Thymosin Alpha-1: what the trials show, status and safety
Summary
Thymosin Alpha-1 is a fully synthetic 28-amino-acid peptide, and a prescription medicine in Italy and China. Its Italian licence covers one use: boosting the response to influenza vaccination in people with weak immune defences. It is licensed for hepatitis nowhere, and the figure of thirty-plus approving countries comes from a company report. The three largest trials missed their primary endpoint.
Key findings at a glance
- Two markets, not thirty. Italy licensed the medicine on 27 April 1993, prescription-only, and China registered it as an import with a licence valid to May 2027. No third approval could be confirmed at the source [1], [2], [3].
- The Italian licence is for one thing only. The whole indication text names an adjuvant to influenza vaccination in immunocompromised people. There is no hepatitis indication in it [4].
- The thirty-country figure comes from a company report. The American regulator addressed it and wrote that it was unable to independently verify the claims of approval in all the specified countries [5].
- The three largest trials all missed their primary endpoint: a double-blind phase 3 trial in 1106 adults with sepsis, a double-blind trial in 508 patients with severe pancreatitis, and a trial in 552 people with hepatitis C [6], [7], [8].
- A Cochrane review rated the evidence very low. Published in September 2026, it pooled ten randomised trials and 1349 participants, and graded the certainty of the evidence very low for every outcome but one [9].
- A regulatory committee voted against it, 4 to 17. On 4 December 2024 an FDA advisory committee rejected it for the list usable in pharmacy compounding, then repeated the vote for the acetate form [10].
- It is not on the 2026 doping list, unlike Thymosin Beta-4, which is sold as TB-500 and is a different molecule entirely [11], [12].
What it is
Thymosin Alpha-1 is a short protein chain of 28 amino acids, with an acetyl group capping one end. Nothing else about it is chemically unusual: no rings, no mirror-image building blocks, no sugar chains [5], [13].
Its two names describe two things: Thymosin Alpha-1 is the biochemical name of the natural peptide, and Thymalfasin the international non-proprietary name of the synthetic medicine with the same sequence [5].
The synthetic point matters. The peptide was first isolated in 1977 from a crude calf-thymus preparation called Thymosin Fraction 5, but the medicine sold today is built in a reactor, not extracted from an animal [5].
The developer was the American company SciClone Pharmaceuticals, and the Italian licence is held by its Italian subsidiary. The product is a freeze-dried powder supplied with its own solvent [1], [4].
Quick facts
| Field | Value | Ref |
|---|---|---|
| International non-proprietary name | Thymalfasin (timalfasina in Italian) | [5], [1] |
| Class | Immunostimulant; WHO classification code L03AX25 | [14] |
| Structure | Linear 28-amino-acid peptide, acetylated at the N-terminus | [5], [13] |
| Sequence | Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN | [5], [13] |
| Formula and mass | C129H215N33O55, 3108.3 g/mol, free base | [13], [5] |
| Half-life | Under three hours after subcutaneous injection; peak level after one to two hours in the published study, after six hours per the Italian product information | [15], [4] |
| Origin | Fully synthetic; sequence-identical to a peptide first isolated from calf thymus in 1977 | [5] |
| Status | Prescription-only medicine in Italy and China; unapproved elsewhere | [1], [2], [16] |
| Developer | SciClone Pharmaceuticals; Italian licence held by its Italian subsidiary | [1] |
| CAS registry number | 62304-98-7 (free base) | [13], [5] |
| PubChem CID, UNII | 16130571, W0B22ISQ1C | [13] |
| InChIKey, ChEMBL, ChEBI | NZVYCXVTEHPMHE-ZSUJOUNUSA-N, CHEMBL2103979, CHEBI:135915 | [13], [17] |
How it works
The proposed mechanism is broad rather than specific. The regulator describes the peptide as acting on several parts of the immune system at once, with no single receptor carrying the explanation [5].
- It may act on a family of immune sensors. The American assessment names signalling through Toll-like receptors, sensors that sit on immune cells and recognise patterns characteristic of microbes, as the mechanism that is at least partly established [5].
- It may push immature immune cells to mature. The Italian product information describes an effect on the development of T-lymphocytes, the cells that coordinate immune responses [4].
- It may raise a surface marker that falls in severe illness. The marker, HLA-DR on monocytes, is used as a read-out of how responsive the immune system still is [18].
- No relationship between amount and effect could be derived. The regulator states this explicitly for the preclinical work, which limits how far the mechanism can be trusted [5].
One boundary is worth drawing early: Thymosin Beta-4, traded as TB-500, comes from the same naming tradition and does something entirely different, binding actin, a structural protein inside cells [12], [19].
