Thymosin alpha-1
Also sold as: Thymalfasin, Tα1, Ta1, Zadaxin, Thymosin α1, Thymosin alfa 1
Thymosin alpha-1 is not FDA-approved and cannot lawfully be compounded in the United States: FDA has approved no drug product containing it, and on December 4, 2024 FDA's Pharmacy Compounding Advisory Committee voted 17 to 4 against adding it to the 503A bulks list, after FDA concluded there was a lack of evidence of effectiveness across all twelve uses it evaluated. Unlike most peptides sold online, thymosin alpha-1 does have a real human evidence base — it has been given to humans in placebo-controlled Phase 3 trials enrolling over a thousand people — but those trials did not find a benefit on their primary endpoints, so the accurate statement is that it was properly tested and the trials came back negative, not that it is untested.
Which molecule this is. A synthetic 28-amino-acid peptide identical to the naturally occurring thymic peptide. FDA's withdrawn-nomination table names it 'Thymosin-alpha 1 (Ta1)'. Do not confuse it with two neighbouring substances that are easy to conflate: THYMULIN ACETATE, a different thymic peptide, which IS in Category 3 of the 503A list (nominated without adequate support); and THYMOSIN BETA-4 FRAGMENT (TB-500), an unrelated molecule with an entirely different FDA record — FDA identified no human exposure data at all for that one, a finding that emphatically does not apply here.
FDA status
FDA has not approved this and it is not in active development toward approval. That says nothing about whether it is being sold — most substances in this category are.
Not an FDA-approved drug for any indication, and not in active development toward approval. That says nothing about whether it is sold — it is.
“Bulk drug substances nominated but withdrawn”Checked against the source on .
503A compounding
The nominator withdrew the nomination. This is not a legalisation event — the substance is not on the 503A bulks list and remains non-compoundable.
Absent from Categories 1, 2 and 3 of the list updated 2026-05-14 — verified by fetching and text-extracting the document directly. 'Withdrawn' rather than 'never-nominated' is not an inference: FDA's Category 2 page lists 'Thymosin-alpha 1 (Ta1)' by name in its table of 'bulk drug substances previously in category 2 of the interim policies [that] were withdrawn by the nominators'. It left Category 2 because the nominators withdrew, not because FDA cleared it. It did not enter Category 1, it is not on the 503A bulks list, and it remains non-compoundable. Note the direction of travel is the opposite of the July 2026 'peptides are becoming legal again' content wave: status moved sideways, and FDA's stated safety concern was never resolved — it was mooted.
“Bulk drug substances nominated but withdrawn”Checked against the source on .
Evidence
There is human data, but efficacy is not established. This includes programmes that were tested and failed.
ADMINISTRATION CHECK PASSED, AND IT MATTERS THAT IT DID. Every study underpinning this tier was opened and confirmed to ADMINISTER exogenous thymosin alpha-1 to humans — subcutaneous injection versus placebo — not to measure an endogenous peptide as a biomarker. This is the distinction that reduces MOTS-c and TB-500 to zero human trials. Thymosin alpha-1 does not fail that test. Its human evidence base is genuine. THE BOUNDARY CALL, ARGUED. 'Proven-in-humans' requires efficacy ESTABLISHED by adequate and well-controlled trials. Two Phase 3 trials meeting that description were run, and both missed. In the 2025 TESTS trial (NCT02867267, n=1106, 22 centres in China, double blinded, placebo controlled — the source cited on this field), researchers reported 28-day all-cause mortality of 23.4% with thymosin α1 versus 24.1% with placebo (HR 0.99, 95% CI 0.77-1.27, P=0.93), with no secondary or safety outcome differing statistically significantly. In a 2012 Phase 3 trial of 552 peginterferon/ribavirin non-responders with chronic hepatitis C (NCT01178996, sponsor sigma-tau — Ciancio et al., cited in full on the hepatitis C FAQ below), researchers reported sustained viral response of 12.7% versus 10.5% on intention-to-treat (P=0.407) and concluded the drug 'seems to play no role in the primary therapy of the disease'. Limitations cut both ways: that trial's significant result (41.0% vs 26.3%, P=0.048) came from a 48-week completer subgroup, not the ITT primary, and completer analyses discard the randomisation