with altered concentrations ¹².

That last point cuts both ways. An endogenous peptide whose levels change in disease is a plausible therapeutic candidate and also a plausible bystander — a marker of the illness rather than a lever on it. Nothing in this file distinguishes those two readings.

The proposed action is immune restoration, and it is measurable

The mechanism is described as restoring immune function rather than suppressing or stimulating it indiscriminately: in HIV, an ability to restore immune responsiveness where antiretroviral therapy leaves persistent inflammation and inefficient cytotoxic T-cell responses ¹¹; in sepsis, modifying the host immune response to help clear infection and restore organ function ¹³; in cancer, restoring immune function and reducing mortality in immunosuppressed patients ¹⁷.

The strongest direct evidence for this is the ETASS biomarker result. Monocyte HLA-DR expression — a standard measure of the immunoparalysis seen in sepsis — improved significantly more with thymosin alpha-1 than control at both day 3 and day 7 ⁷.

This is the most convincing mechanistic finding in the file, because it was measured inside a randomised trial rather than in a separate laboratory study. It is also, precisely, a biomarker. The same trial’s mortality confidence interval includes no effect ⁷.

What the mechanism does not predict

If the mechanism is restoration of immune competence in immunosuppressed states, then acute necrotising pancreatitis — where early-onset immunosuppression is documented and was the explicit rationale for the trial ¹⁶ — is a reasonable place to expect benefit. The trial was designed on that logic, powered adequately, blinded, placebo-controlled, and it found nothing ¹⁶.

A mechanism that is real at the level of a biomarker and absent at the level of an outcome is the recurring shape of this entire project. Here it appears in a compound that is an approved medicine rather than a research chemical, which makes it more instructive, not less.

04 · Key research findings

Hepatitis C, 1996. An open-label trial of thymosin alpha-1 at 1 mg twice weekly combined with lymphoblastoid interferon at 3 MU three times weekly for one year in chronic hepatitis C ¹.

Open label, and the earliest human study cited here. It sets the pattern that recurs throughout: the compound is usually tested as an add-on to an established therapy rather than alone.

The 2001 clinical review. A review of pharmacology, pharmacokinetics, clinical efficacy, adverse effects, dosage and administration, describing thymosin alpha-1 as a synthetic polypeptide then in phase III trials for hepatitis C ².

The hepatitis B meta-analyses, 2008–2020. Thymosin alpha-1 compared against interferon alpha ³; lamivudine with and without thymosin alpha-1 ⁴; interferon with and without it, in Chinese ⁶; and entecavir plus thymosin alpha-1 against entecavir alone, whose authors describe the efficacy and safety of the combination as controversial ¹⁴.

Four meta-analyses of add-on designs in one disease. The 2020 one explicitly frames the question as unsettled, twelve years after the first.

ETASS, 2013 — the sepsis trial. Multicentre, randomised, single-blind, six tertiary teaching hospitals in China, May 2008 to December 2010, 361 patients allocated 1:1, intention-to-treat. Twenty-eight-day all-cause mortality 26.0% versus 35.0%; RR 0.74, 95% CI 0.54 to 1.02; p = 0.062 unstratified and 0.049 by log rank. Monocyte HLA-DR improved significantly at days 3 and 7. No serious drug-related adverse event was recorded. The authors conclude the drug may be effective in a targeted population ⁷.

The confidence interval crosses 1 and the primary p is 0.062. The log-rank p of 0.049 is the number that gets quoted. Single-blind with no placebo, in a trial whose outcome is mortality, is a design limitation the authors do not hide and readers should not skip.

Nonclinical models, 2015. Evaluation in nonclinical models of melanoma and sepsis, framed around immune-suppressing indications ⁸.

The 2015 and 2018 review clusters. A historical review of thymosin alpha-1 in infectious diseases ⁹, a review of its use in chronic hepatitis B ¹⁰, a review of serum levels in normal and pathological conditions ¹², and a review of its use in sepsis ¹³.

Three of these appear in supplement issues of the same journal — Expert Opinion on Biological Therapy, 2015 Suppl 1 and 2018 sup1 — largely devoted to this one compound ^8,9,10,12,13. Journal supplements concentrated on a single molecule are a publication format worth noticing when weighing a literature, and this guide notes it without asserting anything about who paid for them.

HIV, 2017. A review of thymosin alpha-1 in HIV-1, focused on restoring immune responsiveness where antiretroviral therapy leaves persistent inflammation ¹¹.

A comprehensive review, 2020. A survey of the literature describing use in immunocompromised states and malignancies, as an enhancer of vaccine response, and as a means of reducing morbidity and mortality in sepsis and other infections ¹⁵.

Seventeen authors, published in December 2020, and the breadth of its indication list is the point: it is the clearest single statement of how expansively this compound is positioned.

COVID-19, 2023. A systematic review, meta-analysis and meta-regression in moderate to critical COVID-19, suggesting reduced mortality, with the benefit significantly affected by sample size and sex ¹⁸.

A meta-analytic benefit that varies with sample size is a finding about the studies as much as about the drug: it is the signature of small-study effects.

