One of the key components of chocolate is theobromine, or theobromide, also known as xantheose. It has the chemical formula C_{7}H_{8}N_{4}O_{2} 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 AskAVetQuestion.com

[quote]1000 milligrams per kilogram of body weight
[/quote]
Your math is wrong.
1 gram is equivalent to 1000 milligrams.
So In other words, the lethal dose of chocolate is 1 gram per kilogram. ???
Any Mars bar would instantly kill a child. Not to mention I eat some 100g of chocolate per day, and I weigh less than 100 kg.
According to your own calculations : 80 kg human would have to eat 5.7 kg, that means the ration is not 1000:1 but more like 14:1
Calculating this, for every kilogram the lethal dose is around 70g

Thanks for your comment and your calculations. You’re right that 1000 mg is equal to 1 g, but that’s the median lethal dose of theobromine on its own. Dark chocolate has a theobromine content in the order of 14 milligrams for every gram of chocolate, i.e., it’s about 1.4% theobromine. And milk chocolate is only about 0.2% theobromine. This means you need to eat more than the 1 g/kg of chocolate to get a lethal dose of theobromine.

According to Mars, a Mars bar is 40% milk chocolate, which gives 0.08% theobromine. To get their 80 g of theobromine, an 80 kg human would have to eat 100 kg of Mars bars, or over 2700 individual 36 g bars.

Of course, these are all calculations based on published data. I doubt anyone’s actually tried to eat that many at one time…

omg i fed my doggo too much chocolate…

[quote]1000 milligrams per kilogram of body weight

[/quote]

Your math is wrong.

1 gram is equivalent to 1000 milligrams.

So In other words, the lethal dose of chocolate is 1 gram per kilogram. ???

Any Mars bar would instantly kill a child. Not to mention I eat some 100g of chocolate per day, and I weigh less than 100 kg.

According to your own calculations : 80 kg human would have to eat 5.7 kg, that means the ration is not 1000:1 but more like 14:1

Calculating this, for every kilogram the lethal dose is around 70g

The last line should read Calculating this, for every kilogram the lethal dose is around 70 milligrams

Thanks for your comment and your calculations. You’re right that 1000 mg is equal to 1 g, but that’s the median lethal dose of theobromine on its own. Dark chocolate has a theobromine content in the order of 14 milligrams for every gram of chocolate, i.e., it’s about 1.4% theobromine. And milk chocolate is only about 0.2% theobromine. This means you need to eat more than the 1 g/kg of chocolate to get a lethal dose of theobromine.

According to Mars, a Mars bar is 40% milk chocolate, which gives 0.08% theobromine. To get their 80 g of theobromine, an 80 kg human would have to eat 100 kg of Mars bars, or over 2700 individual 36 g bars.

Of course, these are all calculations based on published data. I doubt anyone’s actually tried to eat that many at one time…