Thymosin Alpha-1

01 How it works

Thymosin Alpha-1 appears to act on the immune system’s early-warning sensors (toll-like receptors) on dendritic cells, which then help T-cells mature and respond. The effect is usually described as modulating the immune system rather than simply boosting it: it nudges a sluggish response along without being thought to set off a strong inflammatory one.

02 Common uses

03 Run profile

This follows the schedule of the approved form abroad (Zadaxin®): the same amount twice a week, for example Monday and Thursday, for about six months. The one change is a gentler start, with a half dose in the first week. After a six-month run, take four weeks off.

04 Pairs well with

05 What to watch for

Generally well tolerated in studies: mild redness or discomfort where you inject is the main thing reported. Because it acts on the immune system, anyone with an autoimmune condition, an organ transplant, or on immune-suppressing medication should talk to their doctor first, as should anyone pregnant or breastfeeding. Facial or throat swelling or trouble breathing is emergency care.

06 Evidence & status

Better studied in people than most peptides here. The approved form has decades of use for chronic hepatitis B and as an add-on to vaccines and cancer treatment in some countries. Results in other settings are mixed: a large trial in sepsis did not show a clear survival benefit.

Not FDA-approved in the US. Approved in a number of other countries as Zadaxin® (thymalfasin), mainly for chronic hepatitis B.

Sources

1. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trialThe BMJ, 2025 · Clinical trial
2. The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trialCritical Care, 2013 · Clinical trial
3. Thymosin-α1 for people with chronic hepatitis BCochrane Database of Systematic Reviews, 2026 · Review
4. Thymosin alpha 1: A comprehensive review of the literatureWorld Journal of Virology, 2020 · Review
5. Historical review of thymosin α 1 in infectious diseasesExpert Opinion on Biological Therapy, 2015 · Review
6. The Prohibited ListWorld Anti-Doping Agency, 2026 · Regulator document

Status and sources last checked November 3, 2026. Something out of date? Tell us.

07 How long until it works

Thymosin alpha-1 has more human data than almost anything else on this site, and the data say: slowly, and for specific conditions. The approved use abroad is chronic hepatitis B, where courses run six to twelve months and benefits, where seen, are measured in viral response at the end of treatment; the 2026 Cochrane review rates the certainty of that evidence as low. In the sepsis trials, the largest of which (TESTS, 2025) ran 28 days, it did not reduce deaths.

For the immune-support use people describe, there is no trial and no timescale. The run profile follows the approved course, twice weekly for about six months, because that is the only dosing with a safety record.

08 Thymosin Alpha-1 vs TB-500

They share a name and nothing else, and the confusion is common enough to be worth a section. Thymosin alpha-1 is an immune-modulating peptide, approved in a number of countries as thymalfasin (Zadaxin), with human trials in hepatitis B, sepsis and as a vaccine adjuvant. TB-500 is a fragment of thymosin beta-4, a different protein involved in cell movement and tissue repair, with no approval anywhere and no human trials for its sports uses.

If the goal is immune function, thymosin alpha-1 is the one with evidence, mixed as it is. If the goal is injury recovery, TB-500 is the one people use, without evidence. In sport the two also part ways: TB-500 is named on WADA’s list; thymosin alpha-1 is not.

09 Stacking

NAD+ and MOTS-C are the usual partners in longevity-minded routines. Nothing has tested these combinations. The cautions that matter come from thymosin alpha-1’s own record: anyone with an autoimmune condition, a transplant or on immune-suppressing medicine should not add it without a doctor, whatever else they take.

10 Where it stands legally

Thymosin alpha-1 is not approved in the US. It is approved in more than thirty other countries as thymalfasin (Zadaxin), mainly for chronic hepatitis B and as an adjunct to vaccines and chemotherapy. It was not among the peptides the FDA’s advisory committee reviewed in July 2026 and is not covered by the October 2026 HHS enforcement-discretion policy.

In sport it is not named on WADA’s Prohibited List, and because it is an approved medicine in other countries the S0 “non-approved” category should not apply; tested athletes should still confirm with their anti-doping body.

11 FAQ

Educational information only — not medical advice. The Daily Stack does not sell or supply any products. Talk to a licensed healthcare professional about your own health decisions.