Too many people find it hard to believe that chocolate is poisonous to dogs because they have fed their dog a chocolate treat at one time or another with no ill effects. As with anything poisonous, it’s important to realize that the dose makes the poison. In other words, whether and to what degree your dog will become ill depends on the amount of the toxic ingredient he has ingested and absorbed.
The toxic part of chocolate is a caffeine like component called theobromine that humans can easily metabolize, but dogs can’t. An overdose leads to the same symptoms as an overdose of caffeine: gas-trointestinal upset, rapid heart rate, weakness, and seizures caused by over-stimulation of the nervous system. The result can be fatal.
The toxic dose for a dog weighing about 22 pounds (10 kilograms) is 1000 to 1500 milligrams. Milk chocolate contains 40 to 50 milligrams of theobromine per ounce, semi-sweet chocolate contains 150 milligrams per ounce, and dark or unsweetened baker’s chocolate contains 390 milligrams per ounce (nearly 10 times that of milk chocolate). Therefore, a 22-pound dog would not be expected to show signs of poisoning unless he ate 20-30 ounces of milk chocolate, although some dogs exhibit vomiting and/or diarrhea at much lower doses.
If you believe your dog has eaten a toxic dose of chocolate, immediately attempt to limit his absorption by inducing him to vomit. Most dogs vomit when given one teaspoon (for small dogs) to one tablespoon (for large dogs) of hydrogen peroxide by mouth. Whether or not your dog vomits the chocolate or begins to show signs of illness such as diarrhea, tremors, panting, weakness, or seizures, contact your veterinarian immediately for advice and treatment.