I remember having a biology course when I was a teenager and I remember some fun facts about different plants which had been traditionally used for medicine. According to my teacher, one specific kind of plant was used if you had tapeworms and it could help you to get rid of it.. basically because the plant was poisonous and the tapeworm died because of the poison, when the human just got really sick from eating the plant.
However, luckily we mostly eat pumpernickels and other nice things nowadays instead of dangerous plants.