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Thymosin Alpha-1 vs Thymosin Beta-4 (TB-500): Two Thymic Peptides, Two Research Paths

Short answer: thymosin alpha-1 and thymosin beta-4 share a name, not a structure or a job. Both were first pulled from the same calf-thymus extract, thymosin fraction 5 , but they are unrelated peptides . Thymosin alpha-1 (thymalfasin, 28 amino acids) is an immune signalling peptide. It has real human trial data and is marketed as Zadaxin in more than 30 countries, though not FDA-approved. Thymosin beta-4 (43 amino acids, sold for research as TB-500) is an actin-binding peptide. It is studied in cell-migration and tissue-repair models, has mostly preclinical evidence, and is banned in tested sport .

Plain-English summary. This page compares published research. It is not medical advice. New-U Research Compounds supplies both peptides as laboratory material only, not for human or veterinary use.

Why two unrelated peptides share a name

In the 1960s and 1970s, Allan Goldstein and colleagues prepared a crude extract of calf thymus, called thymosin fraction 5 , and began separating it into individual components. The peptides they isolated were named alpha, beta and gamma according to their isoelectric point, a measure of electrical charge used to separate them. That is the only reason both carry the “thymosin” label.

The name misleads in a second way. Thymosin beta-4 is not specific to the thymus . It is found in almost every cell type and is one of the most abundant peptides inside cells.

Side by side

Thymosin alpha-1 Thymosin beta-4 (TB-500) Length 28 amino acids, N-acetylated 43 amino acids, N-acetylated Origin Cleaved from prothymosin alpha Encoded by the TMSB4X gene Main role studied Immune modulation Actin regulation, cell migration Key targets Toll-like receptors; T-cell, NK-cell and dendritic-cell function G-actin (LKKTETQ motif, residues 17–23) Human evidence Randomised trials (hepatitis B, sepsis), with mixed results Mostly preclinical; limited clinical work Regulatory Marketed as Zadaxin in 30+ countries; not FDA-approved Not approved anywhere as a medicine; FDA advisers backed 503A compounding eligibility for TB-500 in July 2026 (non-binding) Sport — Prohibited under the World Anti-Doping Code

Thymosin alpha-1: the immune path

Thymosin alpha-1 (Tα1) is a 28-residue peptide cut from a larger precursor, prothymosin alpha. Its research story is about the immune system . It engages several Toll-like receptors , the innate sensors that detect viral and bacterial signatures. On the adaptive side, it supports T-cell maturation and dendritic-cell function. Researchers describe it as a rebalancer more than a simple stimulant. It is studied both where immunity is exhausted, as in chronic hepatitis B, and where it is overwhelmed, as in sepsis.

Its human evidence is real but genuinely mixed:

Hepatitis B: randomised studies reported higher viral clearance than in untreated controls.

Sepsis: a 2015 meta-analysis of 12 smaller trials reported lower mortality. The large, rigorous TESTS Phase 3 trial (2025) then found no significant 28-day mortality benefit .

Regulation: marketed as Zadaxin in more than 30 countries, with FDA orphan-drug designations but no FDA approval. In its briefing for the 4 December 2024 Pharmacy Compounding Advisory Committee, the FDA proposed not adding it to the 503A bulk compounding list.

Thymosin beta-4: the structural path

Thymosin beta-4 (Tβ4) is a 43-residue peptide whose day job is holding actin monomers (G-actin). Actin is the protein that builds the cell’s internal scaffolding. By controlling how much free actin is available, Tβ4 influences how cells move and change shape. The central actin-binding motif sits at residues 17–23 ( LKKTETQ ). The N-terminal fragment Ac-SDKP has been studied separately.

