Potatoes actually have the potential to poison you. This toxic compound, called glycoalkaloids, are contained in the leaves, stems, sprouts, and fruits. The poison directly effects your nervous system, potentially causing headaches, diarrhea, cramps, and in severe cases coma and death.
The most common cause of potato poisoning tends to be when the person preparing them doesn't remove all of the green sprouts from a potato that is left out for too long.
Source: http://en.wikipedia.org/wiki/Potato
