Peppermint

Mentha × piperita L. belongs to Lamiaceae, the mint family, with square stems and paired leaves. The × marks a hybrid: NCCIH describes peppermint as a natural cross between water mint (M. aquatica) and spearmint (M. spicata). NCBI Taxonomy files it as taxon 34256. Peppermint is largely sterile and spreads by underground and surface runners, so commercial fields are clones propagated from cuttings. It grows to knee height or more, with dark green, toothed, lance-shaped leaves on stalks, stems often tinged purple, and spikes of small lilac flowers in late summer. It likes moist soil and spreads aggressively in gardens. NCCIH notes that it grows throughout Europe, North America, and the Mediterranean.

Two products come from the plant. Peppermint leaf, dried, is used as tea. Peppermint oil is the essential oil steam-distilled from the fresh flowering aerial parts and leaves (NCCIH). The oil is a very concentrated product: a capsule of 0.2 ml holds the oil from a large quantity of leaf, and its effects and risks are not those of a cup of tea. The EU has separate monographs for the leaf and the oil, and the European Pharmacopoeia sets standards for each. Spearmint, corn mint (M. arvensis, the source of Japanese mint oil and much industrial menthol), and pennyroyal are different plants with different chemistry.

Menthol is the defining compound. Natural peppermint oil contains (−)-menthol (PubChem CID 16666, C10H20O) as its largest component, followed by menthone (CID 26447) and smaller amounts of menthyl acetate, 1,8-cineole, limonene, and others. Two minor constituents matter for safety: pulegone (CID 442495) and menthofuran (CID 329983). EMA’s monograph notes that together they make up about 1–11% of the oil, that pulegone and its metabolites caused liver and urinary-tract tumours in rats and mice through a non-genotoxic mechanism, and that medicinal products must keep combined daily exposure below 37.5 mg per person, or 0.75 mg per kilogram of body weight in children. Pennyroyal oil, rich in pulegone, is notoriously toxic; quality peppermint oil keeps pulegone low.

Mints are ancient medicines. NCCIH notes that mint plants were used for digestive disorders in ancient Greece, Rome, and Egypt and that peppermint oil has been used for centuries for gastrointestinal complaints. Those early references are to mints generally, because peppermint as a named plant is surprisingly recent. The English naturalist John Ray described a hot, pepper-tasting mint found in Hertfordshire in the 1690s, and Linnaeus gave it the name Mentha piperita in 1753. Its hybrid origin was confirmed much later.

Commercial peppermint began in England. Fields around Mitcham in Surrey, the same district famous for lavender, produced peppermint oil from the eighteenth century, and Mitcham peppermint became a quality standard. Cultivation spread to the United States in the nineteenth century, first in New England and New York, then Michigan, and later the Pacific Northwest, which became a major producer of the world’s peppermint oil. Most of it goes into toothpaste, chewing gum, confectionery, and flavourings rather than medicines. Menthol itself entered pharmacy as a counter-irritant and cooling agent in rubs, lozenges, and inhalants.

Modern clinical interest focused on the gut. Peppermint oil was found to relax intestinal smooth muscle, and enteric-coated capsules were developed so the oil would pass the stomach and release in the small intestine, reducing heartburn. Trials in IBS followed from the 1970s and 1980s onward, along with use of peppermint oil to reduce spasm during endoscopy and barium enema. In Germany a 10% peppermint oil solution was licensed for tension-type headache after controlled trials in the 1990s. The EU herbal committee began work on its first peppermint oil monograph in 2007 and adopted revised monographs for the oil and leaf on 15 January 2020. The American College of Gastroenterology included peppermint in its 2021 IBS guideline.

In the gut, EMA’s monograph describes peppermint oil as spasmolytic on gastrointestinal smooth muscle when given orally or applied directly inside the stomach or colon, with additional choleretic (bile-stimulating) and antifoaming effects that may reduce distension and discomfort. MSKCC attributes the antispasmodic action to reduced calcium influx in smooth muscle, the same broad mechanism as some prescription antispasmodics. Menthol and other terpenes are fat-soluble and rapidly absorbed in the upper small intestine, then excreted partly as glucuronides; enteric-coated and modified-release capsules delay and reduce peak absorption (EMA). That is why formulation matters so much: uncoated oil acts in the stomach and oesophagus, where it causes heartburn, while delayed-release oil reaches the small bowel, where the IBS effect is thought to occur.

On skin and mucous membranes, menthol activates TRPM8, an ion channel in sensory neurons that responds to cool temperatures. McKemy, Neuhausser, and Julius (Nature 2002) and Peier and colleagues in Ardem Patapoutian’s group (Cell 2002) independently identified the channel using menthol as the probe. That work was part of the discoveries recognized by the 2021 Nobel Prize to David Julius and Ardem Patapoutian for receptors for temperature and touch. EMA describes the topical analgesic effect as a prolonged cold sensation from stimulation of cold-sensitive receptors. In tension-type headache, the cooling and counter-irritant effect on the forehead and temples is the proposed mechanism.

On drug metabolism, EMA notes some inhibition of CYP3A4 in one clinical study with peppermint oil and one with menthol, and MSKCC cites laboratory evidence of inhibition of several CYP enzymes, with unclear clinical relevance. In infants, menthol can trigger reflex apnoea and laryngospasm, the basis for EMA’s contraindication under two years.

