Peppermint oil is obtained by pressure steam distillation of the Mentha piperita plant. Currently, peppermint oil is used in the treatment of irritable bowel syndrome (IBS) and dyspepsia (heartburn). The active ingredient in peppermint oil is methanol. It is reported to relaxe the muscles of the small intestine, thereby relieving muscle spasms associated with IBS. A recent study reviewed 5 research trials that evaluated the effectiveness of peppermint oil in the treatment of IBS. The trials showed that doses of peppermint oil ranging from 0.2 mL to 0.4 mL taken three times daily significantly improved IBS symptoms. Side effects were mild and included heartburn, nausea, and vomiting. In another trial, peppermint oil also reduced pain from heartburn when used in combination with caraway oil. Enteric coated peppermint oil capsules should not be taken with drugs that lower the pH of the stomach. Peppermint oil also increases levels of the prescription drug cyclosporine. Oral supplements of peppermint oil should not be used by women who are pregnant or breast feeding.