The most toxic component of peppermint oil is menthol (peppermint oil is the distilled product of the whole plant, Mentha piperita). An oral dose of as little as two grams of menthol can be fatal in an adult. Luckily, pure menthol is not readily available; most over-the-counter menthol products are diluted.
However, peppermint oil can contain 50 – 85% menthol by volume, so less than 2.5 grams of the highest-quality peppermint oils could still lead to serious overdose. (Wurges J. Gale Encyclopedia of Alternative Medicine: Peppermint. Gale Group, Inc. 2005)
Peppermint has enjoyed a long history of use as a flavoring, a deodorizer, and a medicine; peppermint is among the oldest of herbal medicinals, having been cultivated by the ancient Egyptians and possibly used as long ago as ten millennia.
Peppermint was mentioned in thirteenth-century Icelandic pharmacopoeias and was admitted to the London Pharmacopoeia in 1721; its near-ubiquitous presence in many modern products offers reassurance of its safety.
While day-to-day consumption of peppermint-containing products is safe, it is feasible that individuals employing peppermint oil for medicinal reasons could be exposed to dangerous levels of its toxic components.
Medicinal Uses for Peppermint Oil That are Supported by Scientific Evidence
The active ingredients of peppermint oil include menthol, menthone, cineol, and other volatile oils. These compounds are responsible for peppermint’s medicinal properties as well as its potential toxicity.
Irritable Bowel Syndrome
- Peppermint oil may be mildly effective for relieving the symptoms of IBS, particularly flatulence, abdominal pain, and distension.
- A 1998 meta-analysis of five clinical trials showed peppermint oil was superior to placebo for the symptomatic treatment of IBS. (Pittler M, Ernst E. Peppermint oil for irritable bowel syndrome: a critical review and metaanalysis. Am J Gastroenterol 1998;93:1131-5)
- A more recent systematic reviewdemonstrated similar findings, although the heterogeneity of the included studies has been called into question. (Spanier J, Howden C, Jones M. A systematic review of alternative therapies in the irritable bowel syndrome. Arch Intern Med 2003;163:265-74)
- These analyses showed peppermint oil to be useful for IBS even in pediatric populations (ages 8 – 17).
Reduction of Spasm During GI Procedures
- Several clinical trials have shown that peppermint oil administered during barium enemas reduces spasm both during and after the procedure. This benefit may also apply to colonoscopy, but studies have not yet been completed. (Kligler B, Chaudhary S. Peppermint oil. Am Fam Phys. 2007;75[7]:1027-30)
Non-ulcer Dyspepsia (Epigastric Pain and Stomach Bloating)
- A combination of peppermint oil and caraway oil helps reduce symptoms of bloating, fullness and spasm. A product available in the U.S. (Iberogast), containing peppermint oil, caraway oil, and other herbs, has proven beneficial for dyspepsia. (Melzer J, et al. Meta-analysis: phytotherapy of functional dyspepsia with the herbal drug preparation STW 5 (Iberogast). Aliment Pharmacol Ther 2004;20:1279-87)
Tension Headache
- Randomized clinical trials have shown that topical application of peppermint oil reduces the severity and duration of tension headaches when compared to both placebo and acetaminophen (Tylenol), and no adverse effects were noted. (Gobel H, Schmidt G, Soyka D. Effect of peppermint and eucalyptus oil preparations on neurophysiological and experimental algesimetric headache parameters. Cephalalgia 1994;14:228-34 and Gobel H, et al. Effectiveness of oleum menthae piperitae and paracetamol in therapy of headache of the tension type [German]. Nervenarzt 1996;67:672-81)
Other Popular Medicinal Uses for Peppermint Oil
Clinical trials evaluating the following uses for peppermint oil have either not been conducted or have shown no benefit:
- Colic
- Gallstones
- Intestinal bacterial overgrowth (e.g., in “cleanses”)
- Nausea
- Respiratory congestion
- Coughs
- Colds
- Breastfeeding support (topical treatment of cracked, sore nipples)
Hazards and Adverse Effects Associated with Peppermint Oil
- Peppermint oil reduces the spasm of the lower esophageal sphincter. This could worsen symptoms in individuals with gastroesophageal reflux. Enteric-coated capsules might help to alleviate this problem.
- Peppermint oil can cause or aggravate jaundice in infants; it should not be used for colic.
- High doses of peppermint oil can cause nausea, loss of appetite, blurred vision, heart problems (palpitations, etc.), and loss of coordination and balance.
- Overdose can lead to kidney failure, liver damage, and death.
- Topical or oral use can cause allergic reactions.
- Peppermint oil may interfere with the hepatic metabolism of several medications, including amitriptyline (Elavil), cyclosporine (Sandimmune), haloperidol (Haldol), and statin drugs.
- Topical application to infants’ faces has caused bronchospasm and respiratory arrest.
Although peppermint is widely used and its safety is established in most applications, the medicinal use of its concentrated oil increases the risks for adverse effects, including death at high doses.
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