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Scientific Name(S): Hedeoma pulegeoides (L) Persoom and Mentha pulegium L. Family: Labiatae

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

The herb Pennyroyal (Mentha pulegium, family Lamiaceae), is a member of the mint genus; an essential oil extracted from it is used in aromatherapy. Pennyroyal has a traditional folk medicine use in inducing abortions and is an abortifacient. These oils are high in pulegone, a highly toxic volatile, which can stimulate uterine activity.

Parts used and where grown

Two similar plants go by the name pennyroyal, one native to Europe (and therefore called European pennyroyal) and one native to North America (and therefore called American pennyroyal). Both are members of the mint family (Lamiaceae) and grow in temperate regions of Europe and the Americas. The flowering tops are used as medicine, but the internal use of the volatile oil should be strictly avoided.

Uses of Pennyroyal:

Pennyroyal is often considered a remedy for indigestion, liver and gallbladder complaints, and skin inflammations, although there is no scientific proof of its effectiveness. It has also been used, again without validation, for gout, colds, and excessive urination. Homeopathic practitioners prescribe it for cramps and respiratory problems.

Side Effects of Pennyroyal:

Used internally in the amounts stated above, pennyroyal is generally safe, though an occasional person may experience intestinal upset or temporary dizziness. Pulegone and its toxic metabolites, particularly menthofuran, damage the liver and nerves if taken in sufficiently large quantities.

Toxicology: Pennyroyal herb teas are generally used without reported side effects (presumably because of low concentration of the oil), but 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.

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. Other symptoms of plant ingestion may also include: Abdominal pain, nausea, vomiting, lethargy, increased blood pressure and increased pulse rate.

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

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. Various metabolite studies are available regarding hepatotoxicity.

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

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. LD50 values for pennyroyal oil have been reported in rats and rabbits. A dog treated for fleas with pennyroyal application suffered vomiting and, despite treatment, died within 48 hours.

Case reports in humans are also widely reported: 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. 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. 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. Another review concluded that pennyroyal oil is toxic as well.

Pennyroyal is contraindicated in pregnancy. It possesses abortifacient actions (because of pulegone content) and irritates the genitourinary tract. 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. The dose at which the herb induces abortion is close to lethal, and in some cases it is lethal. However, one letter does report a pregnancy unaffected by pennyroyal use

Summary: Pennyroyal oil and teas made from the plant continue to find use in a variety of herbal self­treatment practices. Despite this use, these products are potentially toxic to both animal and man and should not be ingested. The principle toxic assaults appear to be on the central nervous system and the liver. The plant is contraindicated in pregnancy because of its abortifacient actions.

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