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Herb library · Herb · Mentha pulegium (European); Hedeoma pulegioides (American)

Pennyroyal

A small mint used for centuries to bring on menstrual periods and end pregnancies. Its oil is highly toxic: taken by mouth it has caused liver failure and deaths, including in infants given home-brewed mint tea. There is no research showing any benefit.

Serious warning

Pennyroyal oil taken by mouth is highly toxic and has caused liver failure and deaths (NIH LiverTox). Two infants given mint tea made from plants containing pennyroyal developed liver failure and brain injury, and one died (Pediatrics, 1996).

Traditional use

Both the European plant and the unrelated American one were used as a warm tea to bring on sweating and menstrual periods, for colds and colic, and as an insect repellent. The oil was widely taken to cause abortion. Spanish New Mexicans have used poleo, a pennyroyal mint, among plants taken to bring on menstruation.

Traditional energetics

What studies show

  • Insufficient

    Any use: there are no studies in people showing a benefit. The research in people consists of poisoning reports: a 1996 review of 18 earlier cases found moderate to severe toxicity in people who took at least 10 mL of the oil.

Be careful of

Cautions

  • PregnancyNever use it in pregnancy. Its long use to cause abortion is exactly how many of the poisonings happened.
  • ConditionNever give pennyroyal or an unidentified homegrown mint tea to a baby or child. In the 1996 infant cases the tea came from mint plants that turned out to contain pennyroyal oil.
  • AmountCase reports link moderate to severe poisoning with as little as 10 mL of the oil; there is no known safe dose to take by mouth.
  • NoteA case of contact dermatitis from European pennyroyal has been reported in a medical journal.
  • Ask a clinicianTalk with a clinician or pharmacist before using this if you take prescription medicines, are pregnant or breastfeeding, or are giving it to a child.

From the old books

What herbals and dispensaries of the past printed. History, in their words.

“It is frequently employed for the purpose of occasioning abortion, but as with all agents of this sort, it is very dangerous.”
Harvey Wickes Felter and John Uri Lloyd, King's American Dispensatory (1905), vol. 2, p. 1361. See the page of King's American Dispensatory, vol. 2, p. 1361 (opens in a new tab) · Read the full passage from King's American Dispensatory, vol. 2, p. 1361

Sources

  1. Pennyroyal Oil (LiverTox: Clinical and Research Information on Drug-Induced Liver Injury) (opens in a new tab) · NIH · read September 25, 2026
  2. Pennyroyal toxicity: measurement of toxic metabolite levels in two cases and review of the literature (1996) (opens in a new tab) · NIH · read September 25, 2026
  3. Multiple organ failure after ingestion of pennyroyal oil from herbal tea in two infants (1996) (opens in a new tab) · NIH · read September 25, 2026
  4. Plants used as abortifacients and emmenagogues by Spanish New Mexicans (1979) (opens in a new tab) · NIH · read September 25, 2026
  5. Mentha pulegium contact dermatitis (2005) (opens in a new tab) · NIH · read September 25, 2026

Reviewed September 25, 2026.