Slippery Elm

What Is Slippery Elm?

Slippery elm is a North American elm whose inner bark is one of the classic herbal demulcents. When wet, the powdered bark swells into a soft, slippery gel that coats and soothes irritated tissue. It is taken as a gruel or lozenge for sore throats and an irritated stomach and bowel, and applied as a poultice to wounds, boils and burns ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

Ulmus rubra is a tree of the eastern and central United States and southern Canada, growing on stream banks, floodplains and lower slopes ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. Its reddish inner bark gives it the names red elm and slippery elm ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. Native American tribes used the bark for the stomach and bowels, coughs and colds, and burns and sores, and early settlers took it up for coughs and diarrhoea ^{26,29Reference 26Coladonato · 1993Ulmus rubra, slippery elmView study →Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}.

The bark’s main constituent is mucilage, a water-loving polysaccharide that makes up about 7% of the dried bark ^{2Reference 2Barnes et al. · 2007ReviewHerbal Medicines (3rd ed.) — reference monograph (pp}. No controlled trial has tested slippery elm on its own. It has been studied in people only as one ingredient in multi-herb formulas ^{3,4Reference 3Hawrelak et al. · 2010Effects of two natural medicine formulations on irritable bowel syndrome symptoms: an open-label clinical pilot studyView study →Reference 4Ried et al. · 2020ObservationalHerbal formula improves upper and lower gastrointestinal symptoms and gut health in Australian adults with digestive disorders — pre-post observational studyView study →}.

Harvesting the bark kills the tree, and slippery elm is on the United Plant Savers At-Risk list ^{24,31Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →Reference 31United Plant Savers · 2026Species At-Risk List (updated 26 August 2026). https://unitedplantsavers.org/species-at-risk-list/View study →}.

How Is Slippery Elm Used?

The dried inner bark is used, powdered and mixed with water. The mucilage swells in water but does not dissolve in alcohol, so water-based preparations are the usual forms ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

• Gruel — a teaspoon of powder mixed to a smooth paste with cold water, then stirred into a pint of boiling water, sometimes flavoured with cinnamon or nutmeg ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.
• Capsules or powder in drinks — for the stomach and bowel.
• Lozenges — for sore throats and coughs ^{24,30Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →Reference 30United Plant SaversSlippery Elm (Ulmus rubra) — species at-risk profileView study →}.
• Poultice — the powder mixed with hot water and spread on cloth over wounds, boils, ulcers and burns ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.
• Essiac tea — one of the four herbs in this formula, with burdock, sheep sorrel and rhubarb ^{11,16Reference 11Leonard et al. · 2006In vitroEssiac tea: scavenging of reactive oxygen species and effects on DNA damage — in vitroView study →Reference 16Zick et al. · 2006ObservationalTrial of Essiac to ascertain its effect in women with breast cancer (TEA-BC) — observational studyView study →}.

Traditional Uses

Native American Medicine

Native American tribes used slippery elm for many purposes, including soothing the stomach and bowels, treating dysentery, coughs, colds and catarrh, dressing burns and sores, as a laxative and to help induce labour ^{29,30Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →Reference 30United Plant SaversSlippery Elm (Ulmus rubra) — species at-risk profileView study →}. The inner bark was also made into a healing salve ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

European settlers took up the bark as a treatment for coughs and diarrhoea ^{26Reference 26Coladonato · 1993Ulmus rubra, slippery elmView study →}.

Western Herbal & Pharmacopoeial Medicine

The inner bark was an official drug of the United States Pharmacopoeia ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}. It is classed as a demulcent, emollient, expectorant and nutritive, a soothing, coating remedy given wherever a mucous surface is raw ^{2,24Reference 2Barnes et al. · 2007ReviewHerbal Medicines (3rd ed.) — reference monograph (ppReference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

Taken as a gruel, it was given for gastritis, mucous colitis and enteritis, and for bronchitis and coughs ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}. Western herbal texts extend it to peptic and duodenal ulcers, diarrhoea and inflammatory bowel disease, and to vaginitis, mouth inflammation, haemorrhoids, anal fissures, varicose ulcers, abscesses and carbuncles ^{23,25Reference 23Braun et al. · 2010Herbs & Natural Supplements: An Evidence-Based Guide (VolReference 25Hoffmann · 2003Medical Herbalism: The Science and Practice of Herbal Medicine}.

