American pennyroyal

In the early 20th century, it was used "in domestic medicine, in the form of a warm infusion, to promote perspiration and as an emmenagogue." Upon ingestion, one of its components, pulegone, metabolizes into hepatotoxic metabolites that depending on dosage can lead to organ failure, seizures, and death. In the 19th century it was recommended for flea control: "Sprigs of wild myrtle, or penny-royal, or small flat camphor-bags dispersed about your under-clothes, and conveniently fastened, will keep fleas from molesting your person during the day. At night, let penny-royal be scattered over the bed-covers, and laid under the pillows and bolster; strewing a large quantity between the sacking and the matrass. Wash yourself before going to bed in water that has had essence of pennyroyal mixed with it." In contemporary usage, it is frequently recommended as low growing ground cover with insect repellent properties, especially against ticks, fleas, and mosquitoes.

The name pulegioides is derived from the Latin pulegium, and means "like pennyroyal", in reference to European pennyroyal (Mentha pulegium). The name pulegium was given to European pennyroyal by Pliny the Elder in the first century CE, for its use in repelling fleas (pulex, plural pulices) when it was spread on floors.