About Chocolate and Dogs

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In recent weeks, there has been a popular meme circulating on social media that states:

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“Chocolate is toxic to dogs. It doesn’t just poison them once but is repeatedly reabsorbed into their body and poisons them many times. This is why it is so dangerous”

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A Science Dog reader brought the meme to my attention and asked me about its veracity. In response, I posted a comment with facts regarding chocolate and theobromine on the meme’s social posting. Unfortunately, the original authors reposted the meme and ignored those facts. In the spirit of promoting evidence-based nutrition, I am providing science-based information about chocolate, theobromine, and dogs here on The Science Dog.

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What is Theobromine?

Chocolate contains a methylxanthine called theobromine, which is toxic to dogs when consumed in large quantities. Three methylxanthine compounds are commonly found in foods; these are caffeine, theophylline, and theobromine. Caffeine is most abundant in coffee, tea, and cola beverages, and theophylline is found primarily in tea. Theobromine is the most abundant methylxanthine that is contained in the cacao bean, which is the source of cocoa and chocolate products.

The main sites of action of xanthine compounds in the body are the central nervous system, cardiovascular system, kidneys, smooth muscle, and skeletal musculature. Theobromine in particular acts as a smooth muscle relaxant, coronary artery dilatator, diuretic, and cardiac stimulant.

Dogs are unusually sensitive to the physiological effects of theobromine, when compared with many other species. This sensitivity appears to be the result of a lower rate of theobromine metabolism, resulting in a longer half-life in the dog’s bloodstream and tissues. Theobromine is metabolized in the liver and its end-products are excreted via the kidneys (in urine). While there is evidence for some reabsorption by the kidney tubules (which is normal metabolism with many metabolites), there is no evidence that this reabsorption causes “multiple opportunities for poisoning” as stated in the meme.

Regarding the half-life of theobromine, we do have some facts. The half-life of theobromine in the plasma of adult dogs is approximately 17.5 hours.  In comparison, theobromine’s half-life in human subjects is 6 hours; in rats it is only 3 hours. It has been theorized that the extended half-life in dogs may potentiate acute toxicity reactions to theobromine after the consumption of foods containing theobromine.

Clinical Signs of Theobromine Toxicity

Dogs with theobromine toxicity experience vomiting, diarrhea, panting, restlessness, increased urination or urinary incontinence, and muscle tremors. These signs usually occur about 4 to 5 hours after the dog has consumed the food containing theobromine. Theobromine toxicity is treated by inducing vomiting as soon as possible. An activated charcoal solution given by gastric lavage may aid in decreasing the quantity of theobromine that is absorbed into the bloodstream. Unfortunately, there is no specific systemic antidote for theobromine poisoning.

How Much Chocolate is Unsafe for Dogs?

Although few controlled studies on the level of theobromine that constitutes a toxic dose have been conducted in dogs, data from long-term studies and case reports indicate that a lethal level of toxicity can occur when a dog consumes a dose of 90 to 100 milligrams (mg)/kilogram (kg) of body weight or more. For a 25 lb. dog, this is equal to between 1.0 and 1.2 total grams (~ 1/3 – 1/2 ounce) of theobromine (not of chocolate – see below). Factors such as individual sensitivity to theobromine, presence of other foods in the gastrointestinal tract, and difference of theobromine content between chocolate products cause wide variations in the susceptibility of individual dogs to theobromine toxicity. Because there is not evidence that suggests a safe upper level of theobromine intake, many veterinarians suggest treating for toxicity when a dog has consumed a dose of 40 mg/kg or greater. This is equal to ~ 0.5 grams of theobromine ingestion in a 25 lb dog.

Not to put too fine a point on this, but theobromine can make us sick also. While actual “Death by Chocolate” is almost impossible to achieve, humans can develop clinical signs of sweating, trembling, nausea and agitation when excess levels of theobromine are ingested. It just takes a lot more because we are not as metabolically sensitive to theobromine as are our dogs. In other words, as with many things in biology, we are looking at a difference in degree here, not in kind.