As a poultice, the powdered bark was one of the most valued dressings for wounds, boils, ulcers, burns and inflamed skin ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

Because the gruel is nourishing and easy to digest, it was fed to infants, invalids and convalescents as a food as much as a medicine ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

Indications

• Sore throat and cough [inner bark; gruel, lozenge]
• Gastritis and an irritated stomach [inner bark; gruel]
• Colitis and inflammatory bowel complaints [inner bark; gruel]
• Peptic and duodenal ulcers [inner bark; Western herbal medicine]
• Reflux and heartburn [inner bark]
• Diarrhoea and dysentery [inner bark; Native American use]
• Constipation [inner bark; Native American use]
• Irritable bowel syndrome [inner bark in combination formulas]
• Wounds, boils and burns [inner bark poultice]
• Nourishment during convalescence [inner bark gruel]

Botany

Slippery elm is a deciduous tree in the elm family (Ulmaceae) ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. It grows 18–35 m tall with an open crown ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. Its bark is brown to red and deeply, irregularly furrowed, and its young twigs are grey and densely hairy ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}.

The leaves are oval, 8–16 cm long, with a lopsided base and doubly toothed edges ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. They feel harsh and sandpapery on top and are downy underneath, with tufts of white hair where the main veins meet ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}.

The flowers are small, greenish to reddish, with reddish anthers, and grow in dense clusters of 8–20 ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. They open in late winter and early spring, before the leaves ^{26,29Reference 26Coladonato · 1993Ulmus rubra, slippery elmView study →Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}.

The seeds are round, papery-winged fruits 12–18 mm across ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. Only the centre over the seed is hairy, with rusty hairs, and the wing edges are smooth ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}.

The inner bark is red-brown and mucilaginous, and its sticky slime gives the tree its common name ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. The accepted name is Ulmus rubra Muhl., and U. fulva is an older synonym still seen on labels ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}.

Slippery elm is often confused with American elm (U. americana) ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. Where their ranges meet, it hybridises freely with the introduced Siberian elm (U. pumila) ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}.

Distribution

Slippery elm grows from southwestern Maine and southern Quebec and Ontario west to the Dakotas, and south to central Texas, northwestern Florida and Georgia ^{26,29Reference 26Coladonato · 1993Ulmus rubra, slippery elmView study →Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. It is most abundant in the southern Great Lakes states and the Midwest corn belt, and uncommon south of Kentucky ^{26Reference 26Coladonato · 1993Ulmus rubra, slippery elmView study →}.

It grows on lower slopes, floodplains, stream banks and wooded bottomlands, up to about 600 m ^{29Reference 29Sherman-Broyles et al. · 1997Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — floraView study →}. It does best on moist, rich soils but is also found on much drier sites, particularly over limestone ^{26Reference 26Coladonato · 1993Ulmus rubra, slippery elmView study →}.

The species is assessed as Least Concern globally, but Dutch elm disease has left very few mature trees in the wild ^{30Reference 30United Plant SaversSlippery Elm (Ulmus rubra) — species at-risk profileView study →}. Dutch elm disease and elm yellows kill it across much of its range, so it seldom reaches full size as a forest tree ^{26Reference 26Coladonato · 1993Ulmus rubra, slippery elmView study →}. It is listed as of special concern in Rhode Island and possibly extirpated in Maine ^{30Reference 30United Plant SaversSlippery Elm (Ulmus rubra) — species at-risk profileView study →}.

Harvesting the medicine kills the tree, because the trunk is stripped of its bark ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}. Taking bark from the healthy mature trees that remain can also remove their disease resistance from the gene pool ^{30Reference 30United Plant SaversSlippery Elm (Ulmus rubra) — species at-risk profileView study →}.

