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Medically reviewed on June 13, 2018

Scientific Name(s): Hedeoma pulegioides (L.) Persoon and Mentha pulegium L. Family: Lamiaceae (mints)

Common Name(s): American pennyroyal , squawmint , mosquito plant , pudding grass


See also: Embeline

Pennyroyal has been used as an insect repellent, antiseptic, fragrance, flavoring, as an emmenagogue, carminative, stimulant, antispasmodic and for bowel disorders, skin eruptions and pneumonia.


Pennyroyal usually is used as the volatile oil as an abortifacient. Because of severe toxicity at doses of 5 g, it should not be used.


No longer considered safe.


Documented adverse effects. Avoid use. Abortifacient, hepatotoxic, and neurotoxic.


None well documented.

Adverse Reactions

Pennyroyal can cause abdominal pain, nausea, vomiting, lethargy, increased blood pressure and increased pulse rate, and dermatitis. In tea form, small amounts have been used without reported side effects.


In large portions, pennyroyal can cause abortion, irreversible renal damage, severe liver damage and death. A small amount of oil can produce delirium, unconsciousness, shock, seizures and auditory and visual hallucinations.


Both plants are members of the mint family and both are referred to as pennyroyal. H. pulegioides (American pennyroyal) grows in woods through most of the northern and eastern United States and Canada while M. pulegium is found in parts of Europe. Pennyroyal is a perennial, creeping herb that possesses small, lilac flowers at the stem ends. It can grow to be 30 to 50 cm in height. The leaves are grayish green and, like other mint family members, are very aromatic. 1 , 2


Pennyroyal has been recorded in history as far back as the 1st century AD, where it was mentioned by Roman naturalist Pliny and Greek physician Dioscorides. In the 17th century, English herbalist Nicholas Culpeper wrote about some uses for the plant including its role in women's ailments, venomous bites and digestion. European settlers used the plant for respiratory ailments, mouth sores and female disorders. 1 The plant's oil has been used as a flea-killing bath, hence the name pulegioides (from the Latin word meaning flea), and has been used externally as a rubefacient. In addition, the oil has found frequent use among natural health advocates as an abortifacient and as a means of inducing delayed menses. The oil and infusions of the leaves have been used in the treatment of weakness and stomach pains. 3


The leaves and flowering tops are the source of pennyroyal oil, which is found in a concentration of 1% to 2% depending on the genus. The oil contains 80% to 92% of the cyclohexanone pulegone. 4 , 5 Other constituents include methone, iso-methone, octanol, piperitenone, pinene, limonene, dipentene and formic, acetic, butyric, and salicylic acids. 6 , 7

Quantitative determination of pulegone from Chilean M. pulegium oil has been performed. 8 Using mass spectrometry, the biliary metabolites, glucuronide, and glutathione conjugates of pulegone have been detected. 9

Uses and Pharmacology

Pennyroyal has been used as an insect repellent and antiseptic. 1 , 2 , 6 , 7 It has been employed as a flavoring agent for food and spice 7 and also as a fragrance in detergents, perfumes and soaps. 2 , 7

The plant has been reported to be of use as an emmenagogue to induce menstruation. It has also been used as a carminative, stimulant and antispasmodic, and for bowel disorders, skin eruptions, pneumonia and other uses. 1 , 2 , 6 , 7


Pennyroyal usually is used as the volatile oil as an abortifacient. Because of severe toxicity at doses of 5 g, it should not be used. 10


Documented adverse effects. Avoid use. Abortifacient, hepatotoxic, and neurotoxic. 11 , 12 , 13


None well documented.

Adverse Reactions

Pennyroyal herb teas are generally used without reported side effects, presumably because of low concentration of the oil. 6


Toxicity for pennyroyal oil is well recognized, with many reports of adverse events and fatalities documented.

American or European pennyroyal can cause dermatitis and, in large doses, abortion, irreversible renal damage, severe liver damage and death. A teaspoonful of the oil can produce delirium, unconsciousness and shock. 7

One case of pennyroyal oil ingestion resulted in generalized seizures and auditory and visual hallucinations following the ingestion of less than 1 teaspoonful (5 ml) of the oil; the patient recovered uneventfully. 14 Other symptoms of plant ingestion may also include abdominal pain, nausea, vomiting, lethargy, increased blood pressure and increased pulse rate. 6

The major component, pulegone, is oxidized by hepatic cytochrome P450 to the hepatotoxic compound menthofuran. 15 Pulegone, or a metabolite, is also responsible for neurotoxicity and destruction of bronchiolar epithelial cells. 5 , 16

Pulegone extensively depletes glutathione in the liver, and its metabolites are detoxified by the presence of glutathione in the liver. Hepatic toxicity has been prevented by the early administration of acetylcysteine following ingestion of pennyroyal oil. 17 Various metabolite studies are available regarding hepatotoxicity. 18 , 19

Pennyroyal toxicity in animals has been documented; intraperitoneal injections of pulegone in mice caused extensive liver injury. 20

Rats given oral doses of pulegone for 28 days (80 or 160 mg/kg/day) developed encephalopathic changes characterized by cyst-like spaces in the cerebellum without concomitant demyelination. This resembles the neuropathy induced in rats by administration of hexachlorophene. 21 LD 50 values for pennyroyal oil have been reported in rats and rabbits. 6 A dog treated for fleas with pennyroyal application suffered vomiting and, despite treatment, died within 48 hours. 22

Case reports in humans are also widespread: One woman who ingested up to 30 ml of the oil experienced abdominal cramps, nausea, vomiting and alternating lethargy and agitation. She later exhibited loss of renal function, hepatotoxicity and evidence of disseminated intravascular coagulation. She died 7 days after ingesting the oil. Another woman ingested 10 ml of the oil and only experienced dizziness. 10 Two infants (8 weeks of age and 6 months of age) who ingested mint tea containing pennyroyal oil developed hepatic and neurologic injury. One infant died, the other suffered hepatic dysfunction and severe epileptic encephalopathy. 23 A review of 18 previous cases reported moderate to severe toxicity in patients exposed to at least 10 ml of the oil, concluding that pennyroyal continues to be an herbal toxin of concern to public health. 24 Another review concluded that pennyroyal oil is toxic as well. 25

Pennyroyal is contraindicated in pregnancy. It possesses abortifacient actions because of pulegone content and irritates the genitourinary tract. 6 The abortifacient effect of the oil is thought to be caused by irritation of the uterus with subsequent uterine contraction. Its action is unpredictable and dangerous. 26 The dose at which the herb induces abortion is close to lethal, and in some cases it is lethal. 2 , 7 However, one letter reports a pregnancy unaffected by pennyroyal use. 27


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