Mint (Mentha spp.): A Comprehensive Reference Article
1. Identity and Botanical Classification
Taxonomy and Species
The genus mint (Mentha) belongs to the Lamiaceae family and includes 42 species, 15 hybrids, and hundreds of subspecies, varieties, and cultivars, which potentially crossbreed when in proximity. It is represented by perennial herbs growing wildly in damp or wet places throughout the temperate regions of Europe, Asia, Africa, Australia, and North America. The two most medically and commercially significant species are Mentha × piperita L. (peppermint) and Mentha spicata L. (spearmint).
Peppermint (Mentha × piperita L.): Botanically, peppermint is a hybrid species resulting from the natural crossing of Mentha aquatica (water mint) and Mentha spicata (spearmint). It originates from the Mediterranean region. The species is a sterile hybrid, propagated exclusively by vegetative means.
Spearmint (Mentha spicata L.): Mentha spicata L., commonly referred to as spearmint, is the predominant source of flavour in various confectionery and food items due to the presence of carvone as the major component in its essential oil.
Other commercially important species include Mentha × gracilis (Scotch spearmint), Mentha canadensis (American wild mint), and Mentha arvensis (corn mint).
Common Names
Peppermint is also known as American mint, balm mint, brandy mint, curled mint, and lamb mint. Spearmint is known as garden mint, common mint, mackerel mint, and our lady's mint. The genus name Mentha derives from the Latin, and the word "menthol" shares this same etymological root.
Botanical Morphology and Natural Source
Different mints are known for a reasonably high content of essential oils (EO), which are deposited in the glandular trichomes, mostly located on the adaxial surface of their leaves. Mint shoots and leaves are used for medicinal and aromatic purposes, such as dried organic extracts, distillates, condiments, and food flavorings. Mints are cultivated as industrial crops in several countries for the essential oil and contain high-value monoterpenes, which find diverse uses in the cosmetic, pharmaceutical, food, confectionery, and liquor industries.
Common Forms and Preparations
- Essential oil: Peppermint oil (PMO) is obtained by steam distillation from the fresh leaves of peppermint (Mentha piperita L).
- Enteric-coated capsules: Peppermint oil is best taken in the form of enteric-coated capsules (containing 0.2 mL of oil), which reduces the risk of heartburn.
- Herbal tea / infusion: Dried or fresh leaves steeped in hot water; widely used as a beverage and traditional remedy.
- Topical preparations: Ethanol solutions, gels, and creams containing peppermint oil or isolated menthol applied to skin.
- Tinctures, spirits, and waters: Medical and pharmacy textbooks of earlier eras described commonly used preparations of mint including the oil, spirit, water, tincture, and troches (lozenges).
- Dried leaf: Leaf preparations are made from either fresh or dried leaves, while the oil is distilled from freshly-harvested sprigs.
2. Traditional and Historical Use
Ancient Egypt
Remains of dried mint leaves have been found in Egyptian tombs dating back more than 3,000 years, indicating that it was used both for medicinal and ceremonial purposes. Peppermint oil has been used to treat abdominal ailments in ancient Egypt, Greece, and Rome.
Ancient Greece and Rome
The ancient Egyptians, Romans, and Greeks used peppermint as a flavoring agent for food and as a medicine, while mint essential oils have been used as perfumes, food flavors, deodorants, and pharmaceuticals. 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. In ancient Greece, mint was considered a symbol of hospitality: it was customary to perfume houses with it when guests arrived, and banquets often ended with an aromatic preparation made from this plant. Arabs used peppermint in their social drinks as a virility stimulant, and Romans would spread peppermint on their floors to help get rid of pests. In the first century AD, the Roman naturalist Pliny noted that the Greeks and Romans used mint to flavor sauces and wine, and it is referenced in a west Nordic pharmacopoeia fragment of the 13th century.
Medieval Europe
During the Middle Ages, powdered mint leaves were used to whiten the teeth. In the Middle Ages, Mediterranean monasteries masterfully made peppermint medicinal preparations and tooth powders. The visionary 12th-century abbess and herbalist Hildegard von Bingen also valued the vital virtue of mint in her extensive treatises on medicinal plants. Mentions of mint as an herbal remedy appear as early as 1240 AD in Icelandic Pharmacopoeias, documenting its known effectiveness for ailments of indigestion and headaches.
