Aug 19, 2002: What is the toxicity of Pennyroyal?

I hope you enjoyed your time during the summer break and the hiatus from Question of the Week.  I spent one week at the beach, one week in Mexico building houses, and one weekend whitewater rafting with two adolescent males.  There was not one dull moment.

Before the interlude, we were discussing herbal remedies.  An herb is defined as a plant, which is used for its medicinal properties.  Not regulated by the FDA, herbs are regulated by the Dietary Supplement Health & Education Act of 1994 (DHSEA).  Dietary Supplements includes vitamins, minerals, herbs, amino acids, and other dietary substances.  The Secretary of HHS on an emergency basis can remove these products if it is deemed they are causing “imminent hazard to public health or safety.” 

In Hispanic and other cultures, minor ailments and colic in infants and children are treated with teas derived from boiled leaves and a variety of mint plants.  Most mint plants are nontoxic, but mint plants that contain the toxic oil pennyroyal may be mistakenly used.  This herbal is available as oil, tablets, tea, leaves, and essence of pennyroyal preparation.  Herbalists use pennyroyal as an abortifacient.  

The main constituent of pennyroyal oil is pulegone that is oxidized by the hepatic cytochrome P-450 to menthofuran, a toxic metabolite.  The parent compound and the metabolite deplete glutathione and cause hepatic injury similar to that caused by acetaminophen.  Within hours of ingestion, GI upset and CNS toxicity including seizures may occur.  Fulminant hepatic failure, acute renal failure, coagulopathy, metabolic acidosis, and GI hemorrhage may follow.  Ingestion of less than 10 cc of the oil results in mild toxicity while greater than 15 cc may be fatal. 

The treatment is supportive.  Early use of N-acetylcysteine should be considered in humans, although animal studies have not demonstrated that it prevents pulegone-induced hepatocellular damage.

As always, if there are any questions, call the MTPC.

I am interested in any questions that you would like answered in “Question of the Week.”  Please e-mail me with any suggestions at

Donna Seger, M.D.
Medical Director
Middle Tennessee Poison Center