Theobromine poisoning or chocolate poisoning is an adverse reaction to the alkaloid theobromine, found in chocolate, tea, cola beverages, açaí berries, and some other foods. Cacao beans contain about 1.2% theobromine by weight, while processed chocolate, in general, has smaller amounts.
The amount found in highly refined chocolate candies (~2 g/kg) is much lower than that of dark chocolate (~10 g/kg) or unsweetened baker’s chocolate (> 14 g/kg ). In general, the amount of theobromine found in chocolate is small enough such that chocolate can be safely consumed by humans. However, occasional serious side effects may result from the consumption of large quantities, especially in the elderly. In extreme cases, emergency room treatment may be required.
Serious poisoning happens more frequently in domestic animals, which metabolize theobromine much more slowly than humans, and can easily consume enough chocolate to cause chocolate poisoning. The most common victims of theobromine poisoning are dogs, for which it can be fatal. The toxic dose for cats is even lower than for dogs. However, cats are less prone to eating chocolate since they are unable to taste sweetness. Theobromine is much less toxic to rats and mice, due to their relative genetic similarity to primates; they and humans all have an LD50 of about 1,000 mg/kg (the lethal dose for 50% of individuals is one gram of theobromine for every kilogram of body weight ). Therefore, eating 13.5 pounds of chocolate would kill half of people of average weight.
Toxic (LD50) doses of theobromine have only been published for humans, cats, dogs, rats, and mice; these differ by a factor of 6 across species. The toxicity for (pet) birds is not known, but it is typically assumed that chocolate is dangerous for birds, especially since birds like to eat chocolate. The first signs of theobromine poisoning are nausea, vomiting, diarrhea, and increased urination. These can progress to cardiac arrhythmias, epileptic seizures, internal bleeding, heart attacks, and eventually death.
In dogs, the half-life of theobromine is 17.5 hours, so in severe cases clinical symptoms of theobromine poisoning can persist for 72 hours. Medical treatment performed by a veterinarian involves inducing vomiting within two hours of ingestion and administration of benzodiazepines or barbiturates for seizures, antiarrhythmics for heart arrhythmias, and fluid diuresis. Theobromine is also suspected to induce right atrial cardiomyopathy other long term exposure at levels equivalent to ~15 g of dark chocolate per kg of weight and per day.
A typical 20 kg (44 lb) dog will normally experience intestinal distress after eating less than 240 g (8.5 oz) of dark chocolate, but won’t necessarily experience bradycardia or tachyarrhythmia unless it eats at least 0.5 kg (1.1 lb) of milk chocolate. According to the Merck Veterinary Manual, baker’s chocolate of approximately 1.3 g/kg of a dog’s body weight is sufficient to cause symptoms of toxicity. For example, a typical 25-gram baker’s chocolate bar would be enough to bring out symptoms in a 20-kilogram (44 lb) dog. Large breeds (> 100 pounds / 45 kilograms) can safely consume chocolate in limited quantities, but care must still be taken, as they can safely eat only about a quarter the amount a human can, and should not be intentionally fed it; peanut butter is often recommended as a safer alternative.
Chemists with the USDA are investigating the use of theobromine as a toxicant to control coyotes that prey on livestock.