Home / Peptides / Thymosin Alpha-1: Is It Approved, and Does It Work?
Thymosin Alpha-1: Is It Approved, and Does It Work?
Thymosin alpha-1 is not FDA-approved or in HHS's policy. What the largest sepsis trial found, what FDA's 2024 review concluded, and what is still unknown.
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Quick facts
Fact sheet
- U.S. status
- Strongest evidence
- Limited human data
- Status verified
Thymosin alpha-1 is promoted for immune support and recovery. It is also a peptide with real clinical trials, including a large, well-run one in sepsis that did not find a benefit. This guide shows what is known, and what is not.
Key takeaways
- Thymosin alpha-1 is not FDA-approved in the US and is not among the six peptides in HHS’s October 2026 interim compounding policy.
- In the largest placebo-controlled trial, TESTS (1,106 adults with sepsis), thymosin alpha-1 did not reduce 28-day mortality (23.4% vs 24.1%). The favorable results come from smaller or lower-quality studies.
- FDA’s 2024 review found a lack of evidence supporting its effectiveness for the conditions it evaluated.
- ClinicalTrials.gov lists about 67 studies, but only 2 have posted results.
- It is a different substance from TB-500 and thymosin beta-4. See our TB-500 guide.
What is thymosin alpha-1?
Thymosin alpha-1 (also written Ta1, or called thymalfasin) is a peptide studied for its effects on the immune system. It is not TB-500 or thymosin beta-4, which are other substances. We do not describe how it is made or used.
Is thymosin alpha-1 FDA-approved?
No. A search of Drugs@FDA on Nov. 6, 2026 found no product listed as thymalfasin or thymosin. That search shows approved products, not pending applications.
FDA says versions of the drug have been approved in other countries (FDA). That is not U.S. approval, and FDA’s review still found a lack of evidence of effectiveness for the uses it evaluated.
Where does it stand for compounding?
Thymosin alpha-1 is not in HHS’s policy. The Oct. 30, 2026 policy names six other peptides, and thymosin alpha-1 is in neither of its appendices (HHS policy). Compounded drugs are not FDA-approved, and FDA does not review them for safety, effectiveness or quality before they are marketed.
| Source | What it says |
|---|---|
| FDA’s advisory committee, Dec. 4, 2024 | Voted against adding it to the compounding list: 4 in favor and 17 against, for each form (minutes) |
| FDA’s Category 2 page | “Thymosin-alpha 1 (Ta1)” is listed among nominations that were withdrawn, with a concern about immunogenicity (FDA) |
| FDA’s 503A categories list | We did not find it (list, updated May 14, 2026) |
| FDA’s list of substances nominated under 503B | Category 3, meaning nominated without sufficient support (list, updated March 21, 2025) |
Claims that it has been reinstated or placed in “Category 1” do not match these documents. We give no legal conclusion about any product.
What did FDA’s 2024 review find?
FDA’s 2024 review found a lack of evidence supporting its effectiveness for the conditions it evaluated. FDA evaluated more than a dozen uses and concluded there was “a lack of evidence to support the effectiveness” of the injected form in hepatitis B and C, HIV, COVID-19, response to vaccines, melanoma, liver cancer, lung cancer, sepsis, infections after transplant, COPD and myalgic encephalomyelitis (FDA).
- Human studies exist, but FDA found them inconclusive, with small samples and design flaws. Some authors report a benefit in hepatitis B; FDA pointed out limitations.
- Animal and lab studies show immune-modulating properties, but FDA said their clinical relevance is difficult to define.
We read FDA’s conclusions and located sections, not the whole evaluation, which runs to more than 100 pages, and we did not read the individual studies.
What did the best trial find?
The sepsis trials are the most informative, because they are large and ask a hard question: do fewer people die?
| Study | Design | People | Result |
|---|---|---|---|
| TESTS, BMJ 2025 | Multicenter, double-blind, placebo-controlled | 1,106 adults with sepsis (1,089 analyzed) | 28-day mortality 23.4% vs 24.1%; hazard ratio 0.99 (95% CI 0.77–1.27). No difference in secondary outcomes or in safety. The authors found “no clear evidence” that it reduces mortality |
| ETASS, Crit Care 2013 | Multicenter, single-blind, randomized, with a control group; the abstract does not describe a placebo | 361 | Mortality 26.0% vs 35.0%; risk ratio 0.74 (0.54–1.02), marginal |
| Meta-analysis, 2025 | 11 randomized trials | 1,927 | Pooled odds ratio 0.73, but no benefit in the high-quality trials (0.82; 0.65–1.03) or the multicenter ones; a sequential analysis said the sample was insufficient |
TESTS is the largest and most rigorous of these, and it did not find a benefit in mortality. The favorable pooled results come from smaller or lower-quality studies. That is a finding about sepsis, a serious illness treated in hospitals. It does not tell us about other uses, and it does not show the drug is harmful.
What about hepatitis, cancer, COVID and other uses?
