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I once had a dog that was fairly frequently given chocolate, and I never noticed any consequences.

I heard somewhat recently that chocolate is bad for dogs. Is this true?

Certainly, too much chocolate is bad, but isn't everything bad in excessive quantities?

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I was walking my new puppy a few years ago and came across a lady who told me she had a similar dog, but her dog ate a block of chocolate and died the next day. –  Craig Apr 7 '11 at 3:53
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My veterinarian said that I mustn't feed my cat with chocolate, because it contain some kind of feline toxin that accumulate in the body over time. He is a real doctor, so this well-known fact, whether if true or not, is widely spread. –  HuBeZa Apr 7 '11 at 12:16
    
I have also heard that raisins and grapes are harmful to dogs –  BlueRaja - Danny Pflughoeft Sep 20 '11 at 22:18
    
Well, you once had a dog. Now you don't. Thus, chocolate is the culprit ;D.... jk.. –  Dr. Nobody Dec 17 '12 at 4:02
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1 Answer

up vote 53 down vote accepted

Vets will tell you that chocolate is toxic for dogs and cats. This page at about.com says:

The toxic dose of Theobromine (and caffeine) for pets is 100-200mg/kg. (1 kilogram = 2.2 pounds). However, various reports by the ASPCA (American Society for the Prevention of Cruelty to Animals) have noted problems at doses much lower than this - i.e. 20mg/kg.

Translated to a "typical" scenario, and using the 20mg/kg as a measure of "problems can be seen at this level of ingestion", a 22.7 kg (50 pound) dog would have to consume about 255 grams (9 ounces) of milk chocolate to consume the 20mg/kg amount of Theobromine. Some dogs won't see problems at this rate. Some may.

So it would seem that a mid-sized dog could probably eat a typical chocolate bar without impact. But a typical mid-sized cat (say 4.5 kg or so) is asking for trouble at 28g (1 oz) of chocolate.

Of course, if you prefer really strong dark chocolates, it will take less weight of candy bar to deliver the same dose as estimated for milk chocolate.

As the about.com piece points out, those are conservative numbers. The actual lethal dose is likely much higher.

One other note: Caffeine is also a problem for dog and cat metabolism. That article claims a similar range for toxic doses as for theobromine. I would be careful about letting the cat finish your tall mocha latte...

Here are some supporting links from the about.com article:

  • Nat Geo has a very visual interactive calculator for dog weight vs. toxic dose for a variety of chocolate products. Its pretty.
  • AskAVetQuestion.com has a toxicity calculator.
  • Another page has technical background on chocolate toxicity, including symptoms to watch.

Moving to a more technical source, Merck has a Veterinary Manual with a reference page on chocolate. The information there generally confirms the About.com article (which should not be surprise because it is cited as a source) and is similar to other summaries for pet owners that Google turns up. It is, however, written with a practicing Vet as the intended audience.

The toxic effect is explained by Merck as follows:

Theobromine and caffeine are readily absorbed from the GI tract and are widely distributed throughout the body. They are metabolized in the liver and undergo enterohepatic recycling. Methylxanthines are excreted in the urine as both metabolites and unchanged parent compounds. The half-lives of theobromine and caffeine in dogs are 17.5 hr and 4.5 hr, respectively.

That means that as long as the lethal dose is not exceeded, and the dog's liver function (and kidney function as well I assume) is not otherwise compromised, the theobromine and caffeine will eventually be excreted. With a half-life of 17.5 hr, it would require about 40 hr to reduce a near lethal dose of 100mg/kg to below the mentioned clinical effect threshold of 20mg/kg. (We want to reduce the dose by a factor of 5 from 100mg/kg to 20mg/kg. So we calculate 17.5 * log2 5 = 17.5 * 2.32 = 40.6 and round that to 40 or so to one significant figure for a reasonable estimate. Two days is also a reasonable estimate.)

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Is anything said about how fast dogs/cats can metabolize Theobromine? In other words, how long does it stay in their bodies? Can it accumulate? –  Raskolnikov Apr 7 '11 at 11:26
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@Raskolnikov, I haven't located much explicit info about cats and chocolate. My vet regularly complains that dogs get all the research attention, and cats are often assumed to just be funny-looking small dogs by the industry, which is just true enough to be useful but occasionally the differences matter. I added a citation to Merk which states a half-life in dogs and a calculation of what that might mean for a dog's owner. –  RBerteig Apr 7 '11 at 21:15
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The edits by ChrisR to change to SI units raise two issues for me. First, there are edits to directly quoted material. You don't go changing quoted material. If the units used are a problem, add a paragraph with a new example in SI units. Second, because they are direct conversions, they produce a false sense of precision. IMHO, it would be better to shift the calculations based on round numbers to appropriate round numbers in SI so that they stick to one significant figure. –  RBerteig Nov 3 '11 at 7:49
    
The leathal dose for cats is different to dogs. Wikipedia en.wikipedia.org/wiki/Theobromine_poisoning has the LD50 as 200mg/kg for cats and 300 mg/kg for dogs. Cats don't generally eat chocolate though. –  Nick Sep 5 '12 at 9:23
    
I'd agree that cats don't seem to seek out chocolate. None of my cats over the years have shown any interest in strong dark chocolate where even a single mouthful might be worrying. I did have a cat that would try to steal bites from a Butterfinger bar if I was inattentive. Luckily for him, even the chocolate coating has very little actual chocolate in it.... –  RBerteig Sep 5 '12 at 18:34
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