While delicious in a variety of our foods and adding pleasing aromas to the home, cinnamon can be toxic to our pets. The active natural compound in cinnamon that gives it flavor is called cinnamaldehyde. Small amounts of ingested cinnamon can cause vomiting and diarrhea. If large amounts of cinnamon are ingested, though, your pet's glucose levels can drop leading to severe health issues, and can even lead to a coma. Long term exposure to cinnamon can also cause liver damage.