Is cinnamon harmful to dogs?

According to the American Society for the Prevention of Cruelty to Animals, cinnamon is not toxic to dogs. It is also safe for cats and horses.

There are several types of human foods that are potential threats to dogs. Chocolate is sometimes dangerous. Darker chocolate has a greater concentration of the harmful ingredients caffeine and theobromine. Twenty ounces of milk chocolate leads to serious consequences, as does just 2 ounces of dark baking chocolate. Grapes and raisins are problematic. Although the cause is unknown, commercial, home-grown and organic varieties of grapes and raisins all are likely hazards. In canines, these fruits sometimes cause kidney failure and even death.