Thymosin Alpha-1
Also known as Ta1, Zadaxin, Thymalfasin, Thymosin a1
Thymosin alpha-1 is a 28 amino acid peptide originally isolated from the thymus that primes T cells and dendritic cells. It is a licensed drug in much of the world for chronic hepatitis B and immune support, and in the research market it is used for infections, immune weakness and general resilience.
Reviewed by the amino101 editorial team. .
Quick start
What people commonly do. Not a prescription.- Typical dose
- 0.5 to 1.6 mg
- How often
- twice weekly, up to daily in short acute protocols
- Where
- Subcutaneous, belly or thigh
- Timing
- any time of day, food does not matter
- Effects timeline
- nothing to feel in the first weeks; immune markers and infection frequency are judged over 2 to 6 months
- Storage
- fridge 2 to 8 C before and after mixing, use within 4 weeks once reconstituted
- Cycle length
- 4 to 12 weeks in community use; 6 months in the hepatitis B labeling
- Break between
- 4 to 8 weeks, or use only around a specific illness or vaccination
A 5 mg vial in 2 mL gives 2.5 mg per mL, so 1.6 mg is 64 units on an insulin syringe.
Overview
Thymosin alpha-1 is a 28 amino acid peptide first isolated from calf thymus tissue in the 1970s. The synthetic version, thymalfasin, is sold as Zadaxin by SciClone and is approved in China, Italy and more than 30 other countries for chronic hepatitis B and as an adjuvant to vaccines and chemotherapy. It has never been approved in the United States. Outside the countries where it is licensed it is sold as a research chemical, and in 2023 the FDA placed it in Category 2 of the bulk substances list, which stopped US compounding pharmacies from preparing it.
This is one of the few peptides on this site with real human trial data behind it. Randomized trials have tested it in chronic hepatitis B and C, in severe sepsis, as a booster for flu and hepatitis vaccines in people who respond poorly, and alongside chemotherapy in melanoma and lung cancer. Results are mixed rather than dramatic. The hepatitis B trials show improved virological response in some but not all studies, and the sepsis trial showed a trend toward lower mortality that did not reach significance. Safety across these trials has been consistently good, which is the strongest argument in its favor.
Thymosin alpha-1 is often confused with TB-500, which is a fragment of thymosin beta-4. The two share a name and nothing else. TB-500 regulates actin and is used for injury recovery, while thymosin alpha-1 acts on immune cells and has no tissue repair effect of its own. The approved dose is 1.6 mg subcutaneously twice weekly, and community protocols tend to use the same dose or lower. This page is educational and describes what appears in labeling and research, not a treatment plan.
How it works
Thymosin alpha-1 acts mainly through toll-like receptors on dendritic cells and other antigen presenting cells, especially TLR2 and TLR9. Activation pushes these cells to mature and present antigen more effectively, which in turn drives differentiation of naive T cells toward the Th1 pattern that handles viral infections and tumors. It increases interleukin-2 and interferon gamma output, raises natural killer cell activity and supports cytotoxic T cell responses. It also appears to dampen excessive inflammation in states like sepsis, which is why it is described as an immune modulator rather than a stimulant. There is no direct antiviral action; the effect comes from a more competent immune response.
Where the research stands
Chronic viral hepatitisModerate evidence
- Hepatitis B. Several randomized trials and a meta-analysis show improved virological response, though individual trials disagree and newer antivirals have largely replaced it.
- Hepatitis C. Trials with interferon showed small additive benefit at best, and a US phase 3 trial did not meet its endpoint.
Vaccine responseModerate evidence
- Poor responders to influenza and hepatitis B vaccines. Randomized trials in older adults and dialysis patients found higher antibody titers when thymosin alpha-1 was given around vaccination.
Severe infection and sepsisEmerging
- Severe sepsis. The ETASS randomized trial found a mortality trend in favor of the drug that did not reach significance; a larger follow up trial has been run in China.
- COVID-19. Observational data from Chinese hospitals suggested benefit in some groups; no randomized trial confirmed it.
Cancer adjuvantEmerging
- Melanoma and lung cancer with chemotherapy. A phase 2/3 melanoma trial showed better response rates with dacarbazine; this is supportive care alongside treatment, never a replacement for it.
- human RCTIn chronic hepatitis B, six months of thymalfasin 1.6 mg twice weekly improved sustained virological response rates over placebo in several randomized trials, with a meta-analysis showing roughly double the response rate at follow up.
- human RCTThe ETASS trial in 361 patients with severe sepsis found a lower 28 day mortality trend with thymosin alpha-1 added to standard care, but the difference did not reach statistical significance.
