Thymosin alpha-1 vs TB-500: Which Is Right for You?
Despite similar names they are unrelated peptides. Thymosin alpha-1 (thymalfasin, Zadaxin) is a 28-amino-acid immune peptide approved in a number of countries outside the US for hepatitis B and as an immune adjuvant; TB-500 is a synthetic version or fragment of thymosin beta-4, studied for tissue repair and never approved.
Side-by-side comparison
| Thymosin alpha-1 | TB-500 | |
|---|---|---|
| Parent protein | Prothymosin alpha | Thymosin beta-4 (43 aa) |
| Main research area | Immune modulation | Tissue repair, actin binding |
| Approval | Approved outside the US (Zadaxin) | None |
| FDA status | Not FDA-approved | Not FDA-approved |
| Sports anti-doping | Not specifically listed | Prohibited (WADA S2) |
Complete comparison (2026)
Key takeaways
- "Thymosin" names a family of unrelated peptides.
- Only thymosin alpha-1 has approvals anywhere.
- TB-500 is prohibited in sport.
What are Thymosin alpha-1 and TB-500?
Thymosin alpha-1 (thymalfasin, Zadaxin) is a 28-amino-acid thymic peptide approved in some countries for hepatitis B; it is not FDA-approved.
TB-500 is a synthetic peptide marketed as a version or fragment of thymosin beta-4, a naturally occurring 43-amino-acid protein that binds actin and is involved in cell migration and wound repair; it is not FDA-approved.
Mechanism differences
Thymosin alpha-1 is reported to enhance T-cell function. Thymosin beta-4 binds actin and was studied for wound and corneal healing; "TB-500" products may contain the full peptide or a short fragment.
Effectiveness
Thymosin alpha-1 has randomized trials in chronic hepatitis B and as a vaccine adjuvant, with mixed results. Thymosin beta-4 was tested in small trials of eye drops for dry eye and corneal injury; TB-500 as sold has no human trials.
Side effect profiles
Thymosin alpha-1 trials reported mild injection-site discomfort. Human safety data for TB-500 products are absent.
Dosing & administration
No US label exists. We don't publish doses.
Cost
Verified TB-500 per-mg prices are on our price comparison.
FDA & regulatory status
Neither is FDA-approved; "research use only" products are not for human use.
Who should choose which
There is no evidence-based reason to choose either for personal use.
What the evidence does not show
- That TB-500 products match the thymosin beta-4 used in trials.
Frequently asked questions
Is thymosin alpha-1 the same as TB-500?
No. They are different peptides from different parent proteins with different functions.
Where is thymosin alpha-1 approved?
As Zadaxin it is approved in a number of countries outside the US, mainly for hepatitis B; it is not FDA-approved.
Is TB-500 banned in sport?
Yes. WADA prohibits thymosin beta-4 and its derivatives.
References
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