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Some substances, after being ingested, can cause a lot of damage if vomited back up. If you know your dog swallowed one of the following substances, do not induce vomiting:  Bleach Drain cleaner Petroleum-containing substance, such as gasoline Getting a dog to vomit can be dangerous if the dog is extremely sick or unresponsive. If your dog is showing signs of severe poisoning, do not induce vomiting. Take your dog to your vet right away. Look for the following signs indicating severe poisoning:  Difficulty breathing Looking depressed Having seizures Slow heart rate Unconsciousness If possible, get your dog to vomit within about two hours after it has ingested something toxic. After two hours, the toxin will have moved into the intestines, making induction of vomiting no longer effective.

Summary:
Research which substances should not be vomited up. Look for signs of serious poisoning. Induce vomiting promptly.