Is chocolate poisonous for dogs?

When did chocolate become part of holiday tradition? Who cares! Everyone loves chocolate. It’s good for your heart, your brain and your psyche. It’s delicious and it goes with everything.

Except dogs. Chocolate and dogs definitely don’t mix.

How can chocolate be toxic?

Methylxanthines are a class of chemicals used as bronchodilators for people with asthma and COPD. There are two methylxanthines naturally present in chocolate: caffeine and theobromine. They have similar effects but the amount of caffeine in chocolate is small and not considered toxic.

Theobromine is another story. Theobromine is chemically related to a drug called theophylline, which was once commonly used to treat asthma. Theophylline tends to cause a lot of side effects and has lost favor as safer, more effective drugs have been developed. Investigations into possible therapeutic uses for theobromine are ongoing, but currently it isn’t considered medically important.

In excess amounts theobromine can cause restlessness and vomiting. In very excessive amounts it can cause tremors, seizures and dangerously elevated heart rate and blood pressure. People don’t often eat enough chocolate to cause these kind of symptoms, but elderly folks may be vulnerable to toxic effects.

But, 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.

Chocolate can be toxic for dogs
No chocolate for you.

But the bigger problem with dogs is that they metabolize theobromine very slowly.

Medically, a half-life is the time it takes for one half of a substance to be metabolized, and it takes five half-lives to be completely broken down.

Whereas theobromine’s half-life in humans is 7-12 hours, in dogs it is 17.5 hours, meaning it will take 87.5 hours for a dose of theobromine to clear your dog’s system. He won’t necessarily be sick that long, but depending on the amount of theobromine on board he could have symptoms for about 72 hours.

What about cats?

Theobromine is also toxic for cats, but as a rule cats aren’t attracted to sweets because they can’t taste them. That’s right: cats are genetically programmed to taste meat and nothing but.  As challenging as a picky-eating cat may be to feed, in the case of chocolate this is a good thing.

Contents may vary

Not every chocolate ingestion is life-threatening to every dog. Whether a dog gets sick from eating chocolate depends on the size of the dog and the type and amount of chocolate eaten. Methylxanthine levels drop as the amount of sugar, milk, cocoa butter and other ingredients increases, so cocoa and dark chocolate will be more toxic than milk chocolate.

The information in the table below is taken from a more complete list on the Hershey website and gives you an idea of how methylxanthine levels vary by product.

How do we know if it’s toxic?

Here’s how a toxicity calculation is done. (You can also use an online toxicity calculator.)

  1. 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.
  2. 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.
  3. 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 different!

Dark chocolate is poisonous to dogs
Too cute to lose.

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 – likely a fatal amount.

This is a perfect example of the dose making 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 sizeServing size (g)Caffeine (mg)Theobromine (mg)Total methyxanthines (mg)
Kisses9 kisses41106878
Milk chocolate bar1 bar (1.5 oz)4396473
Special Dark mildly sweet chocolate bar1 bar (1.5 oz)4120174194
Cocoa1 tablespoon (0.2 oz)58100108
York Peppermint Pattie1 pattie3965359
Reese's Peanut Butter Cups1 package (1.5 oz)4242630
Whoppers1 package (1.7 oz)4922931
Scharffen Berger 82% Extra Dark Chocolate Bar1/2 bar (1.5 oz)4342370412

More info

Chocolate toxicity calculator

Video: Why is chocolate bad for dogs?

ASPCA Animal Poison Control 888-426-4435

ASPCA mobile app (includes chocolate calculator)

Theobromine and caffeine in Hershey products

Lbs to kg calculator

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