Essential oils distilled from common plants are widely sold for use in aromatherapy and massage, and some are taken by mouth as medicines. Though "natural," they are not necessarily harmless. Even essential oils from some herbs commonly used in cooking, such as rosemary and sage, contain concentrated amounts of certain compounds that can cause seizures. Many of these compounds can be harmful when absorbed through the skin, not just when they are taken by mouth. One of these compounds is camphor, also used to repel moths.

One report in a medical journal told of two adults and a child who experienced tonic-clonic seizures for the first time after using some of these oils. The authors of this report (Burkhard et al.) listed 11 herbal essential oils that may cause seizures:

• Eucalyptus (Eucalyptus globulus)
• Fennel (Foeniculum vulgare)
• Hyssop (Hyssopus officinalis)
• Pennyroyal (Mentha pulegium or Hedeoma pulegioides)
• Rosemary (Rosmarinus officinalis)
• Sage (Salvia officinalis)
• Savin (Juniperus sabina)
• Tansy (Tanacetum vulgare)
• Thuja (Thuya occidentalis)
• Turpentine (Pinus species)
• Wormwood (Artemisia absinthium)

Anyone who has epilepsy should avoid the essential oils on this list. Caution with others is also a good idea, not only if you have epilepsy but also if you have other medical disorders or are pregnant. Follow safety instructions about their use, and let your doctor know if you're planning to use any herbal essential oils.

Read more about pennyroyal in the "About Herbs" section of the Memorial Sloan-Kettering Cancer Center website. (If you have not visited the site before, the information on pennyroyal will be preceded by a Disclaimer.)

Some of the information in this article is based on Spinella M: Herbal medicines and epilepsy: The potential for benefit and adverse effects. Epilepsy Behav 2001; 2(6):524-532.

The other article mentioned is Burkhard PR et al: Plant-induced seizures: reappearance of an old problem. J Neurol 1999; 246(8):667-670. (PMID 10460442)

Topic Editor: Steven C. Schachter, M.D.
Last Reviewed:12/15/06