that made the trial informative. WHY THE TRIAL COUNT MISLEADS. A 2025 systematic review of thymosin α1 in sepsis (Frontiers in Cellular and Infection Microbiology, cited in full on the meta-analysis FAQ below) pooled 11 RCTs (967 patients in the thymosin α1 group, 960 in the control group) and reported a significant 28-day mortality reduction (OR 0.73, 95% CI 0.59-0.90, P=0.003) — but the same authors reported that the benefit did not survive restriction to high-quality trials (OR 0.82, 95% CI 0.65-1.03, P=0.09) or to multicentre trials (OR 0.86, 95% CI 0.68-1.08, P=0.20). A pooled effect that disappears as trial quality rises characterises the small trials, not the drug. Counting studies would have produced the wrong tier here just as surely as it does for MOTS-c — in the other direction. NON-US APPROVAL IS NOT FDA APPROVAL. Thymalfasin is marketed outside the United States, and vendors cite the foreign-approval count as though it settled the question. It does not: FDA has approved no drug product containing thymalfasin (verified 2026-07-16 against Drugs@FDA, which returns no match for thymalfasin, Zadaxin or thymosin), and the US development programme that would have produced one did not succeed. On the foreign-approval count itself, FDA did the work and reported the result: it traced the claim to SciClone Pharmaceuticals' 2014 Annual Report and recorded that it 'is unable to independently verify these claims of approval in all the specified countries' (see fdaFindings below). That is stronger than our earlier silence, and it does not change this tier either way — the tier turns on whether efficacy was established, not on how many authorities were persuaded. The precise statement: real, repeated, well-controlled human administration; efficacy not established for any indication; two Phase 3 programmes tested and negative on their primary endpoints. This tier explicitly includes programmes that were tested and failed. That is what this is — and it is a materially stronger evidence base than any other withdrawn-from-nomination peptide in this corpus, which is exactly why the label needs the note.
“This trial found no clear evidence to suggest that thymosin α1 decreases 28 day all cause mortality in adults with sepsis.”Checked against the source on .
What FDA found
FDA’s own words. These are the most citable thing on this site, and the least likely to appear anywhere funded by someone selling the compound.
FDA identified potential significant safety risks for thymosin alpha-1 when reviewing its nomination, placing it in Category 2 before the nominators withdrew it.
Read what this finding is scoped to. It is about the COMPOUNDED BULK SUBSTANCE — immunogenicity by route, peptide-related impurities, and API characterisation — not about whether the molecule has ever been studied. FDA is describing what it does not know about material made outside an approved manufacturing process. A drug can have Phase 3 trials behind it and still leave FDA unable to characterise what a compounder would actually put in a vial. Those are different questions, and the market collapses them.
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks — FDA, 22 April 2026“Compounded drugs containing thymosin-alpha-1 (Ta1) may pose significant risk for immunogenicity for certain routes of administration and may have complexities with regard to peptide-related impurities and API characterization. The safety-related information is inadequate for the agency to sufficiently understand the extent of any safety issues raised by the proposed compounded drug.”
Checked against the source on .FDA did NOT make its 'no human exposure data' finding for thymosin alpha-1, in contrast to five other withdrawn peptides on the same page.
The single most useful thing on this page is what it withholds. On the same withdrawn table, FDA writes that it 'has not identified any human exposure data' for dihexa acetate, KPV, PEG-MGF, MOTs-C and thymosin beta-4 fragment (TB-500). For thymosin alpha-1 it writes something materially weaker and different — that the safety information 'is inadequate for the agency to sufficiently understand the EXTENT of any safety issues'. Inadequate-to-quantify is not absent. FDA chose distinct language for distinct evidentiary situations, and flattening all withdrawn peptides into one 'FDA says there's no human data' claim misreports FDA on both ends: it overstates the record for TB-500's neighbours and understates it here.
