Death by chocolate

Chocolate may have some health benefits, but too much of a good thing can kill you. But it’ll kill your dog more quickly.

One of the key components of chocolate is theobromine, or theobromide, also known as xantheose. It has the chemical formula C7H8N4O2 and it is a bitter alkaloid of the cacao plant – although it’s also found in tea leaves and the kola (or cola) nut. Despite its name, the compound does not contain the element bromine (Br). The name comes from Theobroma, meaning “food of the gods”, the genus of the cacao tree.

It also comes from caffeine: when caffeine is metabolised in the liver, 12% of it is turned into theobromine.

Theobromine is a vasodilator (i.e., it widens blood vessels), a diuretic (makes you urinate) and a heart stimulant. As a result, it can be poisonous.

Fortunately, the median lethal dose for humans is 1000 milligrams per kilogram of body weight. That means that an 80 kg human would have to eat 5.7 kg of unsweetened dark chocolate for it to kill them (going by a theobromine content of 14 milligrams per gram of dark chocolate, although it varies). For milk chocolate, you’d have to eat around 40 kg.

However, domestic animals metabolise it much more slowly than humans. Dogs are the most vulnerable, with a median lethal dose of only 300 milligrams per kilogram of body weight. Although cats do have a lower toxic dose – 200 mg/kg – they’re unable to taste sweetness and so are much less likely to eat enough chocolate.

The first signs of theobromine poisoning are nausea, vomiting, diarrhea, and increased urination. In high doses it goes on to cardiac arrhythmias, epileptic seizures, internal bleeding, heart attacks and eventually death. The half-life of theobromine in dogs is 17.5 hours, and if they’ve eaten enough of it the symptoms can persist for 72 hours.

A typical 20 kg dog will normally experience intestinal distress after eating less than 240 g of dark chocolate, but won’t necessarily experience brachycardia or tachyarrhythmia unless it eats at least 500 g of milk chocolate.

Remember though that humans aren’t totally immune, and the elderly are particularly vulnerable to consumption of large quantities. There have been extreme cases when people have had to go to the emergency room.

But it is your dog you have to watch, so try not to give them chocolate. Or if you can’t stop them, you can find a nifty online theobromine toxicity calculator at


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