I've been taking an olive leaf extract standardized to 18% Oleuropein. I don't know how much Hydroxytyrosol is in it, but I would guess only a little bit.
There are olive extracts standardized for Hydroxytyrosol. Would that be better?
Olea25 is an extract with 25% Hydroxytyrosol. Swanson sells it. In their marketing material they brag that it contains no Oleuropein:
Often considered nature's perfect antioxidant, hydroxytyrosol is one of the key active ingredients in the olive that is largely responsible for the olive's tremendous health benefits. Hydroxytyrosol is a natural phytochemical with the highest antioxidant properties discovered to date.*
Olea25™ is the result of a unique patent pending production and purification process that yields an unprecedented 25% hydroxytyrosol content. The Oleuropein has been completely tranferred through a biotransformation process into the bioactive hydroxytyrosol. No Oleuropein residue remains in final product!