Peaches are not themselves poisonous to dogs, although they can potentially cause diarrhea or loose stools. Much more dangerous, however, are the peach pits which contain a chemical called cyanide. Cyanide is extremely toxic, and can result in hyperventilation, shock, coma, and even death in dogs. Cyanide is also poisonous to humans, and should be avoided. The seeds of peaches also have the potential to cause obstuction in the throat or intestinal tract.