Question

Why can't dogs eat chocolate?

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Answer

Because chocolate contains theobromine, a stimulant that dogs metabolise far more slowly than humans, allowing it to accumulate to toxic levels.

The mechanism. Theobromine is a methylxanthine, chemically related to caffeine, which chocolate also contains. Both stimulate the central nervous system and the heart.

The critical difference is clearance. Humans metabolise theobromine relatively quickly — a half-life of a few hours. In dogs it is far longer, commonly cited around 17 to 18 hours. A dose a person would clear before it mattered persists in a dog long enough to build up and cause harm.

Toxicity depends on three things:

The type of chocolate, which matters enormously. Theobromine concentration varies hugely: cocoa powder and baking chocolate are the most dangerous, dark chocolate is substantially more toxic than milk, and white chocolate contains almost none — it is essentially cocoa butter and sugar, and poses a fat and sugar risk rather than a theobromine one.

The quantity eaten.

The dog's body weight. A small dog is at risk from far less.

The symptoms, appearing typically within 6 to 12 hours: vomiting, diarrhoea, excessive thirst, restlessness and hyperactivity, panting, elevated heart rate, muscle tremors, and in severe cases seizures, cardiac arrhythmias and collapse.

What to do. Contact a vet immediately — do not wait for symptoms. Tell them the dog's weight, the type of chocolate, the estimated amount and the time eaten; keep the packaging. Treatment is far more effective early, and may involve inducing vomiting, activated charcoal and supportive care. Do not try to induce vomiting at home without veterinary instruction.

Other pets: cats and rabbits are also susceptible, though cats rarely eat chocolate, having no sweet taste receptors.

Other common dog toxins worth knowing: xylitol (in sugar-free gum and some peanut butters) is extremely dangerous, plus grapes, raisins, onions, garlic and macadamia nuts.

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