Thymosin alpha-1

Thymosin alpha-1 is unusual on this site in almost every way. It is a real medicine somewhere: approved and marketed outside the United States, holding an international nonproprietary name, and the subject of a pharmacopoeial reference standard. It has 62 registered trials, nine of them at phase 3. It has a measured half-life in people. Most compounds covered here have none of that.

So the question this page answers is not whether anyone has studied it. It is what the studies found, and the answer turns on one trial.

In January 2025 the BMJ published a phase 3 trial of this peptide in 1,106 adults with sepsis: 22 centres, randomised, placebo-controlled, and masked from participants, carers, investigators and outcome assessors alike. Twelve years earlier the same lead institution had run a smaller trial in the same condition and reported a nine percentage point mortality difference with a borderline p-value. The large trial reported a hazard ratio of 0.99.

That sequence is the most instructive thing in this corpus, and it is why this page is written in chronological order rather than by indication.

Key takeaways

• The largest completed trial randomised 1,106 adults with sepsis across 22 centres, masked from participants, carers, investigators and outcome assessors, against placebo. Death from any cause at 28 days occurred in 23.4 per cent of the treated group and 24.1 per cent of placebo: hazard ratio 0.99, 95 per cent confidence interval 0.77 to 1.27, P equal to 0.93. The paper reports that no secondary or safety outcome differed statistically significantly. [Human RCT] [1] [17]
• Reporting from the same lead institution went the other way in 2013, across 361 patients: 28-day mortality of 26.0 per cent against 35.0 per cent, which the paper itself described as carrying a marginal p-value. The compound did not change between the two trials. The size and the masking did. [Human RCT] [2] [18]
• 62 registered trials name this molecule in their interventions, 9 of them at phase 3, and only 2 of the 62 have posted results to the registry. Two 500-participant phase 3 trials in hepatitis C started in 2002, completed, and no results or publication were located for either.
• The published hepatitis C phase 3, in 552 non-responders, reported a sustained virological response of 12.7 per cent against 10.5 per cent on placebo in the intention-to-treat population, P equal to 0.407. The authors' own conclusion is that the peptide seems to play no role in the primary therapy of that disease. [Human RCT] [3] [19]
• FDA lists it among bulk substances that may present significant safety risks for compounding, citing immunogenicity by certain routes and complexities of peptide-related impurities and characterisation. A separate analytical study found 23 identified related impurities above 0.1 mg per gram in a pharmacopoeial reference standard for the molecule.
• The positive literature is real and it is mostly immune-marker endpoints in many small trials. Meta-analyses in acute exacerbations of chronic obstructive pulmonary disease (39 trials, 3,329 patients) and in severe acute pancreatitis (5 trials, 706 patients) both report higher CD4+ counts and a higher CD4 to CD8 ratio with treatment. [Human RCT] [9] [10]

Who researches Thymosin alpha-1?

Three readers arrive here and the record serves them differently.

Someone comparing this against the other thymus peptides wants to know that thymosin alpha-1 and thymosin beta-4 are different molecules that came out of the same bovine thymus extract in the 1970s, which is the entire reason the names get confused. Each has its own page.

Someone who has read that this is an approved medicine wants the qualifier: approved elsewhere, not in the United States, and FDA has separately named it as a compounding substance that may present significant safety risks.

Someone who has read a summary of its clinical record wants to know when that summary was written. A great deal of the material in circulation predates January 2025, and the trial published that month is the largest ever run on the molecule.

• Against thymosin beta-4, the other peptide from the same extract
• Against thymulin, the other thymus hormone
• The immune peptides, side by side

What is Thymosin alpha-1?

Plain-English version: a 28 amino acid piece of a larger protein the thymus gland makes, given by injection to change how the immune system behaves.

The thymus is a gland behind the breastbone where T cells, one of the immune system's main cell types, are trained before they go to work. It shrinks throughout adult life, and that shrinkage is one of the reasons immune function declines with age.

In the 1970s a bovine thymus extract called thymosin fraction 5 was found to restore immune function in animals whose thymus had been removed. That extract was a mixture of many peptides, and researchers separated out the ones that seemed to be doing the work. Thymosin alpha-1 is one of them. Thymosin beta-4 is another, which is why the two names sit next to each other everywhere and describe unrelated molecules with unrelated jobs [5] [14].

