Thymosin Alpha-1 Dosage: What Trials Used

Key takeaways

• No thymosin alpha-1 dose exists for healthy people. The only labeled schedule, used abroad for chronic hepatitis B, is 1.6 mg under the skin twice a week for 6 to 12 months.
• Trials in other diseases used the same 1.6 mg unit on different schedules: every 12 hours for a week in sepsis, twice a week for four weeks around flu vaccination, and up to 6.4 mg alongside chemotherapy.
• The doses did not reliably deliver benefits. The largest trial, in 1,106 adults with sepsis, found no survival difference, and the hepatitis B result was not confirmed by a US Phase 3.
• Online 'immune support' protocols copy the hepatitis dose and apply it, open-ended or daily, to healthy adults. No study tested that.
• There is no legal US product, so there is no US label, no units chart and no reconstitution example on this page.

The direct answer: the dose used in nearly every thymosin alpha-1 trial is 1.6 mg injected under the skin, and the one labeled schedule, for chronic hepatitis B abroad, is twice a week for 6 to 12 months (Singapore label). Everything else, from a week of twice-daily injections in sepsis to 6.4 mg alongside chemotherapy, was a research regimen in sick patients, and several of those trials found no benefit. None of it is a dose for immune support in a healthy adult, because nobody has studied that. The thymosin alpha-1 profile covers the evidence and the US legal status in full, and thymosin alpha-1 vs TB-500 explains why it is not the healing peptide it is often confused with.

Studied doses, trial by trial

Sources for the rows: (Singapore label), (Chien 1998), (Mutchnick 1999), (Sherman 1998), (Gravenstein 1989), (Wu 2025) and (Maio 2010); the Italian label, the Carraro and Shetty schedules and the Gravenstein response rates are as summarized in FDA's 2024 review (FDA 2024).

Why 1.6 mg, and why twice a week

The 1.6 mg figure is a translation. Early studies dosed by body surface area, 900 mcg per square meter, which works out to about 1.6 mg for an average adult, and the pharmaceutical vial holds exactly that amount. The Singapore label still lists both numbers, and gives 40 mcg per kilogram for patients under 40 kg (Singapore label).

Twice a week is not about keeping a steady level, which the drug never reaches. A 1.6 mg injection raises blood concentrations about tenfold within an hour, and they return near baseline within a day (FDA 2024); the half-life is roughly 1.5 hours (Wu 2025). In acute illness, investigators dosed far more often: the TESTS team chose 1.6 mg every 12 hours because an earlier study, which combined thymosin alpha-1 with an anti-inflammatory drug, had reported benefit at 3.2 mg a day but not at 1.6 mg a day. Their trial then found no survival benefit at the higher daily amount (Wu 2025).

Across all of these regimens, FDA's 2024 review found doses of 1 to 16 mg under the skin for up to 12 months generally well tolerated, with injection-site irritation the most common complaint (FDA 2024). Tolerated is not the same as effective.

Why a hepatitis or sepsis regimen is not a wellness protocol

The trial regimens have features that do not survive being copied into a self-injection plan.

• A disease to measure. Hepatitis trials tracked viral DNA, the e antigen and liver biopsies; the sepsis trial counted deaths. A healthy adult has no comparable endpoint, so there is no way to know whether a dose is doing anything.
• A fixed course with monitoring. The labeled hepatitis course is 6 to 12 months, and the label tells physicians how to handle the transient liver-enzyme flares the drug can cause (Singapore label). The sepsis course was seven days in intensive care. None was open-ended.
• A companion treatment. Many of the trials added thymosin alpha-1 to interferon, chemotherapy, chemoembolization or intensive care; the dose was tested as part of that package, not alone.
• A known product. Trials used pharmaceutical vials at 1.6 to 2 mg/mL. FDA noted that the compounded injection proposed to it was 3 mg/mL, a concentration never studied, at which the peptide may be more likely to aggregate and provoke antibodies (FDA 2024).
• Results that were often null. Even in the right patients, the large sepsis trial found no benefit (Wu 2025), and the US hepatitis B Phase 3 did not confirm one (Mutchnick 1999). A dose that did not clearly work in the disease it was designed for has no claim on anyone else.

Seller charts are claims, not studied doses

The dosing pages that come up for thymosin alpha-1 share a pattern. Most copy the hepatitis number, 1.5 to 1.6 mg twice a week, and recommend it for months as general immune support. Others add an 'acute' course of daily injections for a week or two during an illness, a 'low-dose' schedule of 300 to 500 mcg a day for several weeks, or weekly 'maintenance' with breaks. Some describe nasal sprays, which FDA also found being marketed in 2024 (FDA 2024).

None of these schedules traces to a study. No trial gave thymosin alpha-1 to healthy people, none tested sub-milligram daily dosing, none tested a nasal spray, and none ran indefinitely. The charts take a real number from a real trial and attach it to a use the trial never examined.

There is also nothing legal for the chart to apply to. Thymosin alpha-1 is not approved in the US, has no USP monograph and is not on FDA's list of substances pharmacies may compound; FDA proposed in 2024 to keep it off that list (FDA 2024), and its advisory committee agreed, 17 to 4, on December 4, 2024, as our thymosin alpha-1 profile details. The legal tracker has the current status, and our peptide dosage chart covers compounds that do have labels.