What the trials found
The trial record is large in volume and thin in result. The public registry held 64 entries for this substance in September 2026, about five sixths of them from Chinese sponsors [20].
Each of these three trials missed its primary endpoint. Sepsis: multicentre, double-blind, placebo-controlled phase 3 trial, published 2025 [6]. Pancreatitis: multicentre, double-blind, placebo-controlled trial, published 2022 [7]. Hepatitis C: randomised, placebo-controlled trial in people who had not responded to standard treatment, published 2012 [8].
Sepsis
Phase 3 RCT The largest trial recruited 1106 adults with sepsis across 22 Chinese centres between 2016 and 2020. It was double-blind and placebo-controlled, and its primary endpoint was death from any cause within 28 days [6].
It did not reach that endpoint: the authors found no clear evidence that the peptide reduces 28-day all-cause mortality in adults with sepsis, and no secondary or safety endpoint differed either [6].
RCT An earlier trial by the same group, with 361 patients in six teaching hospitals, is the one usually cited as positive. It was only single-blind, had no placebo, and its main statistical test did not reach significance [18].
Meta-analysis A 2025 review pooled 11 randomised trials with 1927 participants. The pooled effect shrank and lost significance once the analysis was restricted to the higher-quality trials, and again when restricted to multicentre trials. The same authors asked whether enough patients have been studied to settle the question, and answered no [21].
Acute pancreatitis
RCT A multicentre, double-blind, placebo-controlled trial enrolled 508 patients with predicted severe necrotising pancreatitis across 16 Chinese hospitals. Almost all of them, 479 of 508, needed intensive care [7].
The primary endpoint was infected pancreatic necrosis during the admission. The authors concluded that treatment did not reduce it, and the result held across all four predefined subgroups [7].
Two later analyses of the same data reported signals in smaller groups, but both were done after the fact and generate questions rather than answer them [22], [23].
Chronic hepatitis B
Cochrane review The most thorough assessment appeared in September 2026. It pooled ten randomised trials with 1349 participants from six countries, published between 1991 and 2018 [9].
Its conclusion is a statement of uncertainty. The reviewers wrote that they were not sure whether the treatment reduces all-cause mortality, serious adverse events or the other outcomes examined. They rated the certainty of the evidence very low for every outcome but one, where it was low, citing risk of bias, imprecision and inconsistency [9].
Sixteen further trials could not be assessed at all, because they were reported too incompletely. Requests to their authors went unanswered [9].
Phase 3 RCT The single best-designed trial in this condition was double-blind and placebo-controlled, with 97 patients. Its authors wrote that their results did not confirm the treatment effects reported in other clinical studies [24].
Chronic hepatitis C
RCT A trial in 552 people who had not responded to standard antiviral treatment added the peptide to that treatment. The primary endpoint was not met [8].
The authors' own summary is blunt: the addition did not increase the on-treatment viral response, and the substance seems to play no role in the primary therapy [8].
That question has since been overtaken. The regulator notes that modern direct-acting antivirals cure more than nine in ten people, while this peptide was only ever tested alongside the older, weaker regimens [5].
Influenza vaccination in immunocompromised people
Pilot study This is the only licensed use, and its evidence base is a pilot study in dialysis patients, 99 of them in the safety population, with three treatment groups and no placebo. The read-out was antibody titres, not illness. Titres were higher in the treated groups at day 21, and by day 42 they had fallen further in those same groups than in the comparison group [25].
Regulatory assessment The regulator reviewed the whole vaccine-adjuvant literature, five studies from 1986 to 2012, two of them available only as conference abstracts. It found the evidence insufficient to reach any conclusion [5].
COVID-19
Meta-analysis One pooled analysis of eight studies is quoted constantly, and it is the only positive one of four. The regulator examined all four and recorded that three found no reduction in mortality. Even the positive one found no difference in the need for mechanical ventilation or in length of hospital stay, and its heterogeneity was very high. Treatment guidelines in the United States and at the World Health Organization do not address the substance at all [26], [5].
RCT An American trial in 194 dialysis patients was randomised against an untreated control group, without blinding or placebo. Only an interim report exists, and the efficacy endpoints were never analysed [27].
Where there is nothing at all
Regulatory assessment For myalgic encephalomyelitis and chronic fatigue syndrome, the regulator searched and found no clinical study of the substance whatsoever, although it is among the most heavily promoted uses online [5].
Regulatory assessment In HIV, the reviewed studies were small and mostly uncontrolled, and immune cell counts are not validated substitutes for clinical outcomes. None of them affected clinical endpoints or the validated marker of viral load [5].
Regulatory assessment In stem cell transplantation, the evidence consists of single-arm studies, a case series and an abstract, which the regulator found did not show fewer infections or fewer infection-related deaths [5].
