Pennyroyal is another herb that many herbalists use. Many use pennyroyal as a tea as a stimulant, carminative, diaphoretic and emmenagogue. American and European pennyroyal consist of 85 to 92% of pulegone, a toxic ketone found in pennyroyal oil. It causes hepatotoxicity in dogs and cats.

Pennyroyal is considered one of the most dangerous herbs mainly because of the damage it can do the the liver, causing severe liver damage even in relatively small amounts. As little a 1/2 teaspoonful of pennyroyal can produce convulsions and coma, leading to death. While pennyroyal may indeed induce abortion, it does so only in lethal doses.

Pennyroyal tea tastes just like insect repellant. This is sold as an 'all natural' flea killing product. The problem is all natural does not mean safe and it's quite a toxic choice

Pennyroyal is toxic even in a small amount should the animal (dog or cat) accidentally ingest it. And this can be done thro licking or scratching where the pennyroyal is. There is a myth that pennyroyal oil is good for preventing ticks on pets but this is false and is actually highly toxic and can induce seizures and causes comatose fits. Even rubbed on the skin can cause irritation