Peppermint leaves yield approximately 0.1–1.0% volatile oil which is composed primarily of menthol (29–48%) and menthone (20–31%). Peppermint oil is classified as a carminative (prevents and relieves intestinal gas). It may also relieve spasms in the intestinal tract. Peppermint oil or peppermint tea is often used to treat gas and indigestion.
Three double-blind trials found that enteric-coated peppermint oil reduced the pain associated with intestinal spasms, commonly experienced in irritable bowel syndrome (IBS). However, another trial found no effect of peppermint on IBS. A double-blind trial found that an enteric-coated combination of peppermint and caraway oils was superior to a placebo for people with gastrointestinal complaints including IBS. A combination of peppermint, caraway seeds, and two other carminative herbs (fennel seeds and wormwood) was reported to be effective for gastrointestinal complaints including IBS in another double-blind study.
A tea of peppermint is a traditional therapy for colic in infants but has never been investigated in a human trial. Peppermint should be used cautiously in infants (see side effects below).
Peppermint oil’s relaxing action also extends to topical use. When applied topically, it acts as an analgesic and reduces pain. A trial of topical peppermint oil applied to the temples of healthy volunteers (with or without eucalyptus oil) found that peppermint oil had a muscle-relaxing action and it decreased tension. Topical peppermint oil alone reduced pain in people with tension headaches as well.