Levels of Theobromine in Chocolate Foods

Most significantly and of practical interest – Chocolate products differ greatly in theobromine content and, therefore, in their ability to produce theobromine poisoning. Here are some comparisons: 

• Baking Chocolate: This is a base substance from which many other chocolate products are produced. The average theobromine content of baking chocolate is about 1.22%. This means that a 1-ounce (oz) square of baking chocolate contains approximately 346 mg of theobromine. Therefore, if a medium-sized dog weighing 25 pounds (11 kg) consumed 3 oz of baking chocolate, a toxic dose of 94 mg of theobromine/kg would be ingested.
• Commercial Cocoa Powder (unsweetened): This form of chocolate has an average theobromine content of 1.89%, which is the highest theobromine content of all commonly consumed chocolate products. However, dogs are generally unlikely to consume baking chocolate or cocoa powder because they are not sweet. The addition of sugar, cocoa butter, and milk solids to baking chocolate to produce sweet chocolates results in a significant dilution of theobromine content.
• Semisweet Chocolate Pieces: The level of theobromine in semisweet chocolate pieces, such as those used to back cookies, is 0.463%. In this case, a 25-lb dog would have to consume approximately 1⁄2 lb of semisweet chocolate to reach a potentially toxic level of 95 mg/kg.
• Milk Chocolate: Similarly, milk chocolate contains 0.153% theobromine. The ingestion of approximately 1 1/2 lbs (24 oz) of milk chocolate would result in a potentially lethal dose for a 25-lb dog.

Why is Chocolate a Danger to Dogs?

Most dogs enjoy the taste of sweet foods and many truly adore the taste of chocolate. Owners occasionally give small bits of chocolate candy or foods containing chocolate to their dogs as a special treat. If a dog’s intake of chocolate is limited to occasional small treats, there is no danger of theobromine toxicity. The published case studies of theobromine toxicity in dogs have been the result of a pet accidentally ingesting a large amount of chocolate. Still, if given the opportunity, many dogs readily will overconsume chocolate-containing foods. Therefore all chocolate products should be stored in areas inaccessible to pets and large amounts of chocolate should never be fed to dogs.

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Take Away for Dog Folks

• Dogs enjoy sweet flavors, including chocolate-containing foods and candies.
• However, chocolate contains the methylxanthine compound theobromine, which is toxic to dogs when consumed in large quantities.
• If a dog’s intake of chocolate is limited to the occasional small treat, there is no risk of theobromine toxicity.
• However, if a dog has the opportunity to overconsume a large quantity of chocolate, there is definitely a risk of toxicity.
• All chocolate-containing foods should be stored in areas that are inaccessible to pets and large amounts of chocolate should never be fed to dogs

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Adapted From: “Canine and Feline Nutrition: A Resource for Companion Animal Professionals” by LP Case, et al. pages 284-285, Mosby/Elsevier, 2011.

Published Studies:

• Houpt KA, Smith SL: Taste preferences and their relation to obesity in dogs and cats, Can Vet J 22:77-81, 1981.
• Gans JH, Korson R, Cater MR, and others: Effects of short-term and long-term theobromine administration to male dogs, Toxicol Appl Pharmacol 53:481-496, 1980.
• Welch RM, Hsu SY, DeAngelis RL: Effect of arvelor 1254, phenobarbital and polycyclic aromatic hydrocarbons on the plasma clearance of caffeine in the rat, Clin Pharmacol Ther 22:791-798, 1977.
• Drouillard DD, Vesell ES, Dvorchick BN: Studies on theobromine disposition in normal subjects, Clin Pharmacol Ther 23:296-302, 1978
• Hoskam EG, Haagsma J: Chocolate poisoning terminating in the death of two Dachshunds, Tijdschr Diergeneesk 99:523-525, 1974.
• Decker RA, Meyers GH: Theobromine poisoning in a dog, J Am Vet Med Assoc 161:198-199, 1972.
• Glauberg A, Blumenthal PH: Chocolate poisoning in the dog, J Am Anim Hosp Assoc 19:246-248, 1983.
• Zoumas BL, Kreiser WR, Martin RA: Theobromine and caffeine content of chocolate products, J Food Sci 45:314-316, 1980.

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