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American pennyroyal essential oil is obtained from H. pulegioides by steam distillation in approximately 0.6 to 1.0% yields. It is a pale-yellow liquid with a much harsher mint-like odor, more bitter and herbaceous than the European oil. The taste is sharp, bitter and slightly burning.

Both plants are members of the mint family and are referred to as pennyroyal. This is an herbaceous pubescent plant having characteristic thin, fusiform, fibrillose roots; numerous prostrate stems; opposite, short-petiolate, oblong or ovate, dentate leaves; pinkish flowers arranged in axillary cymose tops; ovoidal, smooth fruits. M. pulegium L. grows wild in Spain, Morocco and other Mediterranean countries. H. pulegioides (L.) Pers. belongs to the same botanical family, but grows exclusively in the United States. The U.S. variety yields on distillation an essential oil with a more acrid, distinct mint odor; it is also less rich in pulegone than the European essential oil. The part used is the fresh or partially dried flowering plant; pennyroyal has an aromatic, mint-like odor and a bitter taste.

It is a pale-yellow-to-yellow, aromatic oil.

Found in the plant Mentha pulegium L. (Fam. Labiatae).

Fragrance component in soaps, perfumes; flavoring agent; insect repellent.

Extractives and their physically modified derivatives. Hedeoma pulegioides, Labiatae.

By steam distillation of the fresh or partly dried plant Mentha pulegium L.

Depending on the genus, the leaves and flowering tops yield 1 to 2% pennyroyal oil. The oil contains 80 to 96% of the cyclohexanone and pulegone. Other constituents of pennyroyal oil include methone, pinene, octanol, piperitenone, limonene, iso-methone and acetic, butyric, salicylic and other acids.

The main constituents include l-alpha-pinene, l-limonene, dipentene, 1-methy-l3-cyclo-hexanone, l-menthone, d-isomenthone, acids (formic, acetic, butyric, salicylic) and a phenol. Pulegone, the main constituent, is present in lower levels than in the European distilled oil.

Pennyroyal (Hedeoma pulegeoides, Mentha pulegium) is an example of an extremely toxic herb. The plant is a member of the mint family, Labiatae. The dried leaves and flowering tops of the plant contain from 16% to 30% oil, consisting of the monoterpene pulegone. The oil also contains tannins, α- and β-pinenes, other terpenes, long-chain alcohols, piperitenones, and paraffin.
The toxicity of pennyroyal is believed to be a result of the pulegone in the oil. Cytochrome P450 catalyzes the metabolism of pulegone to yield the toxic metabolite menthofuran. Possibly, some of the other terpenes undergo oxidation to active metabolites as well. Menthofuran, metabolites of other terpenes, and pulegone itself deplete hepatic glutathione, resulting in liver failure. This mechanistic hypothesis is supported by the fact that administration of acetylcysteine reverses the toxicity.
Pennyroyal has been used as an abortifacient since the time of Pliny the Elder, an insect repellent (the terpenes in the oil have citronellal-like properties), an aid to induce menstruation, and a treatment for the symptoms of premenstrual syndrome. It has also been used as a flea repellent on dogs and cats. When used as an abortifacient, the drug often causes liver failure and hemorrhage, leading to death. Pennyroyal is sometimes used with black cohosh to accelerate the abortifacient effect. Coma and death have been reported. Pennyroyal is an example of an herb that has no safe uses.