What folk medicine says Ancient Egyptians used the herb to soothe indigestion. American herbalists prescribe it for a number of stomach problems, including colic, nausea, hiccups, and diarrhea. What we know In one study, Taiwanese researchers gave 110 patients with irritable bowel syndrome (IBS) either 0.2 ml of peppermint oil or a placebo three or four times a day. After a month, 79% of the peppermint takers reported feeling less abdominal pain, compared with 43% of those on the placebo. Other research shows that peppermint oil relaxes the smooth muscles of the digestive tract, easing spasms. The herb can increase bile flow, so people with gallbladder problems shouldn’t take it. Due to peppermint’s effect on smooth muscles, it can cause acid reflux and heartburn. (Trouble with heartburn? Here’s how to stop your heartburn cycle.) What research shows Enteric-coated capsules provide peppermint oil’s benefits without the heartburn by dissolving in the intestines instead of the stomach. A German review of 16 studies involving 651 people concluded that enteric-coated capsules containing 180 to 200 mg (0.18 to 0.2 ml) of peppermint oil eased IBS symptoms such as pain, bloating, and gas for 58% of takers; just 29% of those on placebo pills benefited. Side effects were mild—only 2% of the participants complained of heartburn. How to use Before eating, take one enteric-coated peppermint oil capsule, such as Pepogest by Nature’s Way, with water.  More from Prevention: Dealing WithDiarrhea