What is sold and studied today is made synthetically rather than extracted, and it is 28 amino acids long [5]. It has an international nonproprietary name, thymalfasin, which is the generic name a regulator uses rather than a company's trade name.

It is given by injection under the skin. Unlike almost everything else on this site, its behaviour in a person has been measured: absorption is rapid, peak concentration in blood arrives within about two hours, levels return to baseline within 24 hours, and the serum half-life is roughly two hours [13].

28 amino acids. This site did not verify the residue sequence against a primary chemical reference and does not print one · Not stated here. No primary chemical reference was read for this page

How strong is the evidence, claim by claim?

Every claim area this compound is discussed for gets a row, including the ones with the weakest support. The tier records what the row rests on, and the last column states what that work can and cannot show. Each tier links to its definition on the methodology page.

Rolled up, that puts Thymosin alpha-1 at evidence grade B Human data, not settled . Human evidence for the marketed use has read out, and it has not settled the question: the record here does not clear the bar grade A sets, which is two phase-3-scale randomized trials of the marketed use, each cited and each stating whether it met its primary endpoint, agreeing with each other. A grade describes the quality of the research, not whether something works and not whether anyone should use it. The derivation is published.

How Thymosin alpha-1 is thought to work

The mechanism here is better characterised than for anything else on this site, and it is worth understanding precisely because it explains why the compound was expected to work in so many different conditions.

What we do not know

Why the 2013 and 2025 sepsis trials disagree. The larger trial is the better designed one, and nothing on the record explains the earlier result.

Whether the compound does anything for immune support in a healthy adult, which is the use it is sold for. No trial found for this page tested that.

What the two 500-participant hepatitis C phase 3 trials from 2002 found. Both completed, neither posted results, and no publication was located for either.

Whether the melanoma survival difference is real. The trial was open-label, posted no analyses, and showed no dose relationship and no progression-free survival difference.

How many countries register it as a medicine. The figure commonly given is more than thirty, and this site did not verify it against any regulator's register.

Its position on the WADA Prohibited List. The S0 class turns on a substance having no current approval by any governmental regulatory health authority, and this compound has approvals, so the placement is genuinely unsettled rather than resolved in either direction.

Has Thymosin alpha-1 been tested in humans?

62 registered trials name this molecule in their interventions, and 2 of them have posted results. The table below is the completed record that can actually be read, in the order the studies reported.

Where a trial posted results to the registry, the figures come from that posted results section read field by field. Where it was published, they come from the paper.

Why we are not calling this proof

A meta-analysis of many small trials and one large trial are not the same kind of evidence, and where they disagree the large masked trial is the better answer. That is the position this page takes, and it is the reason the 1,106 patient trial leads every section it appears in.

An immune-marker result is not a clinical outcome. CD4+ counts, the CD4 to CD8 ratio and monocyte HLA-DR are measurements of the immune system, and in the larger trials on this page they moved while mortality, recovery and length of stay did not.

A registered trial that completed and posted nothing has told the record only that it happened. Two 500-participant phase 3 trials are in that position, and neither counts as evidence in either direction.

Trials in sepsis, hepatitis, melanoma and COVID-19 are trials in those conditions. None of them tested the use this compound is sold for, which is immune support in a person who is not acutely ill.

Benefits: what the research shows

The matrix above holds each claim with what sits behind it. This section is the shape of the record as a whole.

The honest bottom line on benefits

There are two literatures here and they point in different directions. One is large in trial count and small in individual trial size, reports immune-marker endpoints, and is drawn substantially from databases outside the English-language literature. The other is a handful of large, well-designed, internationally published trials, and its results are 0.99, 0.407 and a survival curve with no progression difference behind it.

Both are facts about the evidence base and this page reports both. Where they disagree, the position taken here is that a 1,106 patient placebo-controlled trial masked from everyone involved is a better answer than a pooled estimate over 39 small ones, and the reason is not that the small trials are dishonest. It is that mortality in sepsis is the kind of question small unmasked trials get wrong in a predictable direction, and this molecule now has a direct demonstration of it: the same institution, the same condition, three times the patients, and the effect went away.

None of that establishes that the compound does nothing. It has measurable effects on immune-cell counts in people, a real pharmacokinetic profile, a pharmacopoeial standard and registration as a medicine in other countries. What the record does not contain is a trial showing that any of it changes an outcome a person would notice, in the use the compound is sold for.

