Feeder Frenzy plays a little cutscene with Maya the next time you speak with her. Unless I made an error, the potion's effect shouldn't go away until after you've spoken with her.
Fetishizer requires multiple to doses to start taking effect. The first one I made does nothing, since the effect is permanent and you need to make every potion at least once to win anyway, I didn't want that to be forced on the player every playthrough. The more does she gets, the likely she is to react positively to more intense events. The highest amount you need for some of it's dialogue is 5 doses.