Thymosin Alpha-1

aka Talpha1, Zadaxin, thymalfasin, thymosin alpha-1 acetate

Immune ModulatorImmune SupportAnti-inflammatoryAntiviralCancer AdjunctPost-viral RecoveryImmune Modulator

Last reviewed April 27, 2026 by Doserr editorial team · 13 references on this page

Information on this page is sourced from published research and is for educational purposes only. It does not constitute medical advice.

TL;DR

What it is: A 28-amino-acid synthetic peptide that mimics a thymic hormone, studied in dozens of controlled human trials for immune modulation.
What it's used for: Primarily studied for chronic hepatitis B, sepsis, and as a cancer immune adjunct, community use centers on chronic Lyme, post-viral syndromes, and general immune support.
Evidence level:moderateModerate -- multiple controlled human RCTs exist, but results are indication-specific and the large TESTS sepsis trial (2025) failed to replicate earlier positive findings.

Dose at a glance

	Beginner	Common	Higher end
Per dose	1.6 mg	1.6 mg	1.6 mg
Daily total	1.6 mg (single dose)	3.2 mg (twice weekly -- not daily)	1.6 mg every other day (during acute illness periods)
Schedule	Once daily	Twice weekly	Every other day
Cycle length	4-6 weeks	6-12 weeks	4-8 weeks

Synthesized from community-reported ranges. Not a recommendation. Route varies by compound — see Common route in What people report below.

Half-life: Approximately 2 hours after subcutaneous injection in humans (t1/2 <3 hours, Tmax 1-2 hours, no accumulation on repeat dosing, PMID: 10027483). Well-characterized in published human pharmacokinetic data.
Typical dose range: Doses below are from published research, not recommendations. Zadaxin label / hepatitis B trials: 1.6 mg SC twice weekly for 6-12 months (PMIDs: 8855175, 15850471, 10607256). Sepsis trials (ETASS/TESTS): 1.6 mg SC twice daily x 7 days (PMIDs: 23327199, 39814420). Influenza vaccine adjuvant: 900 mcg/m2 SC twice weekly x 8 doses (PMID: 2642497). Melanoma: 3.2 mg SC in combination with dacarbazine +/- interferon (PMID: 20194853).
Route: Subcutaneous (SC) in essentially all clinical trials -- the route used in every major RCT and the Zadaxin prescribing information. Community use is near-universally subcutaneous (insulin syringe, 29-31 gauge, into abdominal fat).
Evidence tier: moderate
Some human trials published; results limited or mixed.

Each topic links to the studies behind it. Click a topic to expand.

The large TESTS trial (2025, n=1,089, PMID: 39814420) failed to replicate the ETASS mortality signal in sepsis (HR 0.99, P=0.93), the sepsis indication is now substantially undermined
Hepatitis B evidence is real but clinically obsolete in countries with access to nucleoside analogs (entecavir, tenofovir)
US regulatory status is unsettled as of early 2026: not 503A-listed, PCAC review scheduled for mid-2026 and early.
Community use cases (chronic Lyme, post-COVID, autoimmune flares, general immune support) have no controlled trial basis
General healthy-adult immune support has no RCT data -- not negative, just untested
Active autoimmune disease, organ transplant, and pregnancy are flagged as contraindications by mechanism and Zadaxin prescribing information, formal safety data in these populations are lacking

Reconstitution math, both directions.

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