How long Thymosin alpha-1 stays in the body

This is the only compound on this site sold as a research chemical for which real human pharmacokinetic figures exist. A 2001 review in a pharmacy journal reports rapid absorption after injection, peak serum concentration within about two hours, return to baseline within 24 hours, and a serum half-life of approximately two hours.

Those figures were read from that review's abstract rather than from a primary pharmacokinetic study, and they are reported here as what that review states.

The short half-life is worth holding alongside the trial designs above. The 2025 sepsis trial gave an injection every 12 hours for seven days, and the hepatitis trials gave twice-weekly injections over months. Those are very different exposure patterns for a molecule that clears within a day, and the record does not establish which if either is the right one: a 2015 review names dose and schedule among the questions the field has not properly settled [14].

Rapid absorption, peak within about two hours, serum half-life about two hours, back to baseline within 24 hours. [Human RCT] [13]

What is documented about dosing

Nothing here is a dosing recommendation. Statements about dosing reflect what published studies administered.

Commonly cited protocols (extrapolated, not validated)

Nothing here is a dosing recommendation. Statements about dosing reflect community and research reports only.

The amounts and schedules across this record differ by more than an order of magnitude in exposure, from an injection every 12 hours for a week to twice weekly for a year. That is not a detail. A 2015 review names dose, schedule, combination treatment and choice of endpoint as questions the field has not properly addressed, and says that the more recent trials used higher amounts than the older ones.

The melanoma trial is the only one on this record that tested more than one amount head to head, and its posted results show no relationship between the amount given and the number of tumour responses. The highest of the three amounts produced the fewest.

Commonly cited protocols (extrapolated, not validated) circulate for this compound. They do not come from a trial in the population buying it, because no such trial was found for this page.

Nothing here is a dosing recommendation. Talk to a licensed clinician about anything concerning your health.

Main routes people compare, and what each source class actually reported, are set out on the documented protocols page.

Reported effects and what has been measured

What the largest trial reported

The 2025 phase 3 trial in 1,106 adults states that no secondary or safety outcome differed statistically significantly between the treated group and placebo.

That is the single most useful safety observation on this page, because it comes from the largest, most tightly masked study of the molecule. It is a statement about what that trial measured over its treatment period in critically ill adults, and it is not a general statement about the compound. [Human RCT] [1]

What FDA said, and why

FDA lists thymosin alpha-1 among bulk drug substances for use in compounding that may present significant safety risks. Its stated reasoning, quoted from that page as read on 23 August 2026, is that compounded drugs containing it may pose significant risk for immunogenicity for certain routes of administration and may have complexities with regard to peptide-related impurities and characterisation of the active ingredient, and that the safety-related information is inadequate for the agency to sufficiently understand the extent of any safety issues raised.

Read that sentence carefully, because it is a statement about missing information rather than a finding of harm. The agency is not reporting that the substance injured anyone.

The impurity half of it has an independent measurement behind it. A 2022 analytical study applied high-resolution mass spectrometry to a pharmacopoeial reference standard for this molecule and to three commercial materials, and identified and quantified 23 related impurities above 0.1 mg per gram in the standard itself. More than half of them arise directly or indirectly from the asparagine residue at one end of the sequence, which is a property of the molecule rather than of any manufacturer. [In-vitro] [25] [16]

What the trial literature reports

The 2013 sepsis trial records no serious drug-related adverse event. The COVID-19 treatment pilot records nine serious adverse events among treated patients, all judged by the investigators not to be related to the drug.

A 2015 review describes the safety profile as excellent and virtually devoid of toxicity. That review is written by authors reviewing a field they work in, and it is cited here as their stated assessment rather than as an independent finding.

This site does not describe any compound as safe. What is on the record is what these studies measured, over the periods they measured it, in the populations they enrolled. [Human RCT] [2] [6] [14]

What has been measured about Thymosin alpha-1, and what has never been studied

Talk to a licensed clinician about anything concerning your health.

Sourcing and quality

What a credible product should show

This molecule has something almost nothing else on this site has: a pharmacopoeial reference standard. That means an identity and purity specification exists against which a batch can be measured, which is the thing a certificate of analysis for most research chemicals has no external anchor for.

