Peppermint (Mentha Ă— piperita L.): A Comprehensive Reference
1. Identity, Taxonomy, and Natural Source
Peppermint (Mentha Ă— piperita, also known as Mentha balsamea Wild) is a hybrid mint, a cross between watermint and spearmint. It was given the name Mentha piperita in 1753 by Carl Linnaeus in his Species Plantarum, Volume 2. Linnaeus treated peppermint as a species, but it is now agreed to be a hybrid between Mentha aquatica and Mentha spicata, with M. spicata itself also being considered by some authors to be a hybrid between Mentha longifolia and Mentha suaveolens.
Indigenous to Europe and the Middle East, the plant is now widely spread and cultivated in many regions of the world. Although the genus Mentha comprises more than 25 species, the one in most common use is peppermint. While Western peppermint is derived from Mentha Ă— piperita, Chinese peppermint, or bohe, is derived from the fresh leaves of M. haplocalyx.
Peppermint is a herbaceous, rhizomatous, perennial plant that grows to be 30–90 cm tall, with smooth stems, square in cross section. The rhizomes are wide-spreading and fleshy, and bear fibrous roots. The leaves can be 4–9 cm long and 1.5–4 cm broad. They are dark green with reddish veins, with an acute apex and coarsely toothed margins.
Common Preparations and Dosage Forms
Peppermint oil is the common name for the essential oil obtained from the fresh aerial parts of the flowering plant Mentha Ă— piperita L. Herbal medicines containing peppermint oil preparations are usually available in solid, semi-solid or liquid forms to be taken by mouth, applied to the skin, sprayed in the mouth, or inhaled. Both peppermint leaf (Menthae piperitae folium) and peppermint oil (Menthae piperitae aetheroleum) are official medicines in Europe (European Pharmacopoeia; EMA/HMPC) and are listed in the U.S. National Formulary. Peppermint oil, spirit, and water have official monographs in the United States Pharmacopeia (USP).
- Essential oil: Obtained by steam distillation from the fresh aerial parts of the flowering plant.
- Enteric-coated capsules: The most studied and recommended method for digestive issues is the use of enteric-coated capsules. This special coating prevents the oil from being released in the stomach, avoiding heartburn, and allows it to travel directly to the intestines where the antispasmodic effect is needed.
- Leaf infusion (tea) and dried leaf: Peppermint leaves consist of the fresh or dried leaf of Mentha Ă— piperita L., as well as its preparations in effective dosage. The herb contains at least 1.2 percent (v/w) essential oil.
- Tincture: The monograph of peppermint tincture is listed in the Polish Pharmacopoeia and is usually used orally in dyspepsia, intestinal colic, and flatulence.
- Topical preparations: Peppermint oil, leaf extract, leaf, and leaf water are all obtained from the Mentha piperita plant. The oil is used in cosmetic formulations as a fragrance component.
2. Traditional and Historical Use
Ancient Egypt
The herb has been used as a remedy for indigestion since ancient Egyptian times. Dried peppermint leaves were found in Egyptian pyramids dating back to 1000 B.C. The Ebers Papyrus (c. 1550 BC) documents its carminative and digestive use.
Ancient Greece and Rome
The ancient Greeks and Romans valued it as a stomach soother. Pliny (23–79 AD), Roman scientist and historian, recorded that the Greeks and Romans used peppermint to flavor sauces and their wines. The Greek physician Dioscorides and the Roman naturalist Pliny the Elder documented its benefits extensively. Aristotle (circa 384–322 BCE) referenced peppermint in his writings as an aphrodisiac. Alexander the Great (356–323 BCE) forbade his soldiers to have peppermint because it was thought to promote erotic thoughts and deplete soldiers of the desire to fight.
Middle Ages and Medieval Europe
During the Middle Ages, peppermint was cultivated in monastic gardens and used in traditional medicine. It is mentioned in thirteenth century Icelandic Pharmacopoeias. Peppermint was first listed in the London Pharmacopoeia in 1721.
18th–19th Century Commercialization
Commercial peppermint cultivation in England began around 1750, primarily at Mitcham in Surrey. The peppermint cultivar 'Black Mitcham' has been the most widely grown mint for much of the history of commercial production in the United States, first grown in England in the 1750s, then in colonial New England. Commercial peppermint history in the United States is believed to have begun in Wayne County, New York in the early part of the 1800s.
