Peppermint: Clinical Use. Dosage

In practice, peppermint and its derivatives are used in many forms and administered by various routes. This review will focus only on those methods that are commonly used by the public and preparations that are available OTC, such as oral dose forms, topical applications and inhalations.

IRRITABLE BOWEL SYNDROME

There have been several studies examining the effects of peppermint oil in the treatment of IBS. Newer studies have tended to use pH-triggered, enteric-coated peppermint oil capsules that prevent dissolution of the capsules until they have reached the small intestine, and release into the colon is extended over 10-12 hours. Enteric coating allows administration of a higher dose than would otherwise be possible to tolerate and, importantly, avoids the risk of excessively relaxing the lower oesophageal sphincter and causing reflux.

A recent review identified 15 clinical trials investigating peppermint oil in IBS. Of these, 8 of 12 placebo-controlled studies show statistically significant effects in favour of peppermint oil, with average response for ‘overall success’ being 58% for peppermint oil and 29% for placebo. Three studies that compared peppermint oil to smooth muscle relaxants showed no difference between these treatments. A critical review and meta-analysis of peppermint oil for IBS performed in 1998, which included five double-blind trials, concluded that peppermint oil is efficacious for symptom relief in IBS.

Since then, one randomised, double-blind controlled trial of 42 children with IBS, treatment with enteric-coated peppermint oil capsules reduced the severity of the pain in 75% of the children, and another recent randomised, double-blind study involving 48 patients with IBS without bacterial overgrowth found that treatment with two enteric-coated capsules of peppermint oil twice daily (Mintoil) for 4 weeks produced statistically significant improvement in diarrhea, abdominal bloating, constipation, lower abdomen pain, pain on defecation, feeling of incomplete evacuation and difficulty on evacuation.

Another randomised, double-blind, placebo-controlled clinical study of 110 outpatients with IBS found that one enteric-coated peppermint oil capsule (Colpermin) taken 3-4 times daily, 1 5-30 minutes before meals, significantly reduced symptoms compared to placebo. Of the 41 patients taking the capsule, 79% experienced alleviation of the severity of abdominal pain (29 were pain free), 83% had less abdominal distension, 83% had reduced stool frequency, 73% had less borborygmi, and 79% had less flatulence, with treatment producing minimal side-effects and no significant changes in liver function tests.

Bacterial overgrowth of the small intestine is associated with a number of functional somatic disorders, including IBS, fibromyalgia and CFS. There have been two reports of successful treatment of IBS due to intestinal overgrowth with enteric-coated peppermint oil capsules. This clinical effect may in part be associated with the antimicrobial activities of peppermint oil.

Clinical note — Pathophysiology of IBS

The pathophysiology of IBS is poorly understood, but it is believed to occur when the intestinal muscles are contracting faster or more slowly than normal. Colonic contractions cause abdominal pain, cramping, wind and diarrhea or constipation. It has been proposed that IBS may result from dysregulation of gastrointestinal motor and enhanced sensory functions, as modulated by the CNS. However, clinical and laboratory investigations have failed to uncover any histological, microbiological or biochemical abnormalities in IBS patients. Patients with IBS demonstrate increased motility and abnormal contractions of the intestinal muscles when faced with an emotionally or physically stressful situation. It is likely that IBS is also associated with dietary habits, poor upper digestion and intestinal dysbiosis (bacterial overgrowth of the bowels).

Common symptoms of IBS are:

• cramping pain in the lower abdomen
• bloating and excess gas (wind)
• changes in bowel habits
• diarrhea or constipation, either one dominant or both alternating
• immediate need for a bowel movement on awakening or during or after meals
• relief of pain after bowel movements
• feeling of incomplete emptying after bowel movements
• mucus in the stool.

DYSPEPSIA

In a systematic review of herbal medicines for functional dyspepsia, Coon and Ernst (2002) found 17 randomised clinical trials, 9 of which involved peppermint and caraway combination preparations with 60-95% of patients reporting improvements in symptoms.