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks — FDA, 22 April 2026Checked against the source on .FDA's Pharmacy Compounding Advisory Committee voted 17 to 4 against placing thymosin alpha-1 (free base) on the 503A bulks list on December 4, 2024, and 17 to 4 against thymosin alpha-1 acetate.
The vote question was 'Should Thymosin alpha-1 (free base) be placed on the list?' — Yes: 4, No: 17, Abstain: 0. Identical tally for the acetate. Report the direction carefully: 17 voted AGAINST listing. The four dissenting votes are the honest complication and are recorded here rather than buried. Per the minutes, SOME of the members voting in favour 'commented that this substance should be accessible to patients as an option for use' — an access argument, not an efficacy argument. Read the quantifier exactly: the minutes say 'Some Committee members who voted in favor', and they record no reasoning at all for the rest, so this is not the stated rationale of all four and must not be reported as though it were. What can be said is narrower and still holds: no member is recorded as arguing that the evidence established that it works. The committee's split, so far as the minutes disclose it, was about whether patients should be able to choose an unproven option, not about whether it was proven.
Final Summary Minutes of the Pharmacy Compounding Advisory Committee Meeting, December 4, 2024 — FDA, 4 December 2024“The majority of the Committee members voted against placing Thymosin alpha-1 (free base) on the 503A Bulks List. Several Committee members who voted "No" agreed there was no compelling evidence demonstrating clinical effectiveness and safety in the uses of Thymosin alpha-1 (free base) under review.”
Checked against the source on .FDA states directly that it has approved no drug product containing thymosin alpha-1, and identified a website marketing a compounded thymosin alpha-1 injectable as 'FDA-approved'.
Slide 12, under 'Historical Use in Compounding'. This is the rarest kind of primary source: FDA naming a specific marketing claim about this compound and contradicting it in the same sentence, in its own voice, on the record. Independently confirmed 2026-07-16 against the Drugs@FDA API, which returns no match for thymalfasin, Zadaxin or thymosin. The same slide records that FDA found 'no evidence of compounded drug products containing Ta1 (free base) or Ta1 acetate in the published literature or in outsourcing facility reports', while compounded Ta1 is nonetheless 'marketed online in the United States' for hepatitis B, hepatitis C, HIV, chronic fatigue, inflammation, sepsis, COVID-19, Lyme disease, allergies, cancer, asthma, COPD and psoriatic arthritis. The gap between the indication list being sold and the evidence base FDA could locate is the whole story of this compound.
Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances — FDA presentation to the Pharmacy Compounding Advisory Committee — FDA, 4 December 2024“A website advertises a compounded SC injectable product that is "FDA-approved"; however, FDA has approved no drug products containing Ta1”
Checked against the source on .FDA concluded there is a lack of evidence of effectiveness for thymosin alpha-1 across all twelve uses it evaluated, and that no US clinical practice guideline recommends it.
Slide 68, 'Overall Conclusion on Effectiveness'. The twelve evaluated uses were hepatitis B, hepatitis C, HIV, COVID-19, depressed vaccine response / influenza vaccine adjuvant, malignant melanoma, hepatocellular carcinoma, non-small cell lung cancer, sepsis, infections after haematopoietic stem cell transplantation, COPD, and ME/CFS. FDA published a separate written conclusion for each. Not one came out positive. This is the finding that makes the 'thymosin alpha-1 is an immune-support peptide' marketing frame unanswerable rather than merely unsupported. FDA did not fail to look. It looked twelve times, in the indications the nominators themselves chose, and reported the same answer twelve times.
Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances — FDA presentation to the Pharmacy Compounding Advisory Committee — FDA, 4 December 2024“Lack of evidence to support the effectiveness of SC Ta1 (free base) and Ta1 acetate for the evaluated uses ... None of the clinical practice guidelines for U.S. health professionals recommend Ta1 (free base) or Ta1 acetate ... Studies on the serious and life-threatening conditions considered in the evaluation of effectiveness of Ta1 were inconclusive and limited by small sample sizes and design deficiencies”
Checked against the source on .FDA identified no clinical studies at all of thymosin alpha-1 in myalgic encephalomyelitis / chronic fatigue syndrome, one of the twelve uses for which it was nominated.
Slide 67, and the single most under-reported sentence about this compound. Chronic fatigue is one of the leading consumer marketing claims for thymosin alpha-1 — FDA lists it among the conditions compounded Ta1 is sold for online (slide 12) — and it is the one nominated use where FDA located ZERO studies. Note the scope precisely: this is an evidence-of-effectiveness finding confined to ME/CFS, not the 'no human exposure data' finding FDA made for KPV, MOTS-c and TB-500. Ta1 has abundant human exposure data; it has none in this indication.
Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances — FDA presentation to the Pharmacy Compounding Advisory Committee — FDA, 4 December 2024“FDA did not identify any clinical studies using Ta1 in subjects with ME/CFS. Conclusion: FDA did not identify any data to support the effectiveness of Ta1 in the treatment of ME/CFS.”
Checked against the source on .FDA recorded that there is no USP drug substance monograph for thymosin alpha-1, concluded that both thymosin alpha-1 free base and thymosin alpha-1 acetate are not well-characterized, and found that the nominated 3 mg/mL injectable strength exceeds the substance's measured water solubility of 2 mg/mL with no explanation offered.
Slides 8 and 9, quoted in document order — the solubility figure and the monograph absence are on slide 8 ('Physical and Chemical Characterization (1)'), the not-well-characterized conclusion and the strength-exceeds-solubility finding on slide 9. An earlier revision cited the whole thing to slide 9 and carried the monograph fact in prose only; the monograph absence is load-bearing for the compounding answer, so it is now inside the quote. Product identification, not a regimen — this is what is in the vial, not what to do with it. The finding is quietly devastating and requires no regulatory expertise to evaluate: the nominators asked FDA to permit compounding a solution at a strength more concentrated than the molecule dissolves at, and did not say how. FDA also recorded that no certificate of analysis for Ta1 free base was included in the nomination, and that no impurity limits or testing results were reported from the public domain. The identical monograph finding is recorded for the acetate. This is the criterion on which the nomination was weakest, and it is entirely independent of whether the drug works.
Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances — FDA presentation to the Pharmacy Compounding Advisory Committee — FDA, 4 December 2024“Solubility in water up to 2 mg/mL ... No USP drug substance monograph ... Conclusion: Ta1 (free base) is not well-characterized ... The proposed concentration for injectable product (3 mg/mL) is greater than the solubility of Ta1 (free base) in water (2 mg/mL). No information was provided regarding how a greater solubility is achieved”
Checked against the source on .FDA was unable to independently verify industry claims that thymosin alpha-1 is approved in numerous countries, and recorded that it is not approved in the United States, Japan, or Europe except Italy.
Slide 13. This retires the '30+ countries' talking point, which is the load-bearing claim in nearly every consumer article about this compound. Its provenance, per FDA, is a SPONSOR'S ANNUAL REPORT — SciClone Pharmaceuticals' 2014 filing, SciClone being the company that markets Zadaxin and funds studies of it. FDA notes it could not confirm those claims. An earlier revision of this record declined to assert the '30+ countries' figure because we had no source for it; the correct treatment turns out to be stronger than silence — FDA looked, and could not verify it either. The three major regulators that publish transparent review dossiers are precisely the three where it is not approved.
Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances — FDA presentation to the Pharmacy Compounding Advisory Committee — FDA, 4 December 2024“FDA is unable to independently verify these claims of approval in all the specified countries ... Ta1 is not approved in the United States, Japan, or Europe (except Italy) ... Ta1 is not recognized in the European or Japanese Pharmacopoeias”
Checked against the source on .FDA elected to complete its evaluation of thymosin alpha-1 and take it to the advisory committee even after the nominators withdrew the nomination.
Footnote 5 of the briefing document, and the direct refutation of the loudest claim in the July 2026 peptide-legalisation content wave. The market's inference runs: nomination withdrawn, therefore removed from Category 2, therefore FDA's objection evaporated, therefore compoundable. Every step is wrong, and this footnote breaks the chain at the second one. FDA did not drop the substance when the nominators walked. It finished the review at its own discretion, presented it, and recommended against listing — and the committee agreed 17-4. Withdrawal removed the nominator, not the finding. The evaluation slides make the same point in their own words: 'The nomination was withdrawn, and FDA is evaluating the substances at its discretion.'
FDA Briefing Document, Pharmacy Compounding Advisory Committee Meeting, December 4, 2024 — FDA, 4 December 2024“This nomination was withdrawn by the nominator (FDA-2015-N-3534-0470). However, FDA is electing to proceed with the presentation of thymosin alpha-1-related bulk drug substances (thymosin alpha-1 (free base) and thymosin alpha-1 acetate) to the PCAC.”
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Documented safety signals
FDA: safety-related information inadequate to understand the extent of safety issues; immunogenicity risk for certain routes, plus peptide-related impurity and API characterisation complexities.
'Inadequate information' is not a clean bill of health, and the presence of Phase 3 trials does not answer it. Trials used a characterised, manufactured product; the nomination concerned bulk substance for compounding. Evidence of efficacy in a trial does not transfer to the safety of an uncharacterised bulk API.
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks — FDA, 22 April 2026Checked against the source on .In the 2025 TESTS Phase 3 trial, a prespecified subgroup analysis showed a potential differential effect by age, with a hazard ratio of 1.67 (95% CI 1.04-2.67) for 28-day all-cause mortality in participants under 60 (P for interaction = 0.01).
Handle with care in both directions. This is a SUBGROUP finding from a trial whose primary outcome was null, the confidence interval barely excludes 1.0, and subgroup effects from null trials are unreliable and frequently do not replicate — this is not evidence that the drug kills young people. But it is the direction that should give the consumer market pause: the point estimate in the YOUNGER half favoured placebo, and the younger, healthier, non-septic user is precisely who buys this peptide for 'immune support'. An earlier revision added 'researchers reported it as hypothesis-generating' — that characterisation is not in the paper's abstract and we could not verify it in the full text (HTTP 403), so it is removed rather than softened. It also cut the wrong way: the analysis was PRESPECIFIED, which is the opposite of a fishing expedition, and calling it hypothesis-generating quietly discounted a signal unfavourable to the compound. The caution about subgroup findings from null trials stands on its own without putting words in the authors' mouths. Note also that the same prespecified analysis reported a differential effect by diabetes status in the opposite direction (diabetes: 0.58, 0.35 to 0.99; no diabetes: 1.16, 0.87 to 1.53; P for interaction=0.04) — which is itself the best evidence that these subgroup splits should not be read as findings. The honest summary is that the one large rigorous trial that looked found no benefit overall and nothing reassuring for younger recipients.
The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial — BMJ, 15 January 2025Checked against the source on .FDA's PCAC evaluation records fatal immune haemolytic anaemia and engraftment failure in stem-cell transplant recipients among adverse events reported in thymosin alpha-1 studies, and flags that thymosin alpha-1 could cause or worsen graft-versus-host disease in patients undergoing deliberate immunosuppression.
