Thymosin alpha-1 (thymalfasin): what the studies show and where FDA stands
Thymosin alpha-1 is a small peptide of 28 amino acids that the body makes in the thymus gland. A synthetic version, thymalfasin, has been tested in infections, liver disease and cancer, mostly in trials outside the United States. It is not FDA-approved, and FDA currently lists it among substances that raise significant safety concerns for pharmacy compounding. This page explains the evidence and the limits.
Information current as of November 10, 2026. Educational only. Confirm everything here with your own clinician before starting, stopping or changing any medication.
At a glance
What it is
A 28-amino-acid peptide. The synthetic form is called thymalfasin.
Approval status
Not FDA-approved. No FDA-approved drug contains it. It has been studied under the brand name Zadaxin outside the US.
Pharmacy status
FDA lists it in Category 2, substances that raise significant safety concerns for compounding. It is not among the six peptides in the October 2026 policy.
What the evidence shows
Small and mixed trials in sepsis, hepatitis B and C, vaccine response and cancer. No trial shows it extends life in healthy people.
Main caution
FDA cites the risk of immune reactions to the peptide and impurities in compounded product.
At Summit
Summit does not prescribe it. Dr. Miranda decides whether it fits you after your history and labs.
What it is
What thymosin alpha-1 is
Thymosin alpha-1 was first found in extracts of the thymus, a gland behind the breastbone where T cells mature. The version used in studies is made synthetically and is called thymalfasin. It is a short chain of 28 amino acids, much smaller than an antibody or a protein hormone.
Researchers describe it as an immune modulator. In lab and early human studies it raised the activity of T cells and of some of the signals the immune system uses to fight viruses and tumors. That is a laboratory description. It does not tell you what a person will feel or whether any outcome improves.
You may see it sold online as a longevity or anti-aging peptide. The trials below were not designed to test that, and none shows it slows aging in healthy people. Products sold online as research chemicals are not made under any FDA pharmacy policy.
Evidence
What the studies actually show
Most trials were done in China, Italy and other countries, in people who were already sick. They do not tell us what happens in a healthy adult. Individual results vary, and trials in different populations are not directly comparable.
Sepsis
The ETASS trial randomized 361 ICU patients with severe sepsis in China. Death within 28 days was 26.0% with thymosin alpha-1 and 35.0% with standard care alone. The difference was borderline (P = 0.062), and the relative risk was 0.74 with a confidence interval that crossed 1.0. A 2025 meta-analysis of 11 trials (967 treated, 960 control) found lower 28-day mortality overall (odds ratio 0.73). The higher-quality trials (0.82, 95% CI 0.65 to 1.03) and the multicenter trials (0.86, 95% CI 0.68 to 1.08) did not show a clear benefit, and the authors said the total sample was too small to be sure.
Hepatitis B and C
In hepatitis B, a meta-analysis of four trials (199 patients) compared it with interferon. Results at the end of six months did not favor it, but responses measured six months after treatment did. Another meta-analysis of eight trials (583 patients) found more e-antigen seroconversion when it was added to lamivudine (45.1% vs 15.2%). A 2012 randomized study of 51 patients found no advantage when it was added to peginterferon (23.1% vs 20.0%).
In hepatitis C, a double-blind trial of 19 patients found no benefit on its own, and no patient cleared the virus. A 41-patient pilot found a higher end-of-treatment response when it was added to interferon, but the sustained response did not differ. Hepatitis B and C are now managed with other drugs under a hepatologist, so these trials are mostly of historical interest.
Vaccine response
A pilot study in 94 patients on hemodialysis found stronger antibody responses to a pandemic influenza vaccine when thymosin alpha-1 was added. It was small, did not measure illness, and its authors called for larger studies. A review of earlier trials in older adults reached the same conclusion: promising, and needing more work.
Cancer
Evidence in cancer comes from small phase II studies and retrospective reviews, mostly alongside chemotherapy or immunotherapy. In one review of metastatic melanoma patients, median survival was longer in those who also received an anti-CTLA-4 antibody. That comparison was not randomized, and some authors worked for a manufacturer. It cannot show that thymosin alpha-1 caused the difference.
COVID-19
A phase III trial in India of 105 patients reported deaths in 11.1% on thymosin alpha-1 and 38.5% on placebo. A pooled analysis of eight studies found lower mortality (risk ratio 0.59), but the studies disagreed with each other a great deal. A 49-patient randomized pilot in the United States did not find a significant difference in recovery, though CD4 counts rose faster in some treated patients.
