Peppermint: Background. Actions

2010

Common Name

Peppermint

Botanical Name / Family

Mentha x piperita (family [Labiatae] Lamiaceae)

Plant Parts Used

Leaf or stem — essential oil is distilled from the aerial parts.

Chemical Components

Peppermint leaves contain about 2.5% essential oil, 19% total polyphenolic compounds, 12% total flavonoid compounds (eriocitrin, luteolin-7-O-rutinoside, hesperidoside) and 7% total hydroxycinnamic compounds (including rosmarinic acid). The biochemistry, organisation, and regulation of essential oil metabolism in the epidermal oil glands of peppermint have been defined and research is underway to create ‘super’ transgenic peppermint plants with improved oil composition and yield.

Essential oil

Over 100 constituents have been identified in peppermint oil. The principal constituents are menthol (35-55%), menthones (10-35%), isomenthone, menthyl acetate, menthofuran and cineole. To comply with the European Pharmacopoeia, the oil must not contain more than 4% pulegone and not more than 1% carvone.

Historical Note

The written record of mint dates back to an ancient Greek myth in which the Greek god Pluto was said to have affections for a beautiful nymph named Minthe. His jealous wife Persephone cast a spell on the nymph, transforming her into a plant. When Pluto could not reverse the spell, he gave her a sweet scent that would emanate throughout the garden. Peppermint has been used medicinally for generations as a digestive aid and carminative. More recently, enteric-coated peppermint oil capsules have been widely prescribed for the relief of IBS.

Peppermint: Main Actions

The actions of the leaf as an infusion or liquid extract are largely dependent on the essential oil content. Other compounds, such as the flavonoids, also contribute to the overall activity, especially the antioxidant and anti-allergic activities. Peppermint oil is relatively rapidly absorbed after oral administration and eliminated mainly via the bile.

ANTISPASMODIC

Peppermint oil, ethanol extracts and flavonoids isolated from the leaf have all been shown to have antispasmodic (spasmolytic) effects in vitro (ESCOP 1997) with the effect mediated via smooth muscle calcium channels.

In healthy volunteers, intragastric administration of a dose equivalent to 180 mg peppermint oil reduced intraoesophageal pressure within 1-7 minutes of infusion, while in nine human studies involving 269 subjects peppermint oil produced substantial spasmolytic effects on the smooth muscles of the gastrointestinal tract when used topically (intraluminal) or orally in doses of 0.1-0.24 mL. Enteroplant, an enteric-coated capsule containing 90 mg peppermint and 50 mg caraway oil, has also been shown to act locally in the stomach and duodenum to produce smooth muscle relaxation. Peppermint oil has also been shown to have similar anti-spasmodic activity on the colon to the Chinese herbal medicine Shakuyaku-kanzo-to (TJ-68), as observed by direct observation during colonoscopy.

CARMINATIVE

Peppermint has a carminative activity, which refers to its ability to relax the gastrointestinal sphincters. Carminatives are thought to alleviate symptoms of bloating and gas by facilitating eructation and passage of flatus. The classic carminatives are essential oils, such as spearmint and peppermint. Studies from the 1950s on the effect of carminatives on the gut suggest that they work by inducing relaxation of the lower oesophageal sphincter. A later study has shown that peppermint oil canalised into the gall bladder and duodenal areas was able to counteract morphine hydrochloride-induced constriction of the sphincter of Oddi.

CHOLERETIC

Choleretic activity has been demonstrated for peppermint tea, flavonoids and the essential oil in dogs and rats (ESCOP 1997). Hydrophilic compounds may contribute to the gastrointestinal effects, with aqueous extracts from peppermint leaves having anti-ulcerogenic and choleretic effects. Peppermint oil has been shown to have a relaxing effect on the gall bladder and small intestine, producing complete inhibition of gall-bladder emptying and prolonged orocaecal transit time comparable to that produced by n-butylscopolamine.

