Pennyroyal has been used since ancient times as a cough remedy and digestive aid, as well as a flea repellent. The strong aroma works as a decongestant, helping to remove excess mucus from the lungs; it is therefore useful for coughs. While the dried herb is safe in recommended doses, the oil of the pennyroyal plant should not be ingested, since even small amounts of it are toxic.
WARNING: Present-day practitioners advise against consuming pennyroyal oil in any amount because of its toxicity.
WARNING: Pennyroyal stimulates uterine contractions and should not be used during pregnancy.