Thymosin Alpha-1
Also known as: Thymalfasin, Zadaxin, Tฮฑ1
Thymosin Alpha-1 (also called Thymalfasin or Zadaxin) is a thymic peptide. Thymosin alpha-1 is a 28-amino-acid acetylated peptide cleaved from prothymosin alpha, originally isolated from thymic tissue.
For research use only.
Key Facts
- CAS
- 62304-98-7
- Molecular Weight (MW)
- 3108.3 g/mol
- Half-life
- ~2 hours
- FDA status
- Not Approved
- Evidence level
- Clinical Trial Evidence
- Human dose established
- Yes
- Administration Route
- Subcutaneous
- Frequency
- Twice weekly in outpatient trials; every 12 hours in acute critical-illness protocols
- Last updated
- Sep 26, 2026
- Reviewed
- Aug 30, 2026
- Targets
- T cellsInnate immune receptors
Vendor price snapshot
Each vendor counts once, at the median price per mg of its own listings; the typical range is the middle half of vendors. From public vendor listings collected between Nov 2025 and Sep 2026, so confirm the live price on the vendor site. Peptide Library does not sell peptides.
- Vendors listing this peptide
- 28
- Listed offers
- 40
- Median price per mg
- $8.00/mg
- Typical $6.95โ$11.75/mg
Research summary
28-aa thymic peptide (thymalfasin). Approved in several countries (Zadaxin) for hepatitis B and as an immune adjuvant; not FDA-approved in the US.
Peptide Library's Thymosin Alpha-1 profile summarises 5 cited studies listed in the Science section, the compound's regulatory status, and research-protocol parameters reported for it. It is a research reference, not medical advice.
Thymosin Alpha-1 dosage chart
Thymosin alpha-1 has substantial human dosing evidence, converging on 1.6 mg subcutaneously. Published randomised trials used 1.6 mg twice weekly for 8 weeks in an outpatient prevention setting, and 1.6 mg every 12 hours for 7 days followed by 1.6 mg daily for a further 7 days in critical illness. It is marketed as thymalfasin in a number of countries but has no current FDA labelling in the United States.
| Human dosing established | Yes |
|---|---|
| Studied dose range | 1.6 mg per dose; frequency varies by indication |
| Route | Subcutaneous |
| Frequency | Twice weekly in outpatient trials; every 12 hours in acute critical-illness protocols |
| Duration studied | 7โ14 days in critical illness; 8 weeks in the prevention trial |
| Evidence level | Clinical Trial Evidence |
| Last reviewed | 2026-09-05 |
Research-reported dosing
Doses as studied, one row per regimen. Different trials used different regimens; they are listed separately rather than averaged.
| Study / context | Population | Dose | Route | Frequency | Duration | Outcome studied | Source |
|---|---|---|---|---|---|---|---|
| Severe acute necrotising pancreatitis trial (2022)Clinical trial ยท Randomised placebo-controlled trial | Patients with predicted severe acute necrotising pancreatitis | 1.6 mg every 12 hours for 7 days, then 1.6 mg once daily for 7 days | Subcutaneous | Every 12 hours, then once daily | 14 days total | Immune enhancement and infection | Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial. Intensive Care Med. 2022. |
| COVID-19 prevention pilot trial (2023)Clinical trial ยท Randomised controlled pilot trial | Randomised participants (n=194) | 1.6 mg | Subcutaneous | Twice weekly | 8 weeks | Infection and morbidity | A pilot trial of Thymalfasin (Ta1) to prevent COVID-19 infection and morbidities. Int Immunopharmacol. 2023. |
| NCT02867267 โ phase 3, sepsis, completedClinical trial ยท Phase 3 randomised trial, completed, no results posted | Patients with sepsis (n=1106) | Per trial protocol | Subcutaneous | โ | โ | Efficacy and safety in sepsis | NCT02867267 โ The Efficacy and Safety of Ta1 for Sepsis |
| NCT05086614 โ phase 3, adjuvant after hepatocellular carcinoma resectionClinical trial ยท Phase 3 trial, recruiting | Patients after radical resection of high-risk hepatocellular carcinoma (n=2500) | Per trial protocol | Subcutaneous | โ | โ | Recurrence-free survival | NCT05086614 โ Thymosin-alpha 1 for Adjuvant Treatment After Radical Resection of High-risk Hepatocellular Carcinoma |
Where sources disagree
- The 1.6 mg dose is consistent across trials, but the frequency is not: twice weekly for outpatient immune support versus every 12 hours in acute critical illness. Quoting "1.6 mg" without the interval and the indication conveys almost nothing about the regimen studied.
- Almost all trial evidence is in hospitalised or seriously ill populations โ sepsis, necrotising pancreatitis, hepatitis, cancer adjuvant therapy. Thymosin alpha-1 is sold for general immune support in healthy people, a setting with no comparable trial evidence.
