Thymosin alpha-1 (thymalfasin)
Thymosin α1, Tα1, Ta1, TA-1, Zadaxin
Forms: Thymalfasin is the synthetic medicine (Zadaxin); gray-market vials are sold as 'thymosin alpha-1' or 'TA1'.
A 28-amino-acid immune-regulating peptide first isolated from the thymus. Its synthetic form, thymalfasin (Zadaxin), is a prescription medicine in more than 35 countries.
Legal status: Prescription medicine in over 35 countries, unapproved in others; varies by country. Not named on the WADA List; tested athletes should check its status with their anti-doping agency.
What it gives
What people use it for and what the sources report. Strength is a general category from the literature: mild, clear or strong.
Purpose
Approved for hepatitis B and C and as an immune add-on in other diseases. In sport it is injected for 'immune support' during hard training and sits in recovery peptide stacks; it has never been studied in athletes.
What people seek and what studies show
People hope for fewer infections during heavy training and faster recovery. In patients it strengthens immune (T-cell) responses and has been used in chronic hepatitis, as an add-on in cancer care and to improve vaccine response in people with weak immunity; for hepatitis it has given way to modern antivirals. What it does for healthy athletes' immunity, recovery or performance is unknown.
Effects
Evidence: Approved medicine — studied in people for its medical use
Sought effects by goal (as reported)
Possible side effects
Possible does not mean certain: whether they appear depends on dose, duration, individual response and monitoring. Below — what to watch for and how to notice it early.
3 possible side effects
level · how often it is reportedWhat the levels mean
Level: general category from the literature, not your personal risk
How often
- common
- reported often
- possible
- reported in some people
- rare
- reported occasionally
How to lower the risks
General ways to lower the chance of each side effect. No measure removes a risk completely.
Products obtained without a prescription are often fake, mislabeled or non-sterile, and there is no way to check at home. For legal supplements, look for third-party testing (Informed Sport, NSF).
Low-level side effects
Check-ups and blood tests
Which tests and check-ups to do and when. This is a guide — agree the exact schedule with your doctor.
Which doctors can help
Myth & fact
“Thymosin alpha-1 is the same thing as TB-500.”
No: alpha-1 is an immune peptide, while TB-500 comes from thymosin beta-4, a banned growth factor. The Essendon players who claimed alpha-1 were banned for beta-4.
Combinations
No specific combination notes for this substance yet. The stack check still adds up side effects that several substances share.
Sources
Possible side effects by body system, combinations, how to lower the risks and which tests to do — free.
Open the stack check