ClinicalTrials.gov lists about 67 studies, but only 2 have posted results. This is a raw count of records with thymosin alpha-1 or thymalfasin as an intervention, on Nov. 6, 2026 (69 by free-text search): 33 are phase 2, 8 are phase 3 and 11 are phase 4; 24 are completed, 17 have an unknown status and 11 are recruiting. The most common conditions are sepsis, hepatitis B and lung cancer (ClinicalTrials.gov).
- Hepatitis C. Two phase 3 trials are registered (NCT00039962, 500 people, and NCT01178996, 552). We did not read their results, so we do not cite an effect.
- COVID-19. One registered trial was terminated, and another enrolled 189 people. FDA said the information was insufficient.
- A registry count is not evidence. A completed trial without posted results does not tell us the result, and a registered trial is not a positive one.
What are the risks?
- Both can be true. FDA says it “may raise safety concerns” in compounding, and also that in most clinical studies it was well tolerated (FDA). The first considers populations and the quality of a compounded product; the second describes trial participants.
- Possible immune reactions. FDA’s Category 2 page cites a concern about immunogenicity.
- The conditions studied can be serious. FDA reminds readers that approved treatments exist for them (FDA).
Which claims are not supported?
- “Boosts the immune system.” That describes a mechanism, not a result in people.
- “Approved in many countries, so it’s proven.” A foreign approval is not U.S. approval, and FDA’s review found a lack of evidence for the uses it evaluated.
- “Treats long COVID, Lyme disease or chronic fatigue.” FDA found a lack of evidence for myalgic encephalomyelitis/chronic fatigue syndrome and for COVID-19, and did not evaluate Lyme disease because the nomination lacked information. We found no evidence for long COVID.
- “It’s back in Category 1.” Not according to FDA’s lists.
- “The studies show it saves lives in sepsis.” The largest trial found no reduction in mortality.
What should you ask your doctor?
- What is behind the symptoms or condition that I’m concerned about, and what approved treatments exist?
- If thymosin alpha-1 is suggested, for which condition, and what human evidence supports it given the TESTS trial?
- Could it interact with my medicines, especially if my immune system is suppressed or I have an autoimmune disease?
- If it is a compounded product, who made it, and is it prescribed for me by name?
We do not give doses, cycles or preparation instructions, and we do not recommend sellers.
Frequently asked questions
Is thymosin alpha-1 FDA-approved?
No. Thymosin alpha-1 is not FDA-approved in the US and is not among the six peptides in HHS’s October 2026 interim compounding policy. FDA says versions have been approved in other countries.
Does thymosin alpha-1 work for sepsis?
In the largest placebo-controlled trial, TESTS (1,106 adults with sepsis), thymosin alpha-1 did not reduce 28-day mortality (23.4% vs 24.1%).
Does thymosin alpha-1 boost immunity?
It has immune-modulating properties in lab and animal studies, but FDA said their clinical relevance is difficult to define, and FDA’s 2024 review found a lack of evidence supporting its effectiveness for the conditions it evaluated.
Is thymosin alpha-1 the same as TB-500?
No. They are different substances. See our TB-500 guide.
Is thymosin alpha-1 legal in the US?
We give no legal conclusion. It is not FDA-approved and is not in HHS’s interim policy. An FDA advisory committee voted against adding it to the compounding list in 2024.
From Best Peptides Today
Sources we checked
- FDA evaluation of thymosin alpha-1 for the Pharmacy Compounding Advisory Committee (Dec. 4, 2024)FDA. Accessed .
- FDA Pharmacy Compounding Advisory Committee minutes (Dec. 4, 2024)FDA. Accessed .
- FDA: bulk drug substances that may present significant safety risks (Category 2)FDA. Accessed .
- FDA: bulk drug substances nominated under section 503A, by category (updated May 14, 2026)FDA. Accessed .
- FDA: bulk drug substances nominated under section 503B, by category (updated March 21, 2025)FDA. Accessed .
- Drugs@FDA (searched Nov. 6, 2026; no product listed as thymalfasin or thymosin alpha-1)FDA. Accessed .
- Federal Register: HHS enforcement discretion policy on 503A peptide compounding (Oct. 30, 2026)Other. Accessed .
- HHS: Enforcement Discretion Policy, with Appendices A and BOther. Accessed .
- TESTS trial: thymosin alpha-1 in sepsis, BMJ 2025 (PubMed)PubMed. Accessed .
- ETASS trial: thymosin alpha-1 in sepsis, Crit Care 2013 (PubMed)PubMed. Accessed .
- Meta-analysis of thymosin alpha-1 in sepsis, Front Cell Infect Microbiol 2025 (PubMed)PubMed. Accessed .
- ClinicalTrials.gov search for thymosin alpha-1 (searched Nov. 6, 2026)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT00039962 (thymosin alpha-1, hepatitis C, phase 3)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT01178996 (thymosin alpha-1, hepatitis C, phase 3)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT04487444 (thymosin alpha-1, COVID-19, terminated)ClinicalTrials.gov. Accessed .
- ClinicalTrials.gov NCT04428008 (thymosin alpha-1, COVID-19)ClinicalTrials.gov. Accessed .
Written and maintained by the Best Peptides For Editorial Team. How we rate evidence.