|Animal||Oral toxicity (mg/kg)|
Theobromine poisoning or chocolate poisoning is an overdose reaction to the xanthine alkaloid theobromine, found in chocolate, tea, cola beverages, açaí berries, and some other foods. Lethal (LD50) doses of theobromine have only been published for humans, cats, dogs, rats, and mice; these differ by a factor of 6 across species (see the table in this article).
Cocoa beans contain about 1.2% theobromine by weight, so an ounce (28g) of raw cacao contains approximately 0.3g theobromine. Processed chocolate, in general, has smaller amounts. The amount found in highly refined chocolate candies (typically 1.4–2.1 g/kg or 40–60 mg/oz) is much lower than that of dark chocolate or unsweetened baker's chocolate (> 14 g/kg or > 400 mg/oz). 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.
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. If large numbers of filled chocolate candies are consumed, another serious danger is posed by the fat and sugar in the fillings, which can sometimes trigger life-threatening pancreatitis several days later. 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 less toxic to rats, mice, and humans, who all have an LD50 of about 1,000 mg/kg.
In dogs, the biological half-life of theobromine is 17.5 hours; 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 after long term exposure at levels equivalent to ~15 g of dark chocolate per kg of weight and per day. According to the Merck Veterinary Manual, baker's chocolate of approximately 1.3 g/kg (0.02 oz/lb) of a dog's body weight is sufficient to cause symptoms of toxicity.  For example, 0.4 ounces (11 g) of baker's chocolate would be enough to produce mild symptoms in a 20-pound (9.1 kg) dog, while a 25% cacao chocolate bar (like milk chocolate) would be 25% as toxic as the same dose of baker's chocolate.  One ounce of milk chocolate per pound of body weight is a potentially lethal dose in dogs. 
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.
- Gennaro, M. C.; Abrigo, C. (1992). "Caffeine and theobromine in coffee, tea and cola-beverages". Fresenius' Journal of Analytical Chemistry 343 (6): 523–525. doi:10.1007/BF00322162. ISSN 0937-0633.
- THEOBROMINE from the Hazardous Substances Data Bank
- "Dog owners get chocolate warning". BBC. December 30, 2008. Retrieved July 28, 2009.
- "Greedy dog cheats chocolate death". BBC. April 3, 2009. Retrieved July 28, 2009.
- Biello, David (August 16, 2007). "Strange but True: Cats Cannot Taste Sweets". Scientific American. Retrieved July 28, 2009.
- Gwaltney-Brant, Sharon (February 2001). "Chocolate Intoxication". Veterinary Medicine Publishing Group. Retrieved November 5, 2011.
- H. Gans, Joseph. "Effects of short-term and long-term theobromine administration to male dogs". Elsevier Inc. Retrieved 1 March 2012.
- "Merck Veterinary Manual". Retrieved 6/17/14.
- "PetMD". Retrieved 6/17/14.
- Johnston, John J. (2005). "Evaluation of Cocoa- and Coffee-Derived Methylxanthines as Toxicants for the Control of Pest Coyotes". Journal of Agricultural and Food Chemistry. Retrieved July 28, 2009.
- Theobromine in the ChemIDplus database (September 9, 2004)
- Merck Veterinary Manual (Toxicology/Food Hazards section), Merck & Co., Inc., Chocolate Poisoning. (June 16, 2005)