By David Kiefer, MD
Dr. Kiefer recently completed a fellowship at the Program in Integrative Medicine, College of Medicine, University of Arizona, Tucson.
This common and flavorful member of the mint family has many well-proven uses that extend beyond simply being the tasty after-dinner candy. Peppermint (Mentha x piperita), in leaf form, essential oil extract, or as its primary purified compound, menthol, has been used in a variety of gastrointestinal, biliary, and upper respiratory conditions in the pharmacopeia of many cultures around the world. In addition, there are now many interesting in vitro and clinical research studies refining what we know about its mechanism of action and clinical availability.
History and Traditional Use
Plants in the mint family, including peppermint (Mentha x piperita) and spearmint (Mentha spicata), have a history of culinary and medicinal use dating back to Greek and Roman times, ancient Egypt, and 13th century Iceland, with general use in Western Europe beginning in the 18th century.1 Peppermint leaf tea was well-known to act as a digestive aid in cases of dyspepsia, to increase bile production, and was used as an inhalant to clear upper respiratory symptoms, as well as to relieve the cough of bronchitis and pneumonia.1,2
Topically, peppermint oil has been used as an analgesic for headache. In more recent times, preparations of the oil are prescribed for systemic use in functional gastrointestinal disorders, intestinal spasm, and irritable bowel syndrome (IBS).
Peppermint is a plant known to many cultures around the world and, as such, has a variety of common names, including brandy mint, lamb mint, Pfefferminze and Katzenkraut (German), mente anglaise and menthe poivrée (French), and menta prima (Italian).1,2.
Botany and Pharmacology
Peppermint is an herbaceous perennial in the genus Mentha, in the family Lamiaceae (also called Labiatae), a family that includes other common aromatic plants such as basil, sage, and oregano. Peppermint has stems that are square in cross-section, a common characteristic of this family. Peppermint is a hybrid of spearmint (Mentha spicata) and water mint (Mentha aquatica), which is expressed with an "x" in its scientific name, Mentha x piperita.
The fresh, above-ground parts of Mentha x piperita are distilled to yield peppermint oil.1 The resulting oil contains numerous compounds, including menthol (35-45%), menthone (15-20%), cineole (6-8%), and other volatile oils.1,3
Irritable Bowel Syndrome
IBS is a clinical entity that includes a group of functional bowel disorders with chronic, intermittent, or continuous abdominal complaints or abnormal bowel habits, which are specifically defined by, most currently, the Rome II Diagnostic Criteria.4 Patients with IBS usually can be described as having one of three IBS sub-groups: constipation-predominant, diarrhea-predominant, or alternating IBS.5 Treatments may be most effective when based on these IBS sub-types.6,7 In like manner, it is important to keep these characteristics in mind when interpreting the research behind the use of peppermint oil in IBS.
Mechanism of Action
The use of peppermint oil in IBS stems from several proposed mechanisms of action. Peppermint oil has been shown to reduce gastric motility8 by directly acting on gut calcium channels to relax gastrointestinal smooth muscle, similar to the actions of dihydropyridine calcium antagonists.9 A recent review of peppermint oil supports in vitro research showing that peppermint oil relaxes animal and human gastrointestinal smooth muscle, and that menthol has two distinct calcium-antagonistic activities.3
Peppermint oil also is known to relax the lower esophageal sphincter, which can lead to symptoms of heartburn after oral administration. For this reason, several manufacturers have developed enteric-coated preparations, delivering the peppermint oil to the small bowel, allowing its effects to focus on the area of the gastrointestinal tract most relevant in cases of IBS. These enteric-coated preparations are those that have been studied for their effects in IBS in the clinical trials discussed below.
Peppermint oil has been used for the treatment of IBS for at least three decades.10,11 Recent reviews have addressed the quality of the current clinical evidence for its therapeutic benefits,3,12 generally concluding that the efficacy of peppermint oil in IBS has not clearly been established. These opinions are based on the few published clinical research trials, notable for their varying results and methodological quality.
