Thymosin Alpha 1

What is Thymosin Alpha 1?

Thymosin Alpha 1 (thymalfasin) is a 28-amino-acid immune-modulating peptide originally isolated from thymus tissue by Allan Goldstein's group in the 1970s. Marketed as Zadaxin, it is an approved prescription drug in more than 35 countries for chronic hepatitis B, hepatitis C, and as an immune adjuvant in cancer therapy, with decades of clinical use and millions of patient-treatments. It has never been FDA-approved in the US, primarily for commercial rather than scientific reasons, and its US compounding status is genuinely disputed across sources.

How it’s supplied

Brand / trade names: Zadaxin (thymalfasin; not marketed in the US)

Not FDA-approved or commercially available in the US. Where approved, it is supplied as Zadaxin (thymalfasin) for subcutaneous injection, with the approved chronic hepatitis B protocol commonly 1.6 mg twice weekly for 26 to 52 weeks. In the US it has been prepared by compounding pharmacies during periods when that was permitted, and is sold as a research-grade lyophilized peptide; research-grade products are not FDA-reviewed for potency or sterility.

Dosage Chart

Potential Benefits and Side Effects

Effects reported in published research. Not a promise of results, and not medical advice.

Reconstitution Steps

How to prepare the lyophilized vial. Confirm specifics with your pharmacist or prescriber.

1. Confirm the amount of peptide in the vial and the volume of diluent you intend to use before starting.
2. Wash your hands and gather supplies: the lyophilized vial, the diluent (typically bacteriostatic water), an alcohol swab, and a sterile syringe.
3. Let the vial and diluent reach room temperature if they were refrigerated or frozen.
4. Wipe the rubber stopper of both the peptide vial and the diluent vial with a fresh alcohol swab and let them air dry.
5. Draw the intended diluent volume into the syringe.
6. Insert the needle into the vial and slowly release the diluent down the inside wall rather than directly onto the powder, to avoid foaming.
7. Do not shake. Gently swirl or roll the vial until fully dissolved.
8. Inspect the solution: it should be clear and colorless with no visible particles. Do not use if cloudy or containing particles.
9. Note the resulting concentration (amount divided by diluent volume) so it matches the reconstitution calculator on this page.
10. Label the vial with the reconstitution date and store as directed under reconstituted storage.

US regulatory status

Classifications are public record but can change. For reference only, not legal advice.

Development: Thymosin Alpha 1 was first characterized in 1972 by Allan L. Goldstein and colleagues at George Washington University, who purified thymosin from thymus tissue, with the sequence established in 1977. It became one of the most clinically validated immune-modulating peptides in existence: approved as a prescription drug in more than 35 countries including China, Italy, India, South Korea, the Philippines, Russia, and multiple countries in South America and the Middle East, primarily for chronic hepatitis B and as an immune adjunct in oncology and critical care. Decades of use have generated millions of patient-treatments and a substantial real-world safety record. It was never FDA-approved: SciClone Pharmaceuticals (later acquired) pursued US development for hepatitis C and melanoma, but the peptide is identical to the natural molecule and therefore not patentable, making the estimated cost of US-specific Phase III trials commercially unattractive. The FDA has granted orphan drug designations for malignant melanoma, chronic active hepatitis B, DiGeorge anomaly, and hepatocellular carcinoma, but no marketing approval. Its lack of US approval reflects commercial and regulatory economics rather than a safety or efficacy finding. It was placed in FDA Category 2 in late 2023.

Notes: Thymosin Alpha 1 is not FDA-approved for any indication in the United States, though it is an approved prescription drug (Zadaxin/thymalfasin) in more than 35 countries; foreign approval has no legal effect in the US. It holds FDA orphan drug designations (malignant melanoma, chronic active hepatitis B, DiGeorge anomaly, hepatocellular carcinoma) but no marketing approval. Its US compounding status is disputed: it was placed in Category 2 in late 2023; the February 27, 2026 HHS announcement named it among peptides slated to return to Category 1; but reporting since has variously described it as remaining Category 2 following advisory committee review that flagged immunogenicity concerns, as lawfully compoundable, and as pending a formal FDA rule. It does not appear on the published July 23-24, 2026 or later Pharmacy Compounding Advisory Committee agendas. This should be verified directly against the current FDA list. It is not a controlled substance. (Status current as of mid-2026.)

International status

Pharmacokinetics

Storage and handling

Important Notes

Practical considerations for consistency and safety.

• Thymosin Alpha 1 is approved as a prescription drug in 35+ countries (Zadaxin) but has never been FDA-approved; the reason is commercial economics (it is identical to the natural molecule and therefore unpatentable), not a safety or efficacy failure.
• Its US compounding status is genuinely disputed across sources (Category 2 versus Category 1 versus lawfully compoundable); verify directly against the current FDA list.
• Despite the shared name, it is entirely different from Thymosin Beta-4 / TB-500: 28 versus 43 amino acids, immune modulation versus actin-mediated tissue repair.
• It is a biological response modifier, not a blunt immune stimulant, which is why it has been studied in both immunodeficiency and autoimmune contexts.
• It has FDA orphan drug designations but no marketing approval.

Lifestyle Factors

• Where approved, administered by subcutaneous injection on a twice-weekly schedule under physician supervision, typically in defined courses.
• Not a lifestyle supplement; immune modulation warrants clinical oversight.

References

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