Pennyroyal oil is somewhat controversial due to it supposed ability to induce menstruation and labour. However, no evidence suggests that this is accurate other than anecdotal reports. What is true is that the oil contains the toxic compound Pulegone which can be fatal if ingested in sufficient quantities. As such this oil must not be consumed and should not be used topically during pregnancy.
Nature/Essence – Invigorating & Cooling
Today the most common use for Pennyroyal is as a natural flea repellant for dogs and horses, but not cats (it will interfere with a cats nervous system). It is commonly used in combination with Lemon Scented Eucalyptus (Eucalyptus citriodora) and Tea Tree (Melaleuca alternifolia) for this purpose.