Understanding Why Chocolate Is Toxic for Dogs

Good for humans but not for pets

Dog lying in a bed
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While recent studies have shown that chocolate is beneficial for human health, chocolate can be toxic—and sometimes fatal—for your dogs and cats. Chocolate is made from the fruit of the cacao tree. It contains theobromine, a member of a drug class called methylxanthines. Theobromine has a bitter flavor and gives dark chocolate its bitter taste.

Of all pets, dogs are most commonly affected by chocolate toxicity.

They have a sweet tooth and a superior nose that makes them skilled at finding chocolate. Cats and other pet species are also susceptible to the toxic effects of chocolate. However, cats are less likely to eat a large portion of chocolates because they are unable to taste sweetness.

What Makes Chocolate Toxic for Dogs

The reason chocolate is not toxic for humans but is for dogs is related to the lengthy time it takes dogs to metabolize one of the components of chocolate—theobromine, which is a diuretic, heart stimulant and vasodilator. The amount of theobromine in chocolate is so small that the risk of poisoning in humans is almost non-existent. However, domestic animals metabolize theobromine much more slowly than humans, and they are smaller than humans. A dog that eats a generous portion of chocolate can become a victim of theobromine poisoning, which can be fatal.

Theobromine functions as a stimulant for the central nervous system and as a stimulant for the cardiovascular system.

Symptoms of Theobromine Poisoning in Dogs

If you know or suspect your dog has eaten any chocolate, watch for these symptoms. If they appear, call your vet.

  • Nausea and vomiting
  • Diarrhea
  • Increased urination

If the theobromine poisoning isn't recognized and treated, the animal's condition could deteriorate and the following occur:

  • Seizures
  • Cardiac arrhythmias
  • Internal bleeding
  • Heart attack
  • Death

Why Chocolate Isn't Toxic to Humans

Humans break down and excrete theobromine much more efficiently than dogs. The half-life of theobromine in a dog is long—approximately 17.5 hours.

Some Chocolates Are More Toxic Than Others

Unsweetened baker's chocolate contains eight to 10 times the amount of theobromine as milk chocolate contains. Semi-sweet chocolate falls roughly in between the two for theobromine content. White chocolate contains theobromine, but in such small amounts that theobromine poisoning is unlikely. 

Quick Guide to Theobromine Levels in Types of Chocolate

From The Merck Veterinary Manual, here are approximate theobromine levels of different types of chocolate:

  • Dry cocoa powder - 800 mg/oz
  • Unsweetened (baker's) chocolate - 450 mg/oz
  • Cocoa bean mulch - 255 mg/oz
  • Semi-sweet chocolate and sweet dark chocolate -150-160 mg/oz
  • Milk chocolate - 44 to 64 mg/oz
  • White chocolate contains an insignificant source of methylxanthines