American pennyroyal (Hedeoma pulegioides L.), European pennyroyal (Mentha pulegium L.)
Natural Standard Bottom Line Monograph, Copyright © 2013 (www.naturalstandard.com). Commercial distribution prohibited. This monograph is intended for informational purposes only, and should not be interpreted as specific medical advice. You should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.
While some complementary and alternative techniques have been studied scientifically, high-quality data regarding safety, effectiveness, and mechanism of action are limited or controversial for most therapies. Whenever possible, it is recommended that practitioners be licensed by a recognized professional organization that adheres to clearly published standards. In addition, before starting a new technique or engaging a practitioner, it is recommended that patients speak with their primary healthcare provider(s). Potential benefits, risks (including financial costs), and alternatives should be carefully considered. The below monograph is designed to provide historical background and an overview of clinically-oriented research, and neither advocates for or against the use of a particular therapy.
Aloe herbal horse spray, brotherwort, chasse-puces, churchwort, Cunila pulegioides, dictamne de Virginie, European pennyroyal, flea mint, fleabane, fretillet, Hedeoma phlebitides, herbal horsespray, herbe aux puces, herbe de Saint-Laurent, Labiatae (family), la menthe pouliot (French), Lamiacea (family), Lurk-in-the-Ditch, Melissa pulegioides, mentha pouillot, Miracle Coat spray-on dog shampoo, mock pennyroyal, mosquito plant, Old World pennyroyal, pennyroyal essential oil, petit baume, piliolerial, poley, pouliot royal, pudding herb, pudding grass, pulegium, pulegium oil, Pulegium regium, Pulegium vulgare, pulioll-royall, run-by-the-ground, squaw balm, squawmint, stinking balm, tickweed.
The essential oil of pennyroyal is considered toxic. Death has been reported after the consumption of small amounts. A characteristic noted in most cases of pennyroyal overdose is a strong minty smell on the patient's breath.
A possible role for N-acetylcysteine (NAC) in the management of pennyroyal overdose has been suggested. However, this application has not been confirmed by animal or human studies.
The essential oil of pennyroyal may act as an emmenagogue (menstrual flow stimulant) and induce abortion. However, it may do so at lethal or near-lethal doses, making this action unpredictable and dangerous. Future research to determine the safety and efficacy of the less toxic parts of the pennyroyal plant on the menstrual cycle is needed before a recommendation can be made.
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Abortifacient (uterus contraction stimulant/abortion inducer)
Folkloric use and several human case reports describe the use of the essential oil of pennyroyal to cause abortion. However, it may do so at deadly or toxic doses, making this an unpredictable and dangerous use.
Menstrual flow stimulant (emmenagogue)
Folkloric use and several human case reports describe the use of the essential oil of pennyroyal as an emmenagogue (menstrual flow stimulant). However, it may do so at lethal or near-lethal doses, making this action unpredictable and dangerous.
*Key to grades:A: Strong scientific evidence for this use; B: Good scientific evidence for this use; C: Unclear scientific evidence for this use; D: Fair scientific evidence against this use (it may not work); F: Strong scientific evidence against this use (it likely does not work).
The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious and should be evaluated by a qualified health care professional.
Acaricidal (lethal to mites), acne, antiseptic, anti-spasm, anxiety, asthma, bruises and burns, cancer, chest congestion, colds, colic, cough, cramps, diarrhea, digestion, diuretic (increasing urine flow), dizziness, dysentery, fever, flavoring agent, flea control, flu, fragrance (detergents, perfumes, soaps), fumigant, gallbladder disorders, gas, gout, hallucinations, headache, hysteria, immortality, indigestion, insect repellant, intestinal disorders, itchy eyes, joint problems, kidney disease, leprosy, liver disease, mouth sores, muscle pain, nosebleeds, pneumonia, potpourri, pregnancy, premenstrual syndrome, preparing the uterus for labor, purifier (water, blood), refrigerant, respiratory ailments, sedative, skin ailments (itching, burning, bruising), snake bites (venomous), stimulant, stomach pain, sunstroke, sweating, syncope, toothache, uterine fibroids, whooping cough.
