Thymosin Alpha-1
28-amino-acid thymic peptide (thymalfasin, Zadaxin); not FDA-approved; studied in chronic hepatitis B, sepsis and acute pancreatitis; FDA lists inadequate safety information for compounding.
60-Second Scientific Briefing
Thymosin alpha-1 (thymalfasin, developed as Zadaxin) is a 28-amino-acid peptide originally isolated from thymus extract that influences T-cell maturation and natural killer cell activity. It is not approved by the US FDA, which states that safety information is inadequate for compounding. Randomised trials show mixed results: hepatitis B trials reported sustained responses in some patients, a sepsis trial (361 patients) found a borderline mortality difference, and a 508-patient double-blind trial in severe acute pancreatitis found no reduction in infected necrosis.
What is Thymosin Alpha-1?
Pharmacological Classification & Molecular IdentityThymosin alpha-1 (thymalfasin) is a 28-amino-acid synthetic peptide, originally isolated from thymosin fraction 5, a bovine thymus extract. [1] Expert Rev Anti Infect Ther, 2004 ↗
Verified Chemical & Regulatory Registry Identifiers
Mechanism of Action & Receptor Targets
Biological Pathway and Target BindingReceptor Selectivity: In laboratory studies it influences T-cell production and maturation, stimulates Th1 cytokines such as interferon-gamma and interleukin-2, and activates natural killer cell cytotoxicity. [1] Expert Rev Anti Infect Ther, 2004 ↗
Regulatory & FDA Approval Status
Legal and Regulatory ClassificationsNot approved by the US FDA. Thymalfasin was developed as a medicine under the name Zadaxin (SciClone Pharmaceuticals); approvals outside the US vary by country and are not reviewed here. In its 2026 compounding-risk list, the FDA cites a risk of immunogenicity and inadequate safety information for thymosin alpha-1. [1] U.S. Food and Drug Administration, 2026 ↗
Thymosin Alpha-1 is not approved for commercial sale, prescription therapy, or compounded medication distribution. It exists strictly within authorized scientific and clinical research frameworks.
Human Evidence & Clinical Trials
Clinical Study Readouts and Evidence SynthesesChronic hepatitis B: a 2004 review summarised seven randomised trials in which 6 months of treatment gave higher sustained response rates than untreated controls; a Japanese randomised trial in 316 patients (2005) reported ALT normalisation in 36.4% and HBeAg clearance in 22.8% a year after the higher dose group stopped treatment. Severe sepsis (ETASS, 2013): 361 patients in six Chinese ICUs, single-blind; 28-day mortality 26.0% vs 35.0% (P=0.062 non-stratified; relative risk 0.74, 95% CI 0.54–1.02). Severe acute necrotising pancreatitis (Intensive Care Med 2022): 508 patients, double-blind; infected necrosis 15.7% vs 18.1% with placebo (P=0.48), no difference in other major complications. [1] Intensive Care Med, 2022 ↗ [2] Crit Care, 2013 ↗ [3] J Viral Hepat, 2005 ↗ [4] Expert Rev Anti Infect Ther, 2004 ↗
Clinical Evidence
Chronic hepatitis B: a 2004 review summarised seven randomised trials in which 6 months of treatment gave higher sustained response rates than untreated controls; a Japanese randomised trial in 316 patients (2005) reported ALT normalisation in 36.4% and HBeAg clearance in 22.8% a year after the higher dose group stopped treatment. Severe sepsis (ETASS, 2013): 361 patients in six Chinese ICUs, single-blind; 28-day mortality 26.0% vs 35.0% (P=0.062 non-stratified; relative risk 0.74, 95% CI 0.54–1.02). Severe acute necrotising pancreatitis (Intensive Care Med 2022): 508 patients, double-blind; infected necrosis 15.7% vs 18.1% with placebo (P=0.48), no difference in other major complications.