For the same reason this page has no units table and no reconstitution example. Those belong to products a pharmacist prepared and labeled with a concentration and a beyond-use date. The only thymosin alpha-1 product with a label is a foreign single-use vial, and the US has none.

Bottom line

The thymosin alpha-1 dose is well defined in one narrow sense: 1.6 mg under the skin, twice a week for 6 to 12 months, for chronic hepatitis B, in countries that approved it. Every other regimen was an experiment in sick patients, and the biggest of those experiments found nothing. No study has defined a dose, frequency or duration for immune support, Lyme disease, fatigue or aging, and the schedules sold for those purposes are borrowed numbers attached to an unapproved product.

Frequently asked questions

+−What is the standard dose of thymosin alpha-1?

In nearly every trial and on the labels abroad, the unit dose is 1.6 mg injected under the skin, which corresponds to 900 mcg per square meter of body surface for an average adult. The labeled schedule, for chronic hepatitis B, is twice a week for 6 to 12 months; for hepatitis C, combined with interferon, it is twice a week for 12 months. Those are doses for diagnosed liver disease, not a standard for anyone else.

+−How often is thymosin alpha-1 injected?

It depends entirely on the disease studied. Hepatitis trials and labels used twice a week, with doses 3 to 4 days apart. The sepsis trial gave 1.6 mg every 12 hours for seven days. The flu-vaccine studies gave it twice a week for four weeks around vaccination, or as two doses a week apart. No frequency has been studied in healthy people.

+−Can you take thymosin alpha-1 every day?

Daily and twice-daily dosing has been used only in hospitalized patients for about a week, in sepsis and COVID-19, and in a liver-cancer trial that gave it five times a week for 24 weeks. FDA's review found doses of 1 to 16 mg under the skin for up to 12 months were generally well tolerated in trials. That is a safety observation in patients, not evidence that daily use does anything for a healthy person.

+−What is the thymosin alpha-1 dose for immune support?

There is none. No trial has given thymosin alpha-1 to healthy adults for immune support, so no dose has been studied for that purpose. The 'immune support' schedules online mostly copy the hepatitis B dose of 1.6 mg twice a week and extend it for months, or add daily courses during an illness; none of those schedules comes from a study.

+−How long should you take thymosin alpha-1?

The labeled hepatitis B course is 6 to 12 months, and in the trials that reported a benefit, responses appeared months after treatment stopped. Sepsis and COVID-19 courses lasted about a week, and the vaccine courses four weeks around each vaccination. Open-ended use has never been studied.

+−Is the thymosin alpha-1 dose based on weight?

Partly. Older trials dosed by body surface area, 900 mcg per square meter, which works out to about 1.6 mg for an average adult, and that fixed 1.6 mg became the standard vial. The Singapore label gives 40 mcg per kilogram for patients under 40 kg. Larger fixed doses of 3.2 and 6.4 mg were used alongside chemotherapy in melanoma and around vaccination in dialysis patients.

+−Does a higher dose of thymosin alpha-1 work better?

There is no consistent sign of it. In the melanoma trial, the tumor responses were reported in the 3.2 mg arms, but survival was not significantly better overall. The sepsis trial used 1.6 mg twice a day, chosen because an earlier study had reported benefit at 3.2 mg a day but not 1.6 mg, and still found no survival benefit. Higher concentrations also raise FDA's concern about the peptide clumping into aggregates that can provoke antibodies.

+−How do you reconstitute thymosin alpha-1?

We do not publish reconstitution or units instructions for it, because there is no legal US product to prepare. Abroad, Zadaxin is a single-use vial of 1.6 mg powder that the pharmacist or patient dissolves in the 1 mL of diluent supplied and injects whole. Vials sold in the US are unapproved preparations whose strength and purity no regulator has checked.

Sources

1. LabelZadaxin injection (thymalfasin 1.6 mg), product information. Singapore National Drug Formulary, SIN07483P, accessed October 10, 2026. (2026)
2. StudyChien RN, Liaw YF, Chen TC, Yeh CT, Sheen IS. Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial. Hepatology 1998;27:1383-7. (1998)
3. StudyMutchnick MG et al. Thymosin alpha1 treatment of chronic hepatitis B: results of a phase III multicentre, randomized, double-blind and placebo-controlled study. J Viral Hepat 1999;6:397-403. (1999)
4. StudySherman KE et al. Combination therapy with thymosin alpha1 and interferon for the treatment of chronic hepatitis C infection: a randomized, placebo-controlled double-blind trial. Hepatology 1998;27:1128-35. (1998)
5. StudyGravenstein S et al. Augmentation of influenza antibody response in elderly men by thymosin alpha one. A double-blind placebo-controlled clinical study. J Am Geriatr Soc 1989;37:1-8. (1989)
6. StudyWu J et al. The efficacy and safety of thymosin alpha1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ 2025;388:e082583 (corrected May 2025). (2025)
7. StudyMaio M et al. Large randomized study of thymosin alpha 1, interferon alfa, or both in combination with dacarbazine in patients with metastatic melanoma. J Clin Oncol 2010;28:1780-7. (2010)
8. RegulatoryFDA. Evaluation of thymosin alpha-1 (Ta1)-related bulk drug substances for inclusion on the 503A bulk drug substances list. Briefing document, Pharmacy Compounding Advisory Committee meeting of December 4, 2024. (2024)