What this adds up to
- Signals of benefit in sepsis and in some viral settings, mostly from small or mixed trials.
- Little evidence from large, well-controlled trials in the United States.
- No evidence that it helps healthy people feel better, live longer or avoid infections.
Safety
Side effects and cautions
In the trials above, serious drug-related problems were rarely reported, and the common complaint was discomfort at the injection site. Those trials used a single pharmaceutical-grade product under study conditions. They do not tell you about a compounded product, which can differ between pharmacies.
FDA’s stated concern is different. It says compounded thymosin alpha-1 may carry a significant risk of immunogenicity for certain routes of administration, meaning the immune system could react against the peptide. FDA also cites peptide-related impurities and difficulty characterizing the raw material, and says the safety information is inadequate to understand the extent of the problem.
Call your physician for
- Hives, swelling of the face or lips, or trouble breathing
- A spreading, warm or painful area at an injection site
- Fever or new symptoms of infection
- Any new rash or joint swelling that does not go away
Who should not use it
Who should not use thymosin alpha-1 without specialist advice
Because it stimulates the immune system, the people who most need a specialist to decide are those where immune activity matters:
- People with an organ transplant or who take drugs to suppress the immune system
- People with an autoimmune disease such as lupus, multiple sclerosis or inflammatory arthritis
- People receiving cancer treatment, who should ask their oncologist first
- Anyone who is pregnant, planning pregnancy or breastfeeding, since this page cites no safety data for those situations
- Anyone who has had an allergic reaction to a peptide injection
None of this replaces a physician’s judgment about your history. If you are sick enough to need an immune-directed drug, you need a treating physician, not a supplement.
Regulatory status
Thymosin alpha-1 and pharmacies
A state-licensed 503A pharmacy may compound a bulk substance only if it is a component of an FDA-approved drug, has a monograph in the United States Pharmacopeia, or appears on FDA’s bulk substances list. Thymosin alpha-1 is not a component of an FDA-approved drug. A search of Drugs@FDA data through openFDA and of DailyMed found no US-approved product containing thymosin alpha-1 or thymalfasin. Summit could not confirm a pharmacopeia monograph for it.
FDA’s list of substances that raise significant safety risks, current as of April 22, 2026, names thymosin alpha-1 as a Category 2 substance. Category 2 is the group FDA is concerned about, not the group it has said it will not act against. The substance is not in Category 1 on the May 2026 categories list, which is the group the interim policy allows pharmacies to compound while FDA reviews it.
On October 28, 2026, HHS announced an interim enforcement discretion policy for six other peptides: BPC-157, epitalon, KPV, MOTS-c, semax and TB-500. Thymosin alpha-1 is not one of them, and the law-firm summaries Summit read do not mention it. TB-500 is a fragment of a different protein, thymosin beta-4, and is a separate substance.
What this means in plain terms
A pharmacy’s ability to lawfully compound thymosin alpha-1 is not established. Pharmacies that offer it are relying on a basis FDA has not accepted. Compounded drugs are not FDA-approved, and FDA does not evaluate them for safety, effectiveness or quality before they are sold.
Sport
Anti-doping rules
Summit could not read the current WADA Prohibited List itself, so it cannot say whether thymosin alpha-1 is prohibited in sport. Do not assume that it is allowed. If you compete in tested sport, ask your anti-doping organization or check the current WADA list before any use, because other peptide hormones and related substances are named there.
Summit’s role
What Summit does with thymosin alpha-1
Summit does not prescribe thymosin alpha-1. Dr. Miranda decides whether this fits you after your history and labs, and the pharmacy question above has to be settled first. Summit does not dispense or sell it, and it keeps no stock in the office.
If your interest is infection risk or immune health, a visit can look at what is measurable and treatable, such as vaccines, vitamin levels, sleep and the conditions behind frequent illness. Nothing on this page promises a prescription. See pricing for what the program includes, including labs.
Common questions
Questions people ask
Is thymosin alpha-1 FDA-approved?
No. No US-approved drug contains it. It has been studied under the brand name Zadaxin in other countries, but that does not make it approved here.
Can a pharmacy legally compound it?
