Why Are Dogs Allergic to Chocolate?

Theobromine is a stimulant present in chocolate -- in humans the effect of theobromine is similar to that of caffeine. Dogs cannot process theobromine as well as humans can, so the stimulant effects are longer-lasting and more intense for a dog. Significant quantities of theobromine can have negative effects on the dog's nervous system and heart. A dog that has eaten a sufficient amount of theobromine can have seizures or cardiac arrest as a result.

The more theobromine in a particular kind of chocolate, the more dangerous that chocolate is to your dog. Theobromine is most highly concentrated in baking chocolate and cocoa powder. Dark chocolate contains more theobromine than milk chocolate; white chocolate contains the least theobromine. An ounce of baking chocolate commonly contains 500 milligrams of theobromine per ounce; an ounce of milk chocolate contains only 50 milligrams.

The more your pet weighs, the more theobromine his body can tolerate. Small dogs are therefore at the greatest risk from chocolate toxicity. A 4-ounce portion of milk chocolate -- roughly 2 1/2 regular candy bars -- contains enough theobromine to cause seizures or even death in a dog weighing under 10 pounds. The same quantity of milk chocolate would be unlikely to have measurable toxic effects on a dog weighing over 70 pounds. Even when seizures or toxic symptoms are not observed, theobromine can cause kidney damage to any dog. It's safest to keep all chocolate away from your dog at all times.

If you've come home to find your dog sitting among empty chocolate wrappers, your quick response could be lifesaving. If your dog has eaten any quantity of dark chocolate, cocoa powder or baking chocolate you should call an emergency line straight away. The ASPCA runs an Animal Poison Control hotline that can offer advice quickly. Your local veterinarian may also have a hotline you can call. You should also call a hotline if your dog has eaten any significant quantity of milk chocolate or if you know your dog has a preexisting heart or seizure condition. If your dog has eaten the chocolate within the past two hours, you may be advised to induce vomiting. Otherwise, qualified emergency care will probably be necessary.