Islamic and Arab Medicine
Arab physicians incorporated peppermint into medicinal drinks, recognizing its stimulant and digestive properties. Mint was a staple of medieval Islamic materia medica.
North Africa (Morocco)
Spearmint is a popular herbal tea in present-day Morocco, where many Moroccans drink spearmint tea daily. Ethnobotanical studies researching the cultural and traditional uses of various mints in Morocco found that spearmint has historically been and continues to be used for many common health problems, including digestive issues, burns, headaches, pregnancy concerns, infections, and hypertension. Spearmint is the most commonly used herb in Morocco for throat issues.
Traditional Chinese Medicine
Mentha haplocalyx Briq., a notable member of the Lamiaceae family, occupies a significant role in the realm of health foods and botanical medicines. Traditionally, it has been employed to address various diseases, including colds, coughs, fever, indigestion, asthma, and influenza.
American Military and Civil War Use
Medical and pharmacy textbooks available during the Civil War describe the most commonly used preparations of mint, which included the oil, spirit, water, tincture, and troches (lozenges). The Union Army Standard Supply Table for General Hospitals included peppermint tincture, and the Confederate Army Standard Supply Table for Field Service and General Hospital included oil of peppermint and spearmint herb.
Commercial Cultivation History
Peppermint was first commercially cultivated in England in the late seventeenth century. Today, it is widely cultivated in Europe, Asia, and North America, and is an essential plant in herbal medicine, gastronomy, and the food, cosmetics, and pharmaceutical industries.
3. Key Constituents and Active Compounds
Essential Oil Composition of Peppermint
The major constituents of peppermint oil include the terpenes (−)-menthol (30–50%), (−)-menthone (14–32%), (+)-isomenthone (1.5–10%), (−)-menthyl acetate (2.8–10%), (+)-menthofuran (1.0–9.0%), and 1,8-cineol (3.5–14%). The pharmacologically active ingredient of peppermint oil is menthol, which in nature exists as a pure stereoisomer, (1R,2S,5R)-2-isopropyl-5-methylcyclohexanol. Other significant constituents that contribute to the oil's aromatic profile and biological activity include menthyl acetate, 1,8-cineole, isomenthone, limonene, and various pinenes and caryophyllenes.
Essential Oil Composition of Spearmint
The production of linalool and linalyl acetate is typical for the linalool pathway; menthol, menthone, and menthofuran are constituents of the menthol pathway; and carvone, dihydrocarvone, and carveol characterize the carvone pathway. Spearmint follows the carvone pathway, and its oil is dominated by carvone rather than menthol. The spearmint oil and its main constituent carvone are used extensively for various preparations ranging from medicine to flavored chewing gums, toothpastes, and food products.
Phenolic Compounds and Flavonoids
Recent phytochemical investigations have identified the presence of terpenoids, flavonoids, phenolic acids, anthraquinones, alkanes, and polysaccharides in Mentha haplocalyx, with terpenoids being the primary bioactive constituents. The most abundant polyphenolics in peppermint infusion are eriocitrin, 12-hydroxyjasmonate sulfate, luteolin-O-rutinoside, and rosmarinic acid. Among investigated analytes, Mentha methanolic extracts contain seven hydroxybenzoic acids, six hydroxycinnamic acids, and seven flavonoids.
Toxicologically Relevant Minor Constituents
Pulegone, and its metabolite menthofuran, which are present in peppermint oil, have been considered to be potentially toxic in high doses. In a rat study, ≥80 mg·kg⁻¹·d⁻¹ of pulegone was associated with vacuolization of hepatocytes. In a more recent series of studies from the National Toxicology Program, liver necrosis and cytoplasmic vacuolization were only seen in rats given ≥150 mg·kg⁻¹·d⁻¹ of pulegone for 2 weeks. These findings are at doses far exceeding normal therapeutic human use.
