Chocolate is the product of dried and fermented seeds of the Cacao tree (Theobroma Cacao) and the active ingredient in chocolate is Theobromine.
Chocolate and cocoa products including the mulch made from the seed shells and used in gardening are poisonous to dogs even causing death if the amount ingested is large enough, though it also depends on the type of chocolate and the amount the dog has actually ingested and also the size of the dog compared to the amount that it has eaten.
The key toxic component chemical in the chocolate that harms the dog is called theobromine, which is only produced in chocolate . Humans can metabolise theobromine quickly as the half life of the chemical is only 2-3 hours for humans who then excrete it from the body, but for dogs it is a much slower process with the half life of the chemical taking up to 18hours which can cause a build up in the liver as it metabolises prior to excretion in the urine.Theobromine is known to affect the central nervous system, the cardiovascular system and the respiratory system.
Dark chocolate and cocoa products contain the most theobromine whereas milk or white chocolate contain the least. Bitter dark chocolate used for cooking also contains very high levels and even a vey small amount can be enough to poison even a very large dog, though the lethal dose is roughly between 250mg and 500mg per kilo of the dogs body weight.
However, a dog that eats just a small amount of milk chocolate may still be affected and may develop an upset stomach with diarrhoea and vomiting, it is always wise to seek medical advice however small the amount and however big the dog.
A dog that eats a whole box of chocolates or a large amount of very dark chocolate will require emergency treatment as they may suffer dangerous effects that lead to death.
The onset of the poisoning may be preceded by severe hyperactivity, muscle tremors and an irregular heartbeat, panting and increased thirst, during this time the dog may develop internal bleeding, increased heart rate and finally a heart attack. The signs of chocolate poisoning may not show until 2-24 hours after ingestion and even for a small amount of chocolate ingestion you will need to watch the dog for at least 72hours afterwards.
If you know that your dog has eaten chocolate then you should try to induce the dog to vomit as well as getting advice from the vet. If the dog’s life is in danger then the vet may put the dog on intravenous fluids to flush the stomach contents and may also give charcoal based medication to absorb the poisonous chemical before too much harm is caused.