United Plant Savers lists slippery elm as At-Risk and recommends using cultivated material wherever possible ^{31Reference 31United Plant Savers · 2026Species At-Risk List (updated 26 August 2026). https://unitedplantsavers.org/species-at-risk-list/View study →}. It advises against wild-harvested bark unless it comes from trees that fell naturally ^{30Reference 30United Plant SaversSlippery Elm (Ulmus rubra) — species at-risk profileView study →}. When buying, look for cultivated or plantation-grown bark, or bark salvaged from felled trees. Marshmallow, comfrey and mullein have been suggested by herbalists as alternatives ^{30Reference 30United Plant SaversSlippery Elm (Ulmus rubra) — species at-risk profileView study →}.

Growing Conditions

Cultivation snapshot for Slippery Elm

SunFull sun; tolerates light shadeWaterMedium; adapts wet to drySoilAverage, medium, well-drained; rich moist loamsLifeperennialZoneUSDA 3-9

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Harvesting & Preparation

The bark is collected in spring from the trunk and larger branches, and only the inner bark is kept ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}. Grieve recommends using ten-year-old bark ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

Good powder is greyish or fawn-coloured. A coarse powder is sold for poultices and a fine powder for drinks ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

Because the mucilage swells in water but is not extracted by alcohol, water-based preparations are the usual forms ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}. Older texts also give recipes for enemas, compound cough syrups and ointments ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

Pharmacology & Research

Slippery elm has been used widely but studied little. Its action is mainly physical: the inner bark’s mucilage swells in water into a thick gel that coats the lining of the throat and gut ^{1,2Reference 1Watts et al. · 2012ReviewSlippery elm, its biochemistry, and use as a complementary and alternative treatment for laryngeal irritation — reviewView study →Reference 2Barnes et al. · 2007ReviewHerbal Medicines (3rd ed.) — reference monograph (pp}.

The bark has shown antioxidant, antibacterial and prebiotic effects in cell-free, cell-culture and faecal-culture studies ^{5,6,7,8Reference 5Langmead et al. · 2002In vitroAntioxidant effects of herbal therapies used by patients with inflammatory bowel disease: an in vitro studyView study →Reference 6Choi et al. · 2002In vitroPeroxynitrite scavenging activity of herb extracts — in vitroView study →Reference 7Peterson et al. · 2018Prebiotic potential of herbal medicines used in digestive health and disease — ex vivo studyView study →Reference 8Wijesundara et al. · 2019In vitroBactericidal and anti-biofilm activity of ethanol extracts derived from selected medicinal plants against Streptococcus pyogenes — in vitroView study →}. It has been tested in people only as one ingredient in multi-herb formulas for irritable bowel syndrome and general digestive symptoms ^{3,4Reference 3Hawrelak et al. · 2010Effects of two natural medicine formulations on irritable bowel syndrome symptoms: an open-label clinical pilot studyView study →Reference 4Ried et al. · 2020ObservationalHerbal formula improves upper and lower gastrointestinal symptoms and gut health in Australian adults with digestive disorders — pre-post observational studyView study →}.

Slippery elm is also one of the four herbs in Essiac tea, which has been studied for cancer with mixed to negative results ^{11,12,13,14,15,16Reference 11Leonard et al. · 2006In vitroEssiac tea: scavenging of reactive oxygen species and effects on DNA damage — in vitroView study →Reference 12Cheung et al. · 2005In vitroAntioxidant and anti-inflammatory properties of ESSIAC and Flor-Essence — in vitroView study →Reference 13Ottenweller et al. · 2004In vitroInhibition of prostate cancer-cell proliferation by Essiac — in vitroView study →Reference 14Eberding et al. · 2007In vitroEvaluation of the antiproliferative effects of Essiac on in vitro and in vivo (mouse) models of prostate cancer compared to paclitaxelView study →Reference 15Tamayo et al. · 2000ReviewThe chemistry and biological activity of herbs used in Flor-Essence herbal tonic and Essiac — reviewView study →Reference 16Zick et al. · 2006ObservationalTrial of Essiac to ascertain its effect in women with breast cancer (TEA-BC) — observational studyView study →}.

