Thymosin Alpha-1

Also known as Thymalfasin, Zadaxin

A peptide from the thymus gland that strengthens the immune system. A prescription drug in some countries outside the EU and US.

Quick facts

Status: Not an approved medicine
Evidence: Approved outside EU/US; mixed trial evidence
Taken as: Injection under the skin
Common sizes: 5 mg, 10 mg
Category: Immune peptide

How it works

It helps T-cells — white blood cells that fight viruses — work better.

What people use it for

Hepatitis B (approved in some countries)
Boosting vaccines and immunity

What the research shows

Several clinical trials, mostly from Asia, with mixed results.
Not approved by EU or US regulators.

Side effects & risks

Generally well tolerated
Soreness at the injection site
Products sold online are not the approved medicine

Is it legal?

Approved in several countries (e.g. China) as Zadaxin. Not approved by the EMA or FDA.

Storage & safe handling

Mix with bacteriostatic water: let it run slowly down the inside of the vial and swirl gently — never shake.
Store the mixed vial in the fridge and follow the use-by period on the label.
Wipe the vial top with alcohol and use a new sterile needle and syringe every time.
Rotate injection sites so the same spot is not used again and again.
Put used needles in a sharps container, not the household bin.
Get medical help for redness that spreads, fever, swelling or trouble breathing.

Open in PepTimerTrack your protocol, calculate how much to draw and get reminders — free.Open in PepTimer

Sources: Clinical trials and reviews of thymalfasin (Zadaxin).
Last updated 12 October 2026. Information — not medical advice. PepTimer does not replace a doctor. Many peptides are not approved medicines in the EU, UK or US. Talk to a qualified healthcare provider before starting, changing or stopping any treatment.