What's the difference between TB500 and thymosin beta-4?

Depends on the supplier. Most research-grade "TB500" is the full Tβ4. Some are a fragment (LKKTETQ + stabilizers). Read the COA if you care — mass / molecular weight tells you which.

@theoretic so if I buy "TB500" am I getting the full protein or the fragment?

Thymosin beta-4 (Tβ4) is a 43-amino-acid protein naturally produced in the body. "TB500" is a marketing/research name for a synthetic fragment, often cited as the "active region" of Tβ4. In practice, most "TB500" products are either the full Tβ4 sequence or a fragment, and suppliers label inconsistently. Functionally in the research-peptide world, people use them interchangeably. Mechanistically, they're related but not technically identical.

Practically speaking the outcomes are similar. Most anecdotal reports and the small amount of human data don't distinguish between them because the labeling is chaos.

This is a good thread to bookmark because "what's TB500" is asked weekly and the answer is "the labels are a mess and you should read your COA."

Thanks everyone. COA'd my vial, it's full Tβ4.

Username checks out, confirming that in 4 years of running "TB500" I've used both fragment and full Tβ4 products with indistinguishable subjective outcomes. n=1.

FYI: the "active fragment" story is widely repeated but the underlying claim that the fragment alone is sufficient isn't super well-supported outside marketing material. Full Tβ4 is what almost all the published work uses.