4. Established Mechanisms of Action
Calcium Channel Blockade and Smooth Muscle Relaxation
The principal and most extensively documented pharmacological effect of peppermint oil is its dose-related antispasmodic action on smooth muscle, particularly within the gastrointestinal (GI) tract. This effect is primarily mediated by its main constituent, menthol, which functions as a potent L-type calcium channel antagonist. In vitro studies using guinea pig, rabbit, and human GI smooth muscle tissue have demonstrated that menthol inhibits the influx of extracellular calcium ions (Ca²⁺) into smooth muscle cells. By blocking these voltage-dependent calcium channels, menthol prevents the intracellular calcium surge required for muscle contraction, leading to smooth muscle relaxation. This action is pharmacologically similar to that of synthetic dihydropyridine calcium channel blockers.
TRPM8 Receptor Activation (Cooling Sensation)
Menthol activates the same nerve receptors as the experience of cold, thereby stimulating the cooling sensation of mint when ingested or inhaled. Menthol is a well-characterized agonist of the transient receptor potential melastatin-8 (TRPM8) ion channel, which mediates thermosensation and is also found on sensory neurons in the gut. The menthol derivative WS-12 selectively activates transient receptor potential melastatin-8 (TRPM8) ion channels.
Antimicrobial Activity
The essential oil and its constituents (e.g., menthol, menthone) have displayed activity against Escherichia coli, Helicobacter pylori, methicillin-sensitive and methicillin-resistant strains of Staphylococcus aureus, Pseudomonas spp., Enterobacter aerogenes, and Salmonella enteritidis. Weak antifungal activity has also been shown in vitro. Biofilm development and growth of Listeria was inhibited by peppermint extracts. These findings are primarily in vitro and have not been systematically translated to clinical antimicrobial indications.
Antioxidant Activity
Free radical scavenging and inhibition of lipid peroxidation appear to be the main mechanisms of peppermint's pharmacological antioxidant actions. The oils contain significant amounts of strong radical scavengers, including pulegone, 1,8-cineole, and menthone.
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. Rosmarinic acid, a dominant phenolic in mint infusions, is recognized for anti-inflammatory properties, though its specific clinical mechanisms in humans have not been fully established.
Proposed Antiandrogen Mechanism (Spearmint)
Key constituents of spearmint — particularly rosmarinic acid, carvone, and selected flavonoids — are linked to proposed mechanisms of androgen regulation. The ability to increase the metabolism rate of androgens by inducing cytochrome P450 3A4, or the direct effect of spearmint on the synthesis of androgen hormones, may cause this antiandrogen effect. These mechanisms remain incompletely resolved.
Lower Esophageal Sphincter Relaxation
Peppermint oil has also been shown to relax the lower esophageal sphincter, which can result in gastroesophageal reflux. This finding has led to the popularity of enteric-coated peppermint formulations, which bypass the upper GI tract unmetabolized, thereby facilitating effects in the lower GI tract without effects in the upper tract.
5. Scientific Evidence by Area of Use
5.1 Irritable Bowel Syndrome (IBS)
This is the best-studied application of mint in humans. Evidence focuses almost entirely on enteric-coated peppermint oil capsules.
Meta-analyses and systematic reviews:
A 2014 systematic review and meta-analysis of 9 studies involving a total of 726 participants found peppermint oil to be superior to placebo for global improvement of IBS symptoms and improvement in abdominal pain. A subsequent meta-analysis included twelve randomized trials with 835 patients. For global symptom improvement, the risk ratio from seven RCTs for the effect of peppermint oil versus placebo on global symptoms was 2.39 (95% CI: 1.93, 2.97), I² = 0%. The global improvement in IBS symptoms outcome was upgraded to high quality because of the large magnitude of the effect. The outcome of improvement of abdominal pain was downgraded to moderate because of the risk of bias.
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.
Evidence from recent systematic reviews and meta-analyses consistently indicates that peppermint oil is the most effective botanical agent, particularly for reducing abdominal pain and overall IBS symptom severity.
