474 Handbook of herbs and spices
Most modern human studies have investigated peppermint oil rather than peppermint
leaf as a treatment for stomach ache (May et al., 1996), spastic colon syndrome
(Somerville et al., 1984), postoperative nausea (Tate, 1997), relief of colonic muscle
spasm during barium enema (Sparks et al., 1995), irritable bowel syndrome (Carling
et al., 1989; Dew et al., 1984; Koch, 1998; Lawson et al., 1988; Pittler and Ernst,
1998; Rees et al., 1979), and headaches (Gobel et al., 1994). The use of peppermint
oil for irritable bowel syndrome is based on preparations in enteric-coated capsules,
causing a spasmolytic activity on smooth muscles of the gut. In animal tests, the
probable mechanism of action has been shown to be the inhibition of smooth muscle
contractions by blocking calcium influx into muscle cells (Forster et al., 1980; Giachetti
et al., 1988).
Peppermint oil is the major constituent of several over-the-counter remedies for
symptoms of irritable bowel syndrome (IBS). Pittler and Ernst (1998) conducted a
study to review the clinical trials of extracts of peppermint as a symptomatic treatment
for IBS by computerized literature searches to identify all randomized controlled
trials. The study indicates that peppermint oil could be efficacious for symptom relief
in IBS. In view of the methodological flaws associated with most studies, no definitive
judgement about efficacy could be given.
In one double-blind, placebo-controlled multi-centre trial, Enteroplant®, consisting
of peppermint oil (90 mg) and caraway oil (50 mg) in an enteric-coated capsule, was
studied in 45 patients with non-ulcerous dyspepsia. After four weeks of treatment
both the intensity of pain and the global clinical impression were significantly improved
for the group treated with the peppermint/caraway combination compared with the
placebo group (p = 0.015 and 0.008, respectively) (May et al., 1996).
The British Herbal Compendium reported carminative, spasmolytic, and choleretic
activity (Bradley, 1992). The approved modern therapeutic applications for peppermint
are supportable based on its history of use in well established systems of traditional
and conventional medicines, extensive phytochemical investigations, in vitro studies,
in vivo pharmacological studies in animals, and human clinical studies.
To examine the antibacterial effects of a wide variety of essential oils (including
peppermint oil) on major respiratory tract pathogens, the antibacterial activity of 14
essential oils and their major components was evaluated by agar-plate dilution assay
under sealed conditions. Of the selected strains of four major bacteria causing respiratory
tract infection, Haemophilus influenzae was most susceptible to the essential oils,
followed by Streptococcus pneumoniae and Streptococcus pyogenes (Inoye et al.,
2001).
28.5.3 Other economic uses
Peppermint oil was evaluated for larvicidal activity against different mosquito species:
Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. Application of oil at
3 ml/m^2 of water surface area resulted in 100% mortality within 24 hours for C.
quinquefasciatus, 90% for A. aegypti and 85% for A. stephensi (Ansari et al., 2000).
The oil showed strong repellent action against adult mosquitoes when applied on
human skin. The virucidal effect of peppermint oil against herpes simplex virus was
examined by Schuhmachera et al. (2003). The inhibitory activity against herpes
simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) was tested in
vitro on RC-37 cells using a plaque reduction assay. The 50% inhibitory concentration
(IC50) of peppermint oil for herpes simplex virus plaque formation was determined