Thymosin Alpha-1 Dosage Guide: The 1.6 mg Regimen, Reconstitution & Trial Record

Thymosin Alpha-1 at a glance

What it is

Thymosin Alpha-1 (Ta1; the synthetic form is thymalfasin, marketed as Zadaxin) — a 28-amino-acid peptide identical to a naturally occurring thymic immune-signalling peptide.

Researched for

Chronic hepatitis B and C, immune adjuvant use, and — in the current trial record — as an adjuvant in oncology and critical care.

Commonly reported dosage

1.6 mg subcutaneously twice weekly. This is the figure used in registered trials, not a recommendation.

Route reported

Subcutaneous injection.

Reported frequency

Twice weekly — notably not daily, unlike most peptides in this library.

Reported course length

Extended courses; the current phase 3 colorectal-cancer protocol runs 6 months.

Plasma half-life

Approximately 2 hours, with peak serum concentration within 2 hours and levels back to baseline within 24 hours (Ancell et al., 2001).

Regulatory status

Not FDA-approved — the FDA drug-label database returns no thymalfasin label. Marketed internationally as Zadaxin; research/educational use only domestically.

Reported ranges from research/community — examples, not recommendations.

What it is / mechanism

Thymosin Alpha-1 is an immune modulator rather than a general stimulant, and the distinction matters for how it is studied. It engages Toll-like receptors TLR2 and TLR9 on myeloid and plasmacytoid dendritic cells, driving dendritic-cell maturation and downstream T-cell activation and differentiation, with reported effects on Th1/Th2 balance and cytokine output including interferon-gamma and interleukin-2. It is thought to act on thymocytes by promoting their differentiation into active T cells. That recalibrating mechanism is why it has been investigated as an adjunct in chronic viral infection, as a vaccine adjuvant, and — in the trials running today — alongside chemotherapy and checkpoint inhibitors in oncology, rather than as a standalone agent.

Researched effects

The most substantial controlled evidence is in chronic hepatitis B, and reading it carefully gives a more interesting picture than the summary usually offered. A meta-analysis comparing thymosin alpha-1 against interferon alfa (Yang et al., Antiviral Research 2008) pooled four randomised controlled trials in 199 patients. At the end of six months of treatment, thymosin alpha-1 was not superior to interferon on any endpoint — the odds ratios for virological, biochemical and complete response were 0.62, 0.60 and 0.54, the last favouring interferon with a confidence interval excluding 1. At the six-month follow-up after treatment ended, the position reversed decisively: odds ratios of 3.71, 3.12 and 2.69, all favouring thymosin alpha-1. The pattern is a delayed but more durable response, which fits an immune-modulating mechanism better than a directly antiviral one, and it means any single-timepoint comparison can make the drug look either worse or better than interferon depending on when you measure. Individual trials reported HBV DNA clearance at six months in 9 of 17 patients on Ta1 versus 10 of 16 on interferon and 4 of 15 historical controls, and in a separate randomised trial 40.6% at six months against 9.4% in untreated controls. In hepatitis C the record is weaker and includes an outright negative result: one trial found no significant difference from placebo in the number of patients reaching a normal serum ALT.

Dosage — reported ranges (overview)

The thymosin alpha-1 dosage figure that circulates almost universally is 1.6 mg subcutaneously twice weekly, and unusually for a compound in this library it is possible to point at exactly where it comes from rather than treating it as community consensus. The currently recruiting phase 3 trial in colorectal cancer (NCT05086614) states it in its own registry record: thymosin alpha-1 1.6 mg by subcutaneous injection, twice a week, for six months after radical resection. That is the same regimen used in the international hepatitis programme. So the number is not an extrapolation from animal work or a forum convention — it is the dose in a live registered protocol, which is a stronger provenance than most peptide dosage figures have. What that does not make it is a recommendation: there is no FDA-approved dose because there is no FDA-approved product, and a dose validated for post-surgical oncology adjuvant use in a supervised trial says nothing about any other context.

A printable protocol sheet with a reconstitution reference and an injection log comes with All-Access Lifetime.

Reconstitution — bac-water math

Thymosin Alpha-1 ships lyophilised and is reconstituted with bacteriostatic water. To read a dose in syringe units on a U-100 insulin syringe (100 units = 1 mL): volume in mL = dose divided by concentration, then multiplied by 100 to convert to units. The table works a 10 mg research vial at three water volumes, with columns for 0.8 mg and the 1.6 mg figure used in the registered trial protocol. All six readings fit comfortably on a 1 mL syringe, which is not true of every compound in this library — check your own vial's labelled mass before reusing any of these numbers, because a 5 mg or 20 mg vial changes every value in the table.