What is still unknown
- Whether the sepsis question is settled. The trial sequential analysis says the total number of patients studied is still too small for a firm answer [21].
- What happened in a completed 600-patient trial. A multicentre randomised trial in aortic dissection surgery is registered as completed. Only its study plan has been published, and that plan and the registry disagree on how many patients took part [28], [20].
- Whether people form antibodies against it. No human immunogenicity data exist, although the regulator considers the risk significant [5].
Side effects and safety
The short version repeated online, that it is well tolerated, is the first half of a sentence. The regulator's full assessment attaches three serious reservations to it, and the licensed product information is thinner than modern standards require [5], [4].
- Injection-site reactions are the commonest reported effect. The Italian product information calls the discomfort occasional, mild and transient, and lists nothing else of clinical note [4], [5].
- Rises in a liver enzyme have been reported in people with chronic hepatitis B, and a foreign product label warns about temporary increases [5].
- Thyroid hormone values shifted in hepatitis C studies. The single case in the American adverse event database involved a man on combined treatment, so the cause cannot be separated from the other drug [5].
- A fatal immune-driven anaemia and a graft failure were reported in recipients of stem cell transplants. The regulator warns that an immune stimulant could cause or worsen graft-versus-host disease and lead to graft failure in that group [5].
- Immunogenicity is an open risk. The regulator states the substance may pose a significant risk of the body forming antibodies against it, potentially amplified by aggregation and by peptide-related impurities [5].
- Combining it with a vaccine carries unknown risks. The regulator writes that adding an immunomodulatory product to any vaccine could pose unknown safety concerns, and that data with American influenza vaccines are insufficient [5].
- Autoimmune disease calls for case-by-case judgement, according to the Italian product information, which also advises caution in people with allergies and alongside other immunomodulating medicines [4].
Contraindications in the Italian licence are clear: pregnancy and breastfeeding, and the product must not be used in children or adolescents [4].
Animal work raises two flags rather than settling anything: at the highest level tested, repeated administration produced falls in white cells and platelets, and reproductive studies in mice showed slightly more late losses and delayed skull bone formation [4].
One whole class of long-term animal safety study was never run for either form of the substance. The regulator also notes that the preclinical data come from a company monograph containing summaries, with no underlying data available for review [5].
The data gaps are the honest headline: no human immunogenicity data, nothing beyond a year, no modern pharmacovigilance profile, and no safety data at all on compounded preparations [5], [4].
Why this page lists no doses
This page gives no amounts in any unit. Thymalfasin is a prescription-only medicine in Italy and in China, and European advertising law forbids directing dosing information for such medicines at the general public [1], [4].
There is no research framework that could be quoted instead: the trials used the licensed amounts, so the figures belong in the product information a prescriber and a pharmacist use [5], [4].
Development and approval status
Two approvals are documented at the source. Italy licensed the product on 27 April 1993 and renewed it in May 2008; China registered it as an imported medicine in 2022, with the licence valid to May 2027 [1], [2].
From a calf-thymus fraction to a negative committee vote
- 1977IsolatedThe peptide is isolated from a crude calf-thymus preparation called Thymosin Fraction 5, ref [5]
- 1993Licensed in ItalyAuthorised on 27 April as a prescription-only medicine, for one indication: influenza vaccine adjuvant in immunocompromised people, refs [1], [4]
- 1999The best hepatitis B trial reportsA double-blind placebo-controlled phase 3 trial with 97 patients does not confirm earlier positive reports, ref [24]
- 2012Hepatitis C endpoint missedA trial in 552 non-responders finds no effect on the primary endpoint, ref [8]
- 2022Pancreatitis endpoint missedA double-blind trial in 508 patients finds no reduction in infected necrosis, ref [7]
- 2024Committee votes 4 to 17 againstOn 4 December an FDA advisory committee rejects the substance for pharmacy compounding, twice, ref [10]
- 2025Sepsis endpoint missedA double-blind phase 3 trial in 1106 adults finds no clear evidence of benefit on 28-day mortality, ref [6]
- 2026Cochrane rates the evidence very lowTen randomised trials, 1349 participants, certainty very low for every outcome but one, ref [9]
- 1977 isolated from Thymosin Fraction 5, a crude calf-thymus preparation [5].
- 27 April 1993 Italy grants the licence, prescription-only, for one indication [1], [4].
- 1999 the pharmacokinetic study in nine healthy volunteers appears [15].
- 2022 China's imported-medicine registration is issued, valid to 5 May 2027 [2].
- 4 December 2024 the FDA advisory committee votes against the compounding nomination, twice [10].
