Activated charcoal is used to treat dogs that have eaten a toxin or poison. Charcoal helps to prevent the gastrointestinal tract from absorbing toxins. If a dog has ingested a poison or toxic food, the vet will orally administer liquid activated charcoal to reduce potential contamination and toxic side effects. The use of activated carbon to treat a dog who has been poisoned with rodenticides is most effective in the first several hours after poisoning, before the poison has had time to be absorbed from the gastrointestinal tract into the blood. For this reason, the animal needs to be taken to the vet as soon as possible after the ingestion of the toxic substance.