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Thymosin Alpha-1

Thymosin alpha-1 (thymalfasin) is a thymic peptide studied for sepsis, hepatitis and infections. See the trial evidence, safety notes and regulatory picture.

Content last updated . This page has not been medically reviewed.

Overview and classification

Thymosin alpha-1 (also written Ta1 or Tα1, and called thymalfasin in some trials) is a peptide that occurs naturally in the thymus, an immune organ, and has been studied for modifying immune function. [1] A synthetic version has been tested in hepatitis, sepsis, cancer and infections. It is a different molecule from thymosin beta-4, which is covered in TB-500 and Thymosin Beta-4. Background on the immune side is in Thymic Peptides and Immune Signaling. Evidence labels used: established, promising but limited, mixed, insufficient evidence, evidence of harm, marketing claim.

What research shows

Sepsis. Early trials were small and mostly from single centers. A 2025 meta-analysis of 11 randomized trials (about 1,900 patients) found lower 28-day mortality overall, but not in the high-quality or multicenter subsets, and said the sample size was inadequate. [6] The largest trial, TESTS (BMJ 2025), randomized 1,106 adults with sepsis in 22 Chinese centers to thymosin alpha-1 or placebo for up to seven days; 28-day mortality was 23.4% versus 24.1% (hazard ratio 0.99), with no clear evidence of benefit and no significant difference in safety outcomes. [7] Authors reported funding and grants from the manufacturer SciClone. [7] Subgroup signals (age, diabetes) were exploratory. Label: no good evidence of benefit for mortality in unselected sepsis.

Hepatitis B. A meta-analysis of seven randomized trials (1,144 people, all in mainland China) found entecavir plus thymosin alpha-1 gave a higher complete response than entecavir alone, but differences in viral outcomes were gone by 48 to 52 weeks. [8] Label: promising but limited; the combination was tested with a standard antiviral, not alone.

COVID-19. A meta-analysis of eight studies reported lower mortality with thymosin alpha-1 in moderate to critical illness, with very high heterogeneity, and no difference in ventilation need; the authors said randomized trials were still needed. [9] Label: mixed.

Other uses. Hepatitis C, cancer, vaccine response and sepsis were reviewed historically; the authors noted open questions about dose, schedule and endpoints. [10] Registered trials exist in cancer, vaccine response and sepsis, many without results. [11]

Healthy people and "immune boosting". Proper evidence not found for preventing infection or aging in healthy adults. Marketing of "immune support" is a marketing claim. See How the Immune System Works.

Quality and formulation

Clinical products in trials are manufactured pharmaceutical products. The FDA noted potential impurities and immune-reaction risk for compounded thymosin alpha-1. [2] See Peptide Safety.

Related guides

Approved, Investigational and Unapproved Peptides explains the categories.

Frequently asked questions

Is thymosin alpha-1 the same as TB-500?

No. Thymosin alpha-1 and thymosin beta-4 are different peptides from the thymus family. [1]

Does it help sepsis?

The largest trial found no clear mortality benefit. [7]

Is it FDA-approved?

I found no approved US product; FDA lists it as nominated but withdrawn from compounding category 2. [2]

Is it banned in sport?

Not in the S2 text I read, which does name thymosin-beta4. [4]

Does it boost immunity in healthy adults?

Proper evidence not found.

More details: evidence, limits and cautions

The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.

Regulatory status (read 2026-10-22)
JurisdictionWhat I could read
United States (FDA)Thymosin alpha-1 appears on the FDA page of bulk substances "nominated but withdrawn" from compounding category 2; the FDA states it may pose immune risk and that safety information is inadequate. Page current as of 22 April 2026. [2] I did not find a US-approved thymosin alpha-1 product in the sources read.
Countries where it is approvedCommonly stated, but not verified: I could not read a regulator page listing approvals. A trial summary described a company-branded form (ZADAXIN) in clinical studies. [3]
European Union, UK, Canada, AustraliaNot verified.
SportThymosin alpha-1 is not named in the S2 text I read on the WADA 2026 list (thymosin-beta4 is). [4]

A 2024 narrative review argued the FDA's restriction was unfounded; it is an advocacy-style review and I give it limited weight. [5] This is not legal advice, and laws change.

Safety
A historical review described the safety profile as excellent, [10] and TESTS found no significant safety difference from placebo in sepsis patients. [7] These studies were in supervised hospital or clinic settings with defined products. Safety in people who are immunosuppressed, have autoimmune disease or are pregnant is not established in the sources I read; those with autoimmune conditions or transplants should talk with their specialist, because the drug is meant to stimulate immunity. Never call a product safe because a trial found few side effects.
References
  1. Dominari A et al. Thymosin alpha 1: a comprehensive review of the literature. World J Virol 2020. PubMed 33362999. Read 2026-10-22.
  2. U.S. FDA. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (content current as of 22 April 2026). FDA. Read 2026-10-22.
  3. ClinicalTrials.gov. NCT01031966, A Pilot Study to Evaluate ZADAXIN's (Thymalfasin) Ability to Enhance Immune Response to the H1N1sw Influenza Vaccine. NCT01031966, A Pilot Study to Evaluate ZADAXIN's (Thymalfasin) Ability to Enhance Immune Response to the H1N1sw Influenza Vaccine. Read 2026-10-22.
  4. World Anti-Doping Agency. Prohibited List 2026 (in effect 1 January 2026). Prohibited List 2026 (in effect 1 January 2026). Read 2026-10-22.
  5. Dinetz E, Lee E. Comprehensive review of the safety and efficacy of thymosin alpha 1 in human clinical trials. Altern Ther Health Med 2024. PubMed 38308608. Read 2026-10-22.
  6. Gu B et al. Efficacy of thymosin alpha1 for sepsis: systematic review and meta-analysis. Front Cell Infect Microbiol 2025. PubMed 40969554. Read 2026-10-22.
  7. Wu J et al. The efficacy and safety of thymosin alpha1 for sepsis (TESTS). BMJ 2025. PubMed 39814420. Read 2026-10-22.
  8. Peng D et al. Entecavir plus thymosin alpha-1 versus entecavir monotherapy in HBV-related cirrhosis. BMC Gastroenterol 2020. PubMed 33076834. Read 2026-10-22.
  9. Soeroto AY et al. Thymosin alpha-1 in moderate to critical COVID-19: meta-analysis. Inflammopharmacology 2023. PubMed 37845598. Read 2026-10-22.
  10. Camerini R, Garaci E. Historical review of thymosin alpha 1 in infectious diseases. Expert Opin Biol Ther 2015. PubMed 26098768. Read 2026-10-22.
  11. ClinicalTrials.gov. Search for thymosin alpha 1 / thymalfasin studies, accessed 2026-10-22 (for example NCT07866118, NCT06821100). Search for thymosin alpha 1 / thymalfasin studies, accessed 2026-10-22 (for example NCT07866118, NCT06821100). Read 2026-10-22.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.