- September 2026 the Cochrane review appears; the registry holds 64 entries [9], [20].
| Market | Status | Since or note |
|---|---|---|
| Italy | Approved | 27 April 1993, prescription-only |
| China | Approved | Imported registration, valid to 2027 |
| United States | Unapproved | Bulk ingredient entries only |
| European Union | Unapproved | No central authorisation |
| Germany | Unapproved | Not scheduled |
| United Kingdom | Unapproved | No product listed |
| Canada | Unapproved | Empty register result |
| Switzerland | Unapproved | Not on the medicines list |
| Japan | Unapproved | Per regulatory statement |
| Australia | Unregistered | Not scheduled |
Each blank result above came from a register query run alongside a control substance in the same database. An empty answer therefore means absence, not a broken query [16], [29], [30], [31], [32].
The Australian entry needs one qualification. The Poisons Standard was checked in full text and holds no entry, but the product register could not be reached, so an Australian registration is unproven rather than excluded [12].
The American situation is distinctive. No medicine is approved, but the substance is registered as a bulk ingredient by several firms, two of those entries explicitly for human prescription compounding [33].
That route is closing. An advisory committee voted 4 to 17 against adding it to the list usable under the pharmacy compounding provision [10], [34]. On the parallel list for outsourcing facilities it sits in category 3, nominated without adequate support [35].
The stated reasons were threefold: the substance is not well characterised, the effectiveness evidence is insufficient, and approved alternatives exist for most of the conditions examined [5]. A separate regulatory page adds that compounded products may pose a significant immunogenicity risk for certain routes of administration [36].
The regulator has also documented the online market: products advertised as injectables and nasal sprays, and one website advertising a compounded product as FDA-approved although no such product exists. Two conditions named in that material, chronic fatigue and Lyme disease, are ones for which the same regulator found no clinical study at all [5].
The wider legal picture is under are peptides legal and FDA-approved peptides.
Anti-doping
Thymosin Alpha-1 does not appear on the 2026 prohibited list. A full-text check found no entry under any of its names, while Thymosin Beta-4 and its derivatives appear plainly in the growth-factor class [11]. The catch-all class for non-approved substances does not apply either: that clause requires a substance with no current approval by any government health authority, and the Italian licence defeats it [11].
The German anti-doping annex lists only Thymosin Beta-4, as does the Australian Poisons Standard. Neither absence is a safety statement: an unapproved medicine remains unlawful to supply regardless of doping law [37], [12].
The full picture is at peptides banned in sport.
Compared with related peptides
| Substance | What it is | Status | Ref |
|---|---|---|---|
| Thymosin Alpha-1 | Synthetic 28-amino-acid peptide, defined structure | Prescription medicine in Italy and China | [1], [13] |
| TB-500 (Thymosin Beta-4) | 43-amino-acid actin-binding peptide | Unapproved everywhere; on the 2026 doping list | [11], [12] |
| Thymalin | Undefined calf-thymus polypeptide extract | Prescription medicine in Russia only | [38] |
| Thymulin | Zinc-dependent nine-amino-acid peptide | Unapproved; appears in an American compounding list | [39], [34] |
| Thymopentin | Synthetic five-amino-acid fragment | Separate substance with its own classification code | [40], [14] |
These five are confused constantly, and the confusion has consequences. Thymosin Alpha-1 and Thymosin Beta-4 share three letters and nothing else: different length, different job, opposite doping status [11], [13].
The sharpest contrast is with Thymalin. Thymosin Alpha-1 is one molecule with a sequence, a formula, a CAS number and a classification code, and double-blind trials with four-figure participant numbers behind it [6], [9], [13]. Thymalin is a mixture extracted from calf thymus with none of those, and no trial of it appears in any public registry [38].
What the two do share is their legal class. Both are prescription-only medicines in at least one market, which is why neither page carries doses [1], [38].
Common misconceptions
- "It is licensed for hepatitis B." It is not, anywhere. The entire Italian indication concerns influenza vaccination in immunocompromised people; hepatitis B was studied, and studying is not licensing [4], [9].
- "More than thirty countries have approved it." That figure comes from the manufacturer's 2014 annual report, and the American regulator wrote that it could not independently verify those claims. Two markets are documented at the source [5], [1], [2].
- "It is derived from thymus tissue." It was first isolated from calf thymus in 1977, but the medicine is made synthetically and is merely sequence-identical to the natural peptide [5].
- "It is the same family as TB-500." Thymosin Beta-4 has 43 amino acids, binds actin, and sits on the doping list, in the German anti-doping annex and in Australian Schedule 4. Thymosin Alpha-1 is on none of them [11], [12], [37].
- "Thymalin is the Russian version of it." Thymalin is an undefined extract with no structure, no formula and no registered trials. Results from one cannot be carried over to the other, in either direction [38], [13].