An enteric-coated capsule (Enteroplant) containing 90 mg peppermint oil (WS-1340) and 50 mg caraway oil (WS-1520) has been shown in a double-blind, placebo-controlled multicentre trial with 45 patients to significantly improve symptoms of non-ulcer dyspepsia. Nearly 90% of patients experienced a reduction in pain, and after 4 weeks nearly 95% had improved their Clinical Global Impression scores. Before the start of treatment all patients in the test preparation group reported moderate to severe pain, while by the end of the study 63.2% of these patients were free of pain. The peppermint and caraway oil combination was well tolerated.

Since then there have been three further randomised, placebo-controlled trials of this particular peppermint-caraway oil combination. In one trial with 223 patients with non-ulcer dyspepsia and IBS, the peppermint oil combination was found to significantly reduce pain compared to placebo (P < 0.001). In a further study of 96 outpatients, the same peppermint formulation was found to significantly improve symptoms of functional dyspepsia. After 4 weeks, the average intensity of pain was reduced by 40% versus baseline in the active group and by 22% in the placebo group. The peppermint combination also reduced pressure, heaviness and fullness. A subgroup analysis from this study revealed that Helicobacter pylori-positive patients had a substantially better treatment response, although those who were negative to H. pylori also showed significant improvements compared to those receiving placebo. In a further double-blind, placebo-controlled trial the same oil combination was found to significantly improve disease-specific QOL, as measured by thevalidated Nepean Dyspepsia Index (NDI) compared to placebo.

The same peppermint and caraway oil combination has been compared with cisapride (Prepulsid), which increases the lower oesophageal sphincter pressure, thereby reducing the risk of reflux. Cisapride is also used to treat IBS dominated by constipation, but has been linked to serious cardiac arrhythmias and should be used with caution. In the 4-week study, the peppermint and caraway oil combination (Enteroplant, 2 capsules daily) was shown to be as effective as cisapride in reducing both the magnitude and frequency of pain. Physicians rated the two treatments comparable in regard to other dyspeptic symptoms, in addition to intestinal and extra-intestinal autonomic symptoms. Corresponding results were also found in H. pylori-positive patients and patients who initially presented with intense epigastric pain in the two treatment groups. Both medications were well-tolerated.

A combination herbal preparation (Iberogast) that includes peppermint leaf extract and eight other plant extracts (Iberis amara, Chelidonii herba, Cardui mariae fructus, Melissae folium, Carvi fructus, Liquiritiae radix, Angelicae radix, Matricariae flos) has been demonstrated to significantly relieve dyspepsia in a number of RCTs, including a meta-analysis of three trials, with a fourth RCT showing similar effects to cisapride.

DIFFUSE OESOPHAGEAL SPASM

Diffuse oesophageal spasm (DES) is a relatively rare motor disorder. Associated manometric abnormalities may include hypertensive and repetitive contractions. The lower oesophageal sphincter (LES) may also be hypertensive. Although LES relaxation with deglutition is generally normal, disturbances in LES function are often seen. These abnormalities are, however, not required for the diagnosis. In a study of eight DES patients with chest pain or dysphagia, peppermint oil had no effect on LES pressures or contractile pressures and durations in the oesophagus, yet completely eliminated simultaneous oesophageal contractions in all patients (P < 0.01). The number of multiphasic, spontaneous and missed contractions also improved. Two of the eight patients had their chest pain resolved after taking the peppermint oil.

ANTISPASMODIC

The results from a randomised double-blind, double-dummy, controlled trial suggest that the antispasmodic properties of peppermint oil can be utilised intraluminally during upper endoscopy with superior efficacy and fewer side-effects than hyoscine-N-butylbromide (buscopan) administered by intramuscular injection. The use of peppermint oil solution was subsequently used to successfully extend an endoscope past an area of severe antral stenosis in a case that was unresponsive to buscopan. In a further study of 383 patients receiving double-contrast barium enemas, which compared peppermint oil in the barium, peppermint in the enema tube, buscopan and no treatment, found that peppermint oil in the barium or the enema tube could be safely and effectively used instead of buscopan and that the oil had a stronger antispasmodic effect in the caecum and the ascending colon than a buscopan injection.

