Slippery elm bark

What is slippery elm?

Slippery elm (Ulmus rubra) is a tree native to eastern North America. Its inner bark contains mucilage, a mix of complex carbohydrates that becomes slick and gel-like when mixed with water. Native American communities and later American herbalists used the bark for sore throats, coughs, wounds and digestive complaints. Today, slippery elm is best known as an ingredient in throat lozenges and in herbal powders for the stomach.

The rationale is mechanical: the mucilage may coat irritated tissue in the throat and digestive tract, and it may stimulate nerve endings that increase mucus secretion. It also acts somewhat like a soluble fiber.

What the research says

Direct evidence for slippery elm alone is very thin. We could not find well-designed randomized trials testing slippery elm by itself for digestive symptoms in adults. The human data come from combination products. For example, a 2020 study in Nutrition Research tested a gut formula containing curcumin, aloe vera, slippery elm, guar gum, pectin, peppermint oil and glutamine in 43 adults with digestive disorders. Participants reported large improvements in upper and lower digestive symptoms over 16 weeks. However, the study was a pre-post design without a separate placebo group, and with seven active ingredients, it cannot tell us how much, if anything, slippery elm contributed.

We rate the evidence as preliminary. Slippery elm has a long traditional history and a plausible soothing mechanism, but its effect on its own has not been demonstrated.

How it’s used in supplements

Slippery elm is sold as bark powder (often stirred into water or tea to make a gruel), capsules, lozenges and as part of gut-support blends. It is generally considered gentle. Because the mucilage can coat the digestive tract, many herbalists and pharmacists suggest taking slippery elm a few hours apart from medications, since it might slow or reduce their absorption. Information on its safety during pregnancy is limited, so pregnant women should ask their doctor before using it.

In PrimeBiome, slippery elm bark powder is one of nine ingredients in a 430 mg proprietary blend, so the amount is unknown and likely small compared with the spoonful-sized servings used in traditional preparations.

Anyone hoping slippery elm will ease heartburn or an irritated stomach should remember that frequent heartburn, trouble swallowing or ongoing stomach pain are reasons to see a doctor. Slippery elm can be a gentle comfort measure, but it should not delay evaluation of symptoms that keep coming back.