1. Digestive & GI Soothing

This is slippery elm’s main use. The inner bark is about 7% mucilage, a highly branched polysaccharide built mainly from D-galactose, L-rhamnose and D-galacturonic acid with the marker sugar 3-O-methyl-D-galactose ^{1,2,17,18Reference 1Watts et al. · 2012ReviewSlippery elm, its biochemistry, and use as a complementary and alternative treatment for laryngeal irritation — reviewView study →Reference 2Barnes et al. · 2007ReviewHerbal Medicines (3rd ed.) — reference monograph (ppReference 17Gill et al. · 1946Constitution of the mucilage from the bark of Ulmus fulva (slippery elm mucilage) — chemistryView study →Reference 18Hough et al. · 1950Chemical constitution of slippery elm mucilage; isolation of 3-methyl-D-galactose from the hydrolysis products — chemistryView study →}. It swells into a thick gel rather than dissolving, and coats the lining of the gut.

The human evidence comes from uncontrolled trials of formulas. In an open-label pilot study in 31 people with irritable bowel syndrome, a formula of slippery elm, lactulose, oat bran and licorice improved bowel habit and symptoms in constipation-predominant IBS ^{3Reference 3Hawrelak et al. · 2010Effects of two natural medicine formulations on irritable bowel syndrome symptoms: an open-label clinical pilot studyView study →}. A second formula, for diarrhoea-predominant IBS, of bilberry, slippery elm, agrimony and cinnamon, eased several symptoms but did not improve bowel habit ^{3Reference 3Hawrelak et al. · 2010Effects of two natural medicine formulations on irritable bowel syndrome symptoms: an open-label clinical pilot studyView study →}.

In a 16-week pre-post study in 43 adults, a seven-ingredient “gut relief” formula containing slippery elm improved reflux and lower-gut symptoms and reduced intestinal permeability ^{4Reference 4Ried et al. · 2020ObservationalHerbal formula improves upper and lower gastrointestinal symptoms and gut health in Australian adults with digestive disorders — pre-post observational studyView study →}.

In human faecal cultures, U. rubra increased the share of butyrate-producing bacteria, a prebiotic effect ^{7Reference 7Peterson et al. · 2018Prebiotic potential of herbal medicines used in digestive health and disease — ex vivo studyView study →}.

Because slippery elm was one of several ingredients in every clinical study, the benefit cannot be assigned to the herb itself.

Gap: no controlled trial of slippery elm on its own — the human signal is confounded by co-administered herbs, and the prebiotic data are ex-vivo only.

2. Antioxidant

In a study of herbal remedies used by people with inflammatory bowel disease, slippery elm scavenged superoxide and peroxyl radicals in a dose-dependent way and reduced oxygen-radical release from inflamed ulcerative-colitis biopsies, as 5-aminosalicylic acid did ^{5Reference 5Langmead et al. · 2002In vitroAntioxidant effects of herbal therapies used by patients with inflammatory bowel disease: an in vitro studyView study →}.

In a screen of 28 herbs for peroxynitrite scavenging, slippery elm ranked fifth, behind witch hazel bark, rosemary, jasmine tea and sage ^{6Reference 6Choi et al. · 2002In vitroPeroxynitrite scavenging activity of herb extracts — in vitroView study →}.

The remaining antioxidant data are for Essiac tea, in which slippery elm is one of four herbs. Essiac scavenged hydroxyl and superoxide radicals and protected DNA from oxidative damage in cell-free systems ^{11Reference 11Leonard et al. · 2006In vitroEssiac tea: scavenging of reactive oxygen species and effects on DNA damage — in vitroView study →}, and showed antioxidant capacity in a separate assay ^{12Reference 12Cheung et al. · 2005In vitroAntioxidant and anti-inflammatory properties of ESSIAC and Flor-Essence — in vitroView study →}.

