It’s the theobromine in chocolate that is toxic for dogs, writes veterinarian Julianne Miller, and theobromine levels vary depending on the type of chocolate. Even if an animal doesn’t ingest a toxic dose, Dr. Miller says chocolate can cause diarrhea, vomiting and pancreatitis, so any ingestion should be evaluated by a veterinarian. Also in this article, Dr. Miller explains the importance of vaccinating indoor cats. The Arizona Daily Sun (Flagstaff)
Q: I have heard that chocolate is toxic for dogs, but my dog has gotten into chocolate before and has not had any problems. So I am curious to know if chocolate is actually harmful or not?
A: The simple answer to your question is yes, chocolate is toxic; however, it is the ingredient theobromine that is contained in chocolate that is toxic to dogs. The toxicity is based on the amount of theobromine that the animal ingests when compared to the animal’s weight. It also matters what type of chocolate is ingested because the amount of theobromine in chocolate varies.
Any dose of theobromine over 45 mg/kg is potentially toxic and possibly lethal for dogs and should be treated aggressively by your veterinarian.
As an example, milk chocolate contains 44-64 mg theobromine per ounce of chocolate — so an average sized 80-pound Lab would need to ingest approximately 30-50 ounces of milk chocolate for a toxic dose. That is almost 3 pounds of milk chocolate! However, unsweetened baking chocolate contains 450 mg theobromine per ounce of chocolate. That means that same 80-pound Lab would be at a toxic dose after only 3.5 ounces!
So, you can see that the weight of the animal and the type of chocolate determine the toxic dose. Even if your dog eats chocolate and does not ingest a toxic dose there are other serious consequences to eating the chocolate such as severe stomach and intestinal upset, pancreatitis, diarrhea, vomiting and more. Any ingestion of chocolate is bad for a dog; whether it eats a toxic dose, your dog could suffer some serious adverse reactions. Since even a small dose of theobromine is potentially toxic and possibly lethal for dogs, it is recommended that you contact your veterinarian immediately for advice.