Unusually for this library, the thymosin alpha 1 dosage question has a real answer. The same figure — 1.6 mg — runs through hepatitis, sepsis and COVID trials involving well over a thousand patients.
The short version
The trials used 1.6 mg under the skin. In chronic hepatitis that was twice a week, for up to 48 weeks. In severe sepsis it was twice a day for five days, then once a day for two. Thymalfasin is approved in more than 35 countries, but not by the FDA.
Thymosin alpha-1 is a 28-residue peptide first isolated from thymus tissue. It is the most conventionally developed compound in this library: real trials, real registrations, and a dose that stayed put across two decades of them.
What the thymosin alpha-1 trials administered
| Study | Species | Dose | Route | Duration | n |
|---|---|---|---|---|---|
| Ciancio et al., 2012 | Human (chronic hepatitis C) | 1.6 mg | Subcutaneous, twice weekly | 48 weeks | 552 |
| Iino et al., 2005 | Human (chronic hepatitis B) | 0.8 or 1.6 mg | Not stated in the record | 24 weeks + 72 weeks follow-up | 316 |
| Wu et al., 2013 (ETASS) | Human (severe sepsis) | 1.6 mg | Subcutaneous, twice daily ×5 days then once daily ×2 | 7 days | 361 |
| Wu et al., 2020 | Human (critically ill COVID-19) | 1.6 mg | Once daily or every 12 hours | More than 5 days | — |
A dash means we have no sourced figure for that cell and have not estimated one.
Four trials, one amount. That consistency is worth noticing, because it is what a compound with an actual development program looks like from the outside.
- The amount is stable. 1.6 mg appears in every trial we verified, across three separate indications.
- The schedule is not. Twice weekly, twice daily and every 12 hours all appear, and they are not small differences.
- One trial tested two amounts. Iino and colleagues ran 0.8 mg against 1.6 mg in 316 patients.
The hepatitis trials, which set the figure
Ciancio and colleagues randomized 552 patients with chronic hepatitis C who had not responded to interferon and ribavirin. Thymosin alpha-1 at 1.6 mg twice weekly was added on top, for 48 weeks.
Iino and colleagues had already run 316 Japanese patients with chronic hepatitis B through 0.8 mg or 1.6 mg over 24 weeks, with 72 weeks of observation after. That is the trial in this cluster that most closely resembles a dose-ranging study, and 1.6 mg is the figure that survived it.
What the sepsis trial found
ETASS randomized 361 patients with severe sepsis. The schedule was much denser than the hepatitis one: 1.6 mg twice daily for five consecutive days, then once daily for two.
47 of 181 patients in the Tα1 group (26.0%) and 63 of 180 patients in the control group (35.0%) expired.
Wu et al., Critical Care, 2013 (ETASS)That is a meaningful separation in a hard endpoint, in a population where almost nothing separates. The trial was single-blind rather than double-blind, which is the one real weakness in it.
The amount stayed fixed; the schedule did the work. Twice weekly for a chronic viral infection and twice daily for acute sepsis are two very different total exposures built from the same 1.6 mg injection. Any chart that reports “1.6 mg” without the schedule has dropped the variable that actually changed between indications.
Third-party tested research compounds
Third-party tested research compounds, each shipped with a batch-matched certificate of analysis showing HPLC purity and mass-spec identity — the documentation this site argues you should hold any supplier to.
Where thymosin alpha-1 is approved
Not in the United States. We searched the FDA's drug approval database for thymalfasin and for the Zadaxin brand name, and neither returns a record.
The synthetic form of thymosin alpha 1, thymalfasin, is approved in more than 35 countries for the treatment of hepatitis B and C.
Dominari et al., World Journal of Virology, 2020The European Medicines Agency granted thymalfasin an orphan designation for liver cancer in 2002, and notes that it holds a national authorization in Italy related to influenza vaccination.
- Approved in a country means a regulator there reviewed a dossier and cleared a product.
- An orphan designation is a development incentive. The EMA states on the designation itself that it is not a marketing authorization.
- No FDA record means neither of those happened in the United States.
An orphan designation is not a marketing authorization, and the EMA says so on the designation itself. It is worth separating the two, because reviews of this compound routinely blur them.
Research powder is a different object
The 1.6 mg figure describes a manufactured sterile product with a regulator behind it in the countries where it is registered. Research-grade thymosin alpha-1 is lyophilized powder with, at best, analytical testing on the powder.
The molecule can be the same. The controls around it are not. What research grade guarantees goes through the difference, and the complete guide covers the evidence base.
What if you already have a number?
Thymosin alpha-1 is one of the few compounds here where a published human amount exists to convert.
Turning a figure into a syringe volume is arithmetic, and the peptide calculator does it from the vial strength and the volume of diluent. That part always works.
Which is the trap. A calculator converts an unsourced number as cleanly as a sourced one. The output looks equally precise either way.
