Yes, chocolate is toxic to dogs (and cats!). Chocolate is toxic because it contains a chemical called theobromine, as well as caffeine. Dogs cannot metabolize theobromine and caffeine as well as people can. This makes them more sensitive to the chemicals’ effects.
"The amount of toxic theobromine varies with the type of chocolate."
The darker and more bitter the chocolate, the more dangerous it is to dogs.
To put this in perspective, a medium-sized dog weighing 50 pounds would only need to eat 1 ounce of baker's chocolate, or 9 ounces of milk chocolate, to potentially show signs of poisoning. At doses of more than 60 mg/kg, neurological signs can be seen, including tremors, twitching, and even seizures. Fatalities have been seen at around 200 mg/kg (approximately 100 mg/lb), or when complications occur.
For many dogs, the most common clinical signs are vomiting and diarrhea, increased thirst, panting or restlessness, excessive urination, and a racing heart rate.
"Clinical signs of chocolate poisoning can take hours to develop and last for days."
Many gourmet dog treats use carob as a chocolate substitute.
"Carob looks similar to chocolate and the two are often confused."
Carob looks similar to chocolate and the two are often confused. Some specialty dog bakeries will use a small amount of milk chocolate in their treats. Since the amount of theobromine is typically low, this may be safe for most dogs. However, most veterinarians recommend that you avoid giving your dog chocolate in any form. Remember, ingredients in food are listed in order of concentration in the product, so hopefully carob is lower on the list!