That link to cell migration is why Tβ4 is studied in wound, cardiac, corneal and other tissue-repair models . Most of the evidence is preclinical. Ophthalmic trials of a Tβ4 eye-drop formulation have run, but no Tβ4 product is an approved medicine. On 23–24 July 2026 the FDA’s Pharmacy Compounding Advisory Committee voted 8–6 to recommend adding TB-500 to the 503A bulk compounding list. That vote is non-binding and is not a drug approval (see the July 2026 FDA panel vote). For more detail, see our TB-500 and Thymosin Beta-4 research overview.

A note on the name “TB-500”. Online, “TB-500” is used loosely, sometimes for a short synthetic fragment and sometimes for the full-length peptide. New-U’s TB-500 is supplied as full-length 43-residue thymosin beta-4 , and its sequence is published on the product page.

Why they get confused, and why it matters

Search results, forums and vendor pages often place the two side by side, sometimes as if they were versions of one compound. They are not. They act on different systems , rest on different kinds of evidence , and have different regulatory and anti-doping status . Data on one cannot stand in for the other, and there is no clinical evidence base for combining them.

Both peptides for research

New-U Research Compounds catalogues both as lyophilised laboratory reference peptides:

Thymosin Alpha-1 : 28-residue thymalfasin reference.

TB-500 : full-length thymosin beta-4 reference.

The per-batch Certificate of Analysis is published online for each. Research use only, not for human or veterinary consumption.

Frequently Asked Questions

Are thymosin alpha-1 and thymosin beta-4 the same thing? No. They share a name because both were first isolated from the same thymus extract, thymosin fraction 5, but they are unrelated peptides with different sequences, lengths and functions.

What is the main difference? Thymosin alpha-1 is a 28-amino-acid immune signalling peptide that acts on Toll-like receptors and T-cell maturation. Thymosin beta-4 is a 43-amino-acid peptide that binds actin and is studied in cell migration and tissue-repair models.

Which one has more human evidence? Thymosin alpha-1, by a wide margin. It has been tested in randomised trials in hepatitis B and sepsis and is marketed as Zadaxin in more than 30 countries, although a large 2025 sepsis trial was negative. Thymosin beta-4 evidence is mostly preclinical.

Is either one FDA-approved? No. Neither is FDA-approved. Thymosin alpha-1 holds FDA orphan-drug designations but no approval, and in its December 2024 advisory committee briefing the FDA proposed not adding it to the 503A bulk compounding list. In July 2026 an FDA advisory committee voted to recommend TB-500 for that list, which is a non-binding compounding recommendation, not an approval.

Is TB-500 banned in sport? Yes. Thymosin beta-4 and its analogues, including TB-500, are prohibited under the World Anti-Doping Code at all times. Tested athletes should treat it as off-limits.

Primary sources & further reading

TESTS investigators — The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial, BMJ 2025;388:e082583

Goldstein AL et al. — Thymosin β4 review, Trends in Molecular Medicine 2005 (PMID 16099219)

UniProt — P62328: thymosin beta-4 (human)

U.S. National Library of Medicine — PubMed: thymosin alpha 1

U.S. FDA — Pharmacy Compounding Advisory Committee meeting materials

World Anti-Doping Agency — The Prohibited List

External links are provided for research reference only; New-U is not affiliated with the cited organisations and links carry no endorsement either way.

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Lab-Verified Thymosin Research References

New-U Research Compounds catalogues Thymosin Alpha-1 and TB-500 (full-length thymosin beta-4) as lyophilised reference peptides, with the per-batch Certificate of Analysis published online. Research use only - all claims made on this site are for testing and research use only.

Research-grade · >99% HPLC purity · COA per lot

Buy Thymosin Alpha-1 from New-U Research Compounds

Lab-verified by Janoshik Analytical (RP-HPLC + ESI-MS), sealed vials, discreet tracked worldwide shipping. Research use only - all claims made on this site are for testing and research use only.

PRECISION. PURITY. PERFORMANCE.

Research peptides. Third-party Certificates of Analysis (Janoshik Analytical & Freedom Diagnostics) are published on the website. Supplied strictly for laboratory research use.

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