Slides 20, 21 and 24. Scope this correctly rather than sensationally. FDA's overall clinical-safety conclusion is comparatively mild — in most studies Ta1 'has not been associated with significant adverse events attributable to Ta1', with the most common reactions being local irritation, redness or discomfort at the injection site. The haemolytic-anaemia and engraftment-failure events come from a single small transplant study (Perruccio et al. 2010) in profoundly immunocompromised patients, which is not the consumer population. The transferable point is mechanistic, and it is the one the 'immune support' framing obscures: FDA's concern is that an immunomodulator can act in the direction you did not want. In a transplant recipient, stimulating immunity is how you get graft-versus-host disease. FDA raises the same structural worry about using it alongside influenza vaccines, where it notes that 'adding an immunomodulatory product such as Ta1 to any vaccine could pose unknown safety concerns that warrant further evaluation'. A drug marketed as boosting the immune system is a drug that can perturb it, and FDA's stated position is that it lacks the information to know when.
Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances — FDA presentation to the Pharmacy Compounding Advisory Committee — FDA, 4 December 2024“Potential safety concerns with administering Ta1 in patients who are undergoing deliberate immunosuppression. For example, Ta1 could cause or worsen acute or chronic graft-vs-host disease (GVHD) and lead to engraftment failure in HSCT recipients.”
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Questions people actually ask
Every answer cites the document behind it. Where the honest answer is “nobody knows”, that is the answer you will get.
- Did FDA approve thymosin alpha-1?
No. FDA has approved no drug product containing thymosin alpha-1. In its December 2024 evaluation of the substance, FDA noted that a website advertises a compounded thymosin alpha-1 injectable as "FDA-approved" and stated in response that "FDA has approved no drug products containing Ta1". A search of the Drugs@FDA database on 2026-07-16 returned no approved product under the names thymalfasin, Zadaxin or thymosin. The brand name Zadaxin is marketed only outside the United States.
Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances — FDA presentation to the Pharmacy Compounding Advisory Committee — FDA, 4 December 2024“A website advertises a compounded SC injectable product that is "FDA-approved"; however, FDA has approved no drug products containing Ta1”
Checked against the source on .- Did thymosin alpha-1 become legal again when FDA removed it from Category 2?
No. Thymosin alpha-1 left Category 2 because the nominators withdrew the nomination, not because FDA resolved its concerns, and it did not become compoundable as a result. FDA continued the review anyway: its briefing document records that although "this nomination was withdrawn by the nominator", FDA was "electing to proceed with the presentation of thymosin alpha-1-related bulk drug substances ... to the PCAC". On December 4, 2024 FDA proposed that thymosin alpha-1 not be added to the 503A bulks list and the advisory committee voted 17 to 4 against adding it. Thymosin alpha-1 does not appear on the 503A bulks list updated May 14, 2026, and remains non-compoundable in the United States.
FDA Briefing Document, Pharmacy Compounding Advisory Committee Meeting, December 4, 2024 — FDA, 4 December 2024“This nomination was withdrawn by the nominator (FDA-2015-N-3534-0470). However, FDA is electing to proceed with the presentation of thymosin alpha-1-related bulk drug substances (thymosin alpha-1 (free base) and thymosin alpha-1 acetate) to the PCAC.”
Checked against the source on .- Is there any human evidence that thymosin alpha-1 works?
Yes — thymosin alpha-1 has genuinely been given to humans in large, well-designed trials, which is unusual for a peptide sold online. The largest is a double blinded, placebo controlled Phase 3 trial in 1,106 adults with sepsis across 22 centres in China, published in The BMJ in 2025. It did not find a benefit. Researchers reported 28-day all-cause mortality of 23.4% in the thymosin alpha-1 group versus 24.1% with placebo (hazard ratio 0.99, 95% confidence interval 0.77 to 1.27; P=0.93), reported that no secondary or safety outcome differed statistically significantly between the groups, and concluded there was "no clear evidence to suggest that thymosin α1 decreases 28 day all cause mortality in adults with sepsis". The accurate summary is that thymosin alpha-1 was properly tested and the trial came back negative, which is a different thing from untested — and a different thing from proven.
