I'd think they work against large animals as well. If you were a herbivore mammal and the plant you were eating made you more hungry, thirsty, tired, and sexual

I'd think they work against large animals as well. If you were a herbivore mammal and the plant you were eating made you more hungry, thirsty, tired, and sexual, you'd probably stop eating it and go find water/shelter/mate or otherwise wander off in a haze. And then there's humans, those weirdos, who eat anything no matter how poisonous.