Yes, chocolate is potentially toxic for dogs and cats. It contains both caffeine and a chemical called theobromine, which works similarly on the body. Humans tolerate these chemicals better than dogs, which is why we can eat chocolate without getting sick. The amount of theobromine in the chocolate your dog ingested is the best indicator of how toxic their exposure was.
Because the toxic level of exposure is dose-dependent, a big dog that eats a few ounces of milk chocolate will probably not have any symptoms, while a small dog that eats baking chocolate may be in big trouble. If you are ever concerned about your dog’s level of exposure, call a Waldorf Emergency Care or the Pet Poison Hotline.
Dogs that eat chocolate may find themselves with mild symptoms at a dose of about 20mg/kg, or about 9.1mg/lb. Doses twice this high are very likely to induce symptoms and can cause cardiac problems. The fatal dose is around 200mg/kg, or 90.1mg/lb. Fatalities are rare, but can also occur at lower doses in dogs that experience complications.