Can plants be dangerous?

Plants can pose a danger to human health. Drink a tea made from oleander leaves or chew a mouthful of foxglove and you'll be dead in a hurry. On the other hand, if you use any of the thousands of healthful herbs that have been utilized as traditional medicines over the past few millennia, in dosage ranges that have been determined by centuries of trial and error, you are likely to benefit without side effects.