The 2022 pancreatitis trial — the best evidence in the file, and it is negative. Multicentre, double-blind, randomised, placebo-controlled, in patients with APACHE II ≥ 8 and a CT severity score ≥ 5 admitted within seven days of symptom onset. Five hundred and eight patients, 254 per arm, 94.3% requiring ICU admission. Infected pancreatic necrosis occurred in 40 of 254 (15.7%) on thymosin alpha-1 against 46 of 254 (18.1%) on placebo; difference −2.4%, 95% CI −7.4 to 5.1, p = 0.48. Similar across four predefined subgroups. No difference in new-onset organ failure (10.6% vs 15%), bleeding (6.3% vs 3.5%) or gastrointestinal fistula (2% vs 2.4%) ¹⁶.

Double-blind, placebo-controlled, adequately sized, multicentre, prespecified subgroups, published in an intensive care journal. By every design criterion this is the strongest trial of thymosin alpha-1 in this file, and its answer is no.

Severe acute pancreatitis meta-analysis, 2025. A systematic review and meta-analysis reporting that thymosin alpha-1 alleviates inflammation and prevents infection in severe acute pancreatitis through immune regulation ²⁰.

Published three years after a 508-patient double-blind trial in essentially that population reported no effect on infection ¹⁶. This guide has not read either full text and cannot say how the meta-analysis handled the negative trial — but the juxtaposition is the single most important thing for a reader to know, and it is why Limitation 1 is written as it is.

COPD, 2024. A systematic review and meta-analysis in acute exacerbations of chronic obstructive pulmonary disease, whose own conclusion calls for more high-quality randomised trials ¹⁹.

05 · Evidence overview

06 · Safety profile

Human data, and there is a lot of it. This is among the best-characterised safety profiles in the project. The 508-patient double-blind trial found no difference from placebo in new-onset organ failure (10.6% vs 15%), bleeding (6.3% vs 3.5%) or gastrointestinal fistula (2% vs 2.4%) ¹⁶. ETASS recorded no serious drug-related adverse event across 181 treated patients with severe sepsis ⁷. Adverse effects were reviewed as early as 2001 ².

Two randomised trials totalling several hundred treated patients, in critically ill populations, reporting no attributable harm. For a compound in this project, that is an unusually solid safety position — and it is worth saying plainly that a null efficacy result and a clean safety result often travel together.

What is genuinely unknown. Whether any of the efficacy signals are real, which is the central question and is not a safety question. Long-term exposure: the trials are short, measured in days to weeks, and nothing here addresses months or years. Whether an immune-restoring agent carries risk in people who are not immunosuppressed — every trial cited studies patients with an acute illness, and none studies healthy adults. Interaction with immunosuppressive or immunostimulatory therapy, including checkpoint inhibitors, which the immuno-oncology framing ¹⁷ makes an obvious question and which nothing in this file answers.

And the composition and provenance of any material obtained outside a pharmacy supply chain, on which nothing is published. That gap matters more here than for most compounds precisely because a legitimate pharmaceutical version exists: material sold under this name outside that chain has no established relationship to the product tested in these trials.

07 · US regulatory status

Current as of 6 September 2026. This guide has not consulted a regulatory record in any jurisdiction and therefore makes no statement about current approval status anywhere.

What the literature shows: thymosin alpha-1 holds the international non-proprietary name thymalfasin ⁸; a 2001 US clinical pharmacy review described it as then in phase III trials for hepatitis C and reviewed its dosage and administration ²; and trials from 2008 onward routinely compare it against established antivirals as a clinical option ^3,4,6,14. Those facts are consistent with marketing authorisation in one or more countries, and this guide declines to name which, because it has not looked at the records. That limitation is logged.

It is not a controlled substance in the United States.

Under the World Anti-Doping Code, thymosin alpha-1 does not appear as a named prohibited substance in the classes reviewed for this guide. Note that this is a different molecule from thymosin beta-4, which is covered separately in this project and which does appear on the Prohibited List. Competitors should consult the current list directly rather than rely on secondary summaries, including this one.

08 · Limitations of the evidence

1. The best-designed trial disagrees with the meta-analytic literature, and a meta-analysis published afterwards reaches the opposite conclusion in the same disease. A double-blind, placebo-controlled, 508-patient trial found no reduction in infected pancreatic necrosis, p = 0.48 ¹⁶. A 2025 systematic review reports that the compound prevents infection in severe acute pancreatitis ²⁰. This guide has read neither full text and does not know how the second handled the first — but a reader should not encounter the second without knowing the first exists.

1. The most-cited positive trial was single-blind with no placebo, and its confidence interval crosses no effect. ETASS: RR 0.74, 95% CI 0.54 to 1.02, unstratified p = 0.062 ⁷. In a mortality trial, unblinded care is a route by which expectation can influence outcome, and the authors’ own conclusion is hedged to “may be effective in a targeted population”.

1. The biomarker moves more reliably than the outcome. Monocyte HLA-DR improved significantly at two timepoints in the same trial where mortality did not reach the primary significance threshold ⁷. Immune competence measured in blood is not the same finding as survival.

