Why can’t dogs eat chocolates? — Foods toxic to pets

Scan of a Valentine greeting card circa 1920.

With the celebration of Valentine’s Day last week, some of you may have received flowers or boxes of chocolates from your loved ones. For those of you also lucky enough to have furry friends, share the love but not the chocolates! Read on to find out why.

Cocoa-based foods are very nutritious. Cocoa contains high amount of amino acids, vitamins, minerals, and fat that keeps our body full of energy. Nonetheless, cocoa products, including chocolates, are very poisonous to animals.

It is estimated that about 25% of pet exposure to toxic agents is by chocolates. Also, 80% of pet owners seeking aid for poisoning are dog owners (probably because dogs tend to explore things through mouth more than other animals). Chocolate poisoning for dogs is reported throughout the year, but holidays, such as Easter, Valentine’s day, Halloween, and Christmas, are especially dangerous times for pets, as chocolates tend to be bountiful in the houses.

By toxic, I mean VERY toxic; the pets can get seriously ill. In dogs, symptoms appear within 24hrs of ingestion. Symptoms include vomiting, diarrhea, increased urination, and progress to dehydration, cardiac arrhythmias, internal bleeding, heart attacks, seizures, coma, and then death.


So what makes cocoa products toxic? Cocoa beans are very rich in a compound called theobromine. They also contain caffeine, whose chemistry is very similar to theobromine, but to keep things simple, I will only discuss theobromine in this post. Theobromine can mess up the balance in the body in a couple of ways. For example, it can inhibit components of central nervous system (CNS) called adenosine receptors, which leads to CNS stimulation. It also increases calcium levels inside the cells, which can lead to tachycardia. It may also cause accumulation of an important chemical in the body called cAMP, which will affect many processes in the body, such as CNS and heart contraction.

de: Struktur von Theobromin; en: Structure of ...

Chemical structure of theobromine

The darker (or richer in cocoa) the chocolate is, the more dangerous for pets, as it contains more theobromine. Cocoa powder and cooking chocolate contain the largest amount of the compound and are the most poisonous for animals. For instance, about 25g of cooking chocolate can be poisonous for a 20-kg dog.

So how come humans can eat chocolates? Compared to other animals, we can quickly and safely digest theobromine, so that the amount of theobromine in chocolates is not large enough to cause problems. We owe it to our enzyme cytochrome P450 in the liver, which metabolizes theobromine into harmless compound which then gets excreted out through urine in no time. For animals, theobromine is metabolized much slower, so that enough of the compound accumulates by eating chocolates. Thus the toxicity is dependent on the type of chocolate, the amount consumed, and the body size of the animal.

Cocoa is not the only food poisonous to our furry friends. Fruits of the vine (grapes, raisins, and sultans) are also emerging as a new concern for pet owners. Dogs can get kidney failure after consuming these fruits. Toxic dosage for fruits is not quite established yet, so that any amount should be considered toxic. Nevertheless, it is estimated that as low as 2.8mg/kg of raisins can cause kidney failure in dogs. The mechanism of toxicity in fruits is not known so far.

English: Wine grapes. Español: Uvas de vino ro...

Onions, garlic, leeks, and chives are also toxic to pets. All parts of these plants, in any form (raw, cooked, or dried) are poisonous, so be careful when giving out scraps off your plate. There are several toxic compounds in these plants, but the major one is called n-propyl disulfide, which leads to the damaging of red blood cells and causes hemolytic anemia in 1-5 days. (Rest assured, humans are resistant to n-propyl disulfide!)

Oh my, the list goes on. Avocado is toxic to pets, and so are macadamia nuts. Avocado triggers fluid accumulation in the lungs of animals, causing breathing difficulties and death. Macadamia nuts affect their muscles, digestive system, and nervous system.

Last but not the least, alcohol is deadly to pets. Even small amount of alcohol can lead to liver failure and death in animals. So do not give them alcohol as a joke!

Now that you know your pets cannot enjoy so many of the foods we love, aren’t you glad that you are human? Or are we really protected from the effects of theobromine (and caffeine)? The compound can easily cross placenta and may cause fetal malformation if the developing fetus has not made enzymes to detoxify it. Studies using rats showed that theobromine caused delayed development in fetus—not that studies on animals can always be directly applied to humans.

I don’t mean to scare you, but you should know that scientists are not 100% sure about the toxicity of theobromine to humans. But the common theme seems to be that anything eaten in large excess results in your body not being able to catch up with the breakdown of the compounds, and the build-up of these chemicals causes toxicity. (Remember my earlier post about alcohol metabolism?) So, eat food in moderation; don’t eat crazy amount of chocolates or drink gallons of coffee at a time!

So what CAN dogs eat? Consult your veterinarian or refer to some recipe books for dog treats.

Thank you for reading this post. Next week, I plan to discuss our potential benefit of eating chocolates :)

***Note: Although information here is supported by literature, food toxicity is complex and greatly varies from individual animal to animal. Please consult your veterinarian before making changes to your pet’s diet!

(If you enjoyed this post, you might also be interested in a blog post by Deborah Blum on the toxicity of chocolates.)

Grapes, raisins and sultanas, and other foods toxic to dogs
Some food toxic for pets
Theobromine and the Pharmacology of Cocoa
Recent advances in caffeine and theobromine toxicities: a review

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Filed under Animals in Science, Health, Q&A