Developing Resistance to Olive Leaf Extract

Question:
Can your body build a resistance to olive leaf if taken consistently for months at a time?

Answer:
There is no research to suggest this happens.
As olive leaf does not work primarily by stimulating your immune system, your body does not gradually balance this effect by reducing its normal immune response.

Olive leaf extract inhibits the growth of or destroys certain pathogens, even in a lab culture without any of your body's own resources, hence it can aid your immune system.
Of course it works better in your body, as certain of the olive leaf constituents, when broken down in your body produce other substances with their own anti-viral and other properties but these are still anti-pathogenic in themselves.
It is probable that your body expends less energy fighting pathogens when olive leaf blunts their attack, and redirects it to other essential bodily functions, but this would serve to improve general health and not equate to your body building up resistance to olive leaf.