The merchant answers the question...
"Does Extagen Work" quoted from their site:

Extagen is made from the highest quality herbs and phytonutrients that when combined to exacting tolerances help to increase the natural blood flow to the erectile chambers of your penis. The increased amount of blood flow during arousal causes your erectile chambers to expand therefore producing a larger and thicker feeling erection.

Your penis size is determined by the amount of blood you hold in your erectile tissue chambers (corpora cavernosa). Those are the chambers located inside of your penis that hold blood during an erection. The combination of herbs contained in the Extagen Tablets actually targets those chambers increasing blood flow to them and expanding their size in general.

Hint: Wait for the merchant site to open in the background.