- "Over 11,000 participants prove it is safe." That figure comes from a narrative review in an alternative medicine journal, written expressly to argue the regulator's restriction was unfounded, with no formal grading [41], [9].
Frequently asked questions
What is Thymosin Alpha-1?
It is a peptide of 28 amino acids with an acetyl group at one end. It is identical in sequence to a natural thymus peptide first isolated from calf thymus in 1977, but the medicine itself is made entirely by chemical synthesis. Its international non-proprietary name is thymalfasin, and it carries its own code in the WHO drug classification, L03AX25.
Where is Thymosin Alpha-1 approved, and for what?
In two countries, on primary-source evidence. Italy licensed it on 27 April 1993, prescription-only, and China registered it as an imported medicine with a licence running to May 2027. The Italian licence covers one use only: as an adjuvant to influenza vaccination in people whose immune defences are weakened.
Is Thymosin Alpha-1 approved for hepatitis B?
No, and this is the most persistent error about the substance. The entire Italian indication text concerns influenza vaccination in immunocompromised people, and nothing else. Registers in the United States, the European Union centrally, Germany, the United Kingdom, Canada, Switzerland and Japan hold no product at all. Hepatitis B was studied, but studying is not licensing.
Is Thymosin Alpha-1 really approved in more than thirty countries?
That figure comes from the manufacturer's 2014 annual report, not from any register. The American regulator addressed it directly and wrote that it was unable to independently verify the claims of approval in all the specified countries. This survey found primary-source evidence for exactly two markets, Italy and China.
What did the largest trials of Thymosin Alpha-1 find?
All three missed their primary endpoint. A double-blind phase 3 trial in 1106 adults with sepsis found no clear evidence of benefit on 28-day mortality, a double-blind trial in 508 patients with severe pancreatitis missed its endpoint, and so did a trial in 552 people with hepatitis C.
Is Thymosin Alpha-1 the same as TB-500 or Thymalin?
No, and the differences are legally sharp. TB-500 is Thymosin Beta-4, a 43-amino-acid actin-binding peptide on the 2026 doping list and in Australian Schedule 4; Thymosin Alpha-1 is on neither. Thymalin is an undefined calf-thymus extract licensed only in Russia, with no formula, no CAS number and no registered trials.
Is Thymosin Alpha-1 banned in sport?
Not by name, and not by any catch-all. A full-text check of the 2026 prohibited list found no entry, and the German anti-doping annex and the Australian Poisons Standard list only Thymosin Beta-4. The catch-all class for non-approved substances does not apply either, because that clause requires a substance with no approval from any health authority.
Can pharmacies in the United States compound Thymosin Alpha-1?
The regulatory direction is against it. On 4 December 2024 an FDA advisory committee voted 4 to 17 against adding the substance to the list usable in pharmacy compounding, then repeated the vote for the acetate form. It sits in category 3 of the parallel list for outsourcing facilities, meaning nominated without adequate support.
Why does this page list no doses for Thymosin Alpha-1?
Because it is a prescription-only medicine where it is licensed, and the amounts used in trials are the licensed amounts. Reproducing them would be dosing information for a prescription medicine aimed at the general public, which European advertising law forbids. The figures exist in the product information a prescriber uses.
Sources
- Agenzia Italiana del Farmaco (2026). Banca Dati Farmaci, dataset ZADAXIN, active substance timosina alfa 1, marketing authorisation number 028364026, supply class RR "Soggetto a Prescrizione Medica", holder SciClone Pharmaceuticals Italy S.r.l., classification code L03AX, administrative state authorised, doping flag 0. Queried 17 September 2026. https://medicinali.aifa.gov.it/
- NMPA Information Centre / National Data Centre for Population Health (2023). 注射用胸腺法新 (thymalfasin for injection), imported medicine, registration number 国药准字HJ20171177, holder SciClone Pharmaceuticals Italy S.R.L., manufacturer Patheon Italia S.p.A., issued 6 May 2022, valid to 5 May 2027. Retrieved 17 September 2026. The national regulator's own database refused the query on that day. https://pharm.ncmi.cn/zysjk/ypjkyp/202312/t20231205_400230.html
- Combined register position from sources [1] and [2]; no third market could be confirmed at the source in this survey.
- Agenzia Italiana del Farmaco (2026). Riassunto delle Caratteristiche del Prodotto, ZADAXIN, supplied by the agency on 26 February 2026 and retrieved 17 September 2026. Sections used: 4.1 indication ("ZADAXIN è un adiuvante della vaccinazione anti-influenzale in soggetti immunocompromessi"), 4.3 contraindications, 4.4 warnings, 4.5 interactions, 4.6 pregnancy and lactation, 4.7 driving, 4.8 undesirable effects, 5.1 pharmacodynamics, 5.2 pharmacokinetics, 5.3 preclinical safety, 9 first authorisation 27 April 1993.