During the eighteenth century, peppermint became popular in Western Europe as a folk remedy for nausea, vomiting, morning sickness, respiratory infections, and menstrual disorders.
Arab and Middle Eastern Traditions
Arabs used peppermint in their social drinks as a virility stimulant. Peppermint is an herb prevalent in Europe and North America with a long medicinal history. It is taken orally as a carminative to treat digestive problems, applied topically as a counter-irritant for aches and cold symptoms, and its essential oil is used in aromatherapy.
3. Key Constituents and Active Compounds
Essential Oil Composition
The chemical composition of the essential oil from peppermint (Mentha × piperita L.) has been analyzed by GC/FID and GC-MS. The main constituents were menthol (40.7%) and menthone (23.4%). Further components were (±)-menthyl acetate, 1,8-cineole, limonene, beta-pinene, and beta-caryophyllene. In one analysis of Moroccan peppermint, major constituents were menthol (46.32%), menthofuran (13.18%), menthyl acetate (12.10%), menthone (7.42%), and 1,8-cineole (6.06%).
Peppermint oil is composed primarily of menthol and menthone. Other possible constituents include pulegone, menthofuran, and limonene.
Non-Volatile Constituents
The herb contains at least 1.2 percent (v/w) essential oil, while other ingredients include tannins characteristic of Lamiaceae. Peppermint and its main constituents (menthol and menthone) have been investigated for immunological and anti-inflammatory effects.
4. Mechanisms of Action
Smooth Muscle Relaxation via Calcium Channel Blockade
Peppermint oil contains L-menthol, which blocks calcium channels in smooth muscle, thus producing antispasmodic effects on the gastrointestinal tract. Peppermint oil's benefit in functional gastrointestinal disorders such as irritable bowel syndrome (IBS) has been ascribed primarily to its antispasmodic effect. In vitro studies showed that both peppermint oil and its constituent menthol were capable of blocking calcium channels in guinea pig ileal smooth muscle; further in vitro studies using guinea pig colon and rabbit jejunum smooth muscle suggest peppermint oil reverses acetylcholine-induced contraction and antagonizes serotonin-induced contraction through calcium channel blockade.
Menthol exhibits central and peripheral antispasmodic effects by blocking voltage-dependent calcium channels (CaV) in smooth muscle tissues. This action prevents calcium influx, leading to the relaxation of gastrointestinal, vascular, and bronchial smooth muscles.
TRPM8 and TRP Channel Modulation
Menthol in mints elicits a coolness sensation by selectively activating the TRPM8 channel. Activation of TRPM8 induces a cooling sensation that counteracts nociceptive stimuli and desensitizes pain-transmitting nerve fibers. This sensory modulation reduces the perception of thermal and mechanical pain and is particularly effective in superficial applications such as topical pain relievers and cooling gels. In addition to TRPM8, menthol can also modulate the activity of other ion channels implicated in pain transduction, including voltage-gated sodium channels (NaV).
In irritable bowel syndrome (IBS), menthol can activate the TRPM8 channel to inhibit the chemical and mechanosensory responses of nociceptive TRP channels and diminish the release of pro-inflammatory mediators from nerve endings. Different transient receptor potential channels (TRP) such as TRPM8, TRPV1 and TRPA3 could also be involved in the response since menthol is a ligand of these receptors.
Anti-inflammatory Activity
Peppermint oil possesses antimicrobial, anti-inflammatory, antioxidant, immunomodulating, and anesthetic activities, all of which may be relevant for the treatment of IBS. One in vitro study in a murine macrophage cell line showed decreased production of NO, TNF-α, IL-6, and prostaglandin E-2 (PGE-2) from an ethanol extract of peppermint. The LPS-induced NO production decreased in a concentration-dependent manner.
Preclinical Summary of Mechanisms
Peppermint oil appears to have several mechanisms of action including: smooth muscle relaxation (via calcium channel blockade or direct enteric nervous system effects); visceral sensitivity modulation (via transient receptor potential cation channels); antimicrobial effects; and anti-inflammatory effects.
