Pennyroyal is the common name for two different plants, the American Hedeoma pulegioides and European Mentha pulegium. Both plants are in the family Lamiaceae, or mint, which includes a wide assortment of plants which are useful medicinally and for cooking. Pennyroyal, however, contains a toxin called pulegone, which is extremely dangerous for the liver and kidneys. Despite folklore surrounding pennyroyal's potential medical applications, it is not safe to ingest, especially in the form of essential oil.
Both pennyroyal plants have small opposite oblate leaves on long stems which are capped with blue to purple flowers. European pennyroyal has a more trailing growth habit, while American pennyroyal tends to grow upright. Both plants have a strong and distinctive oder, and can be used fresh, dried, or pressed for the essential oil, which is potent and very pungent. The plant is often used as an herbaceous border, especially in gardens for the blind, as the strong scent helps them find the borders of flower beds.
Although pennyroyal is not safe to ingest, it does have potentially useful applications. Pennyroyal is a highly effective insect repellent, and is often included in commercial products designed to deter insects. Collars made from dried pennyroyal can be used on pets to naturally reduce fleas, and pennyroyal extract can also be applied to pet collars, bedding, and used generally around the house. The pungent odor of pennyroyal will discourage a number of members of the insect community.
Pennyroyal leaves can also be used to make a refreshing skin wash, although the essential oil should not be used directly on the skin. People who are pregnant or have liver sensitivities should avoid pennyroyal altogether, as it can be very dangerous for them. Although some herbalists say that pennyroyal is safe to drink for digestive complaints and menstrual issues, other herbs are far safer for this application.
In all cases, a doctor should be consulted before taking herbs. For digestive problems, other members of the mint family are very soothing for the stomach, such as peppermint and spearmint. Black cohosh, yarrow, fennel, ginger, and sage may be taken to make menstrual cycles more regular and less painful. Pregnant women should be especially careful about which herbs they take.
Popular legend also claims that pennyroyal is an effective abortifacient. Unfortunately, women have died from self-administrations of pennyroyal, the essential oil in particular. If you are facing an unwanted pregnancy, please seek professional help and counseling.