Peppermint oil

Peppermint is a natural hybrid of two mint species, garden spearmint (Mentha spicata) and water mint (Mentha aquatica). Peppermint grows all over the world and, like other mints, has been used for culinary purposes and medicinal effects for thousands of years by various cultures. It has a distinctive, pungent scent, due to the volatile oil present in all parts. When applied to the tongue, peppermint oil has a hot aromatic taste at first, and then produces a sensation of cold in the mouth due to the menthol it contains. The aerial portion of the plant is the part most widely used for medicinal effects with pharmaceutical-grade peppermint oil being produced by distilling the fresh above ground parts of the plant harvested at the very beginning of the flowering cycle.

Peppermints key constituents include essential oil, consisting primarily of menthol and (-) methone, flavonoids including polymerized polyphenols and tannins, and other compounds such as triterpenes, tocopherols, carotenes, betaine, choline, and bitter substances. Typical delivery forms include enteric-coated capsules, essential oil, liquid extract or tincture, dried leaf as infusion (tea), aqueous ethanol preparations, ointments, salves and lozenges.

Peppermint's medicinal actions, which are attributed almost entirely to its menthol components, vary depending upon its application. When used taken orally, peppermint oil has carminative, antispasmodic, choleretic, antitussive, sedative and antimicrobial effects. When used topically, it has analgesic properties and when used as an inhalant, it exerts diaphoretic, nasal decongestant and bronchial antispasmodic/sedative effects.

Peppermint oil and menthol are used extensively in pharmaceutical preparations such as antacids, irritant laxatives, and mouthwash for both their therapeutic and flavoring effects. Peppermint's pharmacological effects offer potential benefit in a number of conditions, most notably irritable bowel syndrome, gallstones, dyspepsia, post-operative nausea, intestinal colic, gallstones, headache, musculoskeletal pain, the common cold, and asthma.

Peppermint herb is generally regarded as safe (GRAS) when used as a tea; however, hypersensitivity reactions to peppermint oil, such as heartburn, gastrointestinal irritation and, very rarely, allergic reactions including headache, flushing, muscle tremor, and skin rashes, have been reported. Applied topically, peppermint oil or menthol preparations can induce contact dermatitis, hypersensitivity reactions or chemical burns. It is considered generally non-toxic, with the high dose feeding of peppermint oil that produced signs of dose-related brain lesions in animals far exceeding the dosages used in humans.

Peppermint oil is contraindicated for individuals with esophageal reflux symptoms, occlusion of the gallbladder passage, cholecystitis and severe liver disease. Heating pads should not be used in conjunction with topically applied menthol-containing preparations. Peppermint oil should not be applied to the nose or face of babies and small children.

If antacids are used, wait two hours before taking enteric-coated peppermint capsules since the decrease in stomach acid caused by antacids could cause premature dissolution of peppermint oil capsule. Similarly, since H2 antagonist medications block gastric acid, enteric-coated peppermint oil should not be taken by individuals who are using these medications.

Typical dosage varies depending upon the form being used and the health care application for which it is being used.

• Essential oil (0.5-4%) consisting primarily of menthol (35-45%) and (-)methone (10-30%).
• Flavonoids (12%), polymerized polyphenols (19% of dry weight), tannins (6-12%)
• Other compounds that may contribute to peppermints medicinal effects include triterpenes, tocopherols, carotenes, betaine, choline, and bitter substances.

The volatile oil of peppermint, its primary medicinally active component, can be found in concentrations of up to 1.5% in the herb, but is usually present in the 0.3-0.4% range. The oils principal components are menthol (35-45%), menthone (10-30%) and menthyl acetate (3-10%). Most of the volatile oil components are terpenoids.

The European Pharmacopeia recommends that whole peppermint leaf contain not less than 12ml/kg and the cut leaf not less than 9ml/kg of essential oil. Pharmaceutical-grade peppermint oil is produced by distilling the fresh above ground parts of the plant harvested at the very beginning of the flowering cycle. The composition of menthol and other volatile oil components is sensitive to climate and latitude, as well as to the maturity of the plant. Pharmaceutical grade peppermint oil is standardized to contain not less than 44% free menthol and a minimum of 5% esters calculated as menthyl acetate. The ketone component (calculated as menthone) usually ranges from 15 to 30% with the remainder of the oil being composed of various terpenoids. Menthol is also synthesized by hydrogenation of thymol.

