what is the difference
Thymosin alpha-1 and thymulin
Two peptides made by the thymus, one carrying the deepest trial record in this catalog outside the metabolic group and the other carrying a nutrition literature, sold beside each other on the strength of a shared syllable.
Thymosin alpha-1 is a 28 amino acid peptide first isolated from thymus tissue, given as a medicine in more than thirty countries under the international non-proprietary name thymalfasin and the brand name Zadaxin. Thymulin is a nine amino acid peptide, described in French endocrinology in the 1970s as facteur thymique serique, and its defining property is that it only takes its active shape when a zinc ion is bound to it [3].
Both are thymic peptides and both are sold to the same audience under an immune heading, which is where the resemblance ends. One has been through phase 3 trials in more than a thousand people. The other has been given, in published work, mostly to rodents. This page sets out what each substance is, what the registry and the literature hold for each, and why a third name, thymalin, belongs in the conversation.
Not medical advice
This page reports what has been documented about a compound. It is not medical advice, not a diagnosis, not a dosing protocol, and not a recommendation to obtain or use anything described here. Talk to a licensed clinician about anything concerning your health. Read the full disclaimer.
Reviewed against editorial standards Updated
The short answer
Thymosin alpha-1 and thymulin are different molecules of different lengths with different histories. Thymosin alpha-1 is 28 amino acids and carries 65 registrations, including phase 3 work; thymulin is nine amino acids, needs a bound zinc ion to be active, and carries one registration, which is observational [10].
Nothing transfers between them. A phase 3 trial of thymosin alpha-1 says nothing about thymulin, and the rodent work on thymulin says nothing about thymosin alpha-1. A third substance is thymalin, a peptide extract of calf thymus developed in the Soviet Union. The published work on that extract sits almost entirely in Russian-language journals [9], and vendors carry more than one of the three.
Side by side
| Property | Thymosin alpha-1 | Thymulin |
|---|---|---|
| What it is | A 28 amino acid peptide first isolated from thymus tissue | A nine amino acid thymic hormone that takes its active shape only when a zinc ion is bound to it [3] |
| Other names | Thymalfasin, the international non-proprietary name, and Zadaxin, a brand name | Zinc-thymulin, FTS, and facteur thymique serique, the name it was described under in the 1970s |
| Registered studies | 65 under thymosin alpha 1 and 65 under thymalfasin, which is one record set indexed twice rather than 130 studies. Of them, 33 are phase 2, 8 phase 3, 10 phase 4 and 2 observational [10] | 1, and it is observational in the sense that matters here: it randomised infants in Pakistan to zinc sulfate or placebo and measured polio vaccine seroconversion. Thymulin appears in the reasoning behind the trial rather than in anyone's arm [10] |
| Largest completed trial | TESTS, a multicentre, double blinded, randomised, placebo controlled phase 3 trial across 22 centres in China, 1,106 adults with sepsis [1] | None. No trial of any phase has administered thymulin to people in the published record found for this page |
| What that trial reported | Death from any cause at 28 days occurred in 23.4 percent of the treated group and 24.1 percent of placebo, a hazard ratio of 0.99, and no secondary outcome separated [1] | Not applicable |
| Longest-standing published use | Chronic hepatitis B, where a 2008 meta-analysis pooled four randomized trials in 199 patients against interferon alpha [2] | Nutritional research on the peptide people already make. Four adults were followed through controlled dietary zinc restriction and repletion in 1988 [4], and a 2021 study compared thymulin activity against other markers of marginal zinc deficiency [5] |
| Where it has been given experimentally | People, in registered trials, across sepsis, hepatitis B and COVID-19 populations [1] [2] [10] | Rodents. Restraint-stressed mice measuring antibody production [6], and a mouse model of severe experimental autoimmune encephalomyelitis [7] |
| Span of the literature | 1970s to 2025, with the largest trial published in 2025 [1] | Concentrated in the 1970s and 1980s, with a small number of later papers [5] [7] and a 2004 review collecting the rodent and neuroendocrine work [8] |
| US approval status | No approved application returned by a query of FDA's approved-products data on 2 August 2026 [11]. It is registered as a medicine in more than thirty other countries | No approved application returned by the same query on the same date [11], and no monograph |
| How many laboratories the record comes from | Many, across several countries, which is checkable from the author lists in the references below | Few. Four of the thymulin papers cited here span 1988 to 2021 and share a single author, Dardenne M, with Bach JF on two of them |
Why the two get mixed up
The names were assigned by where the peptides were found rather than by what they do, and the thymus produced several of them. Thymosin alpha-1, thymulin and thymalin are three separate substances that all trace back to thymic tissue, and a reader scanning a product list has four syllables to work with. The commercial consequence is one direction only: the best-evidenced of the three is the one whose name the other two most resemble.
