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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 US and Canada while M. pulegium is found in parts of Europe. Pennyroyal is a perennial, creeping herb with small, lilac flowers at the stem ends. The leaves are grayish green and, like other mint family members, very aromatic.

Scientific Name(s)

Hedeoma pulegioides, Mentha pulegium

Common Name(s)

Pennyroyal also is known as American pennyroyal, squawmint, mosquito plant, and pudding grass.

What is it used for?

Traditional/Ethnobotanical uses

Pennyroyal has been recorded in history as far back as the first century AD, when 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. 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 (counter-irritant). In addition, the oil has found frequent use among natural health advocates as an abortive 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.

Miscellaneous uses

Pennyroyal has been used as an insect repellent, antiseptic, fragrance, flavoring, as an emmenagogue (to stimulate menstrual flow), carminative, stimulant, antispasmodic and for bowel disorders, skin eruptions, and pneumonia. The abortive 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. Pennyroyal is not considered safe for ingestion for any use.

What is the recommended dosage?

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


No longer considered safe.


Documented adverse effects. Avoid use. Abortive, hepatotoxic (toxic to liver), and neurotoxic.


None well documented.

Side Effects

Pennyroyal may 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.


1. Pennyroyal. Review of Natural Products. factsandcomparisons4.0 [online]. 2005. Available from Wolters Kluwer Health, Inc. Accessed April 19, 2007.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Health Benefits

Despite its serious safety concerns, people have used pennyroyal to treat various conditions. But there is a lack of clinical research evidence to back up the claims for safe and effective use of pennyroyal.

Pennyroyal is sometimes applied to the skin (topical use) for gout. Ingestion is not recommended due to toxicity concerns, but some people have used the leaves or an infusion (tea) for complaints such as breathing problems, stomach pains, or gas.

The traditional uses of pennyroyal include regulating menstrual periods, inducing abortion, controlling muscle spasms, inducing sweating, increasing urine production, and to kill bacteria on the skin. As well, it was sometimes used against tuberculosis or smallpox.

Pennyroyal has been used as a pest repellant and insecticide to keep fleas away from pets and humans and to repel mosquitos, gnats, and other pests. If the plant is used as an insecticide or repellant, the crushed leaves should be used instead of the oil, because the leaves are much less toxic than the oil. 

Some flea collars have pennyroyal oil. However, experts advise that pennyroyal oil should never be used topically (on the skin) on humans or animals, because of its toxic properties.

In addition to the fact that pennyroyal has been linked to severe side effects (such as irreversible kidney or liver damage, organ failure, and death)1 there is not enough clinical research evidence to support its effectiveness in treating any type of illness.

The exact way that pennyroyal works to induce abortions, or to provide purported health benefits, is unknown. 

Possible Side Effects

Special Warning

There have been many reports of toxicity from pennyroyal oil—usually within only a few hours of use.

Just one tablespoon (15 ml) of pennyroyal oil has been known to cause seizures, coma, severe liver and kidney damage, and cardiopulmonary collapse—leading to failure of vital organs and death.2

Early signs and symptoms of pennyroyal oil poisoning may include:

  1. Nausea and vomiting
  2. Agitation and confusion
  3. Abdominal pain

More severe signs and symptoms of pennyroyal toxicity may include:

  1. Cardiovascular collapse
  2. Disseminated intravascular coagulation: A condition in which small blood clots develop throughout the bloodstream, this results in excessive bleeding (as a result of the body’s clotting factors being used up), and can be fatal.
  3. Acute liver injury
  4. Early liver failure
  5. Death

When a person is diagnosed with pennyroyal oil poisoning, unfortunately, there is not an antidote available,3 thus, prevention and early intervention are important.

One treatment that has been used is glutathionine (amino acids), which may slow down the toxic effects of pulegone, but this is only available with early intervention. Also, there is a lack of evidence as to the safety and effectiveness of gluthathionine for treating pennyroyal poisoning.

Side Effects

Side effects from the use of pennyroyal may include:

  1. Dermatitis (itchy skin)
  2. Nausea
  3. Vomiting
  4. Increase in blood pressure
  5. Increase in pulse rate
  6. Hallucinations
  7. Seizures
  8. Liver toxicity
  9. Nerve toxicity
  10. Delirium
  11. Shock


Pennyroyal is no longer recommended for any type of use, but it is particularly unsafe in some conditions, including:

  1. Kidney disease: The oil in pennyroyal may irritate the kidneys, worsening existing kidney disorders
  2. Pregnancy: Pennyroyal leaf tea (or oil) can start menstruation; this could abort the pregnancy
  3. Breastfeeding: Pennyroyal is not safe for breastfed infants
  4. Children: Pennyroyal is unsafe for children; there are reports of two infants who developed severe liver and nervous system problems after taking pennyroyal, and one of the infants died.
  5. Liver disease: Pennyroyal is known to cause liver damage and it may worsen an existing liver condition

Working with products made of pennyroyal oil may cause health problems even if pennyroyal products are not ingested. This is because the volatile oil can be absorbed through the skin, resulting in serious side effects.

Selection, Preparation, and Storage

Because of the proven toxic effects of pennyroyal, there are no recommendations on how to purchase the herbal supplement or the essential oil form of the plant.

There is no safe dosage of pennyroyal, the plant has been known to be severely toxic at doses as small as 5 grams.


The part of the pennyroyal plant that is used is the aerial portion, harvesting is optimal right before the flowering stage of the plant. Pennyroyal leaves are sometimes used to make a tea.2 Not enough is known about the safe use of pennyroyal leaf to consider ingestion (in any form, including tea).

There is also an extract from. Pennyroyal oil is available, but it is not recommended for internal use.

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