Thymosin Alpha-1: The Orphan Drug Register, Legality, and Where to Buy It (2026)

Four orphan drug designations

FDA's orphan drug database records four designations for thymosin alpha-1, all sponsored by SciClone Pharmaceuticals:

• Chronic active hepatitis B, designated May 3, 1991
• DiGeorge anomaly with immune defects, designated January 8, 1998
• Hepatocellular carcinoma, designated March 6, 2000
• Stage IIb through stage IV malignant melanoma, designated March 13, 2006

An orphan drug designation is an incentive status granted early in development for a candidate associated with a rare condition. It is not a finding that the candidate is safe or effective, and it is not permission to market an approved drug. Four entries in the orphan register can therefore coexist with no US approval.

That distinction separates thymosin alpha-1 from tesamorelin's path to an FDA drug label. One record shows multiple development incentives that did not culminate in US approval. The other provides a useful contrast with a peptide that did.

What FDA said in its own review

FDA's December 4, 2024 briefing stated that the agency had approved no drug products containing thymosin alpha-1. The document also stated that thymosin alpha-1 was not approved in the United States, Japan, or Europe, with the exception of Italy, and that it was not recognised in the European or Japanese Pharmacopoeias.

Regarding claims of approval across Asia-Pacific, Latin America, Eastern Europe, and the Middle East, FDA wrote that it was "unable to independently verify those claims of approval".

The immediate regulatory question concerned pharmacy compounding. A 503A Bulks List nomination for thymosin alpha-1 related substances, docket FDA-2015-N-3534-0470, was withdrawn by its nominator. FDA elected to proceed with advisory committee review anyway.

At the December 4, 2024 meeting, FDA's Pharmacy Compounding Advisory Committee first voted 20 yes, 1 no, and 0 abstentions to cast one combined vote for the free base and acetate forms. The substantive vote on whether to include those forms on the 503A Bulks List was 4 yes, 17 no, and 0 abstentions. The published minutes say the majority cited no compelling evidence of effectiveness.

The agency had addressed a different marketing issue four years earlier. In a warning letter dated December 7, 2020, FDA cited sections 505(a) and 502 of the Federal Food, Drug, and Cosmetic Act after a US seller marketed thymosin alpha 1 as an unapproved product for COVID-19.

The clinical trial record

The registered studies show that thymosin alpha-1 moved beyond preliminary laboratory work, but they do not convert orphan designations into approvals.

NCT00040027 was a SciClone-sponsored Phase 3 study of thymalfasin with peginterferon in non-cirrhotic hepatitis C non-responders. It enrolled 500 participants, began in April 2002, and is listed as completed.

A separate Phase 3 study enrolled 552 hepatitis C non-responders between 2004 and 2009. Its analysis of all randomized participants found that sustained virological response did not reach statistical significance, at 12.7 percent against 10.5 percent with p = 0.407. Among participants who completed the course, the difference did reach significance, at 41.0 percent against 26.3 percent with p = 0.048. The two analyses answer different questions, so the completer result does not erase the non-significant primary population result.

The later COVID-19 record is smaller and unfinished. NCT04487444 was a Phase 2 study of thymalfasin in COVID-19 with lymphocytopenia, run at Rhode Island Hospital from September 10, 2020 to February 3, 2023. It was terminated for slow enrolment. Because enrolment ended the study early, this record should not be presented as evidence of benefit.

Not the same as thymosin beta-4

Thymosin alpha-1 and thymosin beta-4 are different peptides. Their shared family name does not make them interchangeable. Alpha-1 is discussed primarily in immune-signalling research, while beta-4 has different molecular biology involving actin and cell structure. The distinction between TB-500 and thymosin beta-4 adds another naming layer: TB-500 is associated with beta-4, not alpha-1.

The anti-doping record preserves that separation. WADA's Prohibited List does not name thymosin alpha-1. Section S2.3, the growth factors category, names thymosin-beta-4 and its derivatives, for example TB-500. A status statement about beta-4 or TB-500 should not be transferred to alpha-1 simply because all three names contain "thymosin."

Is thymosin alpha-1 legal to buy?

