Thymosin alpha-1: what 32 lab results and the FDA record show

Thymosin alpha-1 is sold as a drug abroad and is unapproved in the US. The research-market vials on the public record test well: 32 results, median purity 99.70%, median fill 113.2% of label, 0 fails. These are results vendors and labs chose to publish, not a random sample of what is sold. FDA's compounding advisers voted 17 to 4 against thymosin alpha-1 on 4 December 2024, and the HHS policy of 28 October 2026 left it out.

Thymosin alpha-1 at a glance.

Sources for each row are in the sections below.

What thymosin alpha-1 is.

FDA's briefing document for the December 2024 meeting describes thymosin alpha-1 as an "N-terminal acetylated 28-amino-acid peptide", originally isolated from a crude extract of calf thymus. Thymalfasin is the synthetic version and the same molecule. Zadaxin, made by SciClone Pharmaceuticals, is a finished injectable drug containing it (FDA briefing, 15 Nov 2024).

It is not thymosin beta-4. Research shops sell TB-500 as thymosin beta-4 or a fragment of it, and lab databases list both under "thymosin". When we counted, we kept only alpha-1 certificates.

On approvals, FDA's review is cautious. It names an Italian approval as an adjuvant to the influenza vaccine in immunocompromised people, an Indian approval for chronic hepatitis B, and a Hong Kong listing. It cites SciClone's 2014 annual report for wider approvals across Asia-Pacific, Latin America, Eastern Europe and the Middle East, and adds that FDA "is unable to independently verify" those claims. The European Medicines Agency granted it orphan designation for liver cancer in 2002, which is not a marketing approval.

The US regulatory record.

The vote. The committee first agreed 20 to 1 to vote on both forms together. Because one member said no, FDA took separate votes, and both the free base and the acetate salt failed 4 to 17. Members voting no, in the minutes' words, saw "no compelling evidence demonstrating clinical effectiveness and safety" in the uses reviewed. Some members voting yes said the substance should be accessible to patients.

The safety-risk page. FDA's page on bulk substances that "may present significant safety risks" no longer lists thymosin alpha-1 in Category 2. It sits in a separate table of nominations that were withdrawn, with FDA's risk note that compounded drugs containing it "may pose significant risk for immunogenicity". Coming off Category 2 does not make a substance eligible: it is still not on the 503A bulks list, and the advisory vote went against it.

The HHS policy. The Federal Register notice of 28 October 2026 says HHS will not take enforcement action against licensed pharmacies and physicians compounding peptides "found in Appendix A" while FDA works on rulemaking. The HHS policy text lists six peptides in Appendix A, the six that the July 2026 committee recommended: BPC-157, TB-500, epitalon, KPV, MOTS-c and semax. Thymosin alpha-1 is not one of them. Our HHS policy explainer covers the conditions, and our July vote coverage has the background.

It is not a controlled substance, and federal law does not make possessing it a crime. Selling it for human use is a different matter: without an FDA approval it is an unapproved drug, and a "research use only" label does not change that when a shop markets it for people. Our peptide legality tool keeps the record for 44 compounds, and our FDA enforcement timeline covers the warning letters.

What FDA's review said about the clinical evidence.

FDA's 2024 review read the published studies for a dozen uses, among them hepatitis B and C, HIV, COVID-19, sepsis, vaccine response, melanoma, liver and lung cancer, and COPD. Its overall conclusion was "a lack of evidence to support the effectiveness" of the injected peptide for any of them. The review describes the studies as small, often retrospective or single-arm, and compared against outdated standard care. It also noted that the professional treatment guidelines it checked, such as those for hepatitis B, do not mention thymosin alpha-1.

On quality, FDA said the peptide is "not well-characterized": the nomination came without certificate data on impurities, aggregates, bioburden or endotoxin. The research-market certificates below answer purity and quantity. Most do not answer those other questions.

We make no claim about what thymosin alpha-1 does in people.

What 32 public lab results show.

We pooled thymosin alpha-1 results from the six certificate sources in our 2,087-result purity study, using the same rules for duplicates. Five sources carried it; Swiss Chems' page had none.

The pool carries 22 distinct client names. One Janoshik test (164626) has no label amount, so it counts for purity but not fill.

Fill: how much is in the vial.

The middle half of results sits between 108.8% and 116.6% of label. Across all 1,921 fill results in the wider study, the median was 109.6% and 47.6% of vials were over 110%. Thymosin alpha-1 runs higher: 113.2%, the highest median of any compound with 30 or more results in that pool.

Two Kovera certificates for 10 mg vials sit at the top: client Peptide Partners at 12.84 mg, or 128.4% (KVR-2026-9E35D5, 25 February 2026), and an Ascension Peptides certificate from MZ Biolabs at 12.94 mg, or 129.4% (batch 33-01260229, 7 February 2026). The Kovera certificate prints a specification of "10mg ± 10%" and was still marked a pass when we checked it on 9 October 2026, as our Peptide Partners page records. Kovera graded all 17 of its thymosin alpha-1 results over 110% a pass.