- US Food and Drug Administration, Center for Drug Evaluation and Research (2024). Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances, Pharmacy Compounding Advisory Committee meeting, 4 December 2024. Seventy slides prepared by a 14-person review team, covering identity, characterisation, preclinical and clinical safety, immunogenicity, adverse event database review and an effectiveness assessment of twelve proposed uses. The single most important source for this page. https://www.fda.gov/media/183892/download
- Wu J, Pei F, Zhou L, et al.; TESTS study collaborator group (2025). The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ 388:e082583. PMID 39814420. DOI 10.1136/bmj-2024-082583. Erratum BMJ 2025;389:r1098. 1106 randomised, 22 centres, primary endpoint 28-day all-cause mortality, not met.
- Ke L, Zhou J, Mao W, et al.; Chinese Acute Pancreatitis Clinical Trials Group (2022). Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial. Intensive Care Medicine 48(7):899-909. PMID 35713670. DOI 10.1007/s00134-022-06745-7. 508 randomised, 16 hospitals, primary endpoint infected pancreatic necrosis, not met.
- Ciancio A, Andreone P, Kaiser S, et al. (2012). Thymosin alpha-1 with peginterferon alfa-2a/ribavirin for chronic hepatitis C not responsive to IFN/ribavirin: an adjuvant role? Journal of Viral Hepatitis 19(Suppl 1):52-9. PMID 22233415. DOI 10.1111/j.1365-2893.2011.01524.x. 552 randomised, primary endpoint not met.
- Naing C, Ni H, Aung HH, Aye SN, Nikolova D, Poovorawan Y, Pavlov C (2026). Thymosin-α1 for people with chronic hepatitis B. Cochrane Database of Systematic Reviews 9(9):CD014610. PMID 42713852. DOI 10.1002/14651858.CD014610.pub2. Ten randomised trials, 1349 participants, last search 10 June 2026, certainty of evidence graded very low for all outcomes but one.
- US Food and Drug Administration (2024). Final Summary Minutes of the Pharmacy Compounding Advisory Committee Meeting, December 4, 2024. Votes recorded: 4 yes, 17 no, 0 abstentions for the free base, and the same result for the acetate; the preceding procedural question passed 20 to 1. https://www.fda.gov/media/185642/download
- World Anti-Doping Agency (2026). The 2026 Prohibited List, International Standard. Full text checked 17 September 2026: no entry for thymosin alpha-1, thymalfasin or Tα1. Section S2.3 names "Thymosin-ß4 and its derivatives e.g. TB-500". Section S0 requires a substance with no current approval by any government health authority for human therapeutic use.
- Commonwealth of Australia (2026). Therapeutic Goods (Poisons Standard — June 2026) Instrument 2026, F2026L00633, as made 28 May 2026. Full text of 704,546 characters checked 17 September 2026: the only thymosin entry is "THYMOSIN BETA 4 (THYMOSIN β4)" in Schedule 4 and Appendix D; no entry for thymalfasin, thymosin alpha, thymopentin or thymulin, against a successful control check for somatropin. The product register itself could not be reached that day. https://www.legislation.gov.au/F2026L00633
- PubChem, National Center for Biotechnology Information (2026). CID 16130571, thymalfasin. Formula C129H215N33O55, mass 3108.3, InChIKey NZVYCXVTEHPMHE-ZSUJOUNUSA-N, CAS 62304-98-7, UNII W0B22ISQ1C, CHEMBL2103979, CHEBI:135915. The 28-residue sequence was recalculated residue by residue from the deposited chemical name. Queried 17 September 2026. https://pubchem.ncbi.nlm.nih.gov/compound/16130571
- WHO Collaborating Centre for Drug Statistics Methodology (2026). ATC/DDD Index, group L03AX: L03AX25 thymalfasin, with no DDD assigned; L03AX09 thymopentin in the same group. Retrieved 17 September 2026. https://atcddd.fhi.no/atc_ddd_index/?code=L03AX
- Rost KL, Wierich W, Masayuki F, Tuthill CW, Horwitz DL, Herrmann WM (1999). Pharmacokinetics of thymosin alpha1 after subcutaneous injection of three different formulations in healthy volunteers. International Journal of Clinical Pharmacology and Therapeutics 37(1):51-7. PMID 10027483. Nine volunteers; peak concentration after one to two hours, elimination half-life under three hours, and no accumulation on repeated administration.