Contradictory evidence:
A 2020 randomized, double-blind trial of 190 patients in the Netherlands found that neither small-intestinal-release nor ileocolonic-release peppermint oil, administered over 8 weeks, produced statistically significant reductions in abdominal pain response or overall symptom relief when using U.S. FDA/European Medicines Agency recommended endpoints. A 2021 randomized double-blind, placebo-controlled trial involving 133 participants compared the effects of peppermint oil to placebo for relieving IBS symptoms. The results showed clinically significant improvements after 6 weeks in both groups; however, there were no statistically significant differences between peppermint oil and placebo on any of the outcome measures.
Clinical guideline endorsement:
Clinical guidelines issued in 2021 by the American College of Gastroenterology recommend the use of peppermint to provide relief of global IBS symptoms, though the recommendation is conditional, with "low quality of evidence." A 2021 clinical guideline from the American College of Gastroenterology recommended the use of peppermint oil for relief of overall IBS symptoms and noted that enteric-coated formulations might help with acid reflux and indigestion side effects.
Overall evidence strength: Moderate. Multiple RCTs and several meta-analyses support efficacy, but results are mixed in more recent, rigorously designed trials using current regulatory endpoints. Evidence supports short-term use specifically for enteric-coated formulations.
5.2 Tension-Type Headache (Topical Application)
A limited amount of evidence suggests that peppermint oil applied topically (on the skin) might relieve tension headaches. The most cited study is a 1996 controlled crossover trial in 41 patients.
The study included the analysis of 164 headache attacks of 41 patients of both sexes ranging between 18 and 65 years of age, suffering from tension-type headache in accordance with the IHS classification. Four headache episodes per patient were treated in a double-blind, randomized crossover design. Compared to the application of placebo, a 10% peppermint oil in ethanol solution significantly reduced the clinical headache intensity already after 15 minutes (p < 0.01). This significant clinical reduction of the pain intensity continued over the one-hour observation period. There was no significant difference between the efficacy of 1,000 mg of acetaminophen and 10% peppermint oil in ethanol solution.
A prospective, randomized, double-blind, and placebo-controlled clinical Phase IV trial was performed to assess efficacy and safety of a 10% ethanolic solution of peppermint oil for topical use compared to placebo in patients with episodic tension-type headache. Two hundred eleven study participants were randomly allocated within a parallel-group design, with the pain-free rate at 120 minutes as the primary endpoint. Topical application of peppermint oil was considered an effective and safe treatment option for patients suffering from episodic tension-type headache.
Overall evidence strength: Limited but positive. There are a small number of well-designed trials suggesting benefit, but the overall body of evidence is modest and insufficient for definitive conclusions.
5.3 Nausea and Vomiting (Aromatherapy / Inhalation)
An extensive literature search encompassing randomized clinical trials assessed the influence of peppermint aroma on physical and mental health. Findings indicate peppermint aroma's effectiveness in reducing nausea, vomiting, and anxiety in conditions such as pregnancy, post-operative recovery, and chemotherapy.
A study investigating the effects of peppermint essential oil on nausea, vomiting, and belching in cancer patients undergoing chemotherapy found that applying a drop of peppermint oil on the philtrum three times a day for five days post-chemotherapy reduced the frequency of nausea, vomiting, and belching.
However, systematic review conclusions are more cautious. There is no evidence of an effect for peppermint aromatherapy in reducing nausea severity. There is incomplete evidence for the use of aromatherapy blends and ginger, although individual studies do report evidence of an effect.
Overall evidence strength: Weak to mixed. Individual RCTs suggest benefit in postoperative and chemotherapy-induced nausea; however, a Cochrane-style systematic review found insufficient evidence for peppermint aromatherapy specifically. Many studies use blends rather than peppermint alone, complicating interpretation. Blinding is inherently difficult with aromatic interventions.
5.4 Endoscopic Antispasmodic Use
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. L-menthol, derived from peppermint oil, has emerged as a safer alternative antispasmodic. Through calcium channel blockade, L-menthol promotes GI smooth muscle relaxation. Hyoscine-N-butyl bromide (HBB) is widely used during endoscopy to reduce peristalsis, but HBB is associated with cardiovascular risks, such as tachycardia and arrhythmias, and is contraindicated in patients with certain conditions.