The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.
Adults (over 18 years old)
No safe dose of pennyroyal has been established. Extracts, oils, teas, and infusions have been taken by mouth, but may be toxic. Topical preparations have also been applied to the skin. Pennyroyal has been used as an herbal flea collar for animals by hanging a bag of pennyroyal from a regular collar or using a pennyroyal garland. Safety and effectiveness of these preparations have not been proven.
Children (under 18 years old)
Pennyroyal is not recommended in children due to a lack of scientific study and potential toxicity.
The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Allergic reactions, such as rash, to pennyroyal or to its components, including pulegone, may occur.
Side Effects and Warnings
Pennyroyal herb and volatile oils have been associated with multiple reports of toxicity and adverse effects, including seizures, loss of consciousness, and death. In animals, pennyroyal (taken by mouth or placed on the skin) has been associated with liver, lung, and brain toxicity. Even small amounts of pennyroyal may be associated with death. Cases of human overdose and death have been reported in infants, children, and adults.
Pennyroyal oil toxicity may cause nausea, vomiting, abdominal pain, burning in the throat, difficulty swallowing, diarrhea, excessive sweating, chills, fever, headache, ringing in the ears, dizziness, extreme thirst, muscle spasms, restlessness, tremor, excessive talkativeness, hallucinations, agitation, drowsiness, fatigue, confusion, mania, seizures, organ failure (brain, liver, lung, kidney, heart), altered (low or high) heart rate, altered (low or high) blood pressure, slow breathing, coma, loss of consciousness, and death. Symptoms in pennyroyal overdose may mimic that of acetaminophen (Tylenol®) overdose, and the use of N-acetylcysteine (an antidote used for acetaminophen toxicity) treatment may prove beneficial, although this is not well proven.
Other side effects may include contact dermatitis, rash (when placed on the skin), malaise, lethargy, agitation, abnormal sensations, or change (increase or decrease) in pupil size. There are reports that pennyroyal may cause abortion. Pennyroyal has been used historically as an emmenagogue (menstrual stimulant) and may cause menstrual bleeding. There are reports that large amounts of pennyroyal may be irritating to the urinary tract. Pennyroyal may cause hypoglycemia (low blood sugar), hemolytic anemia (low red blood cell count due to destruction of cells), disseminated intravascular coagulation (widespread abnormal clotting and/or bleeding), and metabolic acidosis.
Pregnancy and Breastfeeding
Pennyroyal should be avoided during pregnancy or breastfeeding, due to the risk of uterine contractions, stimulation of menstruation, and abortion.
Many tinctures contain high levels of alcohol, and should be avoided during pregnancy.
Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy.
Interactions with Drugs
Pennyroyal may interact with hormonal drugs and decrease the effectiveness of fertility agents. Pennyroyal has been reported to cause uterine contractions, stimulation of menstruation, and abortion.
In theory, the toxicity of pennyroyal may be increased when combined with acetaminophen (Tylenol®). Pennyroyal may lower glutathione (a liver substance), which may increase the risk of acetaminophen toxicity. Pennyroyal may increase the risk of liver damage caused by other drugs.
Pennyroyal may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of these drugs may be increased in the blood, and may cause increased effects or potentially serious adverse reactions. Patients using any medications should check the package insert and speak with a healthcare provider, including a pharmacist, about possible interactions.
Pennyroyal may lower blood sugar levels. Caution is advised when using medications that may also lower blood sugar. Patients taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare provider. Medication adjustments may be necessary.
Pennyroyal may have antihistamine effects and may cause increased effects if combined with drugs that have antihistamine action, such as diphenhydramine (Benadryl®), fexofenadine (Allegra®), or loratidine (Claritin®).
Many tinctures contain high levels of alcohol and may cause nausea or vomiting when taken with metronidazole (Flagyl®) or disulfiram (Antabuse®).
Pennyroyal may interact with drugs that lower the seizure threshold; use cautiously.
Interactions with Herbs and Dietary Supplements
Pennyroyal may increase the risk of liver damage when combined with some herbs or supplements, such as kava.
Pennyroyal has been found to inhibit the absorption of iron in meals.