5. Scientific Evidence by Area of Use
5.1 Irritable Bowel Syndrome (IBS)
Overview of Evidence
A small amount of research suggests that peppermint oil in enteric-coated capsules may improve IBS symptoms in adults. A 2022 review of 10 studies (involving 1,030 participants) found that peppermint oil was better than placebo at improving overall IBS symptoms and reducing abdominal pain but caused more side effects than placebo. Most of the side effects were mild and included acid reflux and indigestion.
Systematic Reviews and Meta-analyses
A 2022 systematic review and meta-analysis identified 10 eligible RCTs (1,030 patients). Peppermint oil was more efficacious than placebo for global IBS symptoms (RR of not improving = 0.65; 95% CI 0.43–0.98, number needed to treat [NNT] = 4; 95% CI 2.5–71), and abdominal pain (RR of abdominal pain not improving = 0.76; 95% CI 0.62–0.93, NNT = 7; 95% CI 4–24).
In a systematic review assessing the largest cohort of RCTs published over five decades, twelve randomized clinical trials with 835 IBS patients were included. Overall, treatment with peppermint oil significantly improved abdominal pain and global symptoms of IBS, with a good safety profile. The strength of findings was reflected by the large effect size of peppermint oil over placebo and by the low heterogeneity across included studies.
A meta-analysis of seven high-quality studies including a total of 722 participants found that peppermint oil (PO) improved IBS Global Improvement in Symptoms (IBS-GIS) significantly compared with the placebo group (RR = 1.62, 95% CI: 1.20–2.17, P = 0.002), though improvements in IBS Symptom Severity Scale and quality of life scores were not significantly better than placebo.
Khanna et al. (2014) concluded in their systematic review and meta-analysis that peppermint oil is a safe and effective short-term treatment for IBS, but noted that future studies should assess the long-term efficacy and safety of peppermint oil and its efficacy relative to other IBS treatments including antidepressants and antispasmodic drugs.
A Specific Clinical Trial
A multi-center, open-label, single-arm, phase 3 trial enrolled Japanese outpatients with IBS aged 17–60 years (Rome III criteria). Subjects were treated with an oral capsule three times a day before meals for four weeks. Among sixty-nine subjects treated, the improvement rate of the patient's global assessment (PtGA) was 71.6% at week 2 and 85.1% at week 4.
Older Evidence and Limitations
In an earlier review and meta-analysis, eight randomized controlled trials were located, which collectively indicated that peppermint oil could be efficacious for symptom relief in IBS. A meta-analysis of five placebo-controlled, double blind trials seemed to support this notion, but in view of methodological flaws associated with most studies, no definitive judgment about efficacy was possible.
5.2 Functional Dyspepsia
A number of randomized controlled trials have shown peppermint oil to be effective for functional dyspepsia when used in conjunction with other natural products, primarily caraway. However, to the knowledge of reviewers, peppermint oil had not been studied alone in a randomized, double-blind trial for this indication as of 2017.
A systematic review and meta-analysis of a peppermint oil and caraway oil combination searched multiple databases and included 5 RCTs (578 participants). The combination showed a statistically significant effect in global improvement of functional dyspepsia (FD) symptoms (RR for not much or very much improvement 0.59, 95% CI: 0.49 to 0.71, P < 0.00001, NNT 3) and improvement in epigastric pain (RR 1.61, 95% CI: 1.28 to 2.03, P < 0.0001, NNT 3), with no significant differences in total adverse events between the combination and placebo (NNH 40). The combination was concluded to be an effective and safe short-term treatment for FD.
In one placebo-controlled RCT, 96 outpatients received one enteric-coated capsule twice daily of a fixed combination of 90 mg peppermint oil and 50 mg caraway oil (PCC; Enteroplant), or placebo, for 28 days. On day 29, the average intensity of pain was reduced by 40% vs. baseline in the PCC group and by 22% in the placebo group.
5.3 Tension-Type Headache
A limited amount of evidence suggests that peppermint oil applied topically (on the skin) might relieve tension headaches.
A study that analyzed 164 headache attacks in 41 patients (ages 18–65) with tension-type headache used a double-blind, randomized crossover design. Each headache attack was treated by cutaneous application of the oil preparation (peppermint oil or placebo solution) and oral medication (acetaminophen or placebo). The oil was spread largely across the forehead and temples, repeated after 15 and 30 minutes. A 10% peppermint oil in ethanol solution significantly reduced clinical headache intensity already after 15 minutes (p < 0.01).