The mints, including peppermint, have been used for culinary purposes and for their medicinal effects for thousands of years. The Greeks and Romans crowned themselves with peppermint and decorated their banquet tables with sprays of the herb. Graeco-Roman cooks used peppermint liberally to flavor sauces and wine. Records from the ancient Egyptians mention the cultivation of peppermint and the Icelandic pharmacopeias of the 13th century record its use, although this herb did not come into general use in Western European medicine until the 18th century.

Orally, peppermint was used medicinally to treat flatulent colic, dyspepsia, stomach cramps and spasms, nausea and vomiting, morning sickness and dysmenorrhea. As an inhalant, it was used to relieve the cough of bronchitis and pneumonia and to induce perspiration during the early phase of a cold. Topically, bruised fresh herb was applied over the bowel to allay sick stomach and over the forehead to relieve headaches. Peppermint was also used as an infusion in combination with wood betony and caraway to treat nervous disorders, and in combination with elderflowers, yarrow or boneset to treat colds and mild influenza.

Peppermints medicinal actions, which are attributed almost entirely to its menthol components, include:

• Oral: carminative, antispasmodic, choleretic, antitussive, sedative, antimicrobial
• Topical: analgesic
• Inhalant: diaphoretic, nasal decongestant, bronchial antispasmodic/sedative

Carminative effects

Carminatives promote the elimination of intestinal gas. The carminative effects of peppermint and peppermint oil are well known. Peppermint's carminative action was demonstrated in a study in which 15 drops of peppermint oil in 30 ml of water was directly administered into the stomachs of 27 human subjects, causing relaxation of the lower esophageal sphincter and equalization of intragastric and intraesophageal pressures. Sphincter relaxation lasted approximately 30 seconds and was followed by an esophageal peristaltic wave. Reflux occurred in 25 of the 27 patients within 1-7 minutes after administration. Such relaxation of the esophageal sphincter could explain peppermint's carminative effects since it leads to the release of gas pressure in the stomach.

Antispasmodic effects

Peppermint oil's antispasmodic effects on the gastrointestinal muscles resemble those of calcium antagonist drugs, which block influx of calcium into muscle cells. In in vitro animal experiments, peppermint oil markedly lessened contractile responses to acetylcholine, histamine, serotonin, and substance P in guinea pig taenia coli, and also reduced contractions evoked by potassium depolarization and inhibited potential-dependent calcium currents in rabbit jejunum smooth muscle cells in a dose-dependent manner. Peppermint leaf extract arrested spasms induced in isolated guinea pig ileum by acetylcholine and histamine. Aqueous solution of flavonoids isolated from peppermint inhibited barium chloride-induced contraction.

The effect of enteric-coated and non-enteric-coated preparations containing a peppermint-caraway oil combination with 90mg peppermint oil and 50mg caraway oil was studied on gastroduodenal motility with stationary manometry in six healthy volunteers. The results showed that both enteric-coated and non-enteric-coated preparations decrease the number of contractions and contraction amplitudes seen during the various phases of the migrating motor complex (MMC). Non-enteric-coated preparations have their effects mainly during the first MMC after administration; while enteric-coated preparations have their effects temporally delayed during the second MMC after administration. Researchers concluded that enteric-coated and non-enteric-coated peppermint-caraway oil combinations are safe preparations, acting locally to cause smooth muscle relaxation.

These experiments suggest that the clinical effectiveness of peppermint oil in the treatment of irritable bowel syndrome may be due in part to peppermints inhibition of the hypercontractility of intestinal smooth muscle, thereby returning the muscle to its proper tone.

A peppermint oil solution has also been shown to be helpful in relieving colonic spasms during colonoscopy. In humans, intraluminal administration of peppermint oil (0.1-20ml saline) to the sigmoid colon in 5 normal subjects produced increased intraluminal pressure, abdominal cramps, and the urge to defecate, suggesting either widespread stimulation of smooth muscle or a local irritant effect since the opposite effect was observed on colonic muscle during colonoscopy. Injection of peppermint oil along the biopsy channel of the colonoscope in 220 patients relieved colonic spasm within 30 seconds, thus allowing easier passage of the instrument or assisting in polypectomy. To avoid the potential irritant effect of peppermint oil while achieving its helpful effects in colonosccopy, a diluted suspension is now used.

