Peppermint Oil for IBS: How the Capsules Can Relax the Gut and Who They Are Right For

In 1988, a team led by Hawthorn from the State University of New York at Buffalo studied peppermint oil and menthol in the laboratory. They tested gut muscle from guinea pigs as well as heart muscle and nerve preparations from rats, guinea pigs and chicks. Both inhibited calcium influx and, in a binding assay, displaced a classic calcium channel blocker from its binding site. Menthol was about twice as potent as the whole oil.

The researchers saw this as a possible basis for its use in IBS, but considered further effects likely. For you, this means: the mechanism is biologically plausible, but it was measured in a lab dish.

In 2014, a team led by Amato from the University of Palermo studied muscle strips from the colons of people who had undergone surgery. Menthol reduced the strength of the spontaneous contractions, while their rhythm and the baseline tone stayed the same. A blocker of the cold receptor TRPM8 did not change this, whereas a classic calcium channel blocker weakened the menthol effect.

The researchers conclude that menthol inhibits calcium influx through so-called L-type calcium channels directly at the muscle. For you, this means: the waves of your gut remain, they might just become flatter.

In 2002, two teams described the same receptor almost simultaneously: one led by McKemy and Julius at the University of California, San Francisco, the other led by Peier and Patapoutian in San Diego. The receptor TRPM8 responded to cold and to menthol. It sits on a subgroup of nerve cells that report temperature and pain.

In 2021, Julius and Patapoutian received the Nobel Prize in Physiology or Medicine for their discoveries of receptors for temperature and touch. For you, this means: the cool feeling of mint is a real nerve message, not your imagination.

In 2011, a team led by Harrington and Brierley from the University of Adelaide found TRPM8 on nerve fibers throughout the wall of the colon in mice. When the researchers activated the receptor with icilin, a cooling agent that docks onto TRPM8 like menthol, the nerve fibers responded less strongly to stretch. Icilin also weakened the response to capsaicin, the pungent compound in chili, and prevented an irritant from mustard oil from making the nerves more sensitive.

The researchers conclude that TRPM8 can put the brakes on the alarm receptors TRPV1 and TRPA1. For you, this means: in the gut, cold might work like a dimmer for oversensitive nerves, but this has not been proven in humans.

In 2019, a team led by Alammar and Mullin from Johns Hopkins University in Baltimore analyzed twelve randomized trials with 835 people. With peppermint oil, overall symptoms improved about 2.4 times as often as with placebo, and abdominal pain about 1.8 times as often. Mathematically, three people had to be treated for one additional person to benefit in overall symptoms. For pain, it was four.

Side effects were reported by 9.3 percent with peppermint oil and 6.1 percent with placebo, and the difference was not significant. For you, this means: this analysis paints a favorable picture.

In 2020, a team led by Black and Ford from Leeds compared soluble fiber, antispasmodics, peppermint oil and so-called gut-brain neuromodulators such as tricyclic antidepressants. For overall symptoms, peppermint oil ranked first, while tricyclic antidepressants came out ahead for abdominal pain. However, only 13 of the 51 studies had a low risk of bias.

In direct and indirect comparisons, the active treatments did not differ significantly from one another. For you, this means: a ranking is a hint, not a victory.

A team led by Weerts and Keszthelyi from Maastricht divided 190 people with IBS from four hospitals into three groups. For eight weeks, they received capsules with 182 mg of peppermint oil that released in the small intestine or only at the transition to the colon, or placebo. On the strict primary endpoint of the US Food and Drug Administration (FDA), at least 30 percent less pain in at least four weeks, 46.8 percent responded with the small-intestine capsule and 34.4 percent with placebo. The difference was not significant. In the secondary endpoints, however, the small-intestine capsule eased abdominal pain, discomfort and IBS severity more than placebo.

Side effects were mild, but occurred more often in both peppermint oil groups. For you, this means: an effect is possible, but it is probably smaller than older studies suggested.

In 2021, a team led by Nee and Lembo from Beth Israel Deaconess Medical Center in Boston tested peppermint oil against placebo, with the participation of Harvard Medical School's program for placebo research. People with moderate to severe IBS received 180 mg of enteric-coated peppermint oil or placebo three times a day for six weeks. Both groups improved markedly, on average by around 91 and 100 points on the IBS-SSS symptom score. There was no significant difference between the groups.

For you, this means: in IBS, attention, ritual and expectation can change a lot. That is not an insult, but a resource that lies within you.

In 2022, a team led by Ingrosso from Rome and Ford from Leeds updated the evidence, explicitly because newer trials had raised doubts. In ten trials with 1,030 people, peppermint oil remained superior to placebo: for overall symptoms, four people on average had to be treated for one additional person to benefit, and for abdominal pain, seven. Side effects occurred about 1.6 times as often.