The lowest fill is a 2025 Particle Peptides certificate from Apigenex: 4.7 mg in a 5 mg vial (batch 2025234, 19 March 2025), graded a pass. All four Particle results are 5 mg vials and sit between 4.7 and 5.38 mg, close to label. Particle's is the only source whose median, 99.0%, sits under label.

Purity: how much of the signal is the right molecule.

The median, 99.70%, is a little below the 99.86% of the wider pool, and 21.9% under 99% compares with 6.6% across all compounds. The one result under 98% is the same 2025 Particle certificate: 96.43% by UPLC. Four of the seven under 99% are Kovera certificates from 20 to 26 May 2026, between 98.23% and 98.87%; the other three are Particle certificates. No result was graded a fail, and every one that reported identity confirmed it.

Purity is an HPLC area percentage. It says nothing about the amount in the vial, and nothing about endotoxin or sterility. Our purity study explains the difference.

All 32 results.

Client names are as printed on each certificate on the date of our mirror. The client is whoever commissioned the test, which is not always the seller of a given vial. Kovera report numbers link to Kovera's own verifier; the Particle certificates are in the vendor's downloadable archive.

One result outside the pool.

Our Hello Stacks audit read a Vanguard Laboratory certificate for a 10 mg thymosin alpha-1 vial: 10.49 mg (104.9%), 99.10% purity, tested 1 July 2026, with an endotoxin result of 18.50 EU/mg that the certificate marks a pass. Vanguard is not one of the six sources in the pooled study, so it is not in the 32. Inside the pool, three Particle certificates (batches 2025234, 2025291 and 2026310) report endotoxin as negative or under the reporting limit. Our endotoxin guide works through what an 18.50 EU/mg figure means per vial.

The bias you have to read first.

Every result here is one that a vendor or a buyer chose to send to a lab, and one the lab or vendor chose to publish. Kovera and Janoshik publish fails next to passes, but the client still decides which vials reach them. A vendor with a bad certificate can leave it off its own page. Zero fails in 32 is a statement about the published record. It is not a failure rate for thymosin alpha-1 on the market.

The pool is also small. One result moves the purity median by a few hundredths and the fill bands by about three percentage points. Read the tables as a description of 32 certificates, not as a forecast for the next vial.

Prices.

Our price index does not yet track thymosin alpha-1. The build of 28 October 2026 covers 137 listings at 10 vendors across 15 compounds, and thymosin alpha-1 is not one of them, so we publish no price per mg for it. Price per labelled milligram would mislead here anyway: with a median vial at 113.2% of label, the label understates what most certificates measured.

How to read a thymosin alpha-1 certificate.

1. Check it is alpha-1. Lab listings put thymosin alpha-1 and thymosin beta-4 under one word. The certificate should name alpha-1 or thymalfasin.
2. Read the measured milligrams. On this record, the middle half of results sat between about 109% and 117% of label. One in 30 was under 95%.
3. Read purity, but do not stop there. 21.9% of these results were under 99%, though none under 96%.
4. Look for the panels FDA said were missing. Endotoxin, sterility and impurity profiles are separate tests. Most certificates here do not report them.
5. Verify at the lab and match the lot. Use the lab's own lookup, such as Kovera's verifier or Janoshik's, and our guide to verifying a Janoshik COA. A certificate covers one tested sample.

Our methodology page explains how we read and score lab records, and the peptide index has guides for the compounds named above.

What we read, and what we did not.

We read 32 thymosin alpha-1 certificates in our mirrors of Kovera Labs' public verifier (2 August 2026), Janoshik's public test listing (June 2026), and the certificate pages of Particle Peptides, Ascension Peptides and Injectify. We left out two Janoshik catalogue entries with no readable result and any certificate for thymosin beta-4 or TB-500. We read FDA's 15 November 2024 briefing document, the 4 December 2024 final summary minutes, FDA's safety-risk page (current as of 22 April 2026) and the Federal Register notice 2026-22192. The list of six peptides is from Appendix A of the HHS policy text, as read for our HHS policy explainer on 29 October 2026. We did not test any vial, and we do not publish the client email addresses printed on some certificates.

Sources.

• FDA, Thymosin alpha-1 briefing document, Pharmacy Compounding Advisory Committee, 15 November 2024
• FDA, Final summary minutes, Pharmacy Compounding Advisory Committee, 4 December 2024
• FDA, Certain bulk drug substances for use in compounding that may present significant safety risks, content current as of 22 April 2026
• HHS, Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances, Federal Register document 2026-22192, filed 28 October 2026
• HHS, Enforcement discretion policy with Appendix A and Appendix B, October 2026