All of it is in vitro: there is no animal or human antioxidant data for slippery elm, and the Essiac results cannot be attributed to the elm component.

3. Anti-Inflammatory

Slippery elm reduced the release of oxygen radicals from inflamed colonic tissue in vitro ^{5Reference 5Langmead et al. · 2002In vitroAntioxidant effects of herbal therapies used by patients with inflammatory bowel disease: an in vitro studyView study →}.

Essiac work is mixed. In macrophages, the tea increased nitric-oxide release in unstimulated cells but reduced it in stimulated cells, and it raised expression of several pro-inflammatory genes ^{12Reference 12Cheung et al. · 2005In vitroAntioxidant and anti-inflammatory properties of ESSIAC and Flor-Essence — in vitroView study →}.

The evidence is confined to cell and tissue models; no whole-animal or human anti-inflammatory data exist for the herb.

4. Throat & Respiratory Soothing

Slippery elm is a traditional demulcent and expectorant for sore throat, cough and laryngeal irritation, and it is a common lozenge ingredient ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}. A biochemistry review describes how the mucilage could coat and soothe the lining of the larynx ^{1Reference 1Watts et al. · 2012ReviewSlippery elm, its biochemistry, and use as a complementary and alternative treatment for laryngeal irritation — reviewView study →}. A review of popular remedies for oesophageal symptoms includes slippery elm among the herbal products used ^{10Reference 10Ahuja et al. · 2019ReviewPopular remedies for esophageal symptoms: a critical appraisal — reviewView study →}.

No clinical study has tested it for cough, throat or voice complaints.

5. Antimicrobial

An ethanol extract of slippery elm inner bark was among the five most effective of 14 plant extracts tested against Streptococcus pyogenes in vitro. Its minimum inhibitory concentration was 62.5 µg/mL and its minimum bactericidal concentration 125 µg/mL, and it inhibited biofilm formation at 62.5–125 µg/mL ^{8Reference 8Wijesundara et al. · 2019In vitroBactericidal and anti-biofilm activity of ethanol extracts derived from selected medicinal plants against Streptococcus pyogenes — in vitroView study →}.

An ethanol extract captures the tannins but not the water-swelling mucilage, so the result does not describe a gruel or decoction.

Gap: one in-vitro study, on a single pathogen, using an alcohol extract that is not the demulcent preparation the herb is actually taken as; no in-vivo or clinical data.

6. Wound Healing (Topical)

Slippery elm bark powder is a classic poultice for wounds, boils and inflamed skin ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}. The same mucilage that soothes the gut forms a moist protective layer over damaged skin.

Gap: no wound-healing study has used slippery elm.

7. Vasorelaxant

In a 2022 electrophysiology study, a 1% slippery elm bark extract strongly activated the KCNQ5 potassium channel expressed in frog eggs. The effect was traced to the tannins gallic acid and tannic acid, which are common to several Native American medicinal barks ^{9Reference 9Manville et al. · 2022In vitroKCNQ5 activation by tannins mediates vasorelaxant effects of barks used in Native American botanical medicine — in vitroView study →}.

KCNQ5 activation relaxes vascular smooth muscle. In that study the artery-relaxation experiments were run on red willow, white willow and white oak extracts; slippery elm was tested only at the channel level ^{9Reference 9Manville et al. · 2022In vitroKCNQ5 activation by tannins mediates vasorelaxant effects of barks used in Native American botanical medicine — in vitroView study →}.

It is in-vitro channel activation only, with no vessel, animal or human data for slippery elm.