It also has an international nonproprietary name, thymalfasin, which regulators and the literature use. A material sold under that name is at least claiming to be a defined substance.

The impurity picture is documented rather than assumed. A 2022 study identified 23 related impurities above 0.1 mg per gram in the pharmacopoeial standard itself, in classes including deamination, amination, succinimide formation, amino acid insertion and deletion, dimers and isomers. A reader looking at a certificate of analysis for this compound now knows what the analysis has to be capable of separating.

Red flags

An evidence summary written before January 2025. The largest trial of this molecule published that month and changed what the record says.

The 2013 sepsis result quoted without the 2025 one. The two are the same question asked twice, and the larger, better-masked answer is the second.

The hepatitis C completer analysis quoted as the trial result. The intention-to-treat result was 12.7 per cent against 10.5 per cent at P equal to 0.407, and the completer figures are labelled a hypothesis by the authors themselves.

A trial count for this compound presented without its posted-results count. 62 registrations, 2 with posted results.

Prespecified subgroups from the 2025 trial presented as findings. Its primary outcome was null and its subgroups point in opposite directions.

Approval abroad presented as US approval. An openFDA query on 23 August 2026 found no application under any of this compound's names, and FDA separately lists it as a compounding substance that may present significant safety risks.

Will it show on a drug test?

The position is genuinely unsettled and this site states it as unsettled rather than resolving it. The WADA S0 class covers substances with no current approval by any governmental regulatory health authority, and this compound holds approvals as a medicine outside the United States, so S0's own definition appears not to reach it [26].

This site did not establish whether any other class on the 2026 list names it or reaches it. An athlete should take that question to the relevant anti-doping authority rather than to a page, and should treat an absence from a list as an open question rather than an answer.

Storage

No storage guidance is given here. The impurity chemistry documented for this molecule is dominated by reactions at one end of the sequence, which makes handling a real question rather than a formality, and it is one a characterised product's manufacturer answers rather than this page.

Regulatory status, as of 23 August 2026

The regulatory picture for this compound is the most interesting on the site, because it is genuinely split. It is a medicine somewhere and an unapproved substance in the United States, and both of those are true at once.

The split matters for two things a reader may care about. It is why an anti-doping rule that turns on whether any regulator has approved a substance does not obviously reach it. And it is why the FDA compounding listing is worth reading closely rather than as a verdict: the agency's stated position is that it lacks the information to judge the risks, which is a different statement from a finding that the substance is harmful.

This section is dated and re-checked on review. It records documents, their dates and their contents, not evidence about an effect, and carries no evidence tier for that reason.

Thymosin alpha-1 compared with other immune peptides

Almost every confusion around this compound is a naming confusion, and it has two layers.

The first is that thymosin alpha-1 and thymosin beta-4 share a first name because they were separated out of the same extract, and share nothing else. The second is that TB-500 is a fragment of the second one, not of this one. Each has its own page and its own grade.

The comparison worth understanding is with interferon alpha, because the hepatitis B literature everyone cites is a comparison against that medicine rather than against no treatment. A result that reverses direction between the end of treatment and six months later says something about relative timing between two active drugs. It does not establish an effect against placebo.

What Thymosin alpha-1 typically costs

See the price comparison.

