The correct answer to this question is NOT ALL herbs are toxic to dogs. However, there are a few herbs that have been found to be extremely dangerous for dogs as they can cause several health problems such as liver damage, cancer, heart arrhythmias or irregular heartbeat, high blood pressure, nervous system damage, kidney damage, vomiting, bloating, anemia and most of the time, if not treated early, death.
Here are a few herb plants that are toxic to dogs and that you need to avoid if you have dogs in your household: Pennyroyal which is concentrated and it can kill your dogs, most especially those with existing kidney disease or if they are pregnant. Tea tree oil is also toxic to dogs may they be small or big, comfrey has been found to cause liver damage to dogs, wormwood can damage their nervous system since it contains tannins and volatile oils, yucca can cause vomiting and bloating and can lead to death in untreated, and garlic which can cause anemia.