Why is chocolate bad for dogs and cats?
Karen Collins
You bought some chocolate nibbles to gobble during lockdown but your dog steals and eats some. Will they be OK? It depends how big your dog is, the type of chocolate it was and how much they ate – but you should definitely contact your vet. Let’s take a look at the science behind why chocolate is so toxic for our pets.
During our ‘Soggy Bottom Science’ episode, Professor Megan Povey mentioned theobromine, a bitter alkaloid found in chocolate. Although easily digested by us humans, theobromine is harmful to cats and dogs causing chocolate toxicosis (poisoning). It is your dog you really need to keep an eye on though. Cats rarely eat chocolate because they have no ‘sweet’ taste receptors, but their small size does mean they are more likely to suffer the harmful effects.
What is theobromine? Despite its name, theobromine does not contain bromine! Instead it is named after the Theobroma cacao tree. Seed pods from these trees are used to make chocolate.
Theobromine has a similar structure to caffeine, but with one fewer methyl group. Both chemicals are toxic to cats and dogs and are found in chocolate, but the concentration of theobromine is 3-10 times higher than caffeine.
How much theobromine is in chocolate? It all depends on the type of chocolate and the amount of cocoa solids. Dark chocolate contains about 15 mg/g of theobromine, compared to 2 mg/g in milk chocolate. This means dark chocolate is more toxic for out pets as it contains higher levels of theobromine.
How does theobromine affect the body? Aside from its psychoactive properties in humans, theobromine is a heart stimulant and smooth muscle relaxant. Its structure is similar to adenosine so it can act as a competitive inhibitor (or antagonist) for adenosine receptors, blocking their function. This causes the stimulation of the central nervous system, excess urine production and tachycardia (an abnormal resting heart rate). Dogs find it much harder to absorb and digest theobromine than humans. As a result, the half-life of theobromine (the time taken to reduce the blood concentration by half) in dogs is 17.5 hours, compared to 2-3 hours in humans.
How toxic is theobromine for our pets? The LD50 of theobromine is 100-200 mg per kg of bodyweight of your pet. In toxicology, the LD50 is the dose that would kill 50% of a population of animals being tested. Mild symptoms such as vomiting and diarrhoea, can be seen after only 20 mg/kg and cardiotoxic effects at 40-50 mg/kg. If your dog has eaten more than 60 mg/kg they may suffer from seizures. This means the vet will need to know your dog’s mass, as well as the type of chocolate and how much they have eaten.
If you suspect your dog has eaten chocolate you should contact your vet straight away. There are chocolate toxicity calculators to help determine how hazardous those snaffled chocolates are, but your best bet is to keep them out of paws’ reach of your ‘bad dog’.