Thymalin is worth naming explicitly because it is the third point of the collision. It is a peptide extract of calf thymus developed in the Soviet Union in the 1970s, and the published work on that extract sits almost entirely in Russian-language journals [9]. A calf thymus extract is not a defined single molecule in the way the other two are, and a Soviet-era report on it is evidence about neither of them.
Registration counts make it worse in a specific arithmetic way. Thymosin alpha-1 returns 65 studies under its research name and 65 under thymalfasin, and the temptation is to add them. That is one record set indexed under two names, and the addition would invent a programme twice the size of the real one. The same mistake runs the other way too: reading thymulin's single registration as a small trial of thymulin misdescribes a zinc supplementation study.
What the published record covers for each
The two records are not the same shape, so the useful comparison is what each one asked. The largest trial of thymosin alpha-1 is recent and it is negative: TESTS randomised 1,106 adults with sepsis across 22 centres in China, double blinded and placebo controlled, and death from any cause at 28 days occurred in 23.4 percent of the treated group against 24.1 percent of placebo, a hazard ratio of 0.99, with no secondary outcome separating the arms [Human RCT] [1]. A trial of that size returning a null result is a stronger piece of information than most of what this catalog contains, in either direction.
Its longest-standing use is chronic hepatitis B, where a 2008 meta-analysis pooled four randomized trials in 199 patients against interferon alpha and reported odds ratios favouring interferon at the end of treatment and favouring thymosin alpha-1 six months afterwards, on virological, biochemical and combined response [Human RCT] [2]. A meta-analysis carries the tier of the studies it pooled, never higher, and 199 patients across four trials is a small pool by the standards of a hepatitis programme.
Thymulin's human literature is about the peptide a person's own thymus makes rather than about giving anyone any. In 1988 four adults were studied through a period of controlled dietary zinc restriction and repletion, and serum thymulin activity fell during restriction and returned with repletion, in parallel with changes in T cell subsets; there was no control arm and the study measured endogenous activity [Human open-label] [4] [5].
Where thymulin has been administered, it has been administered to rodents. In restraint-stressed mice, antibody production against sheep red blood cells fell to about half the level seen in unstressed animals, and a short course of thymulin at nanogram-per-kilogram amounts returned it close to the unstressed level while changing nothing in unstressed mice [6]. In a mouse model of severe experimental autoimmune encephalomyelitis, thymulin given into the abdominal cavity alongside or against an inhibitor of NF-kappaB signalling was reported to reduce disease severity and lengthen survival, with the two agents producing no additive effect [Animal] [7] [8]. These results come from mice in laboratory models, not from people. An animal model is a deliberate simplification: the insult is created on purpose, the animal is young and healthy, and the amount is scaled to body weight in a way that does not translate directly. Mechanism is a reason to run a trial rather than a substitute for one.
Our takeOne of these has been given to more than a thousand people under a protocol and returned a null result on its primary endpoint. The other has a nutrition literature about the peptide the body already makes and two rodent studies. Reading a shared syllable as shared evidence is how those two records get treated as one.
Frequently asked questions
Are thymosin alpha-1 and thymulin the same thing?
No. Thymosin alpha-1 is a 28 amino acid peptide sold as thymalfasin and Zadaxin. Thymulin is a nine amino acid thymic hormone whose activity depends on a bound zinc ion [3]. Different lengths, different molecules, and different evidence bases. There is also a third substance, thymalin, which is a peptide extract of calf thymus developed in the Soviet Union [9], and vendors carry more than one of the three.
Does thymosin alpha-1 really have 130 registered studies?
No. A ClinicalTrials.gov search on 2 August 2026 returned 65 studies under thymosin alpha 1 and 65 under thymalfasin [10], which are the same studies indexed under two names for one molecule. Adding them produces a programme twice the size of the real one, which is the commonest way a compound in this category acquires a count it never earned.
What did the largest thymosin alpha-1 trial find?
TESTS was a multicentre, double blinded, randomised, placebo controlled phase 3 trial in 1,106 adults with sepsis across 22 centres in China. Death from any cause at 28 days occurred in 23.4 percent of the treated group and 24.1 percent of placebo, a hazard ratio of 0.99, and no secondary outcome separated the arms [1]. A large, cleanly run trial reporting no separation is published here for the same reason a positive one would be.