8. Anticancer (Essiac Formula)

Slippery elm is one of four herbs in Essiac, with burdock, sheep sorrel and rhubarb, a tea promoted for cancer ^{11,16Reference 11Leonard et al. · 2006In vitroEssiac tea: scavenging of reactive oxygen species and effects on DNA damage — in vitroView study →Reference 16Zick et al. · 2006ObservationalTrial of Essiac to ascertain its effect in women with breast cancer (TEA-BC) — observational studyView study →}. One in-vitro study reported that Essiac slowed the growth of prostate cancer cells ^{13Reference 13Ottenweller et al. · 2004In vitroInhibition of prostate cancer-cell proliferation by Essiac — in vitroView study →}. A second study found no effect in prostate cancer cells or in mice with prostate tumours ^{14Reference 14Eberding et al. · 2007In vitroEvaluation of the antiproliferative effects of Essiac on in vitro and in vivo (mouse) models of prostate cancer compared to paclitaxelView study →}.

A review found that evidence of anticancer activity was limited to anecdotal reports, with no published clinical studies ^{15Reference 15Tamayo et al. · 2000ReviewThe chemistry and biological activity of herbs used in Flor-Essence herbal tonic and Essiac — reviewView study →}. In a retrospective study of 510 women with breast cancer, Essiac users did not have better quality of life or mood than non-users ^{16Reference 16Zick et al. · 2006ObservationalTrial of Essiac to ascertain its effect in women with breast cancer (TEA-BC) — observational studyView study →}.

The one registered clinical trial, of Essiac against placebo for quality of life in women with breast or ovarian cancer, was terminated (NCT00287482).

Gap: the claim is for a four-herb formula, not slippery elm; preclinical results are mixed-to-null, the observational human data were negative, and the only registered trial was terminated.

Mechanisms

The inner-bark mucilage takes up water and forms a thick gel that coats the lining of the throat and gut. In the colon, it has been studied as a food for butyrate-producing bacteria.

The bark’s tannins have been studied as radical scavengers and as activators of the KCNQ5 potassium channel.

Clinical Trials

No trial has tested slippery elm on its own. The completed human studies are all of multi-herb formulas that contain it, and the one registered cancer trial of Essiac was terminated.

Last checked: August 2026.

Phytochemistry

The main constituent of the inner bark is mucilage, about 7% of the dried bark ^{2Reference 2Barnes et al. · 2007ReviewHerbal Medicines (3rd ed.) — reference monograph (pp}. It is held in large cells in the bast ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

The mucilage is a highly branched polysaccharide built mainly from D-galactose, L-rhamnose and D-galacturonic acid, together with the unusual sugar 3-O-methyl-D-galactose, a marker of elm mucilage ^{17,18,22Reference 17Gill et al. · 1946Constitution of the mucilage from the bark of Ulmus fulva (slippery elm mucilage) — chemistryView study →Reference 18Hough et al. · 1950Chemical constitution of slippery elm mucilage; isolation of 3-methyl-D-galactose from the hydrolysis products — chemistryView study →Reference 22Beveridge et al. · 1969Some structural features of the mucilage from the bark of Ulmus fulva — chemistryView study →}. It swells in water rather than dissolving, and it is not dissolved by alcohol ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}.

The bark also contains starch grains and twin crystals of calcium oxalate ^{24Reference 24Grieve · 1931A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.htmlView study →}, along with astringent tannins and the phytosterol β-sitosterol ^{27Reference 27Duke · 2016Duke, J. A. (2016). Dr. Duke’s Phytochemical and Ethnobotanical Databases — Ulmus rubra. USDA. https://phytochem.nal.usda.gov/View study →}. An ethanol extract of the bark contained oleanolic and ursolic or betulinic acid ^{8Reference 8Wijesundara et al. · 2019In vitroBactericidal and anti-biofilm activity of ethanol extracts derived from selected medicinal plants against Streptococcus pyogenes — in vitroView study →}.

Constituent Summary

Reported from the dried inner bark.

Dosage

The two human studies gave slippery elm inside multi-herb formulas and did not report its individual amount.

Research Doses

Traditional Dosage

Traditional use is of the powdered inner bark in water, as a gruel or decoction. The mucilage does not extract into alcohol, so a liquid extract carries little of it.

Safety & Pregnancy

Slippery elm is a food-like herb with no significant toxicity reported for the inner bark. Its one practical caution is that the mucilage can slow the absorption of medicines taken at the same time.

