Pennyroyal (Mentha pulegium or Hedeoma pulegioides) has a long history of use in traditional herbal medicine, particularly in Europe and North America, as an emmenagogue—a substance believed to stimulate menstrual flow. Historical texts and herbal compendia from as early as the ancient Greeks, including writings by Dioscorides and Pliny the Elder, mention pennyroyal being used to induce menstruation and treat amenorrhea (the absence of menstruation). Folk medicine across various cultures has employed pennyroyal tea or extracts for menstrual disorders, based largely on anecdotal evidence and tradition rather than controlled scientific studies.

However, there is a lack of robust scientific evidence to support the efficacy or safety of pennyroyal for amenorrhea. Modern clinical trials are absent, and the mechanism by which pennyroyal would induce menstruation is not well understood. Furthermore, pennyroyal contains compounds such as pulegone, which are known to be toxic and can cause serious liver and kidney damage, as well as potentially fatal outcomes if consumed in significant amounts. Due to these severe safety concerns, medical professionals strongly advise against its use for any purpose, including the treatment of amenorrhea.

In summary, while the use of pennyroyal for amenorrhea is supported by historical and traditional use, it is not backed by scientific validation, and it poses significant health risks.