- DailyMed lists no current FDA-labelled product. Approval as thymalfasin in other countries does not create a US approved dose.
Reconstitution
Common research vial sizes: 1.6 mg, 5 mg, 10 mg.
| Vial | Bacteriostatic water | Concentration | Per 0.01 mL |
|---|---|---|---|
| 1.6 mg | 1 mL | 1.6 mg/mL | 16 mcg per 0.01 mL |
| 10 mg | 2 mL | 5 mg/mL | 50 mcg per 0.01 mL |
These figures are arithmetic only โ they convert a vial and a volume into a concentration. They are not a recommendation to take any dose.
Calculate reconstitution & dose โHandling & administration
- Reconstitution Guide
- 3 mL BAC for 5 mg vial
- Injection Sites
- AbdomenThigh
- Concentration Example
- 5 mg / 3 mL = ~1.67 mg/mL
- Timing Notes
- Morning/evening
- Expected Onset
- 1-2 weeks
How to reconstitute Thymosin Alpha-1
- Check the vial size and diluent volume. The profile example for Thymosin Alpha-1 is: 3 mL BAC for 5 mg vial.
- Swab both vial stoppers and draw the bacteriostatic water into a sterile syringe.
- Add the water slowly down the inside wall of the peptide vial so it does not jet onto the powder, then swirl gently until the solution is clear. Do not shake.
- Record the resulting concentration: 5 mg / 3 mL = ~1.67 mg/mL.
- Label the vial with the date and concentration, refrigerate it (see Storage & stability below), and use the calculator preset to convert a dose in mcg into syringe units.
Open the peptide calculator with the Thymosin Alpha-1 preset โ
Sequence & molecular data
| Amino acid sequence | Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH |
|---|---|
| Molecular formula | C129H215N33O55 |
| Molecular weight | 3108.3 g/mol |
| CAS number | 62304-98-7 |
| Half-life | ~2 hours |
| Appearance | White lyophilized powder |
| Formulation | Lyophilized Powder |
| PubChem CID | 16130571 |
| FDA UNII | W0B22ISQ1C |
| ChEMBL | CHEMBL2103979 |
Identifiers link to the public PubChem, FDA Substance Registration (UNII), ChEMBL and DrugBank records for the same entity.
Science
Mechanism of Action
Thymosin alpha-1 is a 28-amino-acid acetylated peptide cleaved from prothymosin alpha, originally isolated from thymic tissue. It acts as an immune modulator rather than an immune stimulant: it signals through Toll-like receptors, principally TLR2 and TLR9, on dendritic cells and monocytes, promoting their maturation and shifting T-cell differentiation toward a Th1 profile with increased interferon gamma and interleukin-2. It also augments natural killer cell activity and restores T-cell counts in lymphopenic states. Notably it does not appear to drive inflammation in the way a direct cytokine would, which is why it has been studied both in infection and in sepsis. It is approved in several countries outside the United States.
Origin
Synthetic N-acetylated thymosin ฮฑ1.
Targets
Studies
- Comprehensive Review of the Safety and Efficacy of Thymosin Alpha 1 in Human Clinical Trials
- Thymosin ฮฑ-1 in Cancer Therapy: Immunomodulatory Mechanisms, Clinical Applications, and Translational Perspectives
- Aging and Thymosin Alpha-1
- Phenotypic drug discovery: a case for thymosin alpha-1
- Thymosin alpha 1 treatment for patients with sepsis
Regulatory & research status
Thymosin Alpha-1 is not an FDA-approved product. It is sold for laboratory research and has no approved medical use.
| FDA status | Not Approved |
|---|---|
| Availability | Research-Only |
| WADA (sport) | Unknown / Not Listed |
| Library classification | Research-Only |
Benefits
Thymosin Alpha-1 side effects
The effects below are those reported in Thymosin Alpha-1 clinical trials; long-term safety data may still be limited.
Side Effects
- Injection-site reactions
- Flu-like symptoms
Contraindications
- Thymic tumors
Stacking
Common stacking partners
Combinations that include Thymosin Alpha-1, with the proposed rationale, an evidence grade and what is not established, are catalogued in the peptide stacks directory.
Storage & stability
Lyophilized (freeze-dried) peptide powder is far more stable than the reconstituted solution. Keep sealed vials cold, dry and away from light; long-term storage is typically frozen, with short-term refrigeration for vials in use.
Once reconstituted in bacteriostatic water, keep the solution refrigerated, avoid repeated freezeโthaw cycles and agitation, and label the vial with the reconstitution date and concentration. Discard any solution that turns cloudy or shows particulates.