There was no significant difference between the efficacy of 1,000 mg of acetaminophen and 10% peppermint oil in ethanol solution. Simultaneous application of 1,000 mg of acetaminophen and 10% peppermint oil in ethanol solution led to an additive effect which remained below the significance threshold.
When applied topically, peppermint oil provides a local analgesic effect, which is particularly useful for tension-type headaches, achieved through the activation of TRPM8 channels by menthol, which creates a cooling sensation that overrides pain signals, and potentially through local vasorelaxant effects.
5.4 Nausea (Post-operative and Other)
Placebo-controlled studies support the use of peppermint oil in post-operative nausea. Lane et al. reported reduced nausea in women post cesarean section treated with peppermint oil aromatherapy (POA) as compared to an inhaled inert placebo and standard antiemetic therapy (SAT), assessed at 2 minutes (POA vs. placebo: P <0.000, POA vs. SAT: P <0.001) and 5 minutes post treatment (POA vs. placebo: P <0.000, POA vs. SAT: P <0.003).
5.5 Endoscopy and Gastrointestinal Procedures
A small amount of research suggests that peppermint oil might be helpful to reduce spasms during certain procedures, such as endoscopy or barium enema examination. It has been used to facilitate completion of colonoscopy and endoscopic retrograde cholangiopancreatography.
5.6 Cognitive Performance and Alertness
Clinical data suggest benefits of oral peppermint use for modulating cognitive performance. Clinical research indicates that peppermint, alone or in combination formulas, may be beneficial for cognitive performance, though evidence for this use, along with several others such as hirsutism and athletic performance, has not been as extensively studied as its gastrointestinal applications. This area of research is considered preliminary, with most findings from small trials.
5.7 Topical Applications: Pressure Ulcers and Nipple Pain
A limited amount of evidence suggests that a gel containing peppermint oil applied topically might reduce the risk of bed sores (pressure ulcers) in bedridden individuals. Peppermint oil in a gel, water, or cream applied topically to the nipple area of breastfeeding women might be helpful for reducing pain and cracked skin.
5.8 Antimicrobial Activity
The essential oil of M. piperita exercised an important inhibitory activity against all studied bacteria, especially M. luteus and B. subtilis, which showed high sensitivity to this oil. Both peppermint extracts and essential oil have demonstrated antiviral, anti-inflammatory, antioxidant, antibacterial, antifungal, antidiabetic, and antifibrotic effects in preclinical studies. These antimicrobial findings are predominantly from in vitro and animal studies; their clinical relevance in humans has not yet been established.
6. Body Systems and Health Areas
Peppermint oil and its constituents exert smooth muscle relaxant and anti-spasmodic effects on the lower esophageal sphincter, stomach, duodenum, and large bowel. Moreover, peppermint oil can modulate visceral and central nervous system sensitivity.
- Gastrointestinal system: IBS, functional dyspepsia, flatulence, spasms of the gastrointestinal tract, gallbladder and bile ducts. The German Commission E approved peppermint leaf for spastic complaints of the gastrointestinal tract as well as the gall bladder and bile ducts.
- Nervous system / pain: Tension-type headache (topical), visceral pain in IBS.
- Respiratory system: Peppermint essential oil and its component pulegone are effective against acetylcholine- and KCl-elicited contraction of rat tracheal smooth muscle, and suppresses CaClâ‚‚-evoked contraction in rat depolarized trachea, indicating impeded extracellular calcium entry. However, clinical evidence in humans for respiratory applications is limited.
- Immune / inflammatory system: Anti-inflammatory and antioxidant effects have been demonstrated in preclinical settings, with some emerging data in human trials (primarily indirectly through IBS outcomes).
- Skin: Topical counter-irritant, wound-associated pain, nipple cracking in breastfeeding women.
- Nausea: Peppermint oil is used for inhalation in aromatherapy, promoted to treat common colds and cough, to reduce stress, and improve mental function.
7. Regulatory and Monograph Status
The EMA's Committee on Herbal Medicinal Products (HMPC) concluded that, on the basis of its long-standing use, peppermint leaf preparations can be used for relief of digestion-related problems such as indigestion and flatulence. They should only be used in adults and children over the age of 4 years.