HEADACHE

A solution of 10% peppermint oil in ethanol has been shown in a randomised, placebo-controlled, double-blind crossover study to efficiently alleviate tension-type headache. The study analysed 164 headache attacks in 41 patients of both sexes ranging between 18 and 65 years of age, suffering from tension-type headache. The peppermint oil was spread largely across forehead and temples and repeated after 1 5 and 30 minutes. Using a headache diary, the headache parameters were assessed after 15, 30, 45 and 60 minutes. Compared with the application of a placebo, the peppermint oil significantly reduced the intensity of the headache after 15 minutes (P< 0.01). The analgesic effect of the peppermint oil was comparable to 1000 mg paracetamol (acetaminophen). Simultaneous ingestion of 1000 mg of paracetamol and application of 10% peppermint oil in ethanol solution led to a slight additive effect.

Postoperative nausea

Inhalation of peppermint oil vapours has been shown in a study to reduce postoperative nausea in gynaecological patients in a placebo-controlled trial in which patients were free to inhale peppermint oil as frequently as desired. A hot peppermint oil compress is used in China to prevent abdominal distension in postoperative gynaecological patients. In another placebo-controlled trial, a reduction in postoperative nausea was seen equally with inhalation of isopropyl alcohol, peppermint oil or saline, with the authors attributing the effect to the controlled breathing used during inhalation.

RESPIRATORY TRACT INFECTIONS

Peppermint and menthol have an established tradition in the treatment of respiratory infections. Chest rubs containing menthol are frequently used to treat coughs and bronchitis. Inhalation of various antiseptic and anti-inflammatory essential oils is often used in the treatment of respiratory infections, including bronchitis. Peppermint oil has been found to have a pronounced antimycobacterial effect in vitro, and long-term use of peppermint oil in a humidifier has been used in the Ukraine as an adjunctive treatment to multidrug therapy for pulmonary tuberculosis.

ENHANCE COGNITIVE PERFORMANCE

A combination of peppermint oil, eucalyptus oil and ethanol was shown in a crossover double-blind study to increase cognitive performance, and promote relaxation in 32 healthy subjects. Peppermint odour has also been shown to reduce daytime sleepiness and fatigue, and to improve mood, as well as significantly improve performance in difficult tactile tasks and promote a general arousal of attention with improved typing speed and accuracy.

Peppermint: Other Uses

Peppermint or pure menthol is commonly used in heat rub ointments for arthritis, fibromyositis, tendonitis and other musculoskeletal conditions. Commission E approved peppermint oil externally for neuralgia and myalgia.

An oral spray or gargle containing a range of essential oils including peppermint oil is reported to reduce snoring in one double blind study. A case report describes the treatment of post-herpetic neuralgia with the direct application of undiluted peppermint oil containing 10% menthol to the affected area. The pain relief persisted for 4-6 hours after application of the oil. At a 2-month follow-up the patient had only minor side-effects and continued to use the medication.

TRADITIONAL USES

Traditionally, peppermint was believed to increase libido, and used to stop hiccups, relieve pain in childbirth, reduce bleeding and treat menorrhagia. It was also used externally to repress lactation, to treat dermatological conditions, as a mouthwash for painful gums and mouth and applied to the temples to relieve headaches.

Peppermint: Dosage Range

LEAF

• Infusion: 3-6 g three times daily.

• Liquid extract (1:2): 1.5-4.5 mL/day.

These dosages are for adults; adjust according to size for children.

ESSENTIAL OIL

• Digestive disorders: 0.2-0.4 mL three times daily in dilute preparations or in suspension (ESCOP 1997).

• IBS: 0.2-0.4 mL three times daily in enteric-coated capsules or tablets.

• Inhalation: 3-4 drops added to hot water.

• Lozenge: 2-10 mg.

• External use (for analgesic, anaesthetic or antipruritic activity): 0.1-1.0% m/m (ESCOP 1997).

• External use (counterirritant): 1.25-16% m/m (ESCOP 1997).