In an in vitro study, peppermint oil (in concentrations from 1-5mg/ml) inhibited enterocyte glucose uptake in the intestinal lumen via direct action at the brush border membrane. Researchers suggested this effect was due to changes in the charge on tight junctions between cells and to an inhibition of sodium-linked active transport. In humans, the standard bolus dose of peppermint oil is 400mg, which could achieve a local concentration in the intestinal lumen in this range during the fasting state.

Choleretic effects

Choleretics stimulate the flow of bile, which plays an essential role in fat digestion and absorption and serves as a carrier that helps the body eliminate toxins from the liver and waste products from the blood. Menthol and related terpenes have been shown to not only exert a choleretic effect, but to also improve the solubility of the bile, which after secretion by the liver, is stored in the gallbladder until needed. During storage, bile becomes concentrated as water, sodium, choloride amd most other small electrolytes are reabsorbed. By improving bile solubility, the choleretic action of peppermint helps prevent gallstone formation.

External analgesic effects

Menthol's external analgesic and counter-irritant effects are well accepted and have been demonstrated in a number of studies. When applied topically, peppermint oil stimulates the nerves which perceive cold, while simultaneously depressing those for pain. The initial cooling effect is followed by a period of warmth.

Applied topically (at concentrations of 1-30% in ethanol), menthol exhibited a significant antinociceptive effect in the early phase of pain response in the formalin test in mice and also produced nociceptive inhibition in the hot plate test of mice and hind paw pressure test in rats, but did not inhibit carrageenan-induced paw edema in rats and the synthesis of prostaglandin E2 in in vitro. These results suggest that menthols analgesic effects result from activation of the endogenous opioid system and local anaesthetic actions rather than anti-inflammatory effects.

The long-lasting cooling effect produced by topical application of peppermint oil is caused by a steric alteration of the calcium channels of cold receptors. In a double-blind crossover study of 15 healthy subjects, peppermint oil's analgesic effect appeared to be due to central inhibitory effects mediated by cold-sensitive A delta nerve fibers rather than the physical effect of evaporation.

Respiratory Effects

Menthol has demonstrated antitussive effects in chemically induced cough in guinea pigs challenged with aerosolized citric acid for 2 minutes. Menthol inhalation produced a significant reduction in cough frequency and increase in cough latency. Menthol exhibits a surfactant-like effect in vitro and in vivo decreased surface tension between water and air, thus improving lung compliance values.

Inhalation of menthol vapor by healthy volunteers and oral administration of menthol via lozenge in subjects with nasal congestion associated with the common cold brought about a subjective sensation of nasal decongestion but had no effect on nasal resistance to airflow. The subjective effects were found to be due to menthol's significant pharmacological action on nasal sensory nerve endings unrelated to the smell of peppermint.

An ointment containing menthol, camphor and essential oils was found to reduce acetylcholine-induced bronchospasm in animals by 50% when the ointment was insufflated through the respiratory tract. Topical application of the ointment produced only a slight reduction in bronchospasm; however, significant secretolytic effects were noted after both insufflation and topical application.

Antimicrobial Activity

Research suggests that peppermint essential oil and its constituents may be useful as potential antibacterial agents for inhibition of the growth of pathogens.

Peppermint oil has demonstrated significant antibacterial and antifungal activity in several studies. Eighteen different commercial peppermint oils with a variable range of menthone (16.7% to 31.4%), menthol (32% to 49%), and menthofuran (5.1% to 12%) were tested against 25 different species of bacteria and 20 different strains of Listeria monocytogenes isolated from different food sources. Antifungal activity was assessed against Aspergillus nigra, Aspergillas ochraceus, and Fusarium culmorum. Most species of bacteria tested, with the exception of Acaligenes faecalis, Flavobacterium suaveolens, Leuconostoc cremoris, Psuedmonas aerguinosa and Streptococcus faecalis, were inhibited by some of the peppermint oils, and nine species were inhibited by all the oils. All strains of Listeria monocytogenes were inhibited by some peppermint oils, nine strains by all the oils, and one strain by three of the oils. The three filamentous fungi were inhibited by all the peppermint oils, but three oils had low activity against Fusarium culmorum. Oils with the most potent antibacterial activity were least effective against one of the fungal species, and an inverse relationship appeared to exist between the oils antibacterial and antifungal activity.