What to check on the vial
Twenty-eight residues with an acetylated N-terminus is a demanding synthesis. Purity and identity both matter more than they do for a tripeptide, and both are on the certificate of analysis.
How to read a COA and where to buy thymosin alpha-1 cover sourcing. The peptide dosage chart sets this compound beside the rest of the library, which is the fastest way to see how unusual its evidence base is.
Third-party tested research compounds
Third-party tested research compounds, each shipped with a batch-matched certificate of analysis showing HPLC purity and mass-spec identity — the documentation this site argues you should hold any supplier to.
What to know now
- 1.6 mg subcutaneously is the figure across every trial we could verify — hepatitis B, hepatitis C, sepsis and COVID.
- Schedules differ sharply: twice weekly for chronic hepatitis, twice daily for five days in severe sepsis.
- The trials are large by this library's standards: 552, 361 and 316 patients.
- ETASS reported 28-day mortality of 26.0% against 35.0% on control.
- There is no FDA approval. Approval elsewhere, and an EMA orphan designation, are not the same thing.
What we're watching
A large modern sepsis trial is the obvious next data point, and one has been running. ETASS was single-blind, which is the weakest part of an otherwise good result, so a double-blind replication at scale would settle a lot.
We are also watching whether any US regulatory route opens. Right now the gap between 35 countries and zero FDA records is the single most striking fact about this compound.
Frequently asked questions
What dose of thymosin alpha-1 did the trials use?
1.6 mg subcutaneously, twice weekly, across the chronic hepatitis trials. The sepsis trial used the same 1.6 mg amount on a much denser schedule: twice a day for five days, then once a day for two.
Is thymosin alpha-1 FDA-approved?
No. There is no thymalfasin record in the FDA's drug approval database. A published review states it is approved in more than 35 countries for hepatitis B and C, and the EMA granted it an orphan designation for liver cancer in 2002.
How large were the thymosin alpha-1 trials?
Larger than almost anything else in this library. The hepatitis C trial randomized 552 patients, the Japanese hepatitis B trial 316, and the ETASS sepsis trial 361.
What did the sepsis trial find?
28-day all-cause mortality was 26.0% on thymosin alpha-1 against 35.0% on control, in 361 patients with severe sepsis.
Why is the same 1.6 mg used for such different conditions?
Because it came out of the hepatitis development program and carried across. The schedule changes with the indication — twice weekly for chronic infection, twice daily for acute sepsis — but the amount per injection does not.
References
- Ciancio, A., Andreone, P., Kaiser, S., et al. (2012). Thymosin alpha-1 with peginterferon alfa-2a/ribavirin for chronic hepatitis C not responsive to IFN/ribavirin: An adjuvant role? Journal of Viral Hepatitis, 19(Suppl. 1), 52–59. https://doi.org/10.1111/j.1365-2893.2011.01524.x
- Iino, S., Toyota, J., Kumada, H., et al. (2005). The efficacy and safety of thymosin alpha-1 in Japanese patients with chronic hepatitis B: Results from a randomized clinical trial. Journal of Viral Hepatitis, 12(3), 300–306. https://doi.org/10.1111/j.1365-2893.2005.00633.x
- Wu, J., Zhou, L., Liu, J., et al. (2013). The efficacy of thymosin alpha 1 for severe sepsis (ETASS): A multicenter, single-blind, randomized and controlled trial. Critical Care, 17(1), R8. https://doi.org/10.1186/cc11932
- Wu, M., Ji, J. J., Zhong, L., et al. (2020). Thymosin α1 therapy in critically ill patients with COVID-19: A multicenter retrospective cohort study. International Immunopharmacology, 88, 106873. https://doi.org/10.1016/j.intimp.2020.106873
- Dominari, A., Hathaway III, D., Pandav, K., et al. (2020). Thymosin alpha 1: A comprehensive review of the literature. World Journal of Virology, 9(5), 67–78. https://doi.org/10.5501/wjv.v9.i5.67
- European Medicines Agency. Orphan designation EU/3/02/110 — thymalfasin for the treatment of hepatocellular carcinoma, designated 30 July 2002. https://www.ema.europa.eu/en/medicines/human/orphan-designations/eu302110
- Garaci, E., Paci, M., Matteucci, C., et al. (2024). Phenotypic drug discovery: A case for thymosin alpha-1. Frontiers in Medicine, 11, 1388959. https://doi.org/10.3389/fmed.2024.1388959
- Espinar-Buitrago, M. S., Tarancon-Diez, L., Vazquez-Alejo, E., et al. (2023). The use of alpha 1 thymosin as an immunomodulator of the response against SARS-Cov2. Immunity & Ageing, 20(1), 32. https://doi.org/10.1186/s12979-023-00351-x
The absence of a US approval was checked against the FDA's own drug approval database for both the generic and brand names.