Everyone loves chocolate. It’s good for your heart, your brain and your psyche. It’s delicious and it goes with everything. Almost everything, that is. You’ve probably heard dogs shouldn’t eat it. But is chocolate poisonous for dogs?
How can chocolate be poisonous?
Methylxanthines are chemicals that people with asthma and COPD can use to open their airways. Chocolate naturally contains two methylxanthines: caffeine and theobromine. They have similar effects, but the amount of caffeine in chocolate is small and it’s not usually a problem.
Theobromine is another story. Theobromine is chemically related to a drug called theophylline, which was once commonly used to treat asthma. Theophylline has a lot of side effects, though, and there are now safer, more effective drugs.
Too much theobromine can cause restlessness and vomiting. In very large amounts it can cause tremors, seizures and dangerously high heart rate and blood pressure. People usually don’t eat enough chocolate to cause these kind of symptoms. But it’s theobromine that makes chocolate poisonous for dogs.
Theobromine makes chocolate poisonous for dogs
The problem with dogs is that they lack our endless capacity for self-delusion. They won’t nibble chocolate a little at a time, telling themselves this one piece is going to be the last one today. They will eat as much as they can, as fast as they can, and take the entire theobromine hit all at once.
But the bigger problem with dogs is that they metabolize theobromine very slowly.
A half-life is the time it takes for one half of a substance to be metabolized, or broken down into smaller parts. It takes five half-lives to be completely broken down.
Theobromine’s half-life in humans is 7 to 12 hours. But in dogs it is 17.5 hours.
Five times 17.5 hours is 87.5 hours; that’s how long it takes a dose of theobromine to clear your dog’s system. He won’t necessarily be sick that whole time. But depending on how much theobromine he got, he could have symptoms for about 72 hours.
Is chocolate poisonous for cats?
Theobromine could have the same effects on cats. However, as a rule cats don’t eat sweets because they can’t taste them. That’s right: cats are genetically programmed to taste meat and nothing but. It’s challenging when your cat is a picky eater, but in the case of chocolate it’s a good thing.
Chocolate isn’t always poisonous
Not every chocolate ingestion is life-threatening to every dog. The amount of theobromine is what makes chocolate poisonous for dogs. The size of the dog also matters.
Sugar, milk, cocoa butter and other ingredients dilute the amount of theobromine and caffeine in chocolate. So cocoa and dark chocolate are more toxic than milk chocolate, because they are more pure.
“White chocolate,” by the way, is not poisonous. Despite its name it contains no chocolate, and therefore no theobromine.
The information in the table below is taken from a more complete list on the Hershey website [note: no longer found]. It gives you an idea of how methylxanthine (theobromine + caffeine) levels vary by product.
How do we know if it’s poisonous?
Here’s how a toxicity calculation is done. (You can also use an online toxicity calculator.)
First, convert the dog’s weight from pounds to kilograms (kg) either by dividing the number of pounds by 2.2 or by using an online converter.
Let’s say the dog weighs 10 lbs. 10/2.2 = 4.5 kg.
Then, identify the type and amount of chocolate ingested and use the table to find the estimated total methylxanthine content in milligrams (mg).
The dog ate a 1.5 oz bar of milk chocolate. That’s 73mg total methylxanthine content.
Finally, divide the methylxanthine content in mg by the dog’s weight in kg to get the mg/kg.
73mg/4.5kg = 16mg/kg
Surprisingly, that’s not too bad, according to the Merck Veterinary Manual:
20mg/kg – Mild symptoms: Nausea, vomiting, diarrhea, increased thirst, restlessness
40-50mg/kg – Serious symptoms: Hyperactivity, increased urination, rigidity, difficulty walking, tremor
60mg/kg – Severe symptoms: Rapid heart and respiratory rate, cardiac arrhythmias, seizures, fever, coma, death
Dark chocolate is poisonous for dogs!
But what if the dog ate the same amount of dark chocolate? That 1.5oz half-bar of Scharffen Berger 82% Special Dark has a whopping 412mg total methylxanthines.
That would be 412mg/4.5kg = 92mg/kg. That’s likely to be a fatal amount.
This is a perfect example of how the dose makes the poison.
As useful as these calculation tools are, if your dog has gotten into chocolate it’s always a good idea to check in with your vet or poison control.
Animal Poison Control (888-426-4435) charges for calls because that’s how the service is funded. Human poison control (800-222-1222) can help you with calculations but probably won’t be able to give treatment advice.
Hershey product caffeine & theobromine content
|Serving size||Serving size (g)||Caffeine (mg)||Theobromine (mg)||Total methyxanthines (mg)|
|Milk chocolate bar||1 bar (1.5 oz)||43||9||64||73|
|Special Dark mildly sweet chocolate bar||1 bar (1.5 oz)||41||20||174||194|
|Cocoa||1 tablespoon (0.2 oz)||5||8||100||108|
|York Peppermint Pattie||1 pattie||39||6||53||59|
|Reese's Peanut Butter Cups||1 package (1.5 oz)||42||4||26||30|
|Whoppers||1 package (1.7 oz)||49||2||29||31|
|Scharffen Berger 82% Extra Dark Chocolate Bar||1/2 bar (1.5 oz)||43||42||370||412|
ASPCA Animal Poison Control 888-426-4435
ASPCA mobile app (includes chocolate calculator)
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