Quick answer: These three names get used interchangeably across the peptide market, and they should not be. Thymosin alpha-1 is a 28-amino-acid synthetic peptide. Thymulin is a 9-amino-acid synthetic peptide requiring zinc for activity. Thymalin is not a single peptide at all - it is a polypeptide complex extracted from calf thymus. Two are molecules. One is a mixture. The difference determines what a certificate of analysis can actually verify.
Three names that collide
All three originate from the thymus. All three appear in immune research. Two of the three are separated by a single letter in the middle of the word, and at least one chemical supply catalog lists "Thymalin/Thymulin" as though they were synonyms.
They are not synonyms. Here is the short version before the detail:
- Thymosin alpha-1 (Tα1, thymalfasin) - a defined 28-residue synthetic peptide. CAS 62304-98-7. Molecular weight approximately 3108 g/mol.
- Thymulin (serum thymic factor, FTS, nonathymulin) - a defined 9-residue synthetic peptide. CAS 63958-90-7. Molecular formula C₃₃H₅₄N₁₂O₁₅, molecular weight 858.86 g/mol.
- Thymalin - a polypeptide complex extracted from calf thymus. No single sequence, no single molecular formula, no single molecular weight.
That last line is the most practically useful sentence on this page, and we will come back to it.
Thymosin alpha-1: the internationally approved one
Thymosin alpha-1 is a 28-amino-acid peptide, N-terminally acetylated, with the sequence Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN. It is cleaved from a larger precursor, prothymosin alpha, and the sequence is highly conserved across mice, calves and humans.
It was originally isolated from thymosin fraction 5 - a partially purified calf thymus extract - in 1977 in Abraham White's laboratory, then sequenced and chemically synthesized. That trajectory is worth noting: it started as a component of an extract and became a defined molecule once the sequence was known. The synthetic version is structurally identical to the endogenous peptide and is produced by solid-phase synthesis.
Published work describes T lymphocyte differentiation, modulation of interleukin-2, interferon-gamma production, NK cell activity, stimulation of thymopoiesis, and upregulation of MHC Class I expression, with more recent emphasis on dendritic cell activation and Toll-like receptor signaling.
Regulatory position. Under the generic name thymalfasin and the brand Zadaxin, it is approved as a prescription pharmaceutical in more than 35 countries - including China, Italy and India - for chronic hepatitis B, chronic hepatitis C, and as an adjunct to vaccination in immunocompromised patients. It has completed Phase III trials in those indications. It is not FDA-approved in the United States, though it carries orphan drug designation for several indications, and it was placed on FDA's Category 2 list in late 2023.
Thymulin: the zinc-dependent nonapeptide
Thymulin is a nonapeptide with the sequence Pyr-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn - pyroglutamate at the N-terminus, asparagine at the C-terminus. It was first described by Bach in 1977 and is produced by two distinct epithelial populations in the thymus. Its older French name, facteur thymique sérique, survives in the literature as FTS, and it also appears as serum thymic factor or nonathymulin.
The zinc requirement is its defining feature. Thymulin requires zinc coordination for biological activity. The peptide and the zinc-bound form are not equivalent, and metal coordination influences its conformational behavior. This is a genuine experimental variable, and it is the single most important thing to understand about working with the compound - a study that does not control for zinc availability is not measuring what it thinks it is measuring.
Published research reports T-cell differentiation and activation, effects on NK cell and macrophage function, and modulation of cytokine production including TNF-α, IL-1β, IL-6 and IFN-γ. It appears in immunology, inflammation, neuroimmunology and aging literature.
Note that thymulin and thymosin alpha-1 are structurally unrelated. They share a tissue of origin and nothing else - 9 residues versus 28, entirely different sequences, different mechanisms in the published work.
Thymalin: a preparation, not a molecule
Thymalin was developed at the St. Petersburg Institute of Bioregulation and Gerontology by Vladimir Khavinson and Vyacheslav Morozov during the 1970s and 1980s. It is a polypeptide complex extracted from the thymus glands of young calves - a mixture of short peptides, not an isolated sequence.
