Plant Profiler

American pennyroyal (Mentha pulegium)

American pennyroyal (Mentha pulegium) Image
Synonyms / Common Names / Related Terms
Aloe herbal horse spray, alpha-pinene, American pennyroyal, beta-pinene, brotherwort, chasse-puces, churchwort, Cunila pulegioides, dictamne de Virginie, European pennyroyal, fleabane, flea mint, fretillet, Hedeoma phlebitides, hedeomal, herbal horsespray, herbe aux puces, herbe de Saint-Laurent, Labiatae (family), la menthe pouliot (French), Lamiacae (family), lurk-in-the-ditch, Melissa pulegioides, mentha pouillot, menthone, Miracle Coat spray-on dog shampoo, mock pennyroyal, mosquito plant, Old World pennyroyal, paraffins, pennyroyal essential oil, petit baume, piliolerial, piperitenone, poley, pouliot royal, pudding herb, pudding grass, pulegium, pulegium oil, Pulegium vulgare, pulegone, pulioll-royall, Pulegium regium, run-by-the-ground, squaw balm, squawmint, stinking balm, tannins, terpenes (pulegone), tickweed.

Combination product example: PNC (contains pennyroyal, red raspberry, lobelia, blue cohosh, black cohosh, and blessed thistle).

Mechanism of Action


  • Constituents: Constituents of the aerial parts of pennyroyal that are highly concentrated in the essential oil include hedeomal, tannins, terpenes (pulegone), alpha-pinene, beta-pinene, limonene, 3-octanone, p-cymene, 3-octylacetate, 3-octanol, 1-octen-3-ol, 3-methylcyclohexanone, menthone, piperitenone, and paraffins.
  • Genitourinary effects: Traditionally, pennyroyal has been considered to be an abortifacient. Anecdotal evidence and one case report suggest that the essential oil of pennyroyal may function as an abortifacient and emmenagogue. However, it typically does so at lethal or near-lethal doses, making this action unpredictable, dangerous, and not recommended. Future research to determine the safety and efficacy of the less toxic aerial parts of the pennyroyal plant on the menstrual cycle is needed before a recommendation can be made. The mechanism of action is unclear.
  • Hepatic effects: Pulegone, the constituent terpene of the volatile oil of pennyroyal, has been shown to be toxic to the urinary tract and kidneys.1 Menthofuran is a mammalian metabolite of pulegone and may account for some of the hepatotoxic effects.3,4 Pulegone and menthofuran may deplete cellular glutathione levels, leaving hepatocytes vulnerable to free radical damage.5
  • Neurologic/CNS effects: Based on tradition, pennyroyal essential oil may have epileptogenic properties. Burkhard et al. surveyed the literature and found 11 plants to be powerful convulsants (eucalyptus, fennel, hyssop, pennyroyal, rosemary, sage, savin, tansy, thuja, turpentine, and wormwood), due to their content of highly reactive monoterpene ketones, such as camphor, pinocamphone, thujone, cineole, pulegone, sabinylacetate, and fenchone.6


  • Elimination/half-life: The toxic properties of the pennyroyal constituent pulegone appear to follow first order kinetics.1 In rats given a 150mg/kg intraperitoneal injection of pulegone, a terminal half-life of 2.08 + 0.29 and a Cmax of 7.02 + 1.15mcg/mL was found.7
  • Excretion: Pennyroyal oil is reported to be excreted by the kidney following oral ingestion.8
  • In vivo and in vitro studies suggest that the pennyroyal constituent pulegone diminishes the function of rat liver cytochrome P450 in an irreversible, time-dependent fashion.1 In vitro and in vivo research suggests that the pulegone metabolite menthofuran is a potent inhibitor of human liver CYP2A62, and it may account for a significant degree of pennyroyal's hepatotoxic effects3,4. Pulegone and menthofuran may deplete cellular glutathione levels, leaving hepatocytes vulnerable to free radical damage.5


  1. Madyastha P, Moorthy B, Vaidyanathan CS, and et al. In vivo and in vitro destruction of rat liver cytochrome P-450 by a monoterpene ketone, pulegone. Biochem Biophysl Res Comm 1985;128(2):921-927.
  2. Khojasteh-Bakht, S. C., Koenigs, L. L., Peter, R. M., Trager, W. F., and Nelson, S. D. (R)-(+)-Menthofuran is a potent, mechanism-based inactivator of human liver cytochrome P450 2A6. Drug Metab Dispos  1998;26(7):701-704. 9660853
  3. Gordon, W. P., Huitric, A. C., Seth, C. L., McClanahan, R. H., and Nelson, S. D. The metabolism of the abortifacient terpene, (R)-(+)-pulegone, to a proximate toxin, menthofuran. Drug Metab Dispos  1987;15(5):589-594. 2891472
  4. Thomassen, D., Pearson, P. G., Slattery, J. T., and Nelson, S. D. Partial characterization of biliary metabolites of pulegone by tandem mass spectrometry. Detection of glucuronide, glutathione, and glutathionyl glucuronide conjugates. Drug Metab Dispos  1991;19(5):997-1003. 1686249
  5. Thomassen, D., Slattery, J. T., and Nelson, S. D. Menthofuran-dependent and independent aspects of pulegone hepatotoxicity: roles of glutathione. J Pharmacol Exp Ther  1990;253(2):567-572. 2338648
  6. Burkhard, P. R., Burkhardt, K., Haenggeli, C. A., and Landis, T. Plant-induced seizures: reappearance of an old problem. J Neurol  1999;246(8):667-670. 10460442
  7. Thomassen, D., Slattery, J. T., and Nelson, S. D. Contribution of menthofuran to the hepatotoxicity of pulegone: assessment based on matched area under the curve and on matched time course. J Pharmacol Exp Ther  1988;244(3):825-829. 3252034
  8. Briggs CJ. Pennyroyal: A traditional medicinal herb with toxic potential. Canad Pharm J 1989;122:369-372.

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