What You Need to Know About Pennyroyal

Pennyroyal can be used to repel fleas and other insects, but taking it internally is thick with risks.

  • Pennyroyal
    When properly used, the leaves of the pennyroyal plant (Mentha pulegium) can safely deter fleas and insects.

  • Pennyroyal

For 35 years, the writers and readers of Mother Earth News have shared hundreds of ways to use herbs to make life more enjoyable. In our archived articles, European and American pennyroyal (Mentha pulegium and Hedeoma pulegiodes) have been recommended as a way to deter fleas, as a vapor to relieve nasal congestion caused by colds, and as an infusion to cleanse the body of toxins.

We stand by using the pennyroyal plant to deter pests, but new information on the active ingredient in both species of pennyroyal, pulegone, merits a recall of taking pennyroyal into your body. In 1996, two California infants died after being given mint tea, in which the mint turned out to be pennyroyal. Most other pennyroyal incidents involve the use of pennyroyal essential oil (generally used for therapeutic or homeopathic purposes or as an insect repellent), which is so potent that it should be considered a poison. In the interest of safety, never use pennyroyal essential oil for anything, not ever.


Two thousand years ago, pennyroyal was the herb used to terminate unwanted pregnancies. Dr. Art Tucker, research professor at Delaware State University and author of The Big Book of Herbs , says that pennyroyal induces abortions by first damaging the mother's liver. Death sometimes follows. In a well-documented case from 1994, a college student who drank only 2 teaspoons of pennyroyal oil in teas over a two-day period died from it. In 1992, a healthy dog died after licking a similar amount from its fur.

Obviously, there are good reasons to leave pennyroyal oil alone. However, the pennyroyal plant itself, as the most pungent member of the mint family, may have several good uses around your house.

As a flea deterrent . Dried pennyroyal leaves can be scattered around pets' bedding area, and you can roll up some fresh stems in you dog's bandana before you go tromping through the woods. Pennyroyal oil used in flea collars has largely been phased out because it caused miscarriages in cats, so only use the fresh leafy stuff, please. If a pet or person could be expecting, don't use pennyroyal at all.

9/5/2020 6:31:08 AM

Is this the plant that starts growing in the spring along roadsides?

9/4/2020 10:02:46 PM

In my several decades of alternative health work, Pennyroyal CAN cause problems, IF people ingest too much. UNDERSTAND THIS: "The Dose makes the poison". In other words, "take too much, it's toxic; take the right amount, you get desired results as a medicine." It can repel pests [We've used it to repel most insects, most rodents, and some small wild creatures]....FAR better than most other alternative options [including peppermint] [pests seem to instinctively know pennyroyal stops them breeding] and, if planted around the foundations of a house, can repel most pests from getting into your house. Pests instinctively understand it will block them breeding. They go somewhere else. We did that one place we lived; currently, still struggling to get it to start growing around house foundations at this place. I hope to also plant it at spots around the large yard, to repel ground-dweller wasps, as those are dangerous, here. We've also put a few drops of the essential oil onto a cloth collar for each of our cats [over the past 40 years, we've had about 6 or more cats in that time], as a flea and tick deterrent...ALL our pets have done just fine, lived normal healthy lives with it on their collars. They have been protected and, not suffered the toxicity of the flea drugs. Ants, carpenter ants, spiders, etc., go away from it. We've successfully used the old "ballooned brown paper lunch bag" fake-paper-wasp nests in the eaves, to prevent wasps nesting in the eaves...so simple, and free. These things have worked VERY well for us, for over 50 years in these capacities. I will continue to use pennyroyal oil and plants, judiciously, as always. The only problem was, finding seeds to reliably grow this annual. One Amazon seller sent up a huge bag of wrong seeds---looked like giant chickweed, not pennyroyal. Had to look elsewhere for seeds. Then found 2 small plants of it at, of all places, Walmart nursery....those kept growing for a couple years, but then died off....gotta start over. ...The plants need some moisture and good drainage...we have too fast of drainage, and needed to water them daily until established, at least. Once it gets really established, it should reseed itself annually. It makes a pretty ground cover.

4/8/2015 12:47:20 PM

Thank you, I just ordered for my dogs, I will send back ASAP, now! Wow, the person that gave me the information is very lucky their dog is not dead! I was going to put on my cat tat is allergic to flea meds, too. It would of been terrible! I thank my God for sending me over to your information. I will spread the word! You have great information. I am a plant lady, but not an herb specialist! Thanks again, and have a blessed day!! Much love

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