Xylitol is an artificial sweetener found in many sugar-free items like chewing gum, jell-o, and peanut butter. Peanut butter is normally a safe treat for dogs, but if it contains xylitol, it can be dangerous for your dog. Be sure to always check the product label if you give your dog peanut butter as a treat or to give medicine. Xylitol is toxic to dogs, and can cause dangerously low blood sugar, weakness, incoordination, and, in severe cases, death if left untreated. Read more about xylitol from the ASPCA here.