This is concentration math, not a dose recommendation.

Injection / administration basics

Reported administration is subcutaneous and twice weekly rather than daily — the cadence used in the registered trial protocols. General handling concepts such as sterile technique, site rotation and consistent timing are covered here as general information. This is educational information about how the studied regimen is structured, not a personal administration protocol, and a qualified professional should guide any actual use.

Half-life & frequency rationale

Thymosin Alpha-1's serum half-life is approximately 2 hours, and unlike many figures in this library that one is traceable: a clinical pharmacology review (Ancell et al., American Journal of Health-System Pharmacy, 2001) reports rapid absorption with peak serum concentrations within two hours and blood levels returning to baseline within 24 hours. The obvious question follows immediately — how does a peptide cleared within a day get dosed twice a week? The answer is that the dosing interval tracks the immune response rather than the molecule. Thymosin alpha-1 acts by driving dendritic-cell maturation and downstream T-cell differentiation, and those cellular changes persist long after the peptide itself is gone. This is why the compound is a poor candidate for the reasoning that works elsewhere in this library, where a short half-life implies frequent dosing; here the entire published regimen is built on a twice-weekly schedule despite a two-hour half-life, and research into long-acting formulations exists precisely because the native molecule's persistence is not what determines the effect.

Stacking — overview

In the published research literature thymosin alpha-1 is combined with other agents far more often than it is used alone — with interferon alfa-2b in the hepatitis C trials, and with chemotherapy, chemoradiotherapy and PD-1 checkpoint inhibitors in the current oncology programme. That is a meaningful contrast with the community stacking discussion, which pairs it with KPV and BPC-157 in immune and gut research contexts. Both are worth knowing, but only one of them has controlled trials behind it, and it is not the peptide-stack version.

For how combinations are grouped by research context, the named blends, and why a pre-mixed blend vial cannot be calculated from its total milligrams, see the peptide stacks guide.

Storage & handling

• Lyophilised (unmixed): store cold; long-term storage is typically at -20°C, and it is reported as stable refrigerated for shorter periods. Keep sealed and protected from light and moisture.
• Reconstituted: refrigerate at roughly 2-8°C, use within a commonly reported window of about 2-4 weeks, keep away from light and do not freeze once mixed.

Evidence File

The Thymosin Alpha-1 Evidence File: Four Large Trials, One Corrected Result

Thymosin alpha-1 has one of the largest randomised evidence bases in this library and one of the least accurately summarised. Four trials of more than 480 patients each have reported, three of them placebo-controlled and two masked at four separate levels. This file works through the ClinicalTrials.gov record term by term, names every search string used, traces the dose figure the whole market repeats back to its origin in 2001, and states exactly what each registry field does and does not permit anyone to claim.

• Four trade and generic names return one identical 66-record set
• One primary result revised by a post-publication correction
• Sevenfold spread in weekly exposure across registered protocols
• Four records withdrawn at zero enrolment: nothing was tested in them

Sourcing File

The Thymosin Alpha-1 Sourcing File: An Acidic Peptide and an Invisible Impurity

Most peptide sourcing guidance generalises, and for thymalfasin several of the generalisations fail. It is a 28-residue peptide that begins with an acetylated serine followed by an aspartate-alanine pair and ends in an asparagine, and those three structural facts produce compound-specific failure modes, one of which a mass spectrometer cannot detect at all. This file works through the verified identity block, the salt arithmetic recomputed from the molecular formula, the failure modes, the single FDA record that does exist, and a certificate read line by line.

• Two different mass fields returned for one compound by one database
• Acetate salt penalty under 8 percent, well below the generic rule of thumb
• The likeliest impurity here is invisible to mass spectrometry
• One FDA record exists, and its finished flag reads false

Benefit & Outcome Review

The Thymosin Alpha-1 Benefit Review: Twelve Claims, Each Read Against Its Own Comparator

Most benefit reviews grade claims as strong, moderate or weak. For this compound that scale hides the variable that decides everything, which is what each trial compared the peptide against. The comparators in this file are not interchangeable: matched placebo on top of standard care in some, an active drug in another, a historical benchmark rather than the trial's own control arm in a third, no intervention at all in a fourth, and in one case no concurrent comparison group whatsoever. Grading them on one scale produces a false ranking. This review states the tier and the comparator first, every time, and then says what each design can and cannot support.

• Twelve marketed claims, each graded against the comparator actually used
• Over 2,500 randomised participants behind the tolerability record
• Two heavily marketed uses with no trial in either database
• One mechanism whose direction of effect reverses by receptor family

Guide FAQ

Quick answers about guide scope, access, and educational use context.