Thymosin Alpha-1: uses, evidence and status

compound file

The answer, first. A 28-amino-acid thymic peptide isolated from thymus extract in the 1970s and made synthetically since. Sold as the medicine thymalfasin, brand name Zadaxin. The strongest evidence is for influenza vaccine response in older adults, graded A — approval or replicated trials.

Authorised in Italy for this exact use, enhancing the immune response to influenza vaccine ¹¹.

The supporting trial randomised 90 men aged 65 to 99 ¹⁰. One country, one small trial. The other use — sepsis mortality — grades D or E: a claim the human trials have already tested and not supported.

What it is used for

Every use graded on its own evidence, not the compound as a whole. 5 outcomes, ranked by what the human record supports.

#outcome · human · animal · gradewhat the best evidence actually shows

01Influenza vaccine response in older adults1 RCT, n=90 · supportivegrade AAuthorised in Italy for this exact use, enhancing the immune response to influenza vaccine ¹¹. The supporting trial randomised 90 men aged 65 to 99 ¹⁰. One country, one small trial.

02Chronic hepatitis Bsmall RCTs, one null phase III · not the basisgrade CMeta-analysis of 4 randomised trials, 199 patients, found complete response better than interferon alfa 6 months after therapy ended, odds ratio 2.69 ⁴. The one placebo-controlled phase III, 97 patients, was null ³.

03Hepatitis B acute-on-chronic liver failure1 open-label RCT, n=114 · not the basisgrade C90-day transplant-free survival 75.0% versus 53.4% on standard care, 114 patients analysed ⁵. Open-label, and the competing-risk analysis showed no survival difference.

04COVID-19 mortality8 observational studies pooled · not the basisgrade CPooled risk ratio for death 0.59 across 8 studies in moderate to critical COVID-19 ⁶. All retrospective, heterogeneity high at I-squared 84%, and no randomised trial has been run.

05Sepsis mortalityphase 3 RCT, n=1089 · not the basisgrade EThe biggest trial of any peptide on this index. 28-day mortality 23.4% versus 24.1% on placebo, hazard ratio 0.99 ¹. An earlier 361-patient trial had hinted at benefit ².

gradewhat it means

ARegulatory approval, or multiple adequately-powered trials agreeing with each other

BAt least one well-powered human randomised trial, with the direction replicated

CSmall or open-label human trials only

DAnimal or mechanism data only, with no controlled human outcome

EA claim the human trials have already killed

How it works

The proposed mechanism, in three steps. A mechanism is a reason to run a trial, never a substitute for one.

1targetBinds Toll-like receptor 9 on plasmacytoid dendritic cells and Toll-like receptor 2 on myeloid dendritic cells ⁸.

2signalMyD88 signalling drives interleukin-12 and interferon output, and switches on dendritic-cell tryptophan catabolism that expands regulatory T cells ⁸⁹.

3effectMonocyte HLA-DR recovered faster than control in severe sepsis, mean difference 5.8% at day 7 ².

What it does not do

Claims the current record does not support. Worth knowing before you set expectations.

not supported by the evidence

Boosts immunity in healthy adults. Every trial enrolled people with hepatitis, sepsis, cancer or advanced age. Infection rates in healthy adults have not been measured.
Cuts death from sepsis. A 1089-patient phase 3 trial found no mortality difference, and no secondary or safety outcome separated either ¹.
Clears hepatitis B on its own. The one double-blind placebo-controlled phase III trial, 97 patients, did not confirm the efficacy earlier studies reported ³.

How it is used

What published protocols administered, and what the community reports doing. Descriptive on both counts, and never a recommendation.

routeSubcutaneous injection in almost every published trial. Intravenous in some sepsis protocols.

formatLyophilised powder, reconstituted before injection.

published dosesHepatitis and vaccine trials used 1.6 mg, about 900 micrograms per square metre, subcutaneously twice weekly ⁷. The sepsis trials gave 1.6 mg every 12 hours for 5 to 7 days ¹². That is what the studies dosed.

human pharmacokineticsPeak serum concentration within 2 hours, serum half-life about 2 hours, levels back to baseline within 24 hours ⁷.

reported conventionsAs reported on peptide forums and vendor protocol sheets, 2020-2026: the 1.6 mg twice-weekly schedule lifted straight from the hepatitis trials. Blocks of four to eight weeks, often timed around illness or travel. Convention, not guidance.

commonly paired withLL-37 KPV

This site does not publish protocols to follow. The doses above are what studies administered or what users report, stated as facts about the literature and the market. How protocols are structured, mixing and storage and the reconstitution calculator cover the arithmetic.