In the United States, thymosin alpha-1 is legal to purchase as a research chemical for laboratory use. It is not a controlled substance and does not appear on any DEA schedule as of August 2026. What it is not: an approved drug, a dietary supplement ingredient, or a compound cleared for human or veterinary use in any form.

Three boundaries define the current legal picture:

1. Research sale is lawful; human-use marketing is not. FDA has cited peptide sellers whose sites promote human use, and the thymosin alpha-1 record contains one of those letters directly, the December 7, 2020 warning letter over COVID-19 marketing. Courts treat the line seriously. The owner of the vendor Paradigm Peptides was sentenced to 70 months in federal prison in July 2026 for selling unapproved and adulterated drugs. The offense was not stocking peptides. It was selling them for human consumption while faking the paperwork.
2. Compounding is closed for now, not open. The December 2024 advisory vote went 4 yes to 17 no against 503A listing. No lawful compounded or prescription form of thymosin alpha-1 exists in the US as of August 2026.
3. Sport rules run on a different list. WADA does not name thymosin alpha-1 on the 2026 Prohibited List. It names thymosin beta-4 and its derivatives under S2.3. Tested athletes should read the list itself rather than reasoning from the shared family name.

Any supplier operating lawfully sells thymosin alpha-1 strictly for laboratory research, not for human or animal use. Curo's research use only policy sets out what that boundary means in practice.

Where to buy thymosin alpha-1 for laboratory research

Researchers looking for where to buy thymosin alpha-1 face a supplier market that changed sharply in 2025 and 2026. Peptide Sciences closed in March 2026, Amino Asylum went offline after a reported federal raid in June 2025, and Paradigm Peptides ended in a criminal sentencing. Several sites now trade on those dead brand names, so the first check is not price. It is whether the company behind the storefront actually exists. Our guide to the best peptide companies in 2026 covers the current field vendor by vendor.

Five checks separate a documented thymosin alpha-1 source from an anonymous one:

1. A lot-specific COA, published before purchase. The certificate should match the exact lot on the vial, not a generic product-page badge. Several thymosin alpha-1 listings offer a COA only "upon request" after checkout, which is a weaker standard. The help center shows how to verify a certificate against your lot.
2. A named, independent laboratory. A COA is only as good as the lab that issued it. Court records in the Paradigm case showed the defendants admitted faking certificates outright, which is the failure mode this check exists to catch.
3. Identity and purity by more than one method. HPLC purity alone leaves an identity gap. Look for mass-spectrometry identity confirmation and endotoxin results alongside it. For thymosin alpha-1 specifically, mass spectrometry is what confirms the N-terminal acetylation, which HPLC alone may not resolve.
4. An identifiable company. A legal entity, a real contact route, and consistent policies. A brand name alone is not an identity, and the clone sites trading on dead vendors prove it.
5. Payment with recourse. Card payment carries buyer protection. Venmo, Zelle, and crypto-only checkouts remove it.

Curo does not stock thymosin alpha-1. There is no Curo product page and no Curo price for this compound, and this article is a neutral reference profile rather than a listing. The compounds Curo does list appear in the research catalog, every lot is tested by an independent laboratory for identity, purity, and endotoxin under a documented testing standard, and every certificate is publicly readable without an account. Researchers sourcing thymosin alpha-1 elsewhere can apply the same five checks, and the pillar guide to buying research peptides online walks the full sequence.

How much does thymosin alpha-1 cost?

As of August 2026, research-grade thymosin alpha-1 runs roughly $45 to $120 for a 5mg vial and roughly $60 to $125 for a 10mg vial from US suppliers that publish lot-matched, independently issued COAs. The spread is wide because the documentation standard varies inside it: at the low end, published Janoshik or Ethos Analytics reports tied to a named batch; at the high end, ISO 17025 accredited labs running purity, assay, endotoxin, and sterility on the same lot. Cheaper vials exist, including 10mg listings under $45, but they cluster among suppliers that release a certificate only after purchase or not at all, and an unverified lot is unusable as research material at any price. Curo does not sell this compound, so no Curo price applies. Compare the documentation attached to the current batch first, then the price.

