A small dog should be belly-up after eating a handful of holiday chocolates, at least according to pet owners' conventional wisdom. But watching Moose, a friend's five-pound Chihuahua, race around the living room after his sweet snack made me wonder: Is chocolate truly poisonous to dogs?

It is. The cacao bean, the central ingredient in chocolate, can sicken or, in some cases, kill members of the Canidae family.

The Chemical Culprit

Chocolate is processed from the bitter seeds of the cacao tree, which contain a family of compounds known as methylxanthines. This class of substances includes caffeine and the related chemical theobromine. Theobromine is abundant in chocolate, and caffeine occurs in smaller amounts. Both molecules bind to receptors on the surfaces of dogs' cells and block the canine-produced compounds that normally attach there.

Low doses of methylxanthines tend to produce euphoria in humans, but large amounts will cause muscle tremors or even bring on seizures in some dogs (so don't serve them coffee, either). Even relatively small amounts can lead to vomiting or diarrhea. Methylxanthines can also cause a dog's heart to race at up to twice its normal rate, and some dogs may run around as if “they drank a gallon of espresso,” says Tim Hackett, a veterinarian at Colorado State University. Moose, it seems, was on a “theobromine high.”

Doggy Differences

The danger of indulgence also depends on the type of chocolate scarfed down and on the animal's weight. Unsweetened baking chocolate contains more than six times as much theobromine as milk chocolate, although amounts vary among cacao beans as well as among the different brands of chocolate that are manufactured. In general, however, as little as an ounce of milk chocolate can sicken a beagle, and less than four ounces will sometimes kill dogs the size of Moose, according to the Animal Poison Control Center of the American Society for the Prevention of Cruelty to Animals.

Many Survive

Still, people's fear that their dogs will die from eating some chocolate may be overblown, Hackett says. Around every confection-centered holiday—Valentine's Day, Easter and Christmas—at least three or four dogs are hospitalized overnight in the animal medical center at Colorado State, he notes. But in 16 years as an emergency and critical care veterinarian, Hackett has seen just one dog die from chocolate poisoning, and he suspects the animal may have had an underlying disease that made it more vulnerable to chocolate's heart-racing effect. When death does result, it usually stems from abnormal heart rhythms, high fever or breathing difficulties, according to the Merck Veterinary Manual.

Dogs that eat a small amount of milk chocolate or other blends (say, a handful of M&Ms) should be able to cope with the methylxanthines and may even be able to avoid a trip to the vet. But those that eat a lot more or a stronger variety (and thus are poisoned) usually need professional care. Such dogs can generally be treated by inducing vomiting and administering activated charcoal, to absorb any methylxanthines that remain in their gut or are passing through their digestive system.

Ultimately, Moose survived his ill-advised snack. But no matter how you bake it, wrap it, blend it or melt it, chocolate and dogs just don't mix.

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