Safety Profile & Clinical Limitations
Documented Adverse Events and Known UncertaintiesIn the Japanese hepatitis B trial all adverse drug reactions were mild, mostly fluctuations in liver enzymes; no serious drug-related adverse event was recorded in the ETASS sepsis trial. The FDA notes a risk of immunogenicity and inadequate safety information for compounded use. [1] U.S. Food and Drug Administration, 2026 ↗ [2] Crit Care, 2013 ↗ [3] J Viral Hepat, 2005 ↗
The largest double-blind trial (pancreatitis) was negative, the sepsis result was borderline, and many studies are open-label or from single regions. Safety information is considered inadequate by the FDA, and the content of non-pharmaceutical products is unknown. [1] U.S. Food and Drug Administration, 2026 ↗ [2] Intensive Care Med, 2022 ↗
Dose Approval Status
Commercial Dosing Status and Policy DirectivesNo dose is approved in the US. The dose groups used in the trials are part of each trial's design and are described in the linked publications; they are not a recommendation. [1] J Viral Hepat, 2005 ↗
Under Egypt Peptides medical governance policies, no personal dosages, titration intervals, cycles, stacking recommendations, or self-injection instructions may be provided for unapproved investigational compounds. Clinical study protocols represent controlled experimental research parameters exclusively.
What is Known vs. What is Unknown
Evidence Comparison and Clinical Evidence Boundaries✓ Confirmed Scientific Evidence
- Thymosin alpha-1 (thymalfasin) is a 28-amino-acid synthetic peptide, originally isolated from thymosin fraction 5, a bovine thymus extract.
- Targets & Selectivity: In laboratory studies it influences T-cell production and maturation, stimulates Th1 cytokines such as interferon-gamma and interleukin-2, and activates natural killer cell cytotoxicity.
- Chronic hepatitis B: a 2004 review summarised seven randomised trials in which 6 months of treatment gave higher sustained response rates than untreated controls; a Japanese randomised trial in 316 patients (2005) reported ALT normalisation in 36.4% and HBeAg clearance in 22.8% a year after the higher dose group stopped treatment. Severe sepsis (ETASS, 2013): 361 patients in six Chinese ICUs, single-blind; 28-day mortality 26.0% vs 35.0% (P=0.062 non-stratified; relative risk 0.74, 95% CI 0.54–1.02). Severe acute necrotising pancreatitis (Intensive Care Med 2022): 508 patients, double-blind; infected necrosis 15.7% vs 18.1% with placebo (P=0.48), no difference in other major complications.
- Safety considerations: In the Japanese hepatitis B trial all adverse drug reactions were mild, mostly fluctuations in liver enzymes; no serious drug-related adverse event was recorded in the ETASS sepsis trial. The FDA notes a risk of immunogenicity and inadequate safety information for compounded use.
? Unknown / Under Ongoing Investigation
- The largest double-blind trial (pancreatitis) was negative, the sepsis result was borderline, and many studies are open-label or from single regions. Safety information is considered inadequate by the FDA, and the content of non-pharmaceutical products is unknown.
Verified Questions & Answers
10 Verified scientific answers with permanent anchor keysThymosin alpha-1 (thymalfasin, developed as Zadaxin) is a 28-amino-acid peptide first isolated from thymus extract, studied as an immune modulator. It is not FDA-approved.
- Thymalfasin for the treatment of chronic hepatitis B (Expert Rev Anti Infect Ther, 2004-02-01)
In laboratory studies it affects T-cell maturation, increases Th1 cytokines such as interferon-gamma and interleukin-2, and activates natural killer cells.
- Thymalfasin for the treatment of chronic hepatitis B (Expert Rev Anti Infect Ther, 2004-02-01)
No. It is not approved by the US FDA, which cites a risk of immunogenicity and inadequate safety information in its compounding-risk list. Approvals outside the US vary by country.
- Certain bulk drug substances for use in compounding that may present significant safety risks (U.S. Food and Drug Administration, 2026-04-22)
Mixed results. Hepatitis B trials reported sustained responses in some patients; a sepsis trial in 361 patients found a borderline mortality difference (26.0% vs 35.0%, P=0.062); a 508-patient double-blind pancreatitis trial was negative.
