According to WebMD, the caffeine in tea is toxic to dogs. There is no sure antidote for caffeine poisoning, so an excessive amount is often fatal. Caffeine is also found in coffee, cocoa, chocolate, sodas, energy drinks, and cold medicines and pain killers for people.

WebMD identifies several symptoms of caffeine poisoning, including restlessness, rapid breathing, heart palpitations, muscle tremors and seizures. The danger depends upon the amount of caffeine consumed and the size of the dog, Banfield Pet Hospital indicates.

Banfield recommends contacting a veterinarian if a dog ingests caffeine. A vet attempts to remove caffeine from a dog's system by inducing vomiting and dosing with activated charcoal to trap the poison.