Compound guide · Tier A
Thymosin alpha-1
A real approved medicine in about thirty countries, for hepatitis rather than for anything the wellness market buys it for, and not approved at all in the United States.
The short answer
Thymosin alpha-1 has the strongest international regulatory position of any unapproved-in-the-US compound in this catalogue, and that position is narrower than it sounds. Zadaxin is a licensed medicine in around thirty countries, prescribed mainly for chronic hepatitis B and given alongside other therapy, plus use as a vaccine adjuvant in patients whose immune systems are compromised. That is a serious clinical role in a defined patient group. It is not evidence for general immune support, longevity, or resilience in healthy adults, which is what the research market buys it for, and the FDA has never approved it while keeping it in Category 2 for compounding.
At a glance
| Class | 28 amino acid thymic peptide, immune modulator |
| Developer | SciClone Pharmaceuticals |
| Sold as | Zadaxin (thymalfasin) |
| Regulatory status | Approved in around 30 to 35 countries, and not in the United States. Thymalfasin is marketed as Zadaxin with national approvals including China, Italy and the Philippines, principally for chronic hepatitis B, with further approvals covering chronic hepatitis C and use as a vaccine adjuvant in immunocompromised patients. It is not FDA approved. This is the clearest case on the site of a compound whose regulatory status genuinely depends on which country you are standing in. |
| Compounding status | Thymosin alpha-1 sits on the FDA 503A Category 2 bulk substances list in the United States, meaning it cannot lawfully be compounded there pending further review, while simultaneously being an approved prescription medicine in Italy and China. Both statements are true at once and neither cancels the other. |
| Anti-doping | Not specifically named on the prohibited list. Immune modulators should still be checked against the list as published each year. |
| Our evidence tier | Tier A. Approved medicine |
What it is
Thymosin alpha-1 is a 28 amino acid peptide originally isolated from thymic tissue, where it participates in T cell maturation. Synthetic thymalfasin is the pharmaceutical version. It acts on Toll like receptor signalling and on dendritic and T cell function, so its mechanism is genuinely immunological rather than metaphorically so, which distinguishes it from most compounds sold for immune support.
Who it is for, and who actually takes it
The approved populations are people with chronic hepatitis B, chronic hepatitis C in the countries where that indication is licensed, and immunocompromised patients receiving vaccines where it is authorised as an adjuvant. These are supervised clinical settings with monitoring.
It is bought by healthy adults for general immune support, for post viral recovery, and as part of longevity protocols. None of those is an approved indication anywhere, and the trials that produced the approvals were conducted in people with a specific chronic infection.
What the research shows
The approvals rest on virological response rates across national trial programmes with differing designs and combination partners. There is no single controlled comparison that would honestly reduce to one chart.
Dosing
| Stage | Dose |
|---|---|
| Approved indications | Chronic hepatitis B, chronic hepatitis C in some markets, vaccine adjuvant in immunocompromised patients |
| Approved as | Zadaxin (thymalfasin), subcutaneous injection |
| Approving regulators | National authorities in around 30 to 35 countries, including Italy and China |
| United States | Not FDA approved. Listed in 503A Category 2 for compounding |
We reproduce the shape of the approved use rather than a schedule, because the approvals are national and the labelling differs between them, so there is no single published label to reproduce the way there is for an FDA approved product. Where you are matters here more than for any other compound on this site. We publish no reconstitution guidance.
What happens when you come off it
In the approved hepatitis indications, treatment runs as a defined course alongside other therapy and the relevant outcome is the virological response, not a state that persists from the peptide itself. For the immune support use, there is no controlled evidence of any effect to persist or fade.
What it is being studied for
| Area | Stage of evidence |
|---|---|
| Chronic hepatitis B | Approved in around 30 countries |
| Chronic hepatitis C | Approved in some markets, usually in combination |
| Vaccine adjuvant in immunocompromised patients | Approved in some markets |
| Sepsis and critical illness | Studied, including randomised trials, not an approved indication |
| General immune support in healthy adults | No approved indication and no controlled evidence |
The critical care literature is genuinely interesting and genuinely unfinished. It is also the study of a drug given to seriously ill patients in intensive care, which is about as far from a healthy adult buying immune support as clinical medicine gets.
