Thymosin Alpha-1
28-amino-acid thymic peptide hormone with immunomodulatory activity
- Class
- Immune peptide
- Half-life
- ~2 hours
- Route
- Subcutaneous (SubQ)
- Cadence
- Multiple per week
- Evidence
- Human clinical trials
Overview
Thymosin alpha-1 is a 28-amino-acid peptide that mimics a hormone naturally produced by the thymus gland — the organ that trains your T cells before they graduate into circulation. It's approved in 30+ countries (as Zadaxin/thymalfasin) for chronic hepatitis B and C, cancer immunotherapy support, and severe sepsis. In the U.S. it's not FDA-approved for any indication, so all use here is off-label or compounded from research suppliers.
It works by binding to Toll-like receptors (TLRs) on immune cells and pushing them toward a functional, balanced response — boosting underactive immunity (think chronic viral infections, post-chemo immune suppression, age-related immune decline) while also supporting regulatory T cells that prevent runaway inflammation. The dual action is unusual: most immune drugs push one way or the other; thymosin alpha-1 seems to restore homeostasis rather than just amplifying everything.
The evidence base is large but uneven. Over 11,000 people across 30+ trials, mostly in Asia and Europe, spanning hepatitis, sepsis, cancer adjunct therapy, and COVID-19. The strongest human data are in chronic hepatitis B (improved viral clearance, better seroconversion rates) and severe sepsis (lower 28-day mortality in targeted subgroups). Cancer and COVID data are mixed — some trials show benefit, others don't. Safety profile is remarkably clean: mild injection-site reactions in 5–8% of users, almost no serious adverse events even after 12+ months of continuous use.
In February 2026, the FDA reclassified thymosin alpha-1 from Category 2 to Category 1 status under the 503A bulk substance framework, restoring eligibility for routine compounding by licensed pharmacies with a valid prescription.
Safety considerations
A few of the safety signals worth knowing — the full list, with dosing context and what to monitor, is inside AIx Core.
- Not FDA-approved in the U.S. for any indication. All domestic use is off-label or from unregulated research suppliers — purity, sterility, and actual peptide content are not guaranteed unless sourced from a compounding pharmacy with robust testing.
- Do not use if you're deliberately immunosuppressed (e.g., post-transplant on anti-rejection drugs, active autoimmune flare being managed with immunosuppressants). Thymosin alpha-1 activates the immune system and could counteract or destabilize those therapies.
- Injection-site reactions (redness, mild pain) in 5–8% of users. Rare reports of transient muscle atrophy at injection sites, polyarthralgia with hand edema, and rash — these resolved after stopping.
+ 4 more safety notes inside AIx Core →
Commonly monitored
Markers and signals people track when researching Thymosin Alpha-1.
- Complete blood count with differential — track CD4/CD8 ratio and total lymphocyte count
- Subjective immune resilience — frequency of infections, recovery time from illness
- Injection-site reactions — redness, discomfort, or (rarely) local muscle atrophy
- Fatigue or malaise — uncommon but reported in <3% of users
- Baseline and follow-up inflammatory markers (CRP, IL-6) if using for chronic inflammatory condition
Frequently asked questions
What is Thymosin Alpha-1?
28-amino-acid thymic peptide hormone with immunomodulatory activity. Thymosin alpha-1 is a 28-amino-acid peptide that mimics a hormone naturally produced by the thymus gland — the organ that trains your T cells before they graduate into circulation. It's approved in 30+ countries (as Zadaxin/thymalfasin) for chronic hepatitis B and C, cancer immunotherapy support, and severe sepsis. In the U.S. it's not FDA-approved for any indication, so all use here is off-label or compounded from research suppliers.
How is Thymosin Alpha-1 administered?
Subcutaneous (SubQ), typically multiple per week.
What is the half-life of Thymosin Alpha-1?
~2 hours — Short serum half-life; effects on immune cells persist much longer than plasma levels.
Is Thymosin Alpha-1 approved for human use?
Thymosin Alpha-1 is investigational — not approved by the FDA, EMA, or MHRA for human use at the time of writing.
What does the evidence show for Thymosin Alpha-1?
Evidence tier: Human clinical trials. Wu et al. 2013 (ETASS trial, n=662 severe sepsis patients): 1.6 mg subQ twice weekly for up to 28 days reduced 28-day all-cause mortality in a targeted subgroup with baseline immune dysfunction. No serious drug-related adverse events recorded.
What is commonly monitored when researching Thymosin Alpha-1?
Commonly tracked markers + signals: Complete blood count with differential — track CD4/CD8 ratio and total lymphocyte count, Subjective immune resilience — frequency of infections, recovery time from illness, Injection-site reactions — redness, discomfort, or (rarely) local muscle atrophy, Fatigue or malaise — uncommon but reported in <3% of users, Baseline and follow-up inflammatory markers (CRP, IL-6) if using for chronic inflammatory condition.
Related compounds
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