Chronic hepatitis B: a 2004 review described seven randomised trials in which 6 months of treatment produced higher sustained response rates than untreated controls, with responses tending to accumulate after treatment ended. A Japanese randomised trial (2005) of 316 patients compared two doses for 24 weeks; at 72 weeks, 36.4% in the higher dose group had normal ALT and 22.8% had cleared HBeAg, with mild adverse reactions. Severe sepsis (ETASS, Crit Care 2013): 361 ICU patients randomised single-blind; 28-day mortality 26.0% vs 35.0% (non-stratified P=0.062; log-rank P=0.049; relative risk 0.74, 95% CI 0.54–1.02). Severe acute necrotising pancreatitis (Intensive Care Med 2022): 508 patients randomised double-blind; infected pancreatic necrosis 15.7% vs 18.1% (P=0.48), with no difference in organ failure, bleeding or fistula.
- Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial (Intensive Care Med, 2022-07-01)
- The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial (Crit Care, 2013-01-17)
- Efficacy and safety of thymosin alpha-1 in Japanese patients with chronic hepatitis B: randomized clinical trial (J Viral Hepat, 2005-05-01)
- Thymalfasin for the treatment of chronic hepatitis B (Expert Rev Anti Infect Ther, 2004-02-01)
In the published trials adverse reactions were mild (mostly liver-enzyme fluctuations in hepatitis B), and no serious drug-related event was recorded in the sepsis trial. The FDA notes a risk of immunogenicity and inadequate safety information.
- Certain bulk drug substances for use in compounding that may present significant safety risks (U.S. Food and Drug Administration, 2026-04-22)
- The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial (Crit Care, 2013-01-17)
- Efficacy and safety of thymosin alpha-1 in Japanese patients with chronic hepatitis B: randomized clinical trial (J Viral Hepat, 2005-05-01)
The largest double-blind trial was negative and the sepsis result was borderline; many studies are open-label or from one region. The content of non-pharmaceutical products is unknown.
- Certain bulk drug substances for use in compounding that may present significant safety risks (U.S. Food and Drug Administration, 2026-04-22)
- Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial (Intensive Care Med, 2022-07-01)
No dose is approved in the US. The trial dose groups are part of each trial's design and are described in the linked publications; they are not a recommendation.
- Efficacy and safety of thymosin alpha-1 in Japanese patients with chronic hepatitis B: randomized clinical trial (J Viral Hepat, 2005-05-01)
There is no US-approved label, so no official US storage instructions exist.
Thymosin alpha-1 is not named individually on the 2026 WADA Prohibited List. Section S0 covers substances without any current government approval for human therapeutic use; because approvals of thymalfasin differ by country, athletes should ask their national anti-doping organisation before any use.
- WADA Prohibited List (World Anti-Doping Agency)
Egypt Peptides publishes reviewed scientific reference monographs for documentation and research. The site does not give individual medical advice, preparation or injection instructions, combination protocols or off-label use instructions. Decisions about any medicine belong to the treating physician.
- Thymalfasin for the treatment of chronic hepatitis B (Expert Rev Anti Infect Ther, 2004-02-01)
Authoritative Sources & Literature Registry
Regulatory dossiers, clinical trial registries, and published studiesCertain bulk drug substances for use in compounding that may present significant safety risks ↗
https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial ↗
https://pubmed.ncbi.nlm.nih.gov/35713670/
The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial ↗
https://pubmed.ncbi.nlm.nih.gov/23327199/
Efficacy and safety of thymosin alpha-1 in Japanese patients with chronic hepatitis B: randomized clinical trial ↗
https://pubmed.ncbi.nlm.nih.gov/15850471/
Thymalfasin for the treatment of chronic hepatitis B ↗
https://pubmed.ncbi.nlm.nih.gov/15482167/