Has thymulin ever been given to people in a trial?
None was found for this page. The single registration returned by a ClinicalTrials.gov search on 2 August 2026 randomised infants in Pakistan to zinc sulfate or placebo and measured polio vaccine seroconversion; thymulin appears in the reasoning behind that trial rather than in anyone's arm [10]. The human literature on thymulin measures the peptide a person's own thymus produces, mostly in the context of dietary zinc [4] [5].
Is either one approved in the United States?
Neither. A query of FDA's approved-products data on 2 August 2026 returned no application for thymosin alpha-1, for thymalfasin or for thymulin [11]. Thymosin alpha-1 is registered as a medicine in more than thirty other countries, which is a fact about those regulators rather than about the US position.
Why does this page not say which one has better evidence to act on?
Because that is a recommendation, and this site reports what has been documented rather than prescribing what should be done. What can be stated is the shape of each record: thymosin alpha-1 has 65 registrations including phase 3 work and a large null trial [1] [10]; thymulin has a nutrition literature, two rodent studies and one registration that gave zinc [4] [6] [7] [10].
References
- Wu J, Pei F, Zhou L, Li W, Sun R, Li Y, Wang Z, He Z, Zhang X, Jin X, Long Y, Cui W, Wang C, Chen E, Zeng J, Yan J, Lin Q, Zhou F, Huang L, Shang Y, Duan M, Zheng W, Zhu D, Kou Q, Zhang S, Liu Y, Yao C, Shang M, Peng S, Zhou Q, Cheng KK, Guan X, TESTS study collaborator group. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ. 2025. PMID 39814420 DOI 10.1136/bmj-2024-082583
- Yang YF, Zhao W, Zhong YD, Yang YJ, Shen L, Zhang N, Huang P. Comparison of the efficacy of thymosin alpha-1 and interferon alpha in the treatment of chronic hepatitis B: a meta-analysis. Antiviral Res. 2008. PMID 18078676 DOI 10.1016/j.antiviral.2007.10.014
- Bach JF, Dardenne M. Thymulin, a zinc-dependent hormone. Med Oncol Tumor Pharmacother. 1989. PMID 2657247 DOI 10.1007/BF02985220
- Prasad AS, Meftah S, Abdallah J, Kaplan J, Brewer GJ, Bach JF, Dardenne M. Serum thymulin in human zinc deficiency. J Clin Invest. 1988. PMID 3262625 DOI 10.1172/JCI113717
- DiSilvestro RA, Dardenne M, Joseph E. Comparison of Thymulin Activity with Other Measures of Marginal Zinc Deficiency. Biol Trace Elem Res. 2021. PMID 32363520 DOI 10.1007/s12011-020-02159-y
- Okamoto M, Morishita M, Setoguchi C, Nakata K. Restorative effect of short term administration of thymulin on thymus-dependent antibody production in restraint-stressed mice. Int J Immunopharmacol. 1993. PMID 8407057 DOI 10.1016/0192-0561(93)90149-s
- Lunin SM, Khrenov MO, Novoselova TV, Parfenyuk SB, Glushkova OV, Fesenko EE, Novoselova EG. Modulation of inflammatory response in mice with severe autoimmune disease by thymic peptide thymulin and an inhibitor of NF-kappaB signalling. Int Immunopharmacol. 2015. PMID 25662754 DOI 10.1016/j.intimp.2015.01.021
- Goya RG, Brown OA, Pléau JM, Dardenne M. Thymulin and the neuroendocrine system. Peptides. 2004. PMID 15003367 DOI 10.1016/j.peptides.2003.11.002
- Khavinson VKh, Morozov VG. [Experimental and clinical study of a new immunoregulator preparation thymalin]. Voen Med Zh. 1982. PMID 7048731
- US National Library of Medicine, ClinicalTrials.gov. Registry counts run through API v2 on 2 August 2026. Thymalfasin returned 65 studies and thymosin alpha 1 returned 65, being one record set indexed under two names, of which 33 are phase 2, 8 phase 3, 10 phase 4 and 2 observational. Thymulin returned 1, a trial randomising infants in Pakistan to zinc sulfate or placebo. ClinicalTrials.gov. 2026. Registry search
- US Food and Drug Administration. Drugs@FDA approved products data, queried through the openFDA drug/drugsfda endpoint on 2 August 2026 for thymosin alpha-1, thymalfasin and thymulin as active ingredients. No approved application was returned for any of them. openFDA. 2026. Query endpoint