- openFDA (2026). Drugs@FDA endpoint, field openfda.substance_name: queries for THYMALFASIN and THYMOSIN both returned NOT_FOUND, against a successful control query for SEMAGLUTIDE. Queried 17 September 2026. https://api.fda.gov/drug/drugsfda.json
- UniChem, European Bioinformatics Institute (2026). Resolution of InChIKey NZVYCXVTEHPMHE-ZSUJOUNUSA-N to CHEBI:135915, CHEMBL2103979 and DTXSID80211374. Queried 17 September 2026. https://www.ebi.ac.uk/unichem/
- Wu J, Zhou L, Liu J, et al. (2013). The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial. Critical Care 17(1):R8. PMID 23327199. DOI 10.1186/cc11932. 361 randomised in six teaching hospitals; the unstratified main test did not reach significance.
- Combined comparison of sources [11] and [13]; Thymosin Beta-4 is a separate 43-residue actin-binding peptide.
- ClinicalTrials.gov, US National Library of Medicine (2026). API v2 query for interventions naming thymosin alpha-1 or thymalfasin: 64 registry records, about five sixths of them from Chinese sponsors. Four withdrawn records with zero enrolment were not counted as studies, and one record in which the substance was only concomitant medication was excluded. Queried 17 September 2026.
- Gu B, Zhou Y, Nie Y, et al. (2025). Efficacy of thymosin α1 for sepsis: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Cellular and Infection Microbiology 15:1673959. PMID 40969554. DOI 10.3389/fcimb.2025.1673959. Eleven trials, 1927 participants; the pooled effect lost significance in the high-quality and multicentre subgroups, and the trial sequential analysis found the accumulated sample size insufficient.
- Ke L, Mao W, Shao F, et al. (2023). Association between pretreatment lymphocyte count and efficacy of immune-enhancing therapy in acute necrotising pancreatitis: a post-hoc analysis of the multicentre, randomised, placebo-controlled TRACE trial. EClinicalMedicine 58:101915. PMID 37007743. DOI 10.1016/j.eclinm.2023.101915.
- Huang X, Mao W, Hu X, et al. (2024). Immune-enhancing treatment among acute necrotizing pancreatitis patients with metabolic abnormalities: a post hoc analysis of a randomized clinical trial. Gut and Liver 18(5):906-914. PMID 38356344. DOI 10.5009/gnl230326.
- Mutchnick MG, Lindsay KL, Schiff ER, et al. (1999). Thymosin alpha1 treatment of chronic hepatitis B: results of a phase III multicentre, randomized, double-blind and placebo-controlled study. Journal of Viral Hepatitis 6(5):397-403. PMID 10607256. DOI 10.1046/j.1365-2893.1999.00181.x. 97 patients; the authors state their results do not confirm efficacy observations reported in other clinical studies.
- Carraro G, Naso A, Montomoli E, et al. (2012). Thymosin-alpha 1 enhances the immunogenicity of an adjuvated pandemic H1N1v influenza vaccine in hemodialyzed patients: a pilot study. Vaccine 30(6):1170-80. PMID 22178096. DOI 10.1016/j.vaccine.2011.12.014. Three groups, no placebo, 99 in the safety population; titres higher at day 21 and falling faster by day 42.
- Soeroto AY, Suryadinata H, Yanto TA, Hariyanto TI (2023). The efficacy of thymosin alpha-1 therapy in moderate to critical COVID-19 patients: a systematic review, meta-analysis, and meta-regression. Inflammopharmacology 31(6):3317-3325. PMID 37845598. DOI 10.1007/s10787-023-01354-2. Eight studies, very high heterogeneity, no effect on ventilation or length of stay; the only positive one of four such analyses, per source [5].
- Tuthill CW, Awad A, Parrigon M, Ershler WB (2023). A pilot trial of thymalfasin to prevent covid-19 infection and morbidities in renal dialysis patients: preliminary report. International Immunopharmacology 117:109950. PMID 36881981. DOI 10.1016/j.intimp.2023.109950. 194 randomised against an untreated control group, unblinded; efficacy endpoints not analysed at publication.
- Liu H, Qian SC, Zhang YY, et al.; PANDA Trial Investigators (2025). Effect of thymosin α1 on immune response and organ function in acute aortic dissection surgery: PANDA II trial protocol. Future Cardiology 21(7):447-454. PMID 40367062. DOI 10.1080/14796678.2025.2505401. Study plan only, no results; the registry entry records 600 participants and completed status, while the published plan speaks of over 330.