Frequently asked questions

References

1. 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
2. Wu J, Zhou L, Liu J, Ma G, Kou Q, He Z, Chen J, Ou-Yang B, Chen M, Li Y, Wu X, Gu B, Chen L, Zou Z, Qiang X, Chen Y, Lin A, Zhang G, Guan X. The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial. Crit Care. 2013. PMID 23327199 DOI 10.1186/cc11932
3. Ciancio A, Andreone P, Kaiser S, Mangia A, Milella M, Solà R, Pol S, Tsianos E, De Rosa A, Camerini R, McBeath R, Rizzetto M. Thymosin alpha-1 with peginterferon alfa-2a/ribavirin for chronic hepatitis C not responsive to IFN/ribavirin: an adjuvant role? J Viral Hepat. 2012. PMID 22233415 DOI 10.1111/j.1365-2893.2011.01524.x
4. 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
5. Chien RN, Liaw YF. Thymalfasin for the treatment of chronic hepatitis B. Expert Rev Anti Infect Ther. 2004. PMID 15482167 DOI 10.1586/14787210.2.1.9
6. Shehadeh F, Benitez G, Mylona EK, Tran QL, Tsikala-Vafea M, Atalla E, Kaczynski M, Mylonakis E. A Pilot Trial of Thymalfasin (Thymosin-α-1) to Treat Hospitalized Patients With Hypoxemia and Lymphocytopenia Due to Coronavirus Disease 2019 Infection. J Infect Dis. 2023. PMID 36056913 DOI 10.1093/infdis/jiac362
7. Tuthill CW, Awad A, Parrigon M, Ershler WB. A pilot trial of Thymalfasin (Ta1) to prevent covid-19 infection and morbidities in renal dialysis patients: Preliminary report. Int Immunopharmacol. 2023. PMID 36881981 DOI 10.1016/j.intimp.2023.109950
8. Soeroto AY, Suryadinata H, Yanto TA, Hariyanto TI. The efficacy of thymosin alpha-1 therapy in moderate to critical COVID-19 patients: a systematic review, meta-analysis, and meta-regression. Inflammopharmacology. 2023. PMID 37845598 DOI 10.1007/s10787-023-01354-2
9. Cao A, Feng F, Zhou X. Thymosin Alpha 1 Plus Routine Treatment for the Acute Exacerbation of Chronic Obstructive Pulmonary Disease: A Systematic Review and Meta-Analysis. J Coll Physicians Surg Pak. 2024. PMID 39648386 DOI 10.29271/jcpsp.2024.12.1497
10. Tian Y, Yao J, Ma Y, Zhang P, Zhou X, Xie W, Tang W. Thymosin alpha 1 alleviates inflammation and prevents infection in patients with severe acute pancreatitis through immune regulation: a systematic review and meta-analysis. Front Immunol. 2025. PMID 40599771 DOI 10.3389/fimmu.2025.1571456
11. Simonova MA, Ivanov I, Shoshina NS, Komyakova AM, Makarov DA, Baranovskii DS, Klabukov ID, Telepenina KP, Atiakshin DA, Shegay PV, Kaprin AD, Stepanenko VN. Aging and Thymosin Alpha-1. Int J Mol Sci. 2025. PMID 41373628 DOI 10.3390/ijms262311470
12. Dinetz E, Lee E. Comprehensive Review of the Safety and Efficacy of Thymosin Alpha 1 in Human Clinical Trials. Altern Ther Health Med. 2024. PMID 38308608
13. Ancell CD, Phipps J, Young L. Thymosin alpha-1. Am J Health Syst Pharm. 2001. PMID 11381492 DOI 10.1093/ajhp/58.10.886
14. Camerini R, Garaci E. Historical review of thymosin α 1 in infectious diseases. Expert Opin Biol Ther. 2015. PMID 26098768 DOI 10.1517/14712598.2015.1033393
15. Tuthill C, Rios I, McBeath R. Thymosin alpha 1: past clinical experience and future promise. Ann N Y Acad Sci. 2010. PMID 20536460 DOI 10.1111/j.1749-6632.2010.05482.x
16. Cheng Y, Wu P, Kan Y, Li M, Li H. Identification and determination of structurally related peptide impurities in thymalfasin by liquid chromatography-high-resolution mass spectrometry. Anal Bioanal Chem. 2022. PMID 36207535 DOI 10.1007/s00216-022-04336-5
17. ClinicalTrials.gov. NCT02867267, the TESTS trial: a phase 3 multicentre randomized quadruple-masked placebo-controlled trial of thymosin alpha 1 in 1,106 adults with sepsis, sponsored by Sun Yat-sen University with SciClone Pharmaceuticals as collaborator, running September 2016 to March 2021, primary outcome 28-day all-cause mortality. No results are posted to the registry; the trial is published. Read through the v2 API on 23 August 2026. ClinicalTrials.gov. 2026. NCT02867267
18. ClinicalTrials.gov. NCT00711620, the ETASS trial: a multicentre randomized controlled trial of thymosin alpha 1 in 361 patients with severe sepsis, sponsored by Sun Yat-sen University, completed. The registry records masking as DOUBLE, naming participant and outcomes assessor, while the publication's title describes the trial as single-blind. Both are recorded here and neither is resolved. Read through the v2 API on 23 August 2026. ClinicalTrials.gov. 2026. NCT00711620