That is not established. FDA lists it in Category 2, the safety-concern group, and it is not among the six peptides in the October 2026 enforcement policy.
Is thymosin alpha-1 the same as TB-500?
No. TB-500 is a fragment related to thymosin beta-4. Thymosin alpha-1 is a different peptide with a different history and different trials.
Does it boost the immune system in healthy people?
The trials were in people who were already sick. No study cited here shows a benefit for healthy adults.
Does Summit prescribe it?
No. Dr. Miranda decides whether it fits you after your history and labs, and the compounding question comes first.
Is it banned in sport?
Summit could not confirm. Check the current WADA Prohibited List or ask your anti-doping organization before any use.
Sources
Where this comes from
All retrieved November 10, 2026.
- FDA. Certain bulk drug substances for use in compounding that may present significant safety risks (Category 2), content current as of April 22, 2026. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
- FDA. Bulk drug substances nominated for use in compounding under section 503A: categories list, updated May 14, 2026. https://www.fda.gov/media/94155/download
- Venable. HHS announces interim enforcement discretion for section 503A compounding with certain peptide bulk drug substances, November 2026 (law-firm summary). https://www.venable.com/insights/publications/2026/11/hhs-announces-interim-enforcement-discretion
- Wu J et al. The efficacy of thymosin alpha 1 for severe sepsis (ETASS). Crit Care 2013. https://pubmed.ncbi.nlm.nih.gov/23327199/
- Gu B et al. Efficacy of thymosin alpha 1 for sepsis: systematic review and meta-analysis. Front Cell Infect Microbiol 2025. https://pubmed.ncbi.nlm.nih.gov/40969554/
- Yang YF et al. Thymosin alpha-1 versus interferon alpha in chronic hepatitis B: meta-analysis. Antiviral Res 2008. https://pubmed.ncbi.nlm.nih.gov/18078676/
- Zhang YY et al. Lamivudine versus lamivudine plus thymosin alpha-1 in HBeAg-positive hepatitis B: meta-analysis. Virol J 2009. https://pubmed.ncbi.nlm.nih.gov/19467157/
- Kim BH et al. Thymosin alpha-1 plus peginterferon alfa-2a in HBeAg-positive hepatitis B. Scand J Gastroenterol 2012. https://pubmed.ncbi.nlm.nih.gov/22726105/
- Andreone P et al. Double-blind placebo-controlled pilot trial of thymosin alpha 1 in chronic hepatitis C. Liver 1996. https://pubmed.ncbi.nlm.nih.gov/8873009/
- Andreone P et al. Thymosin-alpha 1 plus interferon-alpha for naive patients with chronic hepatitis C. J Viral Hepat 2004. https://pubmed.ncbi.nlm.nih.gov/14738560/
- Carraro G et al. Thymosin-alpha 1 and an adjuvated pandemic H1N1v vaccine in hemodialyzed patients. Vaccine 2012. https://pubmed.ncbi.nlm.nih.gov/22178096/
- Ershler WB et al. Thymosin alpha 1 as an adjunct to influenza vaccination in the elderly. Ann N Y Acad Sci 2007. https://pubmed.ncbi.nlm.nih.gov/17600281/
- Danielli R et al. Long-term follow up of metastatic melanoma patients treated with thymosin alpha-1. Expert Opin Biol Ther 2018. https://pubmed.ncbi.nlm.nih.gov/30063847/
- Shetty A et al. Phase III trial of thymosin alpha 1 in moderate-to-severe COVID-19. Indian J Crit Care Med 2022. https://pubmed.ncbi.nlm.nih.gov/36042753/
- Soeroto AY et al. Thymosin alpha-1 in COVID-19: systematic review and meta-analysis. Inflammopharmacology 2023. https://pubmed.ncbi.nlm.nih.gov/37845598/
- Shehadeh F et al. Pilot trial of thymalfasin in hospitalized COVID-19 patients. J Infect Dis 2023. https://pubmed.ncbi.nlm.nih.gov/36056913/
Confirm with your provider. This page is general education, not medical advice, and it does not diagnose or treat anything. Every medication carries risks and is not right for everyone. Medication is prescribed only after a physician evaluation determines it is appropriate for you. Individual results vary and no outcome is guaranteed. Information current as of November 10, 2026.
Next step
Start with a physician evaluation
Dr. Miranda reviews your history, medications and goals before any decision about thymosin alpha-1.