Overall evidence strength: Preliminary but plausible mechanistically. RCTs exist but are limited in number. The rationale for a safer antispasmodic for endoscopy is well-supported.
5.5 Polycystic Ovary Syndrome (PCOS) and Hirsutism — Spearmint
The case for spearmint tea for hormones rests on two randomized controlled trials in women with PCOS, both showing measurable testosterone reductions with twice-daily use.
The first study was a two-centre, 30-day randomized controlled trial. Forty-two volunteers were randomized to take spearmint tea twice a day for a one-month period and compared with a placebo herbal tea. At the beginning and end of the trial, serum androgen hormone levels and gonadotrophins were checked, the degree of hirsutism was clinically rated using the Ferriman-Galway score, and a dermatology quality-of-life questionnaire was completed. This research trial demonstrated that the use of spearmint herbal tea has significant measurable anti-androgen effects in patients with hirsutism due to PCOS.
The Grant 2010 trial, published in Phytotherapy Research, randomized 42 women with PCOS to either spearmint tea or a placebo herbal tea twice daily for 30 days. By study end, the spearmint group had significantly lower free and total testosterone, along with significantly higher LH and FSH. Hirsutism was assessed using the Ferriman-Gallwey score, and patients in the spearmint arm reported subjective improvement.
A small number of randomized controlled trials have shown promising results, although the overall evidence remains limited and the effects appear modest. Spearmint contains rosmarinic acid and a group of flavonoids that appear to reduce circulating androgens, though the exact mechanism is not fully resolved.
The clinical evidence is for brewed spearmint tea, not capsules or essential oils. Bioavailability of the active compounds, including rosmarinic acid, differs between tea and concentrated extracts, and dose equivalency has not been established.
Overall evidence strength: Preliminary. Only a small number of RCTs exist, with small sample sizes and short durations. Results are statistically significant but clinical relevance of observed hormonal changes is uncertain. This area requires larger, longer-term trials before conclusions can be drawn.
5.6 Dyspepsia (Non-Ulcer) and Upper GI Symptoms
A combination product including peppermint oil and caraway oil seems to be moderately effective in the treatment of non-ulcer dyspepsia. This preparation (marketed as Enteroplant® or similar) has been studied in several European trials. Very little research has been done on peppermint leaf alone. There is not enough evidence to definitely determine whether peppermint leaf is useful for any health condition.
Overall evidence strength: Moderate for the peppermint oil/caraway oil combination; insufficient for peppermint leaf alone in dyspepsia.
5.7 Cognitive Function and Alertness (Aromatherapy)
Peppermint aroma demonstrates potential in managing fatigue, stress, and mild cognitive impairment. The aroma's influence extends to healthcare workers, enhancing alertness, memory, and accuracy, particularly in high-stress environments. The majority of this evidence comes from small experimental studies and the overall evidence base is preliminary; large-scale RCTs are lacking.
Overall evidence strength: Preliminary. Small experimental studies show psychophysiological effects of inhaled peppermint; robust clinical trials are absent.
6. Body Systems and Health Areas Associated with Mint
- Gastrointestinal system: IBS, dyspepsia, nausea, intestinal spasm, flatulence, colonic antispasmodic use during endoscopy.
- Nervous system / pain: Tension-type headache (topical), analgesic effects via TRPM8 activation and peripheral sensory modulation.
- Respiratory system: Menthol is a volatile aromatic and when inhaled acts as a powerful decongestant, helping to clear phlegm from the airways.
- Endocrine system: Potential antiandrogen activity in PCOS and hirsutism (spearmint); early-stage clinical evidence only.
- Integumentary system: 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.
- Oral health: Historically used for tooth whitening and oral hygiene; widely incorporated into modern toothpastes and mouthwashes.
- Antimicrobial defense (in vitro): Activity against a broad range of bacteria; not yet translated to clinical infectious disease indications.
7. Dosage Forms and Reported Dosages
The following dosages are drawn from clinical studies and authoritative sources only.