For example, in a randomized, double-blind controlled trial in 42 children, enteric-coated peppermint oil capsules (Colpermin® capsules, 0.2 mL [187 mg], three times daily before meals; patients 30-45 kg received 0.1 mL three times daily) significantly reduced abdominal pain in acute IBS, though there was little effect on the other symptoms of IBS.13
This is in agreement with one study of 29 adults that showed enteric-coated peppermint oil (Elanco LOK® capsules, 0.2-0.4 mL three times daily) to be superior to placebo in the treatment of IBS abdominal symptoms,14 but contrary to another trial (n = 41 adults) that found no significant difference between peppermint oil (Colpermin capsules, 0.4 mL [374 mg] three times daily) and placebo for IBS abdominal pain.15 To further complicate assessment, one prospective, randomized, double-blind trial (n = 110) compared enteric-coated peppermint oil (Colpermin capsules, 0.2 mL [187 mg] 3-4 times daily before meals) to placebo for four weeks, demonstrating statistically significant improvements in abdominal pain, abdominal distension, stool frequency, and flatulence in the peppermint oil group.16
Some of the methodological problems in the published literature include short treatment duration (usually < 6 weeks), small sample size, and failure to use established IBS criteria in inclusion criteria.
Proprietary blends are also occasionally mentioned in the medical literature, offshoots of some of the peppermint oil research. For example, 90 mg peppermint oil and 50 mg caraway oil (called Enteroplant®), has been studied in functional dyspepsia,17,18 and may affect gastrointestinal motility in healthy volunteers.19 These are interesting results, but difficult to apply directly to IBS.
Dosages and Forms
Enteric-coated preparations are preferred for the treatment of IBS to prevent upper gastrointestinal side effects and to deliver the herb to the desired site of action. The daily dose is 0.6 mL of peppermint oil in enteric-coated tablets or capsules, often dosed as a 0.2 mL of peppermint oil in a capsule or tablet three times daily before food.1,2
Adverse Effects, Contraindications, and Drug Interactions
Peppermint oil is contraindicated in certain clinical situations, such as pregnancy, because it may cause the onset of menstruation; cholelithiasis or cholecystitis, due to its activity in stimulating the production of bile; and hiatal hernia or gastroesophageal reflux disease, because of lower esophageal sphincter relaxation.20 With peppermint tea, one study in rats points to a possible effect on the cytochrome P450 system, specifically by reducing the activity of CYP2E and CYP1A2,21 though the medical literature does not mention a problem with human enzyme systems.
Peppermint (Mentha x piperita) has a long history of use for digestive disorders, and there is both clinical and in vitro research on the whole plant and one of its main phytochemicals, menthol, to support some of its traditional uses. Peppermint oil acts to reduce gastro-intestinal smooth muscle motility by acting as a calcium antagonist. There are both positive and negative clinical trials for the use of peppermint oil in IBS, and some experts state that no conclusions can be drawn from the medical literature, mainly because of poor research methodology. Peppermint oil is dosed at 0.2 mL of peppermint oil per capsule or tablet, three times daily before meals, and it is contraindicated in pregnancy, gall bladder disorders, and gastroesophageal reflux disease.
As with many herbal medicines, high-quality research is needed to definitively prove the efficacy of peppermint oil in IBS. Future studies should use the Rome II Diagnostic Criteria as inclusion criteria, divide treatment trials into IBS sub-types, be of longer duration, and use uniform dosing and herbal formulations. Despite these limitations, there are some positive research trials and well-documented effects via calcium antagonism on gastrointestinal smooth muscle, intriguing results especially for a clinical entity such as IBS where conventional treatments are not always successful. Provided peppermint oil is not contraindicated, the use of an enteric-coated preparation could be considered for a trial in patients with IBS until further research is undertaken to refine clinical use.
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