The authors rated the quality of the evidence as very low, and the uncertainty was large: for overall symptoms, the confidence interval of this number ranged from 2.5 to 71. For you, this means: peppermint oil is worth a try, but it is not a sure thing.

In 2018, the Maastricht team gave eight healthy volunteers both capsule types in turn and measured a breakdown product of menthol in the blood. With the small-intestine capsule, the peak level was reached after a median of about three hours, with the colon capsule after about six. The time until menthol appeared in the blood at all was a median of 37 versus 225 minutes.

The idea was to deliver more oil to the nerves of the colon. For you, this means: a logical idea first has to prove itself in people, and that is exactly what the colon capsule later failed to do.

In 2016, a team led by Cash from the University of South Alabama tested triple-coated peppermint oil microspheres at four study centers in the US in 72 people with diarrhea-predominant or mixed-type IBS. After four weeks, a total symptom score had fallen by 40 percent, compared with 24.3 percent with placebo. A difference appeared as early as 24 hours.

The study was small, and one coauthor worked for the company behind the product. For you, this means: an interesting finding that needs independent confirmation.

In 2019, a team led by Banovcin and Kollarik from Martin in Slovakia infused a menthol solution directly into the esophagus for 20 minutes. Eleven of twelve healthy people mainly felt cold, which they rated as barely unpleasant. All ten people with reflux disease, by contrast, felt heartburn, and it was clearly painful.

The same cold receptor seems to speak a different language in an irritated esophagus. For you, this means: if you are prone to reflux, menthol can trigger at the top the opposite of what it is supposed to do further down.

In 2021, the German societies for gastroenterology (DGVS) and for neurogastroenterology and motility (DGNM) published their updated guideline. Peppermint oil appears in it, among other places, under complementary approaches and under abdominal pain and cramps. In each case, the wording is that it “should be considered”, with recommendation grade A and strong consensus.

According to the guideline, it has been shown to be effective mainly for the symptoms of pain and bloating. On its website, the DGVS states that the guideline is currently being updated. For you, this means: in Germany, peppermint oil is one of the explicitly named options.

In 2021, a team led by Lacy from the Mayo Clinic presented the first IBS guideline of the American College of Gastroenterology. There, peppermint oil can be used to ease overall symptoms, as a conditional recommendation with low quality of evidence. The same guideline recommends a time-limited trial of a low-FODMAP diet and suggests gut-directed psychotherapy.

For you, this means: in the US, too, peppermint oil is an option, but one that is cautiously worded.

In 2007, a team led by Cappello from the University of Chieti-Pescara treated only selected people with IBS. In all of them, bacterial overgrowth, lactose intolerance and celiac disease had been ruled out with breath tests and an antibody test. After four weeks, symptoms had more than halved in 75 percent of those taking peppermint oil, compared with 38 percent with placebo. Four weeks after stopping, the symptom score in the peppermint oil group was still below the baseline value.

The researchers suspected that contradictory results of earlier studies were partly due to undetected overgrowth and intolerances. For you, this means: sorting out the causes gives a clearer view of who the capsule can help.

In 2004, a team led by Barbara from the University of Bologna examined tissue samples from the colons of 44 people with IBS and of controls. In 77 percent of the people with IBS, mast cells took up more area in the mucosa, and they released more tryptase and histamine. The more mast cells lay directly next to nerve fibers, the more severe and frequent the abdominal pain.

A correlation is not yet proof that the mast cells cause the pain. For you, this means: the immune system in your gut wall might have a say when it hurts.

In 2016, a team led by Wouters and Boeckxstaens from KU Leuven examined tissue samples from the rectum of people with IBS. They found that histamine, acting via the H1 receptor, can make the pain and heat receptor TRPV1 in gut nerves more sensitive. In a subsequent trial with 55 people with IBS, 46 percent reported adequate relief with an antihistamine, compared with 13 percent with placebo. Abdominal pain also decreased more.

This is a research finding, not an invitation to treat yourself with antihistamines. For you, this means: in some people with IBS, histamine is a lead worth taking seriously.

In 2004, a team led by Posserud and Simrén from Gothenburg studied 18 people with IBS and 22 controls. A small balloon stretched the rectum before, during and after a mental stress task. In the controls, the threshold at which the stretch became noticeable rose under stress, so their gut temporarily became quieter. In IBS, this dampening did not occur, and the stress hormones CRF and ACTH rose more sharply.

For you, this means: the ache before the important meeting is not a character trait. It could be a stress response in which the natural brake in your gut does not engage.