The sugar substitute xylitol is commonly found in things like sugar-free mints, gum, chewable vitamins and even in some kinds of peanut butter and toothpaste. While it may have fewer calories than real sugar and is safe for diabetics, it can be deadly to man's best friend. When dogs ingest sugar-free items intended for human consumption, xylitol is actually about 100 times more toxic than milk chocolate. When a dog eats xylitol, it causes a rapid decrease in the canine's blood sugar level, which leads to seizures, brain damage and liver failure. If you suspect your dog has eaten xylitol, call the Pet Poison Helpline at 800-213-6680.