In another study, the effects of the essential oils of peppermint, spearmint and Japanese mint, of four major constituents of the essential oil of peppermint, and of three major constituents of the essential oil of spearmint were evaluated on the proliferation of Helicobacter pylori, Salmonella enteritidis, Escherichia coli O157:H7, methicillin-resistant Staphylococcus aureus and methicillin-sensitive Staphylococccus aureus. The essential oils and the various constituents inhibited the proliferation of each strain in liquid culture in a dose-dependent manner. In addition, they exhibited bactericidal activity in phosphate-buffered saline. The antibacterial activities varied among the bacterial species tested but were almost the same against antibiotic-resistant and antibiotic-sensitive strains of Helicobacter pylori and S. aureus.

Vascular Effects

Local application of peppermint oil to the forehead induced a significant increase in skin blood flow in capillaries in healthy subjects and migraine patients, as measured by laser Doppler.

Sedative Action

Dried aqueous extract of peppermint containing approximately 3.3% flavonoids, 18.4% tannins and 1.2% essential oil produced a mild excitatory effect followed by sedative action on mice at a dose of 1000mg/kg.

Anti-carcinogencic Effect

Adding menthol and limonene to the diet of rats exposed to DMBA significantly inhibited DMBA-initiation of rat mammary tumors.

Peppermint oil and menthol are used extensively in pharmaceutical preparations such as antacids, irritant laxatives, and mouthwash for both their therapeutic and flavoring effects. The same is true for peppermint's inclusion in mouthwash preparations and after-dinner mints. Peppermints pharmacological effects offer benefit in a number of conditions, most notably:

• irritable bowel syndrome
• dyspepsia
• intestinal colic
• gallstones
• headache
• musculoskeletal pain
• asthma
• the common cold

Irritable bowel syndrome

Peppermint oil has been used in treating irritable bowel syndrome (IBS) for many years. IBS can include a combination of any of the following symptoms:

• Cramp-like pain in the middle or to one side of the lower abdomen.
• Pain usually relieved with bowel movements
• Loose or more frequent painful bowel movements
• Diarrhea or constipation, usually alternating
• Symptoms of indigestion such as flatulence, nausea, loss of appetite
• Excessive secretion of colonic mucus
• Headache, backache
• Rectal pain
• Fatigue
• Varying degrees of anxiety or depression

A primary finding in IBS is a hypercontractility of intestinal smooth muscle. As described above, peppermint oil inhibits the hypercontractility of intestinal smooth muscle making it useful in cases of the irritable bowel syndrome as well as intestinal colic.

The preferred delivery of peppermint oil in the treatment of IBS is by enteric-coated preparations that prevent the oil from being absorbed in the stomach. Without enteric coating, the high dose of peppermint oil needed to produce benefit will inevitably produce gastric reflux and heartburn. When enteric-coated, the peppermint oil is released in the small and large intestine where it relaxes intestinal muscles.

Several clinical studies have demonstrated that enteric-coated peppermint oil is quite effective in reducing the abdominal symptoms of the irritable bowel syndrome. In an uncontrolled trial of 40 patients with IBS, a 14-day course of enteric-coated peppermint oil capsules was found to prolong intestinal transit time and produce improvement in subjective rating scores for fullness, bloating, bowel noises and abdominal pain. A double-blind follow up trial of 18 patients with IBS who were given 1-2 enteric-coated capsules (0.2ml peppermint oil or placebo) three times daily also produced good results. Patients felt significantly better when taking peppermint oil capsules compared to the peanut oil placebo (p<0.01) and found peppermint oil better than placebo in relieving abdominal symptoms (p<0.05). A second similar double-blind cross-over study of 29 patients produced similar results. Patients taking peppermint oil had a lower daily symptom score, but no effect was noted on the number of bowel movements per day. These two studies were criticized for faulty design and a later double-blind trial with a more rigorous design found no significant difference between peppermint oil and placebo.