- European Medicines Agency (2026). Medicines output, medicines report (spreadsheet, 20,798 text cells), searched 17 September 2026: no match for thymalfasin, thymosin or zadaxin, against a successful control search for semaglutide. https://www.ema.europa.eu/en/documents/report/medicines-output-medicines-report_en.xlsx
- Health Canada (2026). Drug Product Database, active ingredient endpoint. Queries for thymalfasin and thymosin returned empty lists on 17 September 2026, against multiple records for the control substance semaglutide. https://health-products.canada.ca/api/drug/activeingredient/
- Swissmedic (2026). Extended list of authorised human medicines (spreadsheet, 29,625 text cells), searched 17 September 2026: no match for thymos, timos, thymalfas or zadaxin, against a successful control check for semaglutidum.
- Electronic Medicines Compendium, Datapharm (2026). Search for thymalfasin on 17 September 2026 returned "No search results", against 44 occurrences for the control term semaglutide. The national product register could not be queried because its results load dynamically. https://www.medicines.org.uk/emc/
- openFDA (2026). National Drug Code directory, field generic_name "thymosin": 15 records, all of them bulk ingredients, of which eight concern thymosin alpha-1 or its acetate and seven concern thymosin beta-4. Two of the eight carry the category "bulk ingredient for human prescription compounding". A query for thymalfasin returned NOT_FOUND. Queried 17 September 2026. https://api.fda.gov/drug/ndc.json
- US Food and Drug Administration (2026). Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act, content of 14 May 2026. Thymosin alpha-1 appears in none of the three categories; in the same alphabetical range, thymulin acetate appears in category 3. https://www.fda.gov/media/94155/download
- US Food and Drug Administration (2025). Bulk Drug Substances Nominated for Use in Compounding Under Section 503B of the Federal Food, Drug, and Cosmetic Act, content of 21 March 2025. Thymosin alpha-1 listed in category 3, "nominated without adequate support". https://www.fda.gov/media/94164/download
- US Food and Drug Administration (2026). Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks, content of 22 April 2026. Lists the substance among nominated but withdrawn entries with the stated reason that compounded drugs containing it may pose significant risk for immunogenicity for certain routes of administration. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
- Federal Republic of Germany (2023). Annex to section 2(3) of the Anti-Doping Act, official citation BGBl. 2023 I no. 67. Full text checked 17 September 2026: section II.3 names only "Thymosin-beta-4 und seine Derivate, Zum Beispiel: TB-500"; no entry for thymosin alpha-1. The substance is likewise absent from annex 1 of the German prescription-medicines ordinance. https://www.gesetze-im-internet.de/antidopg/anlage.html
- Vidal.ru (2026). Product information for Тималин (Thymalin), lyophilisate for intramuscular injection, holder Samson-Med, St Petersburg; active substance described as thymus polypeptides from the thymus glands of calves; supply condition "по рецепту" (on prescription); current Russian registration granted 21 June 2024. Retrieved 17 September 2026. No CAS number, formula, sequence or classification code exists for this preparation, and no trial of it appears in any public registry. https://www.vidal.ru/drugs/thymalin__23838
- PubChem, National Center for Biotechnology Information (2026). CID 3085284 and CID 71300623, thymulin (facteur thymique sérique). Nine-residue sequence pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn, formula C33H54N12O15, mass 858.9, CAS 63958-90-7, UNII 9H198D04WL. Queried 17 September 2026. The entry also carries "thymalin" among more than thirty depositor synonyms, which is a database artefact and a common source of error.
- PubChem, National Center for Biotechnology Information (2026). CID 451417, thymopentin. Five-residue sequence Arg-Lys-Asp-Val-Tyr, fragment 32 to 36 of thymopoietin, formula C30H49N9O9, mass 679.8. Queried 17 September 2026.
- Dinetz E, Lee E (2024). Comprehensive review of the safety and efficacy of thymosin alpha 1 in human clinical trials. Alternative Therapies in Health and Medicine 30(1):6-12. PMID 38308608. A narrative, explicitly advocacy-oriented review stating that the regulator's restriction appears unfounded. Cited here only as the origin of claims in circulation, not as an evidence source: no systematic search, no risk-of-bias assessment, no formal grading.
Cite this page
Every register behind the status table was queried on 17 September 2026, each alongside a control substance. Two entries are weaker: the Australian product register could not be reached, and the Japanese entry rests on a regulatory statement rather than a query of our own.
myPeptides Research & Editing. (2026). Thymosin Alpha-1: what the trials show, status and safety. Version 1.0, 17 September 2026. myPeptides Peptide Register. Retrieved from https://mypep.app/peptides/thymosin-alpha-1
How pages in this register are compiled and graded is described under methodology; the full register is at peptides.
| Version | Date | Change |
|---|---|---|
| 1.0 | 2026-09-17 | Initial publication |
Last verified: 17 September 2026. Next review: on publication of the completed aortic dissection trial, on any final American rule for pharmacy compounding, or on any change to the Italian or Chinese authorisation.