Herb-Drug Interactions: Pennyroyal

Mentha pulegium L. or Hedeoma pulegioides Pers. (Lamiaceae)

Synonym(s) and related species

Mentha pulegium L.: European pennyroyal. Mentha pulegioides Dumort.Fl.Belg., Pulegium erectum Mill., Pulegium parviflorum (Req.) Samp., Pulegium vulgare Mill.

Hedeoma pulegioides Pers.: American pennyroyal, Squaw mint.

Melissa pulegioides L.


The main constituent of pennyroyal is the toxic volatile oil pulegone. Other components include menthone, isomenthone, piperitone, neomenthol, 2-octanol, camphene and limonene. Pennyroyal also contains polyphenolic acids and flavonoids.

Use and indications

Traditionally, pennyroyal has been used for dyspepsia, colds, skin eruptions and delayed menstruation, and it is reported to be an effective antibacterial and antifungal. It is also believed to be carminative, abortifacient and diaphoretic and it has been used as an insect repellent. The oil from pennyroyal (pulegium oil) is toxic to the liver, kidneys and nerves, and its use is generally considered unsafe.


The toxic effects of pennyroyal are thought to be principally due to metabolites of pulegone such as menthofuran. The metabolism to toxic metabolites and then inactivation has been shown to be subject to cytochrome P450 isoenzyme-mediated metabolism. Preclinical experiments are inconclusive as to which isoenzyme is principally involved. One study using human isoenzymes found that CYP2E1 is the main metaboliser of pulegone and its metabolite menthofuran, with CYP1A2, CYP2C19 and CYP2A6 also contributing to some extent. In contrast, a study in mice found that CYP1A2 is the major metabolising enzyme with CYP2E1 playing a lesser role.

Note that peppermint, contains only small amounts of pulegone.

Interactions overview

Pennyroyal may reduce the absorption of iron compounds.

Pennyroyal + Food

No interactions found.

Pennyroyal + Herbal medicines

I No interactions found.

Pennyroyal + Iron compounds

Pennyroyal tea reduces iron absorption similarly to conventional tea.

Clinical evidence

In a study in 9 healthy subjects, a 275 mL serving of pennyroyal tea reduced the absorption of iron in a 50 g bread roll by about 70%. The tea was prepared by adding 300 mL of boiling water to 3 g of the herbal tea, then infusing for 10 minutes before straining and serving. In this study, the inhibitory effect of pennyroyal tea on iron absorption was modestly less than that of black tea (Assam tea, Camellia sinensis L.), which is known to inhibit iron absorption.Consider also, Tea + Iron compounds.

Experimental evidence

No relevant data found.


The polyphenols in pennyroyal may bind to iron in the intestine and influence its absorption.

Importance and management

The clinical impact of this interaction is not fully known, but be aware that some herbal teas such as pennyroyal reduce iron absorption similarly to conventional tea, which is not generally considered to be a suitable drink for babies and children, because of its effects on iron absorption. Furthermore, the safety of pennyroyal tea is not established, and there are concerns about the toxicity of its major volatile oil, pulegone.