Thymosin alpha-1
Tα1ThymalfasinZadaxin (brand)Evidence
Approved (ex-US)
Half-life
2 h
Typical vial
5 mg
Route
Subcut
What it is
An immune-modulating peptide approved in more than thirty countries for hepatitis B, and studied in sepsis and as a vaccine adjuvant. Not approved in the United States.
Thymosin alpha-1 is a 28-amino-acid peptide originally isolated from the thymus, the organ that trains T cells. It is genuinely a medicine in much of the world: approved in over thirty countries as thymalfasin, principally for chronic hepatitis B, and used in some settings for sepsis and as a vaccine adjuvant.
It is not approved in the United States, which puts it in an unusual position: a compound with substantial clinical use and published trials, sold domestically as a research chemical because the approval happens to be somewhere else.
Unlike TB-500, which is a fragment of a different thymic protein and has no human data, thymosin alpha-1 is the full peptide with real clinical evidence behind it. The names are similar enough that they get conflated constantly, and they are not comparable in evidence.
How it works
Thymosin alpha-1 acts on Toll-like receptors on dendritic cells and influences T cell maturation, pushing the immune response toward a Th1 pattern, the arm that deals with intracellular pathogens and abnormal cells.
It is an immune modulator rather than an immune stimulant, which is a meaningful distinction: the reported effect is on how the response is shaped rather than simply how strong it is. That is also why the caution around autoimmune disease is a genuine one rather than boilerplate.
What it is studied for
Each entry states the evidence behind it. We do not rank indications by effectiveness — for most compounds here, that would be a claim nobody can support.
Chronic hepatitis B
Clinical trialThe main approved indication.
EvidenceClinical trials supporting approval in over thirty countries.
Sepsis
Clinical trialStudied as an adjunct in severe infection.
EvidenceRandomised trials with mixed results. An area of ongoing study, not a settled use.
General immune support
Community practiceThe reason it is used in this community.
EvidenceNot studied as an endpoint in healthy adults. Extrapolated from use in disease states.
Regulatory status
Last reviewed 12 Aug 2026. Positions in this category change frequently, so we date the line.
Approved as thymalfasin in more than thirty countries, principally for chronic hepatitis B. Not approved in the United States, where it is sold as a research chemical with no manufacturing standard behind it.
Identity and clearance
What the molecule is, and how long a dose stays measurable.
Molecule
- Class
- Thymic peptide, immune modulator
- Molecular weight
- 3108.3 Da
- Length
- 28 amino acids
The full naturally occurring peptide, not a fragment. That is what distinguishes it from TB-500.
Pharmacokinetics
Clinical trialShort-acting. That is why approved regimens use twice-weekly subcutaneous dosing over months.
Dose protocols reported in sources
Displayed for reference only. Every row says where it came from, and a trial protocol and a community convention are not the same kind of information. None of this is fed into the calculator, and none of it is a recommendation.
A week-by-week progression is also reported for Thymosin alpha-1. See it against a 5 mg vial, where the syringe units can be worked out.
| Goal | Dose | Frequency | Route | Units, 5 mg vial | Source | Start this protocol |
|---|---|---|---|---|---|---|
| Approved regimen for hepatitis B | 1.6 mg | Twice weekly for six months | Subcutaneous | 64 u | Clinical trial | Start this |
| Commonly described for general use | 450 mcg – 1.6 mg | Two or three times weekly | SubcutaneousBelow the approved regimen, and for an indication that has not been studied. | 18–64 u | Community practice | Start this |
The doses above in syringe units, for the vial you have:
Start this copies a row into a protocol of your own, which you can then edit. Where a source gave a dose range or an ambiguous frequency, those fields arrive empty — we will not pick a number on your behalf.
CheckRows marked community practice describe what people commonly do, drawn from public discussion. They are not derived from any trial and are not evidence that a dose is safe or effective.
Work out what to draw
Pre-filled with a 10 mg vial as a worked example. These are not recommended values — change them to match the vial in front of you.
Draw to 32 units on a 1 mL U-100 syringe. That is 0.32 mL, containing 1.6 mg of Thymosin alpha-1.
32 units sits exactly on a printed line.
BioAlmanac performs arithmetic on values you enter. It does not recommend doses, schedules or compounds, and nothing here is medical advice. Confirm every calculation against your vial and syringe before drawing, and speak with a licensed healthcare provider.
Open this calculation in the full calculator
Units, concentration, bacteriostatic water — the glossary defines the vocabulary, and a unit is not a fixed volume.
Safety
Reported effects, the situations that need care, and the ones that mean stop.
Reported effects
- Injection site redness or discomfortClinical trial
Common in trials
The most frequently reported effect, and generally mild.
- Transient fatigueCommunity practice
Occasionally reported
- Generally well toleratedClinical trial
Documented across trials
Its tolerability in clinical use is one of the better-established things about it.
When to stop
- Any new joint pain, rash, or unexplained fever. These can be early signs of immune activation going the wrong way.
- Any allergic response: rash, hives, facial swelling or difficulty breathing. Seek urgent care.
- A flare of any existing autoimmune condition.
- Signs of infection at an injection site.
Interactions and situations that need care
- Autoimmune diseaseAvoid
This modulates T cell responses toward a more active pattern. In a condition where the immune system already attacks the body's own tissue, pushing that direction is the specific thing you would not want, and it has not been studied.
