Pennyroyal: Mother Nature’s mixed blessing

Despite being dangerously toxic, Pennyroyal deeply intrigue researchers who are seeking out new possibilities in the pharmacological space.

November 1993. American rock band Nirvana is recording live on MTV Unplugged in New York. Mid-concert, Kurt Cobain sings solo: ‘Sit and drink pennyroyal tea. Distil the life that’s inside of me.’ It is a song about inner turmoil, mortality and termination of pregnancy. In April 1994, Cobain dies by suicide.^1–3

Cobain’s dark take on pennyroyal has history, ancient history. Back in the 5th century BCE, Greek physician Hippocrates prescribed it for birth control and abortion, while his contemporary, Aristophanes, wrote of similar uses in his plays Peace and Lysistrata.^4,5

Into the new millennium, Roman naturalist Pliny and Greek physician Dioscorides promoted the pungent plant’s use and reputation as a potent treatment for women’s ailments, as did the ‘people’s herbalist’ Nicholas Culpeper. He included pennyroyal in his 1653 book, The English Physician.^5–7

As historian John Riddle notes, pennyroyal continued to be used ‘as a birth control agent’ until the 19th century when most Western nations made abortion a criminal offence.⁵

Back then, an essential oil or tea made from the leaves or flowering tops of Mentha pulegium, or its North American twin Hedeoma pulegioides, was also used to treat colds, flu, headaches and even cancers. It also helped keep insects away – ‘flea’ in Latin is ‘pulex’.^8,12

What is pennyroyal?

Pennyroyal is an oil derived from leaves of Mentha pulegium or Hedeoma pulegioides, plants of the mint family Lamiaceae. The plant is found worldwide, including in Australia, but is native to Europe, North Africa and the Middle East. It is perennial, fragrant, with small lilac flowers, and grows to be 30–50 cm tall.^5,9,12

Pennyroyal now

Few modern medicine cabinets contain pennyroyal oil. But any that do should post this warning from Moroccan pharmacists Smail Amtaghri, Miloudia Slaoui and Mohamed Eddouks: ‘Pennyroyal essential oil should never be taken internally because it is highly toxic; even in small doses, it can be fatal.’ ⁹

Those small doses can trigger multiple adverse effects. Seizures, coma and cardiopulmonary collapse have been reported, along with liver and kidney damage and multiorgan failure. It is thought that pennyroyal affects the menstrual cycle and triggers pregnancy loss by irritating the uterus.⁸  There is, however, an upside to pennyroyal’s toxic downside. As Amtaghri and his colleagues note, the plant is a ‘great candidate for contemporary therapeutic usage as it contains a wide variety of biologically active compounds’. These range from terpenoids, alkaloids and tannins to saponins.⁹

But wait, there’s more. Other organic compounds in essential oil extracted from the stem, leaves and flowering tops of pennyroyal occur, literally, in the dozens. Given the plant’s scientific name, it is not surprising that minty-scented pulegone tops the list.^9–11

In fact, it is estimated that pennyroyal oil contains 85% pulegone. The compound is converted by cytochrome P450 to organ-damaging, toxic metabolites like menthofuran.^5,8

Pennyroyal’s promise

Still, led by pulegone, the potential pharmacological applications of pennyroyal’s biologically active compounds are enormous. These include antimicrobial, antioxidant, antihypertensive, antidiabetic, anti-inflammatory, anti-proliferative, antifungal, cytotoxic and anticancer treatments.^9–11 

Antibiotic resistance is rising and new approaches are needed.⁹

Hence, scientists like Amtaghri and his colleagues are slowly and carefully returning to research on pennyroyal while Cobain’s lyrical nod remains a notable part of the herb’s cultural history.

REFERENCES

1. Nirvana. Pennyroyal Tea (Live on MTV unplugged, 1993/unedited). 1993.
   2.    Onion A, Sullivan M, Mullen M, et al. Grunge rock icon Kurt Cobain dies by suicide. This Day in History. 2025.
   3.    Nirvana. Pennyroyal Tea lyrics. Genius. 2024. At: https://genius.com/Nirvana-pennyroyaltea-lyrics
   4.    Riddle JM. Contraception and abortion from the ancient world to the Renaissance. Cambridge (MA): Harvard University Press. 1994
   5.    Riddle JM. Eve’s herbs: a history of contraception and abortion in the West. Cambridge (MA). Harvard University Press. 1997.
   6.    Crowther K. Pennyroyal, mifepristone, and the long history of medication abortions. Nursing Clio. 2023. At: https://nursingclio.org
   7.    Steward D. Nicholas Culpeper: lived 1616–1654. Famous Scientists. 2025.
   8.   Memorial Sloan Kettering Cancer Center.  Pennyroyal: purported benefits, side effects & more. About Herbs. 2022. At: www.mskcc.org/cancer-care/integrative-medicine/herbs/pennyroyal
   9.    Amtaghri S, Slaoui M, Eddouks M. Mentha Pulegium: a plant with several medicinal properties. Endocr Metab Immune Disord Drug Targets 2024;24(3):302–20.
   10.   Xiao-Wu C, Erini SS, Sneed, et al. Herbal bioactivation, molecular targets and the toxicity relevance. Chem Biol Interact 2011;192(3): 161–76.
   11.   El Boukhari R, Fatimi A. Pulegone application trends: exploration of uses based on leading patent applicants. Proceedings. 2024;103(1):89.
   12.   National Institute of Diabetes and Digestive and Kidney Diseases. LiverTox: clinical and research information on drug-induced liver injury. Pennyroyal oil. Bethesda (MD). NIDDK. 2020.