Theobromine and caffeine belong to a family of compounds called methylxanthines. In dogs they overstimulate the nervous system and the heart, and because dogs clear them so slowly, the effects build up and can last for many hours. Severity depends on the type of chocolate, the amount eaten, and the dog's weight: a few grams of dark chocolate can be a real problem for a small dog, while the same amount of milk chocolate might only cause an upset stomach in a large one.
Signs usually start with vomiting, diarrhea, restlessness, and increased thirst, and can progress to a racing heart, panting, tremors, and in severe cases seizures. There is no antidote — treatment is supportive, and it works best when it starts early, before symptoms are severe.
Sources
- Chocolate Toxicosis in Animals — Merck Veterinary Manual
- Chocolate Poisoning in Dogs — VCA Animal Hospitals
- People Foods to Avoid Feeding Your Pets — ASPCA Animal Poison Control
This page is informational and is not veterinary advice. If your pet has eaten something risky, contact your vet or an animal poison control line right away.