Hello, I love your site and the info contained, very helpful. I have grown and used Pennyroyal as natural flea repellent for my cats for over 30 years, with no illness or bad side effects. I shared to a cat website I often post on, and a lady responded that Pennyroyal is toxic to cats and kills them. If this is true, I want to remove my post from that site, that states that it is safe to grow in garden and use as natural flea repellent in pet's beds. Thank you, Ann Davis, email is email@example.com. FB page is Ann Davis and Ann L Toboyko. Thanks again!
Yes, they are toxic to cats. There is one thing about cats that should be noted as important. They are strictly carnivores. They do not typically eat vegetation, but sometimes young kittens can be tempted to chew on the wrong things. Most cats will leave it alone, but it is poisonous to cats.
All this being said, it is often used as a repellent. Cats will not usually eat something that is toxic to them. So although it is toxic, there is little chance of a cat actually eating this.
This article will offer some more information: https://www.gardeningknowhow.com/plant-problems/pests/animals/cat-repellent.htm