It belongs to the Soviet-era "bioregulator" program, built on the hypothesis that organs produce short peptide signals regulating their own function, which can be extracted and standardized. The same program produced Epithalamin, the pineal extract behind Epitalon - a parallel we covered in our piece on Epitalon and Semax. Thymalin's active components were later identified as short peptides, principally the dipeptides Glu-Trp, marketed as Thymogen, and Lys-Glu, marketed as Vilon.
Evidence position. The majority of the clinical data comes from a single research group. Studies generally lack the randomization, blinding and sample sizes expected by international standards, and independent replication outside that network is largely absent. The animal-derived preparation also raises source-material questions that a synthetic peptide does not.
The molecular formula test
Here is the practical diagnostic, and it takes five seconds.
An extract cannot have a single molecular formula. If a product is labeled Thymalin but its scientific data lists one molecular formula and one molecular weight - say C₃₃H₅₄N₁₂O₁₅ at 858.86 g/mol - then whatever the name says, the analytical identity being described is a single defined peptide. In that specific example it is thymulin. A polypeptide complex has no single formula to print, because it is not one compound.
This cuts both ways. If a product is sold as a defined peptide and the documentation offers no sequence, no formula and no molecular weight, that is equally informative.
Why this matters for what a COA can prove. For a defined peptide, mass spectrometry confirms identity against a known target mass and HPLC establishes purity relative to that identity. Those numbers mean something precise. For an extract, "purity" is a harder claim to make coherently - pure relative to what? Consistency depends on the extraction process and the source tissue rather than on a synthetic route you can specify, which is why extracts are standardized to a process rather than to a specification.
Naming in this market is unreliable, including upstream. Product names propagate from manufacturer to distributor to retailer, and errors propagate with them. If a listing's name and its scientific data disagree, trust the CAS number, the formula and the molecular weight - those describe the substance. The name describes what somebody typed.
Frequently asked questions
Are Thymalin and Thymulin the same thing?
No. Thymulin is a defined nonapeptide, CAS 63958-90-7, molecular weight 858.86. Thymalin is a polypeptide complex extracted from calf thymus with no single sequence or molecular weight. Some supplier catalogs list them as synonyms, which is incorrect.
Are thymosin alpha-1 and thymulin related?
Only by tissue of origin. Thymosin alpha-1 is 28 amino acids; thymulin is 9. Their sequences are unrelated and the published mechanisms differ.
What is TA1?
A common abbreviation for thymosin alpha-1, also written Tα1. Thymalfasin is its generic pharmaceutical name.
Why does thymulin need zinc?
Zinc coordination is required for its biological activity, and it influences the peptide's conformation. The unbound peptide and the zinc-bound form behave differently in experimental systems.
How can I tell which substance I actually have?
Check the CAS number, molecular formula and molecular weight on the documentation rather than the product name. A single formula and weight indicate a defined peptide; an extract will not have them.
Were any of these part of the July 2026 advisory committee vote?
No. The committee reviewed seven other peptides on July 23-24, 2026. Thymosin alpha-1 has been named in the broader reclassification discussion but was not on that docket.
Where we stand
Naming in this category is genuinely messy, and it is messy at the manufacturer level, not just the retail level. We would rather publish the distinction than let a confused name sell an extra vial.
If you are sourcing anything thymic - from us or from anyone - read the CAS number and molecular weight before the product title, and ask the supplier to reconcile them if they disagree. A supplier who can answer that question quickly knows what they are selling. A supplier who cannot is passing along a label they never checked.
Our API is synthesized at a WHO/GMP and ISO 9001 certified laboratory in California and tested to greater than 99% purity. Documentation is available on request, and our team in Chandler, Arizona will go through it with you: (888) 745-1505 or our contact page.
All products sold by BioPure Peptides are intended strictly for in-vitro laboratory and research use only. They are not for human or animal consumption. These statements have not been evaluated by the U.S. Food and Drug Administration, and these products are not intended to diagnose, treat, cure, or prevent any disease.