Thymosin alpha-1 is approved in more than 35 countries (as Zadaxin / thymalfasin) but is not FDA-approved in the United States. The figures below come from registered clinical trial protocols and are reported as evidence about how it has been studied — not as a schedule for anyone to follow.
Overview
Thymosin alpha-1 has an unusually consistent unit dose across its literature: 1.6 mg by subcutaneous injection, reconstituted from lyophilised powder immediately before use. What varies enormously is how often that 1.6 mg is given, and for how long.
This is the opposite of the situation with most peptides discussed on this site, where a milligram figure is guessed and the schedule is arbitrary. Here the amount is well established and the schedule is the thing that carries all the clinical judgement.
The 1.6 mg unit dose, and its schedules
| Setting | Dose | Frequency | Duration |
|---|---|---|---|
| Sepsis (TESTS phase 3) | 1.6 mg subcutaneous | every 12 hours | up to 7 days |
| Chronic hepatitis B, as an adjunct | 1.6 mg subcutaneous | twice weekly | 24 weeks and beyond |
| Chronic hepatitis C, as an adjunct | 1.6 mg subcutaneous | twice weekly | 48 weeks |
| HBV-related hepatocellular carcinoma, adjuvant | 1.6 mg subcutaneous | twice weekly | 12 months |
The sepsis figure is from the TESTS protocol, which specified 1.6 mg reconstituted in 1 mL of the supplied diluent and injected every 12 ± 2 hours for no more than seven days (ClinicalTrials.gov NCT02867267); the trial itself found no mortality benefit (BMJ 2025; PMID 39814420). The twice-weekly hepatitis schedules come from registered adjunct trials including NCT03448744 (thymalfasin plus entecavir in HBeAg-positive patients) and NCT01178996 (thymosin alpha-1 with peginterferon and ribavirin in hepatitis C).
Note what is absent from that table: no schedule for general immune support, anti-ageing, or preventive use in healthy adults. Every studied schedule is attached to a diagnosis.
Why the frequency changes so much
The 84-fold difference between twice weekly and twice daily is not a dosing disagreement. It reflects two different therapeutic intentions.
In sepsis, the goal is to intervene during an acute window of immune dysregulation lasting days, so exposure is dense and short. In chronic hepatitis, the proposed benefit accrues slowly — the hepatitis B meta-analyses found thymosin alpha-1's advantage over interferon appearing after treatment ended rather than during it (Antiviral Research 2008; PMID 18078676) — so exposure is sparse and sustained for months.
Borrowing a frequency from one setting into the other has no evidentiary basis, and the schedules were not designed to be transferable.
How it is administered
Thymosin alpha-1 is given by subcutaneous injection. Like other peptides of its size it is not orally active — it would be broken down in the gut before absorption — and no approved oral or intranasal presentation exists anywhere.
Approved and trial material is supplied as lyophilised powder with a matched diluent, so 1.6 mg is a verified delivered amount rather than a calculation. With research-grade powder the delivered dose depends on how much diluent was added and on reading syringe units as a volume, layered on top of an unverified starting quantity of peptide. The 1.6 mg figure describes a characterised pharmaceutical product; it does not describe the contents of an unlabeled vial.
Why oversight matters
With this compound the dosing question is really an indication question. The studied schedules exist because a clinician established a diagnosis, chose a course length appropriate to it, and coordinated timing with the antiviral or critical-care therapy the peptide was meant to support — thymosin alpha-1 has essentially always been studied as an adjunct, not as a standalone treatment.
There is also a hard limit on what the evidence covers. The best-powered trial in the compound's history was negative for its primary outcome, and no trial has evaluated indefinite use in healthy adults. A dose figure from a well-designed trial is a fact about that trial, not a licence to extend the schedule to a population it never enrolled.