Dogs should never eat avocado, bread dough, chocolate, grapes, raisins, hops, moldy foods, onions, garlic, xylitol or dairy products. Dogs should also never drink alcohol, milk or caffeinated liquids. The extent of damage these foods and liquids can cause depends upon the dog's size and breed.
Dogs have a different metabolism than humans and therefore cannot eat many foods that are considered safe for people. Various types of avocado can be toxic to canines and may cause nausea and vomiting. Bread dough is especially harmful because the yeast can swell, resulting in an obstruction in the dog's intestine. Chocolate can be toxic to the nervous system and heart due to the amount of caffeine and theobromine levels. Grapes and raisins contain an unknown toxin that can damage a dog's kidneys.
Cultivated hops, used for brewing beer, can be life-threatening if ingested by a dog. Mild flu-like symptoms may develop after the ingestion of macadamia nuts, and while the nuts alone are not toxic, the symptoms could cause further internal injuries.
Moldy foods can contain potentially fatal toxins. Onions and garlic contain compounds that can cause damage to a dog's red blood cells and result in death. Xylitol, a calorie-free sweetener found in chewing gum and candy, can cause canine liver damage if ingested in large quantities.