1. The indication list is too long to be independent evidence. Hepatitis B, hepatitis C, sepsis, pancreatitis, COVID-19, COPD, HIV and cancer ^{1,5,7,10,11,16,17,18,19}. Positive results across conditions sharing one proposed mechanism are correlated, not corroborating, and breadth of this kind is equally consistent with an endpoint that is easy to move.

1. Geographic and design concentration. The major trials and most meta-analyses come from China ^{6,7,14,16,19,20}. That is not a criticism of the research — the 2022 negative trial is Chinese and is the best study in the file — but it does mean the evidence base has not been replicated across regulatory and clinical cultures.

1. Several foundational reviews sit in single-compound journal supplements ^8,9,10,12,13. Supplements are a legitimate format and also one where editorial independence and funding differ from a regular issue. This guide records the format and asserts nothing about sponsorship, having not examined it.

1. Most trials test the compound as an add-on. Combined with interferon ¹, lamivudine ⁴, entecavir ¹⁴ or standard care ^7,16. Add-on designs answer whether the compound adds anything to a given regimen, not what it does on its own, and this file contains no monotherapy trial in a serious indication.

1. Publication bias is indicated directly in one analysis. The COVID-19 meta-regression found the mortality benefit significantly affected by sample size ¹⁸, which is the standard signature of small-study effects.

1. No long-term data. Every trial cited runs for days or weeks. Nothing addresses repeated or chronic administration, in any population.

1. No regulatory record was consulted, so this guide cannot state where the compound is approved, for what, or on what evidence — which for a compound of this maturity is a substantive gap rather than a technicality.

1. This guide has read abstracts, not full texts, including for both major trials. The numbers reported above are those the abstracts state.

1. Nothing is known about non-pharmacy material. No published analysis has examined the identity or purity of any thymosin alpha-1 product obtained outside a regulated supply chain.

09 · References

1. Rasi G, DiVirgilio D, Mutchnick MG, Colella F, Sinibaldi-Vallebona P, Pierimarchi P, Valli B, Garaci E. Combination thymosin alpha 1 and lymphoblastoid interferon treatment in chronic hepatitis C. Gut. 1996 Nov;39(5):679–683.

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2. Ancell CD, Phipps J, Young L. Thymosin alpha-1. Am J Health Syst Pharm. 2001 May 15;58(10):879–885. Review.

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3. Yang YF, Zhao W, Zhong YD, Yang YJ, Shen L, Zhang N, Huang P. Comparison of the efficacy of thymosin alpha-1 and interferon alpha in the treatment of chronic hepatitis B: a meta-analysis. Antiviral Res. 2008 Feb;77(2):136–141.

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4. Zhang YY, Chen EQ, Yang J, Duan YR, Tang H. Treatment with lamivudine versus lamivudine and thymosin alpha-1 for e antigen-positive chronic hepatitis B patients: a meta-analysis. Virol J. 2009 May 25;6:63.

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5. Sherman KE. Thymosin alpha 1 for treatment of hepatitis C virus: promise and proof. Ann N Y Acad Sci. 2010 Apr;1194:136–140.

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6. Mao HY, Shi TD. [Treatment with interferon and thymosin alpha-1 versus interferon monotherapy for HBeAg positive chronic hepatitis B: a meta-analysis]. Zhonghua Gan Zang Bing Za Zhi. 2011 Jan;19(1):29–33. Chinese.

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8. King RS, Tuthill C. Evaluation of thymosin alpha 1 in nonclinical models of the immune-suppressing indications melanoma and sepsis. Expert Opin Biol Ther. 2015;15 Suppl 1:S41–S49.

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9. Camerini R, Garaci E. Historical review of thymosin alpha 1 in infectious diseases. Expert Opin Biol Ther. 2015;15 Suppl 1:S117–S127. Review.

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14. Peng D, Xing HY, Li C, Wang XF, Hou M, Li B, Chen JH. The clinical efficacy and adverse effects of entecavir plus thymosin alpha-1 combination therapy versus entecavir monotherapy in HBV-related cirrhosis: a systematic review and meta-analysis. BMC Gastroenterol. 2020 Oct 19;20(1):348.

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16. Ke L, Zhou J, Mao W, Chen T, Zhu Y, Pan X, Mei H, Singh V, Buxbaum J, Doig G, He C, Gu W, Lu W, Tu S, Ni H, Zhang G, Zhao X, Sun J, Chen W, Song J, Shao M, Tu J, Xia L, He W, Zhu Q, Li K, Yao H, Wu J, Fu L, Jiang W, Zhang H, Lin J, Li B, Tong Z, Windsor J, Liu Y, Li W; Chinese Acute Pancreatitis Clinical Trials Group. Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial. Intensive Care Med. 2022 Jul;48(7):899–909.

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20. Tian Y, Yao J, Ma Y, Zhang P, Zhou X, Xie W, Tang W. Thymosin alpha 1 alleviates inflammation and prevents infection in patients with severe acute pancreatitis through immune regulation: a systematic review and meta-analysis. Front Immunol. 2025 Jun 17;16:1571456.

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