How people get it: Not approved in the US. Sold as a prescription medicine (Zadaxin) in some other countries.
FDA status, evidence and safety
Approved abroad onlyNot approved in the US; a prescription drug in other countries
- FDA status
- Not FDA-approved. A 2009 review said it was approved in over 35 countries for hepatitis B and C and to boost the immune system. FDA listed it among substances that may pose significant safety risks in compounding, then moved it to a list of withdrawn nominations. PubMed ↗FDA safety-risk list ↗
- What's changing
- It isn't one of the six peptides in HHS's draft compounding policy of October 30, 2026, so nothing has changed for pharmacies. See what's changing →
- In people so far
- TESTS, a phase 3 trial in 1,106 adults with sepsis at 22 hospitals in China: within 28 days, 23.4% died on thymosin alpha-1 and 24.1% on placebo, no difference. Possible differences in subgroups, such as people with diabetes, need further study. PubMed ↗
- An earlier, smaller trial (361 people with severe sepsis, 2013) had reported 26% deaths against 35% with usual care. The larger TESTS trial did not confirm it. PubMed ↗
- A 1989 trial gave it with the flu vaccine to 90 men aged 65 to 99 to test whether it raised antibody levels. PubMed ↗
- Safety
- The FDA says compounded thymosin alpha-1 may cause immune reactions, and that the safety information it has is inadequate. FDA safety-risk list ↗
- In sport
- Not named on the World Anti-Doping Agency's 2026 Prohibited List. WADA ↗
One of the peptides we follow. We don't give doses or say where to buy. Talk to your doctor before trying any of them.
The basics
We're still gathering this from reference sources like the NIH and MedlinePlus. Sections appear here once every sentence is checked against its source.
What it is
Not enough reliable information yet.
How it's thought to work
Not enough reliable information yet.
What people use it for
Not enough reliable information yet.
What the research has found so far
On Thymosin alpha-1 and aging, PubMed lists 41 trials in people, 29 studies that watched people over time, 11 animal and lab studies. See the counts and searches
Stage 2 because 41 published trials and 66 registered trials in people have been found, but no large ones yet.
A stage shows how far research has got, not whether it will work for you. How stages work
Side effects and risks
Not enough reliable information yet.
Who should be careful, and drug interactions
Not enough reliable information yet.
What to expect
Not enough reliable information yet.
Amounts used in studies
What studies or labels describe, not a recommendation.
Not enough reliable information yet.
Roughly what it costs
We don't have prices for this yet.
Questions to ask your doctor
- Is Thymosin alpha-1 a sensible option for me, given my health and the medicines I take?
- Could Thymosin alpha-1 interact with any medicine or supplement I already take?
- What side effects should I watch for, and when should I stop or call you?
- How would we tell whether it is helping, and when should we review it?
This is general information gathered from the sources listed, not medical advice. Talk to your doctor before starting anything new.
What experts say
No expert views collected yet. Each one we add names the person and links to where they said it.
Recent research
Review maps studies of thymosin alpha 1 as an add-on treatment for cancer
This review summarized 26 studies, mostly from China, using a drug called thymosin alpha 1 with cancer care.
A review of thymosin alpha-1, a immune-boosting peptide, in cancer treatment
This review sums up lab, animal, and patient studies of thymosin alpha-1 in cancer.
Thymosin alpha-1 with an immune drug for older adults with advanced melanoma
This trial will test whether adding thymosin alpha-1 to an immune drug shrinks melanoma in people 60 and older.
Immune peptide Thymosin alpha-1 protects brain cells in stroke studies in mice
Scientists found a thymus peptide may shield brain cells from dying after stroke.
Trials
None of the registered trials of Thymosin alpha-1 is one we have linked as aging-related yet.
ClinicalTrials.gov lists 66 registered trials that mention Thymosin alpha-1, for any condition (the count in The science below). Here we show the ones about aging. See them all ↗
The science
Counted from PubMed and ClinicalTrials.gov on Oct 30, 2026, using one search for Thymosin alpha-1 in relation to aging. Each link opens the exact search.
- Randomized trials in people
- 29 search ↗
- Large trials (multicenter or phase 3)
- 8 search ↗
- Phase 3 trials
- 2 search ↗
- Trials in people
- 41 search ↗
- Studies that watched people over time
- 29 search ↗
- Animal and lab studies
- 11 search ↗
- Registered trials
- 66 search ↗
PubMed search used
("thymosin alpha 1"[tiab] OR "thymosin alpha-1"[tiab] OR "thymosin α1"[tiab] OR thymalfasin[tiab] OR zadaxin[tiab]) AND (aging[tiab] OR ageing[tiab] OR longevity[tiab] OR healthspan[tiab] OR "older adults"[tiab] OR "older people"[tiab] OR elderly[tiab] OR "Aged"[mh])
Counts are search results, so they include some records that only mention Thymosin alpha-1. How we count
Cite or share this page
Longevity Progress. (n.d.). Thymosin alpha-1: Research stage and evidence. Retrieved October 30, 2026, from https://longevityprogress.com/treatments/thymosin-alpha-1
<iframe src="https://longevityprogress.com/embed/stage/thymosin-alpha-1" title="Thymosin alpha-1: research stage on Longevity Progress" width="340" height="72" style="border:0" loading="lazy"></iframe>
The badge shows this treatment's current research stage and links back here. It updates by itself when the stage changes.