Thymosin Alpha-1
Thymalfasin · Ta1 · TA-1 · Thymalfasin · Zadaxin
Thymic peptide that tunes T-cell function; licensed abroad as thymalfasin for hepatitis B.
Typical dose
1600 mcg
2x weekly, spaced 3-4 days apart
Range
800–1600
mcg
Half-life
2 h
see Dosing
Evidence
Human trials
Subcutaneous
What it is
Thymosin alpha-1 is a 28-amino-acid, N-terminally acetylated fragment of prothymosin alpha, secreted by the thymus. It is by far the most clinically developed compound in this group: as thymalfasin (brand name Zadaxin) it is licensed in more than 30 countries for chronic hepatitis B, chronic hepatitis C and as a vaccine adjuvant. It has never been approved in the United States.
Rather than pushing the immune system in one direction, it behaves as a modulator. It drives immature T-cells toward maturation, restores CD4 and CD8 counts in lymphopenic patients, raises NK-cell activity and dendritic-cell maturation, and at the same time blunts runaway inflammatory signalling. That dual character is why the same peptide shows up in trials for both viral infection and sepsis.
In the peptide-using community it gets run for recurrent infections, slow recovery from illness, and immune support during heavy training blocks or long calorie deficits. It is one of the better-tolerated compounds in this category, and the human safety database from two decades of hepatitis trials is genuinely large by research-peptide standards.
How it works
Thymosin alpha-1 is a Toll-like receptor agonist, acting mainly at TLR2 and TLR9 on dendritic cells and monocytes. Engaging those receptors drives dendritic-cell maturation and IL-12 output, which pushes naive T-cells down a Th1 path and raises CD4+, CD8+ and NK activity. It also increases MHC class I expression on infected cells, making them easier for cytotoxic T-cells to find and kill.
The modulating side comes from the same signalling running in the opposite direction. In over-inflamed states it has been shown to lower IL-1 beta, IL-6 and TNF-alpha output and to reverse exhausted T-cell phenotypes, with PD-1 and Tim-3 expression falling. It does not force a single direction; the effect tends to normalise whichever way the immune picture is skewed.
Dosing
1.6 mg twice weekly is the licensed Zadaxin dose and the best-supported schedule. Acute-illness trial protocols instead use 1.6 mg once daily for 5-10 days, which is a far higher weekly total.
Reconstitution calculator
Pre-loaded with Thymosin Alpha-1’s vial size, water volume and typical dose. Change anything.
Typical: 1600 mcg · range 800–1600
Draw to
32 u
0.32 mL · 1.6 mg
Concentration
5 mg/mL
50 mcg per unit
Doses per vial
3.1
Vial lasts
11 days
Draw to 32 units on the barrel.
Once mixed
Refrigerate at 2-8 C and use within about 30 days; only bacteriostatic water containing 0.9% benzyl alcohol is suitable for multi-dose vials.
1 mL of bacteriostatic water into a 5 mg vial gives 5 mg/mL, so a 1.6 mg dose is 0.32 mL, or 32 units on a U-100 syringe. Going to 2 mL is also common but pushes a full dose to 64 units, which is a lot of volume for a subcutaneous shot. Aim the water down the vial wall rather than onto the cake, then swirl until clear instead of shaking.
Storage
Before mixing
Sealed lyophilised vials are stable for 2 years or more refrigerated at 2-8 C and longer at -20 C; brief room-temperature shipping excursions are tolerated.
After mixing
Refrigerate at 2-8 C and use within about 30 days; only bacteriostatic water containing 0.9% benzyl alcohol is suitable for multi-dose vials.
Reported benefits
- ▪Raises CD4+, CD8+ and NK-cell counts in people who are lymphopenic
- ▪Licensed human efficacy data in chronic hepatitis B and as a vaccine adjuvant
- ▪Reverses T-cell exhaustion markers in severe infection
- ▪Anecdotally reduces frequency and duration of recurrent viral infections
- ▪Bidirectional: modulates rather than blanket-stimulates immune output
- ▪Large human safety record relative to almost any other research peptide
Side effects
- ▪Injection-site redness, swelling or discomfort, the most common finding in trials
- ▪Transient fatigue or mild flu-like feeling during the first week
- ▪Short-lived joint aches or muscle discomfort
- ▪Rash or urticaria, uncommon
- ▪Transient ALT elevation (a 'flare') during hepatitis B courses, read in those trials as immune-mediated viral clearance rather than drug toxicity
Do not use if
- ▪Active autoimmune disease, where a Th1 push can aggravate the underlying condition
- ▪Organ transplant recipients on maintenance immunosuppression
- ▪Anyone on deliberate immunosuppressive therapy for any indication
- ▪Known hypersensitivity to the peptide or to the mannitol excipient
Evidence level — Human trials
Controlled human clinical data exists.
Approved as thymalfasin in more than 30 countries but not FDA-approved in the US, where it is sold only as a research chemical.
Commonly run with
Thymulin
Zinc-dependent thymic nonapeptide studied for T-cell maturation and inflammatory pain.
250 mcg · once daily
LL-37
The only human cathelicidin: broad antimicrobial and biofilm-disrupting innate immune peptide.
250 mcg · once daily
BPC-157
Gastric-juice-derived pentadecapeptide studied for tendon, ligament and gut healing.
250 mcg · 1x daily (some split into 2x daily during an acute injury)
Thymosin Alpha-1 FAQ
Is thymosin alpha-1 the same thing as TB-500?+
No, and the shared name is a historical accident. Thymosin alpha-1 is a 28-amino-acid immune modulator from prothymosin alpha; TB-500 is a fragment of thymosin beta-4, a 43-amino-acid actin-binding peptide used for tissue repair. Different parent proteins, different receptors, different purpose.
Should I dose it twice weekly or daily?+
Twice weekly at 1.6 mg is the licensed schedule and what most long-term users run. Daily 1.6 mg dosing appears in acute-infection trial protocols and is generally kept to short 5-10 day blocks when you are actually sick, then dropped back.
Will it do anything if my bloodwork is already normal?+
The clearest trial benefits are in people who are lymphopenic or immune-suppressed. If your CD4/CD8 ratio and white cell counts sit in normal range there is much less headroom, and any effect is likely to be subtle. It is a correction, not an enhancement.
Can it be run year-round?+
There is no established ceiling. Hepatitis courses run 6-12 months continuously without cumulative toxicity showing up. Most people cycle 4-12 weeks around illness season or a hard training block, mainly on cost grounds rather than safety.
References
- 1.Pharmacokinetics of thymosin alpha1 after subcutaneous injection of three different formulations in healthy volunteers — International Journal of Clinical Pharmacology and Therapeutics (1999) PMID 10027483
- 2.Thymosin Alpha 1 Reduces the Mortality of Severe Coronavirus Disease 2019 by Restoration of Lymphocytopenia and Reversion of Exhausted T Cells — Clinical Infectious Diseases (2020) PMID 32442287
- 3.Comparison of the efficacy of thymosin alpha-1 and interferon alpha in the treatment of chronic hepatitis B: a meta-analysis — Antiviral Research (2008) PMID 18078676
- 4.Thymosin alpha-1 — American Journal of Health-System Pharmacy (2001) PMID 11381492
More immune & inflammation
ARA-290
EPO-derived peptide targeting the innate repair receptor, trialled for small-fibre neuropathy.
2 mg · once daily
LL-37
The only human cathelicidin: broad antimicrobial and biofilm-disrupting innate immune peptide.
250 mcg · once daily
Thymulin
Zinc-dependent thymic nonapeptide studied for T-cell maturation and inflammatory pain.
250 mcg · once daily