In the largest follow up trial, a prospective, randomized, double-blind, placebo-controlled study of 110 patients with IBS, peppermint oil was once again found to produce significant symptomatic improvements. Patients were given an enteric-coated capsule containing 187mg peppermint oil or placebo, 3-4 times per day, 15-30 minutes before meals for 1 month. Significant improvements were noted in abdominal pain, abdominal distension, stool frequency, gas and flatulence compared to placebo (p<0.05). No adverse effects were noted on upper GI symptoms.

In a randomized, double-blind controlled trial, 42 children with IBS were given pH-dependent, enteric-coated peppermint oil capsules or placebo. After 2 weeks, 75% of patients receiving peppermint oil had reduced severity of pain associated with IBS. Researchers concluded, \"Peppermint oil may be used as a therapeutic agent during the symptomatic phase of IBS.\"

Gallstones

Rowachol, a propriety choleretic formula containing menthol (32%) and related terpenes (pinene (17%), menthone (6%), borneol (5%), camphene (5%), and cineole (2%)) dissolved in olive oil, significantly lowers the cholesterol saturation index in human bile, and has demonstrated efficacy in several studies in dissolving gallstones. This approach to gallstone removal offers an effective alternative to surgery and has been shown to be safe even when consumed for prolonged periods of time (up to 4 years). Terpenes, like menthol, help to dissolve gallstones by reducing bile cholesterol levels while increasing bile acid and lecithin levels in the gall bladder. As menthol is the major component of Rowachol, peppermint oil, especially if enteric-coated, may offer similar benefits.

Dyspepsia

In a double-blind, placebo-controlled multi-center trial, 54 patients with non-ulcer dyspepsia were given one enteric-coated capsule per day containing 90 mg peppermint oil and 50 mg of caraway oil. After 4 weeks, intensity of pain was significantly decreased and global clinical impressions were significantly improved for those receiving the oil combination vs. placebo. Before treatment, all patients given the peppermint caraway oil combination reported moderate to severe pain; by the end of the study, 63.2% of these patients were pain free and 26.3% reported reduction in their pain.

In another study, peppermint oil was shown to accelerate the rate of gastric emptying in both dyspeptic patients and controls. The gastric emptying rate in dyspeptic patients became comparable to that of aged match controls after administration of 0.2ml peppermint oil in 25ml of water.

The most recent trial, a follow up of the earlier trial on the efficacy of a combination of peppermint and caraway oil on patients with functional dyspepsia, also showed very positive results. For 28 days, a total of 96 patients received one capsule twice daily containing 90mg peppermint oil and 50mg caraway oil or placebo. On day 29, the average intensity of pain was reduced by 40% vs. baseline in the group receiving the peppermint caraway oil combination and by 22% in the placebo group. With regards to pressure, heaviness and fullness, a 43% reduction was observed for peppermint caraway oil group vs. 22% for placebo. In terms of clinical global impressions, 67% of patients receiving the peppermint caraway combination vs. 21% of those given placebo were described as much or very much improved. In all three target parameters, the superiority of the peppermint caraway oil preparation over placebo was statistically significant. Six patients, 5 of those given the peppermint caraway combination and 1 given placebo, reported adverse events, either unrelated to the trial, or attributable to an aggravation of their dyspepsia. Eructation with peppermint taste did not occur. Researchers concluded that their results demonstrate good tolerability and a favourable risk-benefit ratio in the use of peppermint and caraway oil for the treatment of functional dyspepsia.

Post-Operative Nausea

In a placebo-controlled trial involving 18 gynecological patients, incidence of post-operative nausea was significantly reduced (p=0.02) in those who inhaled peppermint oil.

Tension Headache

In a double-blind, placebo-controlled, randomized cross-over trial, topical application of peppermint oil in ethanol solution (10g peppermint oil in a 90% ethanol solution) was compared to acetaminophen (1g) and placebo in the treatment of 164 chronic tension headaches in 41 patients of both sexes. Peppermint oil solution was spread across the forehead and temples and the application repeated after 15 and 30 minutes. Peppermint oil significantly reduced headache intensity after 15 minutes compared to placebo and (p<0.01) and was found to be as effective as acetaminophen. Simultaneous administration of peppermint oil with acetaminophen produced an additive effect (p<0.001)

In another study of experimentally induced headache in 32 healthy men, a peppermint oil and ethanol preparation produced a significant analgesic effect with reduction in sensitivity to headache (p<0.01 for experimental ischemia, p<0.001 for experimental heat stimuli). Topical application to the forehead and temples resulted in a statistically significant decrease in muscle tension as reported subjectively and measured objectively by EMG activity of the temporal muscle. In addition, the oil application resulted in decreased pain sensitivity. The pharmacological and clinical results indicate that peppermint oil has both central and peripheral activity.