- human RCTOlder adults and hemodialysis patients given thymosin alpha-1 alongside influenza or hepatitis B vaccine produced higher antibody titers than vaccine alone.
- human RCTA phase 2/3 trial in metastatic melanoma found thymosin alpha-1 added to dacarbazine improved response rate and a trend toward longer survival.
- rodentIn mice, thymosin alpha-1 activated dendritic cells through TLR9 and improved survival in fungal infection models, which established the receptor level mechanism.
- clinical (approved drug)Across clinical trials totaling thousands of patients, adverse events were mostly limited to injection site discomfort, with no pattern of serious drug related toxicity.
Rodent and in vitro mean no human data for that finding. Human pilot means small, often uncontrolled. Human RCT means randomized and controlled. Clinical means an approved drug with regulatory data.
Levels over time
Modeled from the half-life. Illustrative, not measured.A half-life of 2 h against dosing every 24 h means each dose has cleared before the next. Nothing stacks; you start from zero every time, and the tissue effect is what carries over.
The short plasma half-life does not match the twice weekly schedule, which works because the peptide changes how immune cells behave for days after it has cleared. The approved schedule was set by clinical trial, not by pharmacokinetics.
Thymosin Alpha-1 dosage and protocols
The approved hepatitis B course is 6 months of twice weekly injections without a break. Community protocols are shorter, typically 4 to 12 weeks, with a pause of a month or two before repeating. There is no loading phase and no taper. Short daily courses of 5 to 7 days around an acute infection are borrowed from the sepsis trial design.
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| Approved hepatitis B schedule | 1.6 mg | twice weekly for 6 months | Subcutaneous |
| Vaccine adjuvant | 1.6 mg | twice weekly for 4 weeks starting at vaccination | Subcutaneous |
| General immune support, community | 0.5 to 1 mg | 2 to 3 times weekly | Subcutaneous |
| Acute illness, community | 1.6 mg | once daily for 5 to 7 days | Subcutaneous |
Food, training and sleep do not affect it. Twice weekly doses are spaced 3 to 4 days apart. When used around a vaccine, trials started dosing on the day of vaccination. It mixes with bacteriostatic water like any lyophilized peptide and does not need to be kept separate from other injections.
The approved labeling uses 1.6 mg twice weekly. Community protocols commonly run 0.5 to 1.6 mg, two to three times a week, with some daily protocols during acute illness.
Dose calculator
U-100 insulin syringeUnits are a volume on the syringe, not an amount of peptide. Concentration changes every time you change the water volume. The standalone calculator explains the math.
| Vial | Suggested water | Concentration | Low dose draw |
|---|---|---|---|
| 5 mg | 2 mL | 2.5 mg/mL | 20 units |
| 10 mg | 2 mL | 5 mg/mL | 10 units |
How to reconstitute Thymosin Alpha-1
- 1
Wash your hands and wipe the work surface. Swab both vial stoppers with alcohol and let them dry.
- 2
Pick the water volume with the calculator above and write it on the vial. The concentration means nothing without it.
- 3
Draw the bacteriostatic water into a mixing syringe.
- 4
Insert at an angle and let the water run down the inside wall. Never squirt it straight onto the powder.
- 5
Swirl gently or leave it to dissolve. Do not shake.
- 6
Label with the date and water volume. Store in the fridge at 2 to 8 C and use within about 4 weeks.
- 7
Unmixed vials keep for months in the fridge and longer in the freezer, sealed and out of light.
- Full walkthrough with syringe reading and site rotation: reconstitution guide.
- ✓White, fluffy cake
Lyophilized powder should look like a small white puck or fluffy cake at the bottom of the vial. That is a proper freeze-dry.
- ✓Clear after mixing
Once dissolved the solution should be water-clear with nothing floating in it.
- !Slight clumping
Small clumps that dissolve with gentle swirling are fine. Shipping compacts powder.
- ✕Collapsed or melted
Powder stuck to the sides, glassy, or shrunken means it got hot in transit. Contact the vendor.
- ✕Cloudy or particles
Persistent cloudiness or visible particles after mixing means degraded or contaminated product. Do not use it.
- Week 1 to 2
Usually nothing noticeable beyond mild injection site redness; some people report feeling slightly run down or warm after the first doses.
- Week 3 to 8
Any change in infection frequency or recovery speed is first judged here; there is no acute feeling to track, and bloodwork on lymphocyte subsets is the only objective measure.
- Month 3 to 6
This is the window the hepatitis B trials used for virological response, and the earliest point where a chronic infection goal can fairly be evaluated.
