Thymosin alpha-1

Not FDA-approved

Also known as: Thymalfasin, Tα1, TA-1

Structure source: PubChem CID 16130571 (thymalfasin); matches residues 2–29 of human prothymosin alpha (UniProt P06454)

Thymosin alpha-1 is a natural peptide of 28 amino acids, first identified in the thymus. Lab studies suggest it acts as an immune regulator, able to support some immune responses while keeping others in check. In a large trial in sepsis, it did not reduce deaths.

How it works

In lab and mouse studies, it acts on dendritic cells, the immune cells that show germs to T cells, through a sensor called TLR9.
In those studies, the same signal switched on IDO, an enzyme that breaks down the amino acid tryptophan. This led to more regulatory T cells, which calm immune responses.
In mice, it helped dendritic cells start a protective response to a fungal infection while keeping inflammation in check.
In a look-back study of people with severe COVID-19, those given it had more T cells and fewer signs of T-cell exhaustion.

Evidence

Sepsis

Tested: no benefit shownCEBM Level 1b

In a placebo-controlled trial of 1,106 adults with sepsis, deaths at 28 days were about the same with it as with placebo (23% vs 24%).

Severe COVID-19

Early human evidenceCEBM Level 3

In a look-back study of 76 hospital patients in Wuhan, fewer of those given it died (11% vs 30%). It was not a randomized trial, so it cannot show that the treatment caused the difference.

Caveats

It is avoided during an active flare of an autoimmune disease.
It is avoided in organ-transplant recipients taking anti-rejection drugs, because it could raise the risk of rejection.
It is avoided in pregnancy and breastfeeding.
In the large sepsis trial, side effects were no more common than with placebo.

References

Reviewed by Shubham Gupta, MD — Founder & President · October 31, 2026

This page is for education only. It is not medical advice. Decisions about any treatment belong with a physician who knows your history.