Pulegone

• monoterpene present in essential oils (see: silly aromatherapy nonsense) from plants of the Lamiaceae (mint) family
• particularly high levels are found in the European (Mentha pulegium) and American (Hedeoma pulegioides) varieties of pennyroyal
• has an odour similar to peppermint and camphor
• used as a flavouring agent, an ingredient in perfumes, and a flea repellent (so perfect for hippies)
• pennyroyal tea (and oil) is/was used in traditional folk medicine to promote menstruation and as an abortifacient to initiate self-abortion
• there is a crappy Nirvana song about this (bring it, haters!)
• there is no scientific evidence available to support its efficacy in this regard (read: this is a bad idea)
• ingestion of high doses has been reported to cause organ toxicity and death
• pulegone and one of its metabolites (menthofuran) are bioactivated by liver enzymes to reactive intermediates that permanently bind to cellular proteins and cause liver damage

Anderson IB et al. Pennyroyal toxicity: measurement of toxic metabolite levels in two cases and review of the literature. Ann Intern Med. 1996 Apr 15;124(8):726-34.
http://en.wikipedia.org/wiki/Pulegone