What to expect

Where a trial measured it, the trial. Where only the community reports it, that is said out loud.

onsetTrials measured immune markers before anything clinical moved. Monocyte HLA-DR separated from control by day 3 in severe sepsis ². In hepatitis B the response accumulated after treatment stopped rather than during it, across 6 months of follow-up ⁴.

most common reportAs reported: nothing felt at the injection. The compound is judged on bloodwork or on not falling ill, not on sensation.

adverse effectsInjection-site irritation was the main finding across the hepatitis trials ⁷. In the 1089-patient sepsis trial no safety outcome differed from placebo ¹. The vaccine trial in 90 older men recorded no toxicity ¹⁰.

the stop signalTrials ran fixed courses and stopped on schedule, 7 days in sepsis and 6 months in hepatitis B ¹³. No stop signal is described anywhere in the literature.

Approval and status

What regulators and sport bodies have actually said, separately from what the evidence shows.

approvalAuthorised in Italy. No approval in the United States.

FDANo US approval. Nominated for compounding under section 503A, placed in category 2, nomination later withdrawn ¹².

sport [WADA]Not on the 2026 Prohibited List ¹³.

sold asresearch chemical

Check the vial

The grade above describes a molecule studied under controlled conditions. It says nothing about the powder in a particular vial.

That gap is the one part of this market a reader can actually close. How to read a certificate of analysis covers the five measures in five minutes, and the 2026 audit grades vendors on the documents they publish against a rubric printed in full.

Questions we get

What is Thymosin Alpha-1 used for?

In medicine, enhancing the immune response to influenza vaccine. That is its authorised use in Italy ¹¹. It is also an adjunct in chronic hepatitis B and in hepatitis B liver failure ⁴⁵.

In the research market it is bought as a general immune support compound. That last use has no trial behind it. Its largest study, a 1089-patient phase 3 in sepsis, was negative ¹.

How is Thymosin Alpha-1 used?

Descriptively, and from published protocols only. The hepatitis and vaccine trials injected 1.6 mg subcutaneously twice weekly ⁷. The sepsis trials gave 1.6 mg every 12 hours for 5 to 7 days ¹². Serum half-life is about 2 hours ⁷. What circulates in the research market copies the twice-weekly schedule.

How long does Thymosin Alpha-1 take to work?

Depends entirely on what is being measured. Monocyte HLA-DR, an immune marker, separated from control by day 3 in severe sepsis ².

Hepatitis B response built up in the 6 months after dosing ended rather than during treatment ⁴. No trial has measured how long anything takes in a healthy person, because no trial has enrolled one.

Is Thymosin Alpha-1 an approved drug?

Partly. Thymalfasin is authorised in Italy for enhancing influenza vaccine response, and holds European orphan designation for hepatocellular carcinoma granted in 2002 ¹¹.

It has no United States approval. On our index it is graded human trials on clinical evidence and moderate on community adoption. An approval in one country does not extend to a research-market vial or to an off-label goal.

References

Wu J, et al. The efficacy and safety of thymosin alpha-1 for sepsis [TESTS]: multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ. 2025. PMID 39814420
Wu J, et al. The efficacy of thymosin alpha 1 for severe sepsis [ETASS]: a multicenter, single-blind, randomized and controlled trial. Crit Care. 2013. PMID 23327199
Mutchnick MG, et al. Thymosin alpha1 treatment of chronic hepatitis B: results of a phase III multicentre, randomized, double-blind and placebo-controlled study. J Viral Hepat. 1999. PMID 10607256
Yang YF, et al. Comparison of the efficacy of thymosin alpha-1 and interferon alpha in the treatment of chronic hepatitis B: a meta-analysis. Antiviral Res. 2008. PMID 18078676
Chen JF, et al. Safety and efficacy of Thymosin alpha-1 in the treatment of hepatitis B virus-related acute-on-chronic liver failure: a randomized controlled trial. Hepatol Int. 2022. PMID 35616850
Soeroto AY, et al. The efficacy of thymosin alpha-1 therapy in moderate to critical COVID-19 patients: a systematic review, meta-analysis, and meta-regression. Inflammopharmacology. 2023. PMID 37845598
Ancell CD, Phipps J, Young L. Thymosin alpha-1. Am J Health Syst Pharm. 2001. PMID 11381492
Romani L, et al. Thymosin alpha 1 activates dendritic cells for antifungal Th1 resistance through toll-like receptor signaling. Blood. 2004. PMID 14982877
Romani L, et al. Thymosin alpha1 activates dendritic cell tryptophan catabolism and establishes a regulatory environment for balance of inflammation and tolerance. Blood. 2006. PMID 16741252
Gravenstein S, et al. Augmentation of influenza antibody response in elderly men by thymosin alpha one. A double-blind placebo-controlled clinical study. J Am Geriatr Soc. 1989. PMID 2642497
European Medicines Agency. EU/3/02/110, orphan designation for thymalfasin for treatment of hepatocellular carcinoma. Designated 30 July 2002. ema.europa.eu
US Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Category 2 lists. fda.gov
World Anti-Doping Agency. The 2026 Prohibited List. In force 1 January 2026. wada-ama.org

Inside Your Peptides is published by the owners of the next lab, a vendor graded elsewhere on this site. We sell nothing here, and this page carries no vendor link. Grades follow the published criteria in our editorial policy — never referral terms. Research and education only. Not medical advice.