Thymosin Alpha-1 vs Thymosin Beta-4
A side-by-side comparison of Thymosin Alpha-1, Thymosin Beta-4 by independent evidence grade, FDA status, mechanism of action, key safety considerations, and which FDA 503B outsourcing facilities report compounding each.
| 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... |
Key differences
Thymosin Alpha-1 carries the stronger evidence grade (B versus D): grade b: human evidence, not approved for this use, against grade d: preclinical or anecdotal only for Thymosin Beta-4. Both are not fda approved. Mechanistically, Thymosin Alpha-1 works by 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, whereas Thymosin Beta-4 works by 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.
What the evidence shows
Thymosin Alpha-1 B
Thymosin alpha-1 (thymalfasin; brand name Zadaxin) is not FDA-approved in the United States for any indication, though it holds orphan drug designation for several conditions. It is approved in more than 35 countries for chronic hepatitis B and as an immune enhancer. The human evidence base is substantial but...
Compounding: Not FDA-approved in the United States. The FDA proposed in late 2024 not to include thymosin alpha-1 on the 503A bulk compounding list, and it is not on the 503B bulk drug substances list....
Thymosin Beta-4 D
Evidence is limited primarily to animal and preclinical studies; the evidence base for systemic injectable use in humans is early and incomplete. Thymosin Beta-4 (TB-4) is an endogenous actin-sequestering peptide with roles in cell migration, wound repair, and inflammation modulation, studied in animal models for...
Compounding: The nomination to add Thymosin Beta-4 to the FDA 503A or 503B bulk-substances list was withdrawn; it is not on an active FDA bulks list and is not eligible for routine pharmacy compounding.
Where these are compounded
Thymosin Alpha-1: no FDA 503B facility in our directory currently reports compounding it.
Thymosin Beta-4: no FDA 503B facility in our directory currently reports compounding it.
From the FDA Outsourcing Facility Product Report. PeptideGrids does not sell or source any compound.
Frequently asked questions
Is Thymosin Alpha-1 or Thymosin Beta-4 FDA approved?
Thymosin Alpha-1 is not fda approved. Thymosin Beta-4 is not fda approved.
Which has stronger clinical evidence, Thymosin Alpha-1 or Thymosin Beta-4?
Thymosin Alpha-1 holds the stronger grade (B versus D). PeptideGrids grades evidence A to D; see each compound page for the cited trials.
What is the difference between Thymosin Alpha-1 and Thymosin Beta-4?
Thymosin Alpha-1: Thymosin alpha-1 is a synthetic 28-amino acid peptide derived from thymosin fraction 5 that stimulates T-lymphocyte.... Thymosin Beta-4: Thymosin Beta-4 sequesters G-actin monomers, modulating actin polymerization dynamics involved in cell migration, wound....
Full profiles: Thymosin Alpha-1, Thymosin Beta-4. Browse all GLP-1s and therapeutic peptides.