Common myths
It is FDA approved.
It is not, and it remains on the FDA 503A Category 2 list for compounding in the United States. It is approved in around thirty other countries including Italy and China. Both facts are true and vendors tend to cite only whichever suits.
Approved for hepatitis means it boosts immunity generally.
It means it has a demonstrated role in a specific chronic viral infection, usually alongside other treatment, in patients under clinical supervision. Immune modulation is not a dial that turns up.
It is from the thymus, so it just restores what ageing takes away.
Thymic involution with age is real and the inference is not. No controlled trial has shown that administering thymosin alpha-1 to healthy older adults reverses immune ageing or improves any clinical outcome.
It was proven in COVID, so it works for viral illness.
It was studied during COVID, including in registered trials, and studied is not proven. None of that work produced an approval for that indication.
Verifying a purchase
Thymosin alpha-1 is a 28 amino acid peptide with an acetylated N terminus, and the acetylation is easy to omit in synthesis and invisible on HPLC purity alone. Confirm the mass against 3108.3 Da by mass spectrometry, check CAS 62304-98-7, and require the batch code from your vial on the report. An unacetylated analogue would look clean and would not be the same molecule.
The general method is set out in our guide to reading a certificate of analysis, which covers the eleven checks that apply to any compound. The points above are the ones specific to Thymosin alpha-1.
Caveats and safety
The safety record in the approved hepatitis indications is reasonable and it was accumulated under prescription with monitoring. Deliberately modulating T cell function is not a trivial intervention, and it is a poor idea in anyone with an autoimmune condition or on immunosuppressive therapy, which is exactly the kind of assessment a prescriber makes and a web order does not.
Where to get it
Where to get it
CertaPeptides Romania, EU. Volume discounts at 3+, 5+ and 10+ units.
| Vial | Price |
|---|---|
| 2 mg | €20.99 |
| 5 mg | €49.49 |
| 10 mg | €97.49 |
Stated purity. ≥98% stated batch specification. Published lot report #212159 returned 99.63% on a 5 mg vial.
Documentation. Selected lots independently tested by Janoshik Analytical (Czech Republic), HPLC plus mass spectrometry, reports searchable on the Janoshik public portal and at certapeptides.com/verify.
Thymosin alpha-1 is sold as laboratory research material. The vendor states it is not for human consumption and that it is not approved by the FDA, the EMA or any other regulator for use in humans or animals. Read the evidence tier at the top of this page before the price.
View Thymosin alpha-1 at CertaPeptidesAffiliate link. We earn a commission if you buy, at no extra cost to you. It does not change a word of the assessment above. Every product we have priced, in one list.
Sources
- European Medicines Agency medicine records
- FDA bulk drug substances nominated for use under section 503A
- Registered thymalfasin trials, ClinicalTrials.gov
- Thymosin alpha-1 literature, PubMed
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Disclosure. PeptoPurity is an affiliate of CertaPeptides and earns a commission on qualifying purchases made through the vendor link on this page, at no additional cost to you. That relationship does not set the evidence tier, alter the verdict, or change a word of the assessment. Our Tier C and Tier D pages carry the same links as our Tier A pages, with the same conclusions we would publish if we earned nothing. Where the registered, prescribed route is the better option, we say so on the page that would otherwise pay us.
Scope. This is an evidence review, not medical advice. Where an approved label schedule is reproduced it is a record of what a regulator has published about a licensed medicine, not a recommendation and not a schedule for anyone to follow unsupervised. For unapproved compounds we report only the doses used in published studies, attributed to those studies, and we publish no protocols and no reconstitution guidance for any compound. Regulatory status differs between countries and changes over time. Material sold for laboratory research is not approved for human use. Decisions about treatment belong with a qualified prescriber.