Is chocolate poisonous in dogs?

Above, the topic of Alison Snyder's February 2, 2007 Scientific American article.

Long story short: it is.

Here's the piece.

Fact or Fiction? Chocolate Is Poisonous to Dogs

Chocolate can affect canines in different ways — from the mildly upsetting to the downright dangerous

A small dog should be belly-up after eating a handful M&M's, at least according to conventional wisdom. But watching "Moose," a friend's five-pound Chihuahua, race around a living room after his sweet snack makes one 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.

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 up to twice its normal rate, and some dogs may run around as if "they drank a gallon of espresso," say Tim Hackett, a veterinarian at Colorado State University. Moose, it seems, was on a "theobromine high."

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 between cocoa beans as well as different brands of chocolate. 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.

Still, people's fear that their dogs will die from eating some chocolate may be overblown. 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 cocoa snack. But no matter how you bake it, wrap it, blend it or melt it, chocolate and dogs just don't mix.