Irritable bowel syndrome is the best-studied use. Ford and colleagues (BMJ 2008) pooled four placebo-controlled trials with 392 patients and found a relative risk of persistent symptoms of 0.43 with peppermint oil, larger than the effect for fibre or most antispasmodics. Alammar and colleagues (BMC Complementary and Alternative Medicine 2019) pooled 12 trials with 835 patients and found peppermint oil more than doubled the chance of global symptom improvement (risk ratio 2.39), with three patients needing treatment to prevent persistent symptoms in one. Ingrosso and colleagues (Alimentary Pharmacology and Therapeutics 2022), updating the Ford review with 10 trials and 1,030 patients, again found peppermint oil better than placebo for global symptoms (number needed to treat 4) and abdominal pain (7), but with more adverse events and very low quality evidence. NCCIH cites that 2022 review.

The newest large trial was more sobering. In the Dutch PERSUADE trial (Weerts, Gastroenterology 2020), 190 people with IBS by Rome IV criteria took 182 mg of small-intestinal-release peppermint oil, 182 mg of ileocolonic-release oil, or placebo for eight weeks. Neither formulation met the US FDA abdominal pain response end point (46.8% and 41.3% versus 34.4% on placebo) or the EMA overall relief end point. The small-intestinal-release oil did improve abdominal pain, discomfort, and IBS severity as secondary outcomes, and the ileocolonic version showed no promise. Cash and colleagues (Digestive Diseases and Sciences 2016) reported a 40% versus 24% reduction in total IBS symptom score over four weeks with a sustained-release small-intestinal formulation in 72 patients with IBS with diarrhoea or mixed IBS. The ACG’s 2021 guideline suggests peppermint for global IBS symptoms, a conditional recommendation based on low-quality evidence, and notes that enteric-coated formulations may reduce reflux and indigestion side effects.

Tension-type headache: Göbel and colleagues (Nervenarzt 1996) treated 164 headache attacks in 41 patients in a double-blind crossover trial. A 10% peppermint oil solution in ethanol, spread across the forehead and temples, reduced headache intensity within 15 minutes compared with placebo, and its effect did not differ from 1,000 mg of paracetamol (acetaminophen). EMA accepts this as well-established use in adults for mild tension-type headache. A 2016 review by the same group notes that 10% solutions are licensed in Germany for adults and children over six; EMA’s monograph does not recommend the headache use under 18 because of limited data.

Other uses have smaller evidence bases. NCCIH reports that oral or inhaled peppermint may reduce chemotherapy-related nausea and vomiting (a 2024 review included four aromatherapy studies with 290 participants), that peppermint oil may reduce spasm during endoscopy or barium enema, that topical peppermint products may help nipple pain and cracking during breastfeeding if wiped off before feeding, and that a peppermint gel might reduce pressure ulcers. Combination products containing peppermint oil plus caraway oil, or peppermint leaf with other herbs, may help functional dyspepsia, but peppermint oil alone may worsen indigestion. EMA’s traditional uses for the oil include coughs and colds (inhaled, in lozenges, or as chest rubs), localized muscle pain, and itching on intact skin; for the leaf, tea for indigestion and flatulence.

EU well-established use, oral (EMA/HMPC/522410/2013, revision 1, adopted 15 January 2020): peppermint oil in gastro-resistant (enteric-coated) solid dosage forms, 0.2–0.4 ml per dose, 0.6–1.2 ml per day divided into two or three doses, for adolescents and adults; children aged 8 to 11, 0.2 ml three times daily. Not recommended under 8. Take 30 minutes before meals and swallow whole; breaking or chewing releases the oil early and irritates the mouth and oesophagus. Use until symptoms resolve, usually within one to two weeks; for persistent symptoms, courses can continue for up to three months. Avoid taking with food or antacids, H2 blockers, or proton pump inhibitors, which can dissolve the coating early.

EU well-established use, topical: for mild tension-type headache in adults, a 10% peppermint oil preparation in ethanol rubbed on the forehead and temples, repeated twice at 15-minute intervals, once per treatment day. Keep it away from the eyes; touching the eyes with unwashed hands after application can cause irritation. Not recommended under 18 for this use. Other peppermint oil products should be avoided during treatment.

EU traditional use: inhaled peppermint oil (0.08–0.16 ml in hot water, up to three times daily), lozenges or oral spray, and rubs or ointments applied to the chest, back, or around the nostrils for coughs and colds; 5–20% preparations on the skin for localized muscle pain or itching, at lower strengths for adolescents and children over four. Peppermint leaf tea (EMA/HMPC/572705/2014): 1.5–3 g of dried leaf in 100–150 ml of boiling water three times daily for adults, 1–2 g for children aged 4 to 11 and adolescents, for indigestion and flatulence; tinctures 2–3 ml three times daily. Leaf preparations are not recommended under 4. For all traditional uses, see a doctor if symptoms last longer than two weeks.

Never apply peppermint oil, menthol rubs, or inhalants to the face or near the nose of babies and young children; EMA contraindicates such use under two years because menthol can cause reflex apnoea and laryngospasm, and NCCIH gives the same warning. Undiluted essential oil is not for internal use outside a formulated capsule. Keep essential oils locked away from children.