Thymosin alpha-1

Where it comes from

Made in

Thymus and many other tissues, as the start of prothymosin alpha; whether the body cuts it out at all is debated

Sent out by

Unclear in the body; what is studied is the injected peptide

Acts on

• Dendritic cells
• T cells
• Natural killer cells

What it does

• Matures dendritic cells and pushes T cells toward a Th1 response
• Raises natural killer activity
• Restrains inflammation in some settings

In medicine

• Thymalfasin is approved in a number of countries, China among them, for hepatitis B; in Italy it is authorised to strengthen the response to influenza vaccine. It has no FDA approval, and none through the EMA ¹
• A trial in 1,106 adults with sepsis at 22 Chinese hospitals, published in 2025, found no reduction in death at 28 days ²

Beyond the body’s own use

• It is one of the peptides most often offered outside approved medicine. Reviewing thymosin alpha-1 as a bulk substance for pharmacy compounding, the FDA said the safety information was inadequate, and pointed to immune reactions and peptide impurities ³
• Unapproved and compounded preparations are not reviewed for safety, effectiveness or quality
• The COVID-19 work shows the pattern of this peptide’s evidence: many small studies at different doses, pooled into meta-analyses that favour it, with no single trial large enough to settle the question ⁴