Chocolate contains both caffeine and theobromine, a stimulant that affects the central nervous system and the heart. Although both of these chemicals are dangerous to dogs, theobromine is the more dangerous of the two because dogs metabolize it very slowly. Symptoms of chocolate poisoning in dogs include vomiting, diarrhea, hyperactivity, arrhythmia, increased urination and excessive panting. When they ingest high levels of theobromine, dogs can experience muscle tremors, seizures and comas. Chocolate can even cause death. Because different types of chocolate contain different amounts of theobromine, dangerous chocolate levels depend upon the type of chocolate the dog ingests. In general, it takes between 45 and 68 mg of theobromine per pound to cause symptoms. To be safe, if your dog consumes any chocolate, go immediately to the vet as your dog, especially if he is old or ill, might have increased sensitivity to the chemical.
White chocolate is by far the least dangerous type of chocolate for dogs because 1 oz. of white chocolate contains only 1 mg of theobromine. At these levels, your dog would have to eat 45 oz. per pound to reach toxic levels. For a 10-lb. dog, that would mean 450 oz., or more than 28 lbs., of white chocolate.
Milk chocolate contains 60 mg of theobromine per ounce. At these levels, it takes approximately 1 oz. per pound to poison a dog. For a 10-lb. dog, 10 oz., or .625 lbs., will produce symptoms of chocolate poisoning.
Semi-sweet chocolate contains high levels of theobromine. Because 1 oz. of the chocolate contains 260 mg, it takes only .3 oz per pound to poison a dog. A 10-lb. dog would only have to eat 3 oz. of semi-sweet chocolate to become poisoned.
Unsweetened baking chocolate contains the highest levels of theobromine, an astonishing 450 mg per ounce. It takes only .1 oz. per pound to poison a dog. After eating only 1 oz. of baking chocolate, a 10-lb. dog can acquire toxic levels of theobromine. Luckily, because the bitter taste of this type of chocolate is not appealing to dogs, they are not tempted to eat it.