Thymosin α1 (Tα1) is one of the few peptides in this space where a specific dose has actually been pinned down — because, unlike most “research” molecules, it is a genuine approved medicine in much of the world. Yet the way the number gets used online detaches it from everything that gave it meaning. The dose that appears across the clinical record is narrow and repeatable, but it was chosen for ill patients under supervision, and it does not translate into a wellness instruction. For what the drug does and where its evidence is real, start with the thymosin α1 evidence monograph.
The dose the trials used: 1.6 mg subcutaneously, twice a week
Across the human literature, Tα1 dosing converges on a single regimen: 1.6 mg, injected subcutaneously, two times per week. In a large multinational hepatitis C trial, patients received peginterferon and ribavirin plus thymosin α1 dosed precisely as 1.6 mg subcutaneously twice weekly over a 48-week course.[1] That same twice-weekly subcutaneous schedule recurs through the hepatitis literature where Tα1 has been formally studied as an immune adjunct.[2] The peptide is given by injection because, like most peptides, it would be broken down in the gut if swallowed.
Where the 1.6 mg figure comes from
The number is not a wellness convention; it is the dose investigators selected when they ran controlled trials in patients. The hepatitis C study that defined the modern regimen randomized 552 nonresponders to standard antiviral therapy with or without 1.6 mg twice-weekly Tα1, and read out hard virologic endpoints over nearly a year.[1] The same broad approach — a fixed, modest twice-weekly subcutaneous dose layered onto standard care — underpins the meta-analytic work pooling interferon plus Tα1 against interferon alone in chronic hepatitis B.[3] In other words, the “dose” people quote is a clinical-trial dose attached to a specific liver-disease indication, not a generic recipe.
The route, and why it matters
Tα1 is a 28-amino-acid peptide, and the studied route is consistently subcutaneous injection — the same delivery used in its approved immune-adjunct settings.[4]There is no oral form in the clinical record, and the twice-weekly cadence reflects how the drug was administered in the trials that generated its evidence, not a pharmacokinetic optimum somebody can safely improvise. Schedules in other indications — critical-care use in severe sepsis, for instance — were set by the trial protocol and the treating physicians, not by a one-size dose.[5]
Approved-abroad dosing is not a US prescription
Here is the distinction that the marketing erases. Thymosin α1 is approved and sold as Zadaxin in dozens of countries, with defined clinical dosing for indications such as chronic viral hepatitis and use as an immune adjunct.[6] But it has no FDA marketing approval in the United States. That means there is no US label, no US-sanctioned dose, and no domestic titration schedule. The 1.6 mg twice-weekly figure is a fact about how trials and approved-abroad use are conducted — it is emphatically not a regulator-endorsed instruction an American buyer can follow at home with a gray-market vial.
The “wellness” dosing gap
Notice what is missing from the clinical record: there is no validated dose of Tα1 for healthy adults seeking “immune optimization,” anti-aging, or general longevity. The trials dosed sick patients for defined immune problems; nobody has established a safe, effective wellness dose for well people, because the indication itself isn’t supported. So the gray market simply borrows the clinical 1.6 mg twice-weekly figure and reuses it out of context — lending a precise, medical-sounding number to a use the evidence never tested. The precision is real; the relevance to a healthy user is not. It is also worth stressing that Tα1 is not the same molecule as thymosin β4 / “TB-500,” whose marketing and dosing belong to a different peptide entirely; see our TB-500 / thymosin beta-4 review.
The honest bottom line
Reduced to what the evidence supports: thymosin α1 was dosed at 1.6 mg subcutaneously, twice weekly, in the trials and approved-abroad use that gave it its reputation.[1][2] That dose is well defined — but it belongs to supervised treatment of specific immune and liver-disease indications, not to a longevity injection for a healthy person. There is no FDA-approved Tα1 in the US, no domestic dose, and no wellness regimen validated by trials. Any decision to use it, and at what dose, belongs with a clinician treating a real indication — not with a forum protocol. To see how it grades against other peptides, use our peptide evidence matrix, and weigh routes and prices in peptide therapy cost.
