Thymosin Alpha-1 vs Thymosin Beta-4

Comparing 2 compounds by evidence grade, FDA status, mechanism, and key safety considerations: Thymosin Alpha-1, Thymosin Beta-4.

	Thymosin Alpha-1	Thymosin Beta-4
Evidence grade	Grade B: Human evidence, not approved for this use	Grade D: Preclinical or anecdotal only
FDA status	Not FDA approved Not FDA-approved in the United States for any indication; approved in over 35 other countries for hepatitis B and immune enhancement; FDA has proposed exclusion from compounding bulk lists.	Not FDA approved Not FDA-approved; removed from Category 2 restriction April 2026, compounding pathway unresolved pending July 2026 PCAC advisory.
Mechanism	Thymosin alpha-1 is a synthetic 28-amino acid peptide derived from thymosin fraction 5 that stimulates T-lymphocyte maturation and function, enhancing cell-mediated immunity via dendritic cell and T-helper cell activation.	Thymosin Beta-4 sequesters G-actin monomers, modulating actin polymerization dynamics involved in cell migration, wound healing, and inflammatory signaling; this mechanism is established in vitro and in animal models.
Key safety	Human clinical trial data from international studies suggest thymosin alpha-1 is generally well-tolerated at studied doses, with injection site reactions being...	Systemic injectable TB-4 has limited human safety data beyond early-phase studies. The Phase I data described mild and tolerable adverse events in healthy volun...