What a thymosin alpha-1 certificate of analysis should show

Thymosin alpha-1 is synthesized by many suppliers, so material quality is something a lab confirms rather than assumes. Identity, purity, endotoxin load, and fill accuracy all vary by manufacturer and by lot. A certificate worth relying on shows:

• The exact lot number that appears on the vial.
• The issuing laboratory's name and report identifier.
• HPLC purity with the chromatogram, not a bare percentage.
• Mass-spectrometry identity confirmation against the expected 3108.3 g/mol, including the acetylation mass shift.
• An endotoxin result, since a pure peptide can still carry bacterial contamination from synthesis.
• A way to verify the document independently, through a public lookup or the lab itself.

A well-tested lyophilized peptide can still be degraded by poor handling after receipt. See storing research peptides and bacteriostatic water for the storage side, and responsible handling of research-use-only materials for the intended-use boundary.

For a broader framework on separating documentation from marketing when comparing suppliers, see how to evaluate research peptide companies and the companion piece on purity claims and COA batch documentation.

Further reading

The name collision is the single most common error in this area, and it is worth settling before reading any thymosin literature. TB-500 is associated with thymosin beta-4, a different molecule with different biology and a different anti-doping status, and the commercial name and the registry molecule are themselves not the same thing. That is covered in how TB-500 relates to thymosin beta-4.

Tesamorelin makes the opposite regulatory case: a peptide that carried its development through to an approved US drug label. Reading it against thymosin alpha-1's four unconverted orphan designations shows what the designations do and do not mean, in tesamorelin, a peptide with a drug label.

Frequently asked questions

Is thymosin alpha-1 FDA approved?

No. FDA stated in its December 2024 briefing that it had approved no drug products containing thymosin alpha-1. An orphan designation and a clinical trial registration are both development records, not approvals.

Is thymosin alpha-1 legal to buy in the US?

Yes, as a research chemical for laboratory use. It is not a controlled substance as of August 2026. It is not approved for human use, and no lawful compounded form exists after the December 2024 advisory committee voted 4 to 17 against 503A listing.

Where can a researcher buy thymosin alpha-1?

From suppliers that publish lot-specific, independently issued COAs and operate as identifiable companies. Several well-known vendors closed or faced federal action in 2025 and 2026, and clone sites now trade on their names, so verify the company before the price. Curo does not stock thymosin alpha-1 and does not list it for sale.

How much does thymosin alpha-1 cost?

As of August 2026, US suppliers that publish lot-matched third-party COAs typically charge about $45 to $120 for a 5mg vial and about $60 to $125 for a 10mg vial. Listings priced under those ranges usually release documentation only after purchase, if at all.

Why are four orphan designations important?

They show sustained formal interest across four rare-condition development programs from 1991 through 2006. Their meaning is limited but specific: each made regulatory incentives available for development. None established safety, effectiveness, or approval.

What is thymalfasin?

Thymalfasin is the international nonproprietary name for synthetic thymosin alpha-1. Zadaxin is the trade name used in markets outside the United States. Neither naming difference creates a separate US approval status.

Is thymosin alpha-1 banned in sport?

WADA's 2026 Prohibited List does not name thymosin alpha-1. It names thymosin beta-4 and its derivatives, including TB-500, under section S2.3. The two are different peptides, and the beta-4 entry should not be read across to alpha-1.

Does Curo stock thymosin alpha-1?

No. Curo has no thymosin alpha-1 product page and does not list the compound for sale. This article documents its identity, orphan designations, FDA review, trial history, legal status, and distinction from thymosin beta-4.

What should a certificate of analysis for thymosin alpha-1 show?

Lot-specific identity and purity data from chromatographic and mass-spectrometry methods, plus endotoxin results, tied to the exact lot number on the vial and verifiable through a public lookup. The mass-spectrometry result should confirm the N-terminal acetylation.

What is the clearest reading of the record?

Thymosin alpha-1 is neither an unexamined research idea nor a US-approved drug. It is a documented immune peptide with four orphan designations, several substantial clinical studies, no US approval, a 2024 advisory vote against compounding, and an FDA review that set unusually clear limits on what the agency could verify.