Pennyroyal may interfere with the way the body processes certain herbs or supplements using the liver's "cytochrome P450" enzyme system. As a result, the levels of these herbs or supplements may be increased in the blood and may cause increased effects or potentially serious adverse reactions. It may also alter the effects that other herbs or supplements possibly have on the P450 system, such as St. John's wort.
Pennyroyal may lower blood sugar levels. Caution is advised when using herbs or supplements that may also lower blood sugar, such as American ginseng.
Pennyroyal and black cohosh have been taken together to induce abortion, and this combination has been associated with toxicity and death.
Pennyroyal and blue cohosh have traditionally been taken together to normalize the menstrual cycle in women. In theory, the combination of the two herbs may act together to increase menstrual flow. Notably, blue cohosh has been associated with multiple dangerous effects including stroke.
Severe psychotic episodes and seizures have been reported in a young pregnant woman after ingesting an unknown dose of pennyroyal and "Widow Welch's Female Pills," a combination of ferrous sulfate, sulfur, licorice (Glycyrrhiza glabra), and turmeric (Curcuma longa). The exact cause is unknown.
This information is based on a systematic review of scientific literature edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).
Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.
Anderson IB, Nelson SD, Blanc PD. Pennyroyal metabolites in human poisoning. Ann Intern Med 1997;126(3):250-251.
Anderson IB, Mullen WH, Meeker JE, et al. Pennyroyal toxicity: measurement of toxic metabolite levels in two cases and review of the literature. Ann Intern Med 4-15-1996;124(8):726-734. View Abstract
Bakerink JA, Gospe SM Jr, Dimand RJ, et al. Multiple organ failure after ingestion of pennyroyal oil from herbal tea in two infants. Pediatrics 1996;98(5):944-947. View Abstract
Black DR. Pregnancy unaffected by pennyroyal usage. J Am Osteopath Assoc 1985;85(5):282. View Abstract
Buechel DW, Haverlah VC, Gardner ME. Pennyroyal oil ingestion: report of a case. J Am Osteopath Assoc 1983;82(10):793-794.
Carmichael PG. Pennyroyal metabolites in human poisoning. Ann Intern Med 2-1-1997;126(3):250-251. View Abstract
Ciganda C, Laborde A. Herbal infusions used for induced abortion. J Toxicol Clin Toxicol 2003;41(3):235-239. View Abstract
Conway GA, Slocumb JC. Plants used as abortifacients and emmenagogues by Spanish New Mexicans. J Ethnopharmacol 1979;1(3):241-261. View Abstract
Giorgi DF, Lobel D, Morasco R, et al. N-acetylcysteine for pennyroyal oil toxicity. Vet Human Toxicol 1994;36(4):358.
Gordon WP, Huitric AC, Seth CL, et al. The metabolism of the abortifacient terpene, (R)-(+)-pulegone, to a proximate toxin, menthofuran. Drug Metab Dispos 1987;15(5):589-594. View Abstract
Khojasteh-Bakht SC, Chen W, Koenigs LL, et al. Metabolism of (R)-(+)-pulegone and (R)-(+)-menthofuran by human liver cytochrome P-450s: evidence for formation of a furan epoxide. Drug Metab Dispos 1999;27(5):574-580. View Abstract
Mack RB. "Boldly they rode ... into the mouth of hell." Pennyroyal oil toxicity. NC Med J 1997;58(6):456-457. View Abstract
Martins HM, Martins ML, Dias MI, et al. Evaluation of microbiological quality of medicinal plants used in natural infusions. Int J Food Microbiol 8-15-2001;68(1-2):149-153. View Abstract
Mazur LJ, De Ybarrondo L, Miller J, et al. Use of alternative and complementary therapies for pediatric asthma. Tex Med 2001;97(6):64-68. View Abstract
Sullivan JB Jr, Rumack BH, Thomas H Jr, et al. Pennyroyal oil poisoning and hepatotoxicity. JAMA 12-28-1979;242(26):2873-2874. View Abstract
Copyright © 2013 Natural Standard (www.naturalstandard.com)
The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.
March 22, 2017