Enteric-Coated Peppermint Oil Capsules (IBS)
The therapeutic dosage range studied in most IBS trials was 0.2 to 0.4 mL of peppermint oil taken three times daily in enteric-coated capsules. 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 non-serious constipation and diarrhea associated with IBS. The recommended dosage for adults is 1 to 2 enteric-coated capsules three times a day, and for children older than 8 years, one capsule three times a day.
Topical Application (Tension Headache)
In the key clinical crossover trial, each headache attack was treated by the cutaneous application of the oil preparation (peppermint oil or placebo solution). The oil was spread largely across the forehead and temples, which was repeated after 15 and 30 minutes. The preparation used was a 10% peppermint oil in ethanol solution. The phase IV trial assessed efficacy and safety of a 10% ethanolic solution of peppermint oil for topical use.
Spearmint Tea (PCOS/Hirsutism)
Patients were randomised to two groups. The first were asked to drink two cups of spearmint tea for a period of 30 days. The second group were given a placebo tea. This twice-daily regimen is the dose reflected in both available RCTs.
Inhalation Aromatherapy
In one randomized controlled trial, 182 patients received aromatherapy with peppermint, ginger, and lavender, each diluted to 1% (each dose as pure essential oil was 0.01 mL). No standardized inhalation dose has been established in clinical guidelines.
8. Safety Considerations and Drug Interactions
General Safety Status
Menthol is listed as generally regarded as safe (GRAS) by the US Food and Drug Administration. Few adverse events have been reported in peppermint trials. In those studies reporting adverse events, no differences were noted between peppermint oil and placebo groups except in studies where heartburn was more common in the peppermint oil group.
GERD and Esophageal Reflux
Peppermint oil can relax the lower esophageal sphincter and may worsen symptoms in people with gastroesophageal reflux disease (GERD) or frequent heartburn. In theory, enteric-coated formulations of peppermint oil facilitate release distal to the stomach, thereby minimizing the risk of gastroesophageal reflux.
Adverse Effects at Clinical Doses
Common side effects at clinical doses include heartburn, allergic reactions, nausea, vomiting, vision changes, and perianal burning. Although there were no serious adverse events in one recent RCT, there was a higher rate of adverse events, as well as adverse event-related dropouts, in the peppermint oil group compared to placebo.
Menthol and Infants
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. Peppermint oil should therefore be used only after breastfeeding and then wiped off before the next breastfeeding session.
Drug Interactions
Peppermint oil has been reported to raise serum levels of simvastatin and felodipine in at least one case report. Specifically, peppermint oil may influence metabolism of felodipine via inhibition of CYP3A4, elevating felodipine plasma concentrations and increasing the pharmacologic effects and adverse reactions. Peppermint oil 600 mg in water increased the area under the curve (AUC) of felodipine by 40%.
Decreased cyclosporine levels were reported in a patient consuming herbal tea containing peppermint and 8 other herbs. CYP3A4 inhibitors (weak), including peppermint, may increase the serum concentration of aripiprazole; monitoring is recommended. Absorption of a single dose of caffeine 200 mg was delayed by menthol 100 mg in healthy volunteers.
The midazolam effect was enhanced and prolonged significantly by chronic peppermint oil intake at higher doses, while acute intake of peppermint oil did not change this effect. Gut motility was increased only by acute intake of a higher dose. Regarding the fact that peppermint oil produces changes in tested drug effects, the interaction between drugs and phytopreparations containing peppermint oil should be additionally followed and confirmed in humans.
Pulegone Toxicity
Pulegone and its metabolite menthofuran, which are present in peppermint oil, have been considered to be potentially toxic in high doses. Regulatory agencies, including the European Medicines Agency, set limits for pulegone content in licensed peppermint preparations. Toxicity observed in animal studies occurred at doses far exceeding any typical human therapeutic exposure.
Contact Allergy
Menthol is a recognized contact allergen. Topical application in sensitive individuals can cause contact dermatitis. Patch testing may be warranted in individuals with known sensitivities to plants of the Lamiaceae family before repeated topical use.
References
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