Image credits to The Spruce Pets

Chocolate is bad for dogs because it contains theobromine, an alkaloid compound found in the cacao plant, from which chocolate is derived. Chocolate also contains caffeine, which, like theobromine, is classified as a methylxanthine, a compound found in large quantities in tea, coffee, and chocolate, that humans have consumed for centuries because of its psychoactive properties.While people can easily digest these compounds, dogs cannot, and even small amounts of chocolate can lead to a range of symptoms including nausea and vomiting, with death occurring in very serious cases.In general, darker and bitter chocolates are more dangerous for dogs.

What Makes Chocolate Harmful to Dogs?

Most pet owners know that dogs and chocolate don't mix, but many people aren't sure precisely why. Chocolate is derived from the roasted seeds of the cacao plant, which contains two primary components that are toxic to dogs: theobromine and caffeine. Part of the methylxanthine group of compounds abundant in human food and beverages, people can easily digest these compounds, with the half-life (the time it takes for the concentration of a substance in the body to decrease by half) of theobromine being only between two and three hours on average.

In dogs, the half-life of theobromine is 18 hours on average. This long processing time is part of what makes chocolate so dangerous for dogs, as high concentrations of these compounds remain in the animal's system. Theobromine and caffeine stimulate the heart rate and nervous system of dogs, which is why hyperactivity is often one of the first symptoms of chocolate poisoning. While chocolate poisoning is rarely fatal, it is important to seek immediate medical attention for your pet 

How Much Chocolate Can a Dog Eat?

How much chocolate can kill a dog will vary depending on the size and breed of dog. A toxic amount of chocolate for a Chihuahua could produce little to no symptoms in a Great Dane. In general, bitter, darker, chocolates are more dangerous to dogs, because these chocolates contain more cacao, meaning that they also contain more theobromine and caffeine. According to the FDA, theobromine content in chocolate can vary as follows:

Dark chocolates contain a range of theobromine, with amounts as high as 450 mg of theobromine per ounce. White chocolate poses a very low risk of chocolate poisoning, with only 0.25 mg of theobromine per ounce.

In general, the minimum toxic theobromine dose in dogs ranges from 46 to 68 mg of theobromine per pound of dog weight. Half the dogs that consume 114 to 228 mg of theobromine per pound of dog weight or greater can die. There are other factors at play, including how sensitive a particular dog is to these compounds.