The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial — BMJ, 15 January 2025“This trial found no clear evidence to suggest that thymosin α1 decreases 28 day all cause mortality in adults with sepsis.”
Checked against the source on .- Did thymosin alpha-1 work in the hepatitis C trial?
No, not for treating the infection. A Phase 3 trial published in 2012 randomised 552 patients with chronic hepatitis C who had not responded to peginterferon plus ribavirin to receive either thymosin alpha-1 or placebo alongside standard care. Researchers reported sustained viral response rates in the intention-to-treat population that were "similar between thymosin alpha-1 and placebo (12.7%vs 10.5%; P = 0.407)" and concluded that "Thymosin alpha-1 seems to play no role in the primary therapy of the disease". A higher response rate did appear among the subset of patients who completed all 48 weeks of therapy (41.0% versus 26.3%, P = 0.048), but a completer analysis discards the randomisation that made the trial informative, and the authors framed it as raising a hypothesis about a possible secondary adjuvant role rather than as a result. This trial is why the plural in "Phase 3 trials" is accurate: two independent programmes, two negative primary endpoints.
Thymosin alpha-1 with peginterferon alfa-2a/ribavirin for chronic hepatitis C not responsive to IFN/ribavirin: an adjuvant role? — Journal of Viral Hepatology, 1 January 2012“SVR rates in the intention to treat population were similar between thymosin alpha-1 and placebo (12.7%vs 10.5%; P = 0.407) ... The addition of thymosin alpha-1 to the standard of care did not increase the on-treatment HCV viral response. Thymosin alpha-1 seems to play no role in the primary therapy of the disease.”
Checked against the source on .- Do the meta-analyses showing thymosin alpha-1 reduces sepsis mortality prove it works?
No, and the clearest statement of why comes from a meta-analysis itself. A 2025 systematic review pooled 11 randomised controlled trials of thymosin alpha-1 in sepsis (967 patients in the thymosin alpha-1 group, 960 in the control group) and did report a statistically significant reduction in 28-day mortality (odds ratio 0.73, 95% CI 0.59-0.90, P = 0.003) — the number vendors cite. The same authors then reported that the effect disappeared when they restricted the analysis to high-quality trials (OR 0.82, 95% CI 0.65-1.03, P = 0.09) and to multi-center trials (OR 0.86, 95% CI 0.68-1.08, P = 0.20). A pooled benefit that evaporates as trial quality rises is a description of the low-quality trials, not of the drug. This is consistent with the largest and most rigorous individual trial, the 1,106-patient BMJ trial, which found no benefit.
Efficacy of thymosin α1 for sepsis: a systematic review and meta-analysis of randomized controlled trials — Frontiers in Cellular and Infection Microbiology, 3 September 2025“Out of 3003 identified studies, 11 RCTs met the inclusion criteria (967 patients in Tα1 group and 960 patients in control group). The comprehensive meta-analysis demonstrated a significant reduction in 28-day mortality associated with Tα1 administration (OR 0.73, 95%CI: 0.59-0.90, P = 0.003). Nonetheless, analyses of high-quality (OR 0.82, 95%CI: 0.65-1.03, P = 0.09) and multi-center (OR 0.86, 95%CI: 0.68-1.08, P = 0.20) subgroups did not reveal a mortality benefit.”
Checked against the source on .- Is thymosin alpha-1 approved in 30 countries?
