Thymosin Alpha-1
Thymosin alpha-1 (thymalfasin)
What is Thymosin Alpha-1?
Thymosin Alpha-1: 28-amino-acid thymic peptide (thymalfasin, brand Zadaxin) that modulates T-cell maturation, dendritic and NK cells. The sources cited here most often discuss it for: Chronic hepatitis B; Stronger vaccine response; Sepsis, mixed results. Evidence label: Trial-backed.
- Type
- Peptide
- Family
- Immune & Gut
- Evidence label
- Trial-backed (4 of 5)
- Regulatory status
- Not FDA-approved; in a December 2024 briefing, FDA staff concluded the criteria weigh against adding it to the 503A compounding list, though thymalfasin (Zadaxin) is approved abroad, including in Italy, India and Hong Kong.
- Goals discussed
- Immunity, Heart, Liver & Kidney
- Also called
- thymalfasin, Zadaxin, Ta1, thymosin α1, TA-1, Thymosin A-1
- Last reviewed
- 2026-10-11
- 28-amino-acid thymic peptide (thymalfasin, brand Zadaxin) that modulates T-cell maturation, dendritic and NK cells; approved in Italy, India, Hong Kong, Singapore and others mainly for chronic hepatitis B/immune adjuvant use; not FDA-approved, and FDA advisers voted against adding it to the US compounding list (Dec 2024).12
Regulatory status Not FDA-approved; in a December 2024 briefing, FDA staff concluded the criteria weigh against adding it to the 503A compounding list, though thymalfasin (Zadaxin) is approved abroad, including in Italy, India and Hong Kong. 1
This trial found no clear evidence to suggest that thymosin α1 decreases 28 day all cause mortality in adults with sepsis.
Phase 3 placebo-controlled trial in 1,106 adults with sepsis at 22 centres in China.
What is Thymosin Alpha-1 researched for?
The three outcomes most discussed for Thymosin Alpha-1 in the sources below, as those sources report them. humanpeptides.fyi makes no claims of its own: a listed benefit can be unproven or can have failed in trials, and the label on each line says which.
What do researchers and users say about Thymosin Alpha-1?
Injectable routes of administration may present a particular risk for immunogenicity.
FDA staff assessment of compounded injectable thymosin alpha-1, citing possible aggregation and peptide-related impurities.
I had my first restful night in 12 weeks, my HRV is returning to normal, and I feel energetic.
Long COVID patient the day after a first injection; six weeks later the same person reported that post-exertional symptoms persisted.
What side effects of Thymosin Alpha-1 are reported?
- Generally mild in trials; no safety difference vs placebo in sepsis RCT8
- Users report flu-like reactions, MCAS/autoimmune flares, water retentionanecdotal12
- Possible immune reactions against the peptide itself: FDA flagged immunogenicity risk from aggregation and impurities in compounded injectable forms.FDA briefing1
- In the sepsis trial, a prespecified subgroup under age 60 had higher 28-day mortality with thymosin alpha-1 (hazard ratio 1.67), a signal the trial was not designed to confirm.human RCT subgroup8
- Mild injection-site reactions.practitioner resource13
- Some users report feeling acutely ill for a day or two after an injection, with fever, diarrhea and tingling in one severe report.anecdotal14
What do peptide guides say about Thymosin Alpha-1?
- Dr. Axe Dr. Axe lists thymosin alpha-1 as research-only and not FDA-approved, noting a randomized sepsis trial found no clear mortality benefit and that this is not evidence for routine wellness use. 15
- PepEdHub PepEdHub describes it as a 28-amino-acid thymus peptide that activates dendritic cells, T cells and NK cells, calling it an immune conductor that can both boost and calm responses. 13
- Seek Peptides Seek Peptides lists chronic infections, hepatitis and cancer-treatment support among common uses, but cautions that in autoimmune conditions it may help or harm. 16
- BMJ In a 1,106-patient sepsis trial, death rates were nearly identical with thymosin alpha-1 or placebo, though prespecified subgroups hinted at worse outcomes under age 60 and better outcomes with diabetes. 8
- FDA FDA's briefing notes thymalfasin is approved abroad, for example in Italy as a flu-vaccine adjuvant for immunocompromised people, and in India and Hong Kong. 1
What does the research say, system by system?
How strong is the evidence for Thymosin Alpha-1?
Approved abroad; multiple human RCTs (positive for hepatitis B/vaccine response, negative for sepsis)
Larger randomized human trials exist, positive or negative, but no US approval for the uses discussed. How tiers work
Questions about Thymosin Alpha-1
What is Thymosin Alpha-1?
28-amino-acid thymic peptide (thymalfasin, brand Zadaxin) that modulates T-cell maturation, dendritic and NK cells.
Is Thymosin Alpha-1 FDA-approved?
Not FDA-approved; in a December 2024 briefing, FDA staff concluded the criteria weigh against adding it to the 503A compounding list, though thymalfasin (Zadaxin) is approved abroad, including in Italy, India and Hong Kong.
What is Thymosin Alpha-1 researched for?
The sources cited on this page most often discuss three outcomes: Chronic hepatitis B; Stronger vaccine response; Sepsis, mixed results. Each line above shows what the source reports and how strong that evidence is.
What side effects of Thymosin Alpha-1 are reported?
Reported in the cited sources: Generally mild in trials; no safety difference vs placebo in sepsis RCT; Users report flu-like reactions, MCAS/autoimmune flares, water retention; Possible immune reactions against the peptide itself: FDA flagged immunogenicity risk from aggregation and impurities in compounded injectable forms. The list is not complete, and few listed risks does not mean a compound is safe.
How strong is the evidence for Thymosin Alpha-1?
Evidence label: Trial-backed. Approved abroad; multiple human RCTs (positive for hepatitis B/vaccine response, negative for sepsis).
What else is Thymosin Alpha-1 called?
Names used for it include thymalfasin, Zadaxin, Ta1, thymosin α1, TA-1, Thymosin A-1.
Does humanpeptides.fyi recommend Thymosin Alpha-1?
No. humanpeptides.fyi makes no claims and no recommendations of its own. It summarizes and links to what others have published and posted. Nothing here is medical advice; talk to a licensed clinician.