Peppermint essential oil has good clinical evidence for use in particular gastrointestinal problems and has recognized herbal medicinal products; however, the data is not directly applicable to other peppermint extracts or food supplements, since these have different health claims and formulations.
Menthol is listed as generally regarded as safe (GRAS) by the U.S. Food and Drug Administration (FDA).
8. Dosages Reported in Studies
Up to 1,200 mg daily (180 to 400 mg three times daily) of peppermint oil in enteric-coated capsules has been used to treat IBS-associated symptoms. A review of clinical trials investigated dosages of up to 1,200 mg/day of enteric-coated peppermint oil (capsules containing 180 to 200 mg of peppermint oil, administered as 1 to 2 capsules 3 times daily) over 2 to 4 weeks.
For functional dyspepsia, a fixed combination of 90 mg peppermint oil and 50 mg caraway oil in enteric-coated capsules was studied, administered as one capsule twice daily for 28 days.
For tension-type headache, a 10% peppermint oil in ethanol solution was applied cutaneously across the forehead and temples, with applications repeated after 15 and 30 minutes.
Enteric-coated, gastro-resistant formulations of peppermint oil should not be taken immediately after eating. These products should preferably be taken 30 to 90 minutes before a meal with water.
9. Safety Considerations and Interactions
General Safety Profile
Few adverse effects have been reported in peppermint oil trials. Peppermint oil is a natural product which has been used successfully for several clinical disorders and appears to have a good safety profile.
Gastrointestinal Reflux and Lower Esophageal Sphincter
Peppermint oil should not be administered to patients with gastroesophageal reflux or active gastric ulcers because the oil decreases esophageal sphincter pressure. Ingestion of peppermint oil rich in menthol may cause heartburn due to relaxation of the lower esophageal sphincter, thereby promoting gastroesophageal reflux, and can occasionally induce burning sensations in the anal or perianal region.
Enteric-Coated Formulation Precautions
Enteric-coated peppermint oil should not be used in individuals with achlorhydria (a stomach condition in which the stomach is not producing hydrochloric acid), because the enteric coating might dissolve too early in the digestive process. Enteric-coated peppermint oil could cause anal burning in individuals who have diarrhea.
Use in Infants and Children
Menthol, which is in peppermint oil, should not be inhaled by or applied to the face of an infant or small child because it may negatively affect their breathing. Enteric-coated preparations are not recommended for use in children younger than 8 years.
Use During Breastfeeding
Peppermint oil in a gel, water, or cream applied topically to the nipple area of breastfeeding women might be helpful for reducing pain and cracked skin. Peppermint oil should be used only after breastfeeding and then wiped off before the next breastfeeding session.
Drug Interactions
A moderate interaction is noted for cyclosporine. Some medications that decrease stomach acid might cause the enteric coating of peppermint oil products to dissolve too quickly, which can lead to heartburn and nausea. Such medications should be taken at least two hours after coated peppermint oil products; these include cimetidine (Tagamet), ranitidine (Zantac), nizatidine (Axid), and famotidine (Pepcid).
There is evidence that menthol can enhance the dermal penetration of other agents. Formulators and clinicians should note that this enhanced penetration can affect the safety of other topically co-applied ingredients whose safety assessment was based on their lack of absorption.
Toxicologically Relevant Constituents
Pulegone and its metabolite menthofuran, present in peppermint oil, have been considered to be potentially toxic in high doses. In rat studies, ≥80 mg/kg/day of pulegone was associated with vacuolization of hepatocytes. In a series of studies from the National Toxicology Program, liver necrosis and cytoplasmic vacuolization were only seen in rats given ≥150 mg/kg/day of pulegone for 2 weeks. These effects were observed at doses far in excess of those used therapeutically in humans.
Because of the toxicity of pulegone, the safe concentration of this constituent is limited to ≤1% in cosmetic formulations. This concentration is achievable both by controlling the time of harvest and processing technique.
Gallbladder Disease
Patients with gallstones (stones in the gallbladder) and any other bile-related problems should be cautious when using peppermint leaf preparations. In case of gallstones, use only after consultation with a physician.
References
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