External analgesic

Animal studies suggest that menthol produces antinociceptive effects by activation of the endogenous opioid system and/or partially by local anesthetic actions. In a double-blind, crossover study of 15 healthy human subjects, topical application of menthol demonstrated analgesic activity via central inhibitory effects mediated by cold-sensitive A delta nerve fibers, rather than by anti-inflammatory effects. Menthol and related substances should therefore be considered in addition to anti-inflammatory agents for their ability to provide another form of analgesic benefit in the treatment of arthritis, fibromyositis, tendonitis, and other inflammatory conditions involving the musculoskeletal system. As shown in its effectiveness in the treatment of tension headache, the combination of peppermint with an anti-inflammatory analgesic can produce an additive effect in pain reduction.

Common cold

Peppermint tea may be of benefit during the common cold. Peppermint, as well as other members of the mint family, has demonstrated significant antiviral activity as well as a mild diaphoretic effect. Peppermints most active antiviral components, its polyphenols, are concentrated in the tea.

Peppermint oil is thought to relieve respiratory symptoms caused by the common cold by increasing salivation, which increases the swallowing reflex, suppresses the cough reflex, reduces bronchial secretions, and can have nasal decongestant activity. The long-term popularity of menthol and peppermint oil in topical nasal decongestants, cough and throat lozenges, ointments, salves, and inhalants used in the treatment of the common cold, evidences their ability to help make breathing easier during the common cold. The best method for using menthol or peppermint oil is to apply ointment or salve preparations to the upper chest during periods of rest, so the vapors can be inhaled continuously.

Asthma

The effect of inhaled menthol vapor on asthma was studied in a placebo-controlled trial of 23 patients. The menthol vapor did not produce immediate bronchodilatory effects, but inhalation over 4 weeks resulted in a decreased diurnal variation in peak expiratory flow rate (p<0.05), a value which signifies a reduction in airway hyperresponsiveness.. The number of metered dose inhaler inhalations were also significantly reduced in the menthol group (p<0.01).

• Enteric-coated capsule: Peppermint oil is mainly absorbed in the upper gastrointestinal tract unless enterically coated and should be taken in this form for treatment of IBS, both to prevent the side effect of gastric reflux and to ensure its release and activity in the intestines.
• Essential oil
• Liquid extract or tincture
• Dried leaf as infusion (tea)
• Aqueous ethanol preparations
• Ointments, salves
• Lozenge

• Antacids: The decrease in stomach acid and resulting elevation of gastric pH caused by antacids could cause premature dissolution of enteric-coated peppermint oil. If antacids are taken, enteric-coated peppermint capsules should not be taken for at least 2 hours.
• H2 Blockers: H2 antagonists block gastric acid. The decrease in stomach acid and resulting elevation of gastric pH caused by H2 blockers could cause premature dissolution of enteric-coated peppermint oil. If any of the following H2 antagonist drugs are used, enteric-coated peppermint capsules should not be taken: Cimetidine, ranitidine, famodidine, nizatidine; proton pump inhibitors: omeprazole, lansoprazole, rabeprazole, pantoprazole; and misoprostil. (NMDB 787).

The LD50 of menthol in rats is 3.3g/kg. The lethal oral dose in humans is 1g/kg. High dose feeding of rats for 28 days with peppermint oil produced signs of dose-related brain lesions, but the dosage (40mg/kg) far exceeds those used in humans.

Oral administration of a spray-dried infusion of peppermint (4g/kg) in mice over a 7 day period did not result in any macroscopic signs of toxicity or death.

• viduals with esophageal reflux symptoms should avoid substances, including peppermint, which decrease lower esophageal pressure.
• Peppermint oil is contraindicated for internal use in occlusion of the gallbladder passages, cholecystisis and severe liver disease.
• Peppermint oil should not be applied to nose or face of babies and small children.
• Patients with achlorhydria should not use enteric-coated peppermint oil since achlorhydria increases gastric pH, which may result in premature dissolution of the enteric coating.