The answer to “how much chocolate is toxic” varies widely on the type of chocolate, the size of dog or cat, and how much they have consumed. Here are some guidelines and calculators to see how much is too much for each situation.
The toxic dose of Theobromine (and caffeine) for pets is 100-200mg/kg. (1 kilogram = 2.2 pounds). However, various reports by the ASPCA 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 50-pound dog would have to consume 9 ounces (+/-) of milk chocolate to consume the 20mg/kg amount of Theobromine. Some dogs won’t see problems at this rate, but some may.
This is a much more conservative toxic level calculation than the standard of 100-200mg/kg, but better safe than sorry. The bottom line: A dog sneaking a couple M&M’s shouldn’t have a problem, but it isn’t a good habit to get into.
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
If the theobromine poisoning isn’t recognized and treated, the animal’s condition could deteriorate and the following occur:
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