ANTIMICROBIAL

Antibacterial

Peppermint oil has been shown to have significant antibacterial activity, as has the juice of peppermint leaves. Peppermint oil has been shown to inhibit Helicobactor pylori, Staphylococcus aureus, Escherichia coli, Salmonella enteritidis, Listeria monocytogenes and multiresistant strains of Shigella sonnei and Micrococcus flavus.

Fungistatic, fungicidal

Peppermint is also fungistatic and fungicidal with its activity against Trichophyton tonsurans and Candida albicans being considerably greater than the commercial fungicide bifonazole. Peppermint oil and its main constituent menthol has also been shown to have significant antibacterial, antifungal and antiplasmid activity and to potentiate the antibiotic effect of oxytetracycline.

Peppermint oil has further been shown to have significant antimycobacterial activity in vitro and inhalation of peppermint oil has been successfully used as a supplement to combined multidrug therapy for pulmonary tuberculosis.

Antiviral

Peppermint oil also has virucidal activity against HSV -1 and -2, including activity against an acyclovir-resistant strain of HSV-1 with a 50% inhibitory concentration determined at 0.002% and 0.0008% for HSV-1 and HSV-2, respectively. The oil was also found to affect the virus before, but not after, penetration into the host cell.

ANTI-ALLERGIC

A 50% hydro-ethanolic extract of peppermint leaves inhibited chemically induced histamine release from rat peritoneal mast cells in vitro. The peppermint extract was also shown to reduce nasal symptoms (sneezing and nasal rubbing) in rats with experimentally induced allergic rhinitis. Significant inhibition of sneezing and nasal rubbing was observed at oral doses of 300 and 1000 mg/kg, respectively.

The flavonoid luteolin-7-O-rutinoside isolated from the aerial parts of peppermint has been shown to inhibit histamine release from rat peritoneal mast cells in a dose-dependent manner (100-300 mg/kg) and to reduce antigen-induced allergic nasal symptoms, although it would be difficult to achieve such doses of luteolin with a commercially available peppermint extract or oil. An extract of the whole herb, however, may be beneficial in alleviating nasal symptoms associated with allergic rhinitis in association with other medicines.

ANTIOXIDANT

The polyphenolic compounds in peppermint, such as luteolin-7-O-rutinoside, eriocitrin and rosmarinic acid, have been shown to have antioxidant and free radical scavenging activity. Peppermint oil, and its constituents menthone and isomenthone, exert antioxidant activity. It has been suggested that this antioxidant effect confers chemopreventive and antigenotoxic effects.

STIMULANT

Intraperitoneal and intravenous injections of peppermint oil and its constituents, 1,8-cineol, menthone, isomenthone, menthol, pulegone, menthyl acetate and caryophyllene, dramatically increased ambulatory activity in mice. It is thought that the effect is mediated via a dopaminergic effect of menthol. This may explain the traditional use of peppermint for mental fatigue. Inhalation of peppermint oil has also been shown to have a stimulant effect on mice in a forced swimming test, with the effect remaining when over-agitation was induced by intraperitoneal caffeine.

COOLANT

Peppermint oil interacts with smooth muscle calcium channels. In the peripheral nerves this effect may be responsible for the characteristic cooling sensation experienced on oral ingestion of mint.

ANALGESIC

Peppermint and caraway oil have been shown to synergistically modulate post-inflammatory visceral hyperalgesia in a rat model. A significant analgesic effect, with a reduction in sensitivity to headache, was observed in a double-blind, placebo-controlled, randomised, 7-day cross-over study that used a combination of peppermint oil and ethanol applied externally in 32 healthy males undergoing artificial pain stimulation.

Peppermint: Other Actions

A spray-dried peppermint infusion has been found to be mildly diuretic and produce weak sedative action in several tests when administered orally to mice. Peppermint tea has been found to significantly increase FSH and LH levels and reduce total testosterone levels in rats.