Peach pits, if ingested in large enough quantities, can poison and even kill humans. However, the pits have to be chewed or ground up to produce cyanide in the body. Accidental cyanide poisoning from ingesting fruit seeds or pits is extremely rare.
Peach pits contain cyanogenic glycosides, compounds that are metabolized into cyanide by the body. The pits and seeds of other common fruits such as apples, apricots, cherries, nectarines, pears and plums also contain these cyanide-like compounds.
According to the Centers for Disease Control, symptoms of cyanide poisoning include dizziness, headache, nausea and vomiting, difficulty breathing and loss of consciousness. Cyanide prevents the cells from using oxygen, causing them to die.