19. ClinicalTrials.gov. NCT01178996, a phase 3 multicentre double-masked trial in 552 patients with chronic hepatitis C who did not respond to prior peginterferon and ribavirin, sponsored by sigma-tau i.f.r. S.p.A. with SciClone Pharmaceuticals as collaborator, completed July 2009, primary outcome sustained virological response at week 72. No results are posted to the registry; the trial is published. Read through the v2 API on 23 August 2026. ClinicalTrials.gov. 2026. NCT01178996
20. ClinicalTrials.gov. NCT00039962 and NCT00040027, two phase 3 randomized double-masked trials of thymalfasin plus peginterferon alfa-2a in hepatitis C non-responders, 500 participants each, sponsored by SciClone Pharmaceuticals, both started in 2002 and both recorded as completed. Neither has results posted, and no publication was located for either. Read through the v2 API on 23 August 2026. ClinicalTrials.gov. 2026. NCT00039962
21. ClinicalTrials.gov. NCT00911443, a phase 2 open randomized dose-ranging trial in 488 participants with malignant melanoma, sponsored by sigma-tau i.f.r. S.p.A., completed September 2007, five arms of 97 to 99. Posted results: overall tumour response (complete plus partial) 7, 10, 6 and 12 in the four thymosin-alpha-1 arms against 4 in the dacarbazine plus interferon control arm; median overall survival 9.3, 8.6, 10.3 and 9.3 months against 6.6; median progression-free survival 1.9, 1.8, 1.8 and 2.0 months against 1.8. No statistical analyses are posted for any outcome. Read through the v2 API on 23 August 2026. ClinicalTrials.gov. 2026. NCT00911443
22. ClinicalTrials.gov. NCT04428008, a randomized open-label trial of thymalfasin to prevent COVID-19 in 189 renal dialysis patients, completed January 2023. Posted results: COVID-19 infection in 5 of 91 on treatment against 7 of 98 in the control arm; hospitalisation 27 against 26; non-COVID infections 8 against 6; deaths 3 against 7. No analyses are posted. The record's limitations field states that the introduction of vaccine during the study made detection of infection by seroconversion unreliable. Read through the v2 API on 23 August 2026. ClinicalTrials.gov. 2026. NCT04428008
23. ClinicalTrials.gov. Registry sweep for thymalfasin, thymosin alpha 1, thymosin alpha-1, Zadaxin and the bare term thymosin, run through the v2 API on 23 August 2026. The five queries return 91 distinct records, of which 62 name thymosin alpha-1 in their interventions: 9 at phase 3 including one phase 2/3, 32 at phase 2 including phase 1/2 and 2/3, 7 at phase 4, and 2 observational. Two of the 62 have posted results. The remaining 29 records in the union are almost entirely thymosin beta-4, a different molecule covered separately on this site. ClinicalTrials.gov. 2026. ClinicalTrials.gov
24. US Food and Drug Administration. Drugs@FDA approved drug products, queried through the openFDA drugsfda endpoint on 23 August 2026 for thymalfasin, thymosin and Zadaxin across the generic name and brand name fields. All three queries returned NOT_FOUND: there is no approved US application under any of these names. openFDA. 2026. openFDA drugsfda
25. US Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. The category 2 table carries the row Thymosin-alpha 1 (Ta1), with the stated reasoning that compounded drugs containing it may pose significant risk for immunogenicity for certain routes of administration and may have complexities with regard to peptide-related impurities and API characterization, and that the safety-related information is inadequate for the agency to sufficiently understand the extent of any safety issues raised. Page content current as of 22 April 2026, fetched with a browser user agent and read on 23 August 2026. FDA human drug compounding. 2026. FDA category 2 list
26. World Anti-Doping Agency. The 2026 Prohibited List. Cited here only for the definition of class S0, which covers substances with no current approval by any governmental regulatory health authority for human therapeutic use. Thymosin alpha-1 holds approvals as a medicine outside the United States, so that definition appears not to reach it. This site did not establish whether any other class on the list names or reaches this compound, and states the placement as unsettled rather than resolved. The URL serves zero bytes to automation and is ledgered in tools/unverified-sources.json. World Anti-Doping Agency. 2026. WADA 2026 Prohibited List