Chocolate poisons dogs because of theobromine

It’s all over the Internet so I am not going to go over old ground, however, the problem with dogs eating chocolate is that they cannot metabolise theobromine and caffeine both of which are in chocolate. Interestingly theobromine is toxic to humans as well but it has to be in much higher concentrations. It would be toxic to a person at 1000 mg per kilogram of bodyweight. It can cause nausea and anorexia in humans and is linked to sweating, severe headaches and trembling. The thing is that humans can metabolise theobromine whereas dog process it much more slowly allowing it to build up to toxic levels. It can lead to muscle tremors, seizures, and irregular heartbeat and a heart attack in dogs.

Theobromine in chocolate is poisonous to dogs because they can't metabolise it

Theobromine in chocolate is poisonous to dogs because they can’t metabolise it. Photo: Pixabay.

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The amount of theobromine in chocolate varies depending upon the type of chocolate. Darker chocolate is more bitter and more dangerous to dogs. VCA hospitals tell us that a 50 pound dog eating 1 ounce of Baker’s chocolate or 9 ounces of milk chocolate potentially show signs of poisoning. When the concentrations are as low as 20 mg per 1 kg of bodyweight it can be toxic. In layman’s language this means that chocolate is about 50 times more toxic to dogs than to humans. At doses of 60 mg per 1 kg of bodyweight neurologic signs can be seen which may even include seizures. Fatalities can occur at around 200 mg per 1 kg of bodyweight.

So what is theobromine? It was formerly known as xantheose which is a bitter alkaloid of the coca plant. It is also found in the tea plant and the kola nut. The compound contains no bromine so the name is misleading. It’s effects on people’s nervous system is similar to that of caffeine.

In 2014 four American black bears died of theobromine poisoning. It caused heart failure after they consumed 41 kg (90 pounds) of chocolate and doughnuts placed at the site as a bait. The chocolate was placed there to kill animals; perhaps the bears. Cruel, I’d say.


There is story in the online news media today which highlights the dangers. It concerns a dog called Bailey who fell ill after eating an Easter egg. He needed life-saving treatment from veterinarians. He actually ate a book chocolate egg. PDSA vets apparently treat hundreds of sick dogs after eating chocolate every year and Bailey is a classic example. His owner, Tracy, 39, felt sure that something was wrong when he started to behave strangely. She found the foil covering of the Cadbury egg ripped open and all the contents gone. He became lethargic and simply wasn’t himself. Bailey was taken to the PDSA and they induced vomiting to prevent him ingesting the theobromine which is the chemical that can harm dogs.