Tier C — preclinical
TB-500 / Thymosin β4 fragment
TB-500 is a synthetic fragment corresponding to the actin-binding region of Thymosin β4, a naturally occurring protein.
Evidence
Preclinical. Thymosin β4 itself (the full protein) has had some human trials in specific indications — ophthalmic and wound applications, for example. TB-500-the-fragment as sold is not the same molecule as the full protein studied — that distinction is one of the most commonly conflated facts in this category.
Mechanism
Actin sequestration, cell migration, angiogenesis.
Regulatory status
Not approved. On WADA's prohibited list.
The limitation nobody mentions: evidence for the full Thymosin β4 protein does not transfer to the fragment sold as TB-500, any more than topical evidence transfers to injectable use elsewhere in this category. Same source protein, different molecule, different evidence base.
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