Chocolate is toxic for dogs. Theobromine is the toxic ingredient.
Signs of toxicity include vomiting, diarrhea, hyperactivity, tremors, seizure and abnormal heart rhythms. Death is possible with severe overdoses.
9 mg of theobromine per pound of body weight causes mild signs and 18 mg per pound causes severe signs of toxicity.
Milk chocolate contains 44 mg/ounce, semisweet chocolate contains 150 mg/ounce and baking chocolate contains 390 mg / ounce. For a 50 lb dog, this is about 20 ounces of milk chocolate, 7 ounces of dark chocolate or 2.3 ounces of baking chocolate.
If you can get the chocolate out of the dog's system within 30 minutes by causing it to vomit, further treatment should not be needed. If toxic signs occur, hospitalization and treatment are needed. It takes about 4 days for theobromine to be cleared from the body.