- Immunosuppressant therapy or transplantAvoid
Immunosuppression after a transplant exists to prevent rejection. An immune modulator works directly against that, and the consequence of getting it wrong is organ loss.
- Pregnancy and breastfeedingAvoid
No reproductive or developmental safety data.
What to expect
What the sources describe over time, and how confident anyone can be about it.
- The clinical evidence concerns hepatitis B and sepsis, in people with those conditions. General immune support in healthy adults is not what was studied.
- Approved regimens run for months, not weeks. In its evidenced use this is not a short course.
- Its tolerability is well established, which is genuinely unusual for anything on this site.
- Material sold in the United States is not the approved product, so the trial evidence does not follow it.
Storage and combinations
How to keep it, and what it does and does not go with.
Storage and handling
- Freeze-dried powder
- Refrigerated at 2–8 °C, protected from light.
- After mixing
- Refrigerated at 2–8 °C. Do not freeze once mixed.
- Long-term, frozen
- Unopened powder is stable at −20 °C or colder.
With other peptides
- Thymalincaution
Thymalin is an undefined calf thymus extract, and thymosin alpha-1 was originally identified as a component of exactly that kind of preparation. Running both is probably taking the same thing twice, once in a known quantity and once in an unknown one.
- Thymulincaution
Both are thymic peptides acting on T-cell function. Thymosin alpha-1 has registered clinical use in several countries and thymulin has none, so running both adds an unstudied compound to a studied one for overlapping effect.
Stacks with Thymosin alpha-1 in them
Documented combinations and plans people have published, with full schedules.
Published by people running it. Their plans, not ours — one person doing something is not evidence that it works.
Checking your vial
Research chemicals carry no manufacturing standard, so what the vial looks like is often the only quality signal available before you use it.
White cake, clear solution
Standard for a peptide of this size.
Collapsed cake or cloudy solution
Indicates heat damage or degradation.
Vocabulary on this page
- Research chemical
- A legal label, not a quality grade. It describes what a seller is permitted to sell you, and says nothing about what is in the vial.
- Evidence level
- The category of human evidence behind a compound, from preclinical through to approved. Stated on every profile here as a category, not an adjective.
- Injection site
- Where on the body an injection is given. Rotating between sites is standard practice for anything given repeatedly.
- Peptide
- A short chain of amino acids: the same building blocks as a protein, in a chain short enough to behave differently.
- Protocol
- One compound, with a dose, a frequency and a length: the plan, as opposed to what was actually taken.
Questions
- Is thymosin alpha-1 the same as TB-500?
- No, and the confusion is common. Thymosin alpha-1 is a full 28-amino-acid peptide with clinical trials and approvals in over thirty countries. TB-500 is a fragment of thymosin beta-4 — a different protein — and it has no completed human trials. Similar names, entirely different evidence.
- Why is it not approved in the United States?
- It holds approvals in more than thirty countries but has not completed the US regulatory pathway for its indications. That is a regulatory fact rather than a safety finding.
References
Everything on this page that came from a source, with the source.
Thymosin alpha-1: from bench to bedside, clinical development and use
Annals of the New York Academy of Sciences / review literature, 2012 · Review of clinical trials and approved use
Humans
Reviews approval for chronic hepatitis B across multiple jurisdictions, trial evidence in sepsis and as a vaccine adjuvant, and a consistently favourable tolerability profile.
Commonly reported community protocols
BioAlmanac editorial summary of public community sources, 2026 · Not a study
Summarises dose ranges described for general immune use, an indication with no supporting trials. Carries no evidential weight.
Compiled community protocols
BioAlmanac editorial summary of a public protocol compilation, 2026 · Not a study
Records a week-by-week progression described on a vendor-adjacent protocol site, retrieved August 2026. Only the doses are taken from it. Its own syringe-unit conversions were checked against the vial sizes it states and several understate the volume by half, so nothing computed by that source is reproduced here — the units on this site are worked out from the vial in front of you. Carries no evidential weight about safety or effect.
Related compounds
Thymalin
A thymus extract used as a medicine in Russia for decades. Not a single defined peptide, which is the fact that governs everything else on this page.
Thymulin
A genuine thymic hormone with real immunology behind it, and no clinical development. It only works with zinc bound to it, which is the most useful fact about it.
BPC-157
A synthetic 15-amino-acid peptide studied in animals for effects on tendon, ligament and gut tissue repair. No completed human trials.
TB-500
A synthetic fragment of thymosin beta-4, a naturally occurring protein involved in cell migration and tissue repair. Animal evidence only.
Next
What to do with Thymosin alpha-1
- Keep a record of itTurn a dose and a schedule into a protocol, then log what you actually take. Thymosin alpha-1 is filled in for you.
- See what it costsPer-milligram prices read from vendor sites and confirmed by a person, so vial sizes compare.
- Check a combinationWhat our profiles record about Thymosin alpha-1 alongside each other compound — including the pairs where nothing is recorded.
Keep this page honest
If something here is wrong, out of date, or missing a source, tell us and we will fix it and say that we did.
This page is educational. It describes what published research reports, not what you should do. Peptides discussed here are largely not approved for human use, and nothing on BioAlmanac is medical advice. No clinician reviews these pages.
Page last updated 12 Aug 2026