Interactions and stacking
LL-37compatible
Community immune stack combining adaptive immune priming with a direct antimicrobial peptide; no interaction known and no trial of the pair.
Glutathionecompatible
Often run together for immune resilience; the two work on unrelated systems and do not interfere.
TB-500compatible
Different peptides for different purposes; no interaction, but check labels carefully since vendors sometimes mislabel the thymosins.
BPC-157compatible
Appears together in recovery and gut protocols; no known interaction.
Interferon and antiviral drugssynergistic
The approved use pairs it with interferon in hepatitis; it was designed to add to antiviral therapy rather than replace it.
Immunosuppressants after transplantavoid
The label advises against use in transplant patients because stimulating T cell activity could promote rejection.
Autoimmune disease treatmentcaution
Raising Th1 activity could in theory worsen conditions like lupus, multiple sclerosis or rheumatoid arthritis; no trial has tested this, so it is a judgment call with a clinician.
An immune focused pairing in community protocols: thymosin alpha-1 primes adaptive immunity while LL-37 is used for its direct antimicrobial action. The combination has no trial data.
Both are used in protocols aimed at immune resilience and recovery from chronic infection; glutathione covers antioxidant capacity while thymosin alpha-1 works on T cell function.
Not for the same purpose despite the similar name. Some recovery protocols run both, with TB-500 for tissue repair and thymosin alpha-1 for immune support, and there is no known interaction.
Safety
- ▲Injection site redness, soreness or small lumps
- ▲Mild muscle aches or fatigue for a day after a dose
- ▲Low grade fever or chills in a small minority
- ▲Transient nausea
- ▲Rare rash or itching away from the injection site
- ▲Not FDA approved. Approval elsewhere does not make a research vial a pharmaceutical product; purity and dosing accuracy depend entirely on the vendor.
- ▲Immune stimulation is a theoretical concern in autoimmune disease and in people on immunosuppressants after transplant. The approved label advises against use in transplant recipients.
- ▲Treated as prohibited in sport by WADA under the S0 non-approved substances heading, and athletes have been sanctioned for it.
- ▲Trial benefits in hepatitis B and sepsis were modest and inconsistent. Community claims about curing chronic infections go well beyond the data.
- ▲Do not confuse it with TB-500. Different peptide, different target, different dose.
- ▲Injection site redness and mild aches are the most common side effects; anything beyond that is unusual and worth investigating.
- ■Signs of an allergic reaction such as hives, swelling of the face or throat, or trouble breathing
- ■A flare of a known autoimmune condition
- ■You receive an organ transplant or start immunosuppressive therapy
- ■Persistent fever or feeling unwell after doses, which should be investigated rather than pushed through
- ■You are subject to anti-doping testing in sport
Community poll
Self-reported by visitors. Not clinical evidence.Thymosin Alpha-1: frequently asked
What is the thymosin alpha-1 dosage used in trials?
The approved dosage for chronic hepatitis B is 1.6 mg subcutaneously twice weekly for six months. Vaccine adjuvant trials used the same 1.6 mg dose for a few weeks around vaccination, and the sepsis trial used 1.6 mg twice daily for five days then once daily for two days. Community protocols usually stay at or below 1.6 mg per injection.
Is thymosin alpha-1 the same as TB-500?
No. TB-500 is a fragment of thymosin beta-4, a cell structure protein used for injury recovery. Thymosin alpha-1 is a separate 28 amino acid peptide that acts on immune cells. They share the thymosin name because both were originally isolated from thymus extract, and that is where the similarity ends.
Why is it approved in other countries but not the US?
SciClone pursued approval mainly in Asia and Europe, where hepatitis B is more common, and never completed a US pivotal program. A US phase 3 trial in hepatitis C with interferon did not meet its endpoint. The FDA has not reviewed it for approval, and in 2023 it was placed in Category 2, which blocks compounding.
Does it help with colds, long COVID or chronic fatigue?
There is no controlled evidence for any of these. Observational reports from the COVID-19 pandemic in China suggested lower mortality in some hospitalized patients who received it, but those were not randomized and later analyses were mixed. For everyday viral infections or fatigue the evidence is anecdote only.
References
- Thymosin alpha 1 in the treatment of chronic hepatitis B: a meta-analysis. Alimentary Pharmacology and Therapeutics, 2001
- The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial. Critical Care, 2013
- Thymosin alpha 1 in combination with dacarbazine in metastatic melanoma: a phase II/III trial. Annals of Oncology, 2010
- Thymosin alpha 1: a historical overview. Annals of the New York Academy of Sciences, 2007
- Zadaxin (thymalfasin for injection) prescribing information. SciClone Pharmaceuticals, 2014