FDA could not verify the foreign-approval claims it was given, and did not itself state any country count. What FDA reviewed in December 2024 was SciClone Pharmaceuticals' 2014 Annual Report — SciClone being the company that funds studies of its thymosin alpha-1 product Zadaxin — which said thymosin alpha-1 was "approved" in countries in the Asia-Pacific region, Latin America, Eastern Europe and the Middle East. FDA wrote that it "is unable to independently verify these claims of approval in all the specified countries", and recorded that thymosin alpha-1 "is not approved in the United States, Japan, or Europe (except Italy)" and "is not recognized in the European or Japanese Pharmacopoeias". So the honest answer is that the number is a sponsor's claim no regulator has confirmed, and that the three major regulators which publish transparent review dossiers are precisely the ones where it is not approved. A marketing authorisation from another country is also not an FDA approval and does not make a substance eligible for compounding in the United States.
Thymosin Alpha-1 (Ta1) Related Bulk Drug Substances — FDA presentation to the Pharmacy Compounding Advisory Committee — FDA, 4 December 2024“According to the SciClone Pharmaceuticals' 2014 Annual Report, Ta1 is "approved" for use in countries in the Asia-Pacific region, Latin America, Eastern Europe, and the Middle East ... FDA is unable to independently verify these claims of approval in all the specified countries ... Ta1 is not approved in the United States, Japan, or Europe (except Italy) ... Ta1 is not recognized in the European or Japanese Pharmacopoeias”
Checked against the source on .- Can I get thymosin alpha-1 from a compounding pharmacy?
Not lawfully. FDA's guidance on compounding under section 503A of the Federal Food, Drug, and Cosmetic Act sets out three doors a bulk drug substance can come through: it must comply with an applicable USP or NF monograph if one exists; or, if no monograph exists, be a component of a drug approved by the Secretary; or, if neither, appear on the 503A bulks list developed by regulation. Thymosin alpha-1 comes through none of them — FDA's December 2024 evaluation records that there is no USP drug substance monograph for it and that FDA has approved no drug products containing it, and it does not appear in Category 1, 2 or 3 of the 503A list updated May 14, 2026. Each of those three facts is documented separately on this page. FDA has also noted that compounded thymosin alpha-1 is nonetheless marketed online in the United States, including by at least one website describing it as FDA-approved.
Interim Policy on Compounding Using Bulk Drug Substances Under Section 503A of the Federal Food, Drug, and Cosmetic Act — Guidance for Industry — FDA, 7 January 2025“One of the conditions that must be met for a compounded drug product to qualify for these exemptions is that a licensed pharmacist or licensed physician compounds the drug product using bulk drug substances that: (1) Comply with the standards of an applicable United States Pharmacopeia (USP) or National Formulary (NF) monograph, if a monograph exists, and the USP chapter on pharmacy compounding; (2) If such a monograph does not exist, are drug substances that are components of drugs approved by the Secretary of the Department of Health and Human Services (Secretary); or (3) If such a monograph does not exist and the drug substance is not a component of a drug approved by the Secretary, appears on a list developed by the Secretary through regulations issued by the Secretary under subsection (c) of section 503A.”
Checked against the source on .- What did FDA's advisory committee decide about thymosin alpha-1?
FDA's Pharmacy Compounding Advisory Committee voted 17 to 4 against placing thymosin alpha-1 on the 503A bulks list at its meeting on December 4, 2024, with the same 17-4 tally for both the free base and the acetate form. According to the meeting's final summary minutes, several members voting against "agreed there was no compelling evidence demonstrating clinical effectiveness and safety in the uses of Thymosin alpha-1 (free base) under review", while some of the members who voted in favour commented that the substance "should be accessible to patients as an option for use" — an access argument rather than a claim that it had been shown to work. FDA had proposed that thymosin alpha-1 not be included on the list, and the committee agreed.
Final Summary Minutes of the Pharmacy Compounding Advisory Committee Meeting, December 4, 2024 — FDA, 4 December 2024“The majority of the Committee members voted against placing Thymosin alpha-1 (free base) on the 503A Bulks List. Several Committee members who voted "No" agreed there was no compelling evidence demonstrating clinical effectiveness and safety in the uses of Thymosin alpha-1 (free base) under review.”
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