Degradation rates differ by sequence: peptides containing methionine, cysteine, asparagine or glutamine are more prone to oxidation and deamidation, so shelf life after reconstitution is compound-specific rather than universal.
Read the full guide: how to store peptides before and after reconstitution โ
Source: Manning MC, Chou DK, Murphy BM, Payne RW, Katayama DS. Stability of protein pharmaceuticals: an update. Pharm Res. 2010;27(4):544โ575. (PMID 20143256). General guidance for research handling; not product-specific instructions.
Thymosin Alpha-1: frequently asked questions
What is Thymosin Alpha-1?
28-aa thymic peptide (thymalfasin). Approved in several countries (Zadaxin) for hepatitis B and as an immune adjuvant; not FDA-approved in the US. Thymosin alpha-1 is a 28-amino-acid acetylated peptide cleaved from prothymosin alpha, originally isolated from thymic tissue. It acts as an immune modulator rather than an immune stimulant: it signals through Toll-like receptors, principally TLR2 and TLR9, on dendritic cells and monocytes, promoting their maturation and shifting T-cell differentiation toward a Th1 profile with increased interferon gamma and interleukin-2.
What are the side effects of Thymosin Alpha-1?
Side effects recorded for Thymosin Alpha-1 from clinical-trial reports include injection-site reactions and flu-like symptoms. Cautions recorded on this profile: thymic tumors. This is reference information, not medical advice.
How does Thymosin Alpha-1 work?
Thymosin alpha-1 is a 28-amino-acid acetylated peptide cleaved from prothymosin alpha, originally isolated from thymic tissue. It acts as an immune modulator rather than an immune stimulant: it signals through Toll-like receptors, principally TLR2 and TLR9, on dendritic cells and monocytes, promoting their maturation and shifting T-cell differentiation toward a Th1 profile with increased interferon gamma and interleukin-2.
Is Thymosin Alpha-1 FDA approved?
No. Thymosin Alpha-1 is not approved by the FDA for any indication and is categorised as research-only. It has not been reviewed for safety or efficacy as a medicine, and published research should be read as investigation rather than established use.
What is the half-life of Thymosin Alpha-1?
Reported half-life for Thymosin Alpha-1 is ~2 hours. Half-life describes how long the compound persists in circulation, not how long any effect lasts, and published figures vary with route of administration, formulation and the population studied.
What is the amino acid sequence of Thymosin Alpha-1?
Thymosin Alpha-1 has the sequence Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH, giving a chain of 30 amino acids. Its molecular formula is C129H215N33O55.
What peptides are similar to Thymosin Alpha-1?
Compounds most often compared with Thymosin Alpha-1 include Thymalin, Thymogen (Oglufanide), Thymopentin and Thymulin. They are grouped by shared mechanism or research area rather than by equivalence, and their regulatory status and evidence base differ.
How long does Thymosin Alpha-1 take to show effects in research protocols?
The research protocol on this profile lists an expected onset of 1-2 weeks. This is a protocol note describing when studies and researchers report observing changes, not a measured clinical outcome, and it varies with the model, dose and endpoint studied.
Where is Thymosin Alpha-1 administered in research protocols?
Research protocols on this profile use subcutaneous administration, with recorded sites including abdomen, thigh. Site rotation and sterile technique are standard practice in the research literature; this describes protocol conditions and is not guidance for use.
References
- Comprehensive Review of the Safety and Efficacy of Thymosin Alpha 1 in Human Clinical Trials โ Altern Ther Health Med, 2024External reference
- Thymosin ฮฑ-1 in Cancer Therapy: Immunomodulatory Mechanisms, Clinical Applications, and Translational Perspectives โ Eur J Pharmacol, 2026External reference
- Aging and Thymosin Alpha-1 โ Int J Mol Sci, 2025External reference
- Phenotypic drug discovery: a case for thymosin alpha-1 โ Front Med (Lausanne), 2024External reference
- Thymosin alpha 1 treatment for patients with sepsis โ Expert Opin Biol Ther, 2018External reference
Related research, comparisons & guides
- Thymosin Alpha-1: An Approved Immune Drug in Much of the World
- Thymalin: A Thymus Extract From the Soviet Peptide Programme
- Peptide stacks: combinations by research goalStacks
- Peptide dosage chart: dose, route and frequencyCategory
- Peptide calculator with the Thymosin Alpha-1 preset
- How to store peptides before and after reconstitution
Related peptides
Compiled by Peptide Library Editorial ยท Reviewed Aug 30, 2026 ยท Updated Sep 26, 2026 ยท Version 6
This Thymosin Alpha-1 profile is compiled from published literature (5 cited studies linked above), public regulatory records and chemical registries. It describes what research reports; it is not medical advice, and nothing here is a dosing recommendation for humans. Peptide Library does not sell peptides. Editorial policy ยท How profiles are compiled ยท Report an error
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