Full Safety & Interactions Detail

General safety. Slippery elm is used as a food-grade demulcent, and no significant toxicity has been reported for the inner bark. The safety record rests on food use and tradition rather than formal testing ^{1,2Reference 1Watts et al. · 2012ReviewSlippery elm, its biochemistry, and use as a complementary and alternative treatment for laryngeal irritation — reviewView study →Reference 2Barnes et al. · 2007ReviewHerbal Medicines (3rd ed.) — reference monograph (pp}.

Drug absorption. The mucilage forms a coating gel that may reduce the absorption of medicines, herbs and nutrients taken at the same time. Soluble fibres such as guar gum and psyllium are known to reduce drug absorption ^{32Reference 32Fugh-Berman · 2000ReviewHerb-drug interactions — reviewView study →}. Take oral medicines at least 1–2 hours apart from slippery elm. This is a physical effect, not an effect on liver enzymes. A review of herb–drug interactions in older people with inflammatory bowel disease includes slippery elm among the herbs to ask about ^{19Reference 19Rahman et al. · 2017ReviewDrug-herb interactions in the elderly patient with IBD: a growing concern — reviewView study →}.

Allergy. Allergic reactions are uncommon, but people sensitive to elm pollen may react.

Detox products. Slippery elm is a common ingredient in “detox” blends. In a randomised, double-blind, placebo-controlled trial in healthy young women, one such eight-herb product had no effect on body composition, waist size, blood markers or digestive symptoms ^{20Reference 20Tinsley et al. · 2019RCTA purported detoxification supplement does not improve body composition, waist circumference, blood markers, or gastrointestinal symptoms in healthy adult females — randomised, double-blind, placebo-controlled trialView study →}.

References

1. Watts, C. R., & Rousseau, B. (2012). Slippery elm, its biochemistry, and use as a complementary and alternative treatment for laryngeal irritation — review. Journal of Investigational Biochemistry. https://doi.org/10.5455/jib.20120417052415
2. Barnes, J., Anderson, L. A., & Phillipson, J. D. (2007). Herbal Medicines (3rd ed.) — reference monograph (pp. 545–546). London: Pharmaceutical Press.
3. Hawrelak, J. A., & Myers, S. P. (2010). Effects of two natural medicine formulations on irritable bowel syndrome symptoms: an open-label clinical pilot study. J Altern Complement Med. https://pubmed.ncbi.nlm.nih.gov/20954962/
4. Ried, K., Travica, N., Dorairaj, R., & Sali, A. (2020). Herbal formula improves upper and lower gastrointestinal symptoms and gut health in Australian adults with digestive disorders — pre-post observational study. Nutr Res. https://pubmed.ncbi.nlm.nih.gov/32151878/
5. Langmead, L., Dawson, C., Hawkins, C., Banna, N., Loo, S., & Rampton, D. S. (2002). Antioxidant effects of herbal therapies used by patients with inflammatory bowel disease: an in vitro study. Aliment Pharmacol Ther. https://pubmed.ncbi.nlm.nih.gov/11860402/
6. Choi, H. R., Choi, J. S., Han, Y. N., Bae, S. J., & Chung, H. Y. (2002). Peroxynitrite scavenging activity of herb extracts — in vitro. Phytother Res. https://pubmed.ncbi.nlm.nih.gov/12112294/
7. Peterson, C. T., Sharma, V., Uchitel, S., Denniston, K., Chopra, D., Mills, P. J., & Peterson, S. N. (2018). Prebiotic potential of herbal medicines used in digestive health and disease — ex vivo study. J Altern Complement Med. https://pubmed.ncbi.nlm.nih.gov/29565634/
8. Wijesundara, N. M., & Rupasinghe, H. P. V. (2019). Bactericidal and anti-biofilm activity of ethanol extracts derived from selected medicinal plants against Streptococcus pyogenes — in vitro. Molecules. https://pubmed.ncbi.nlm.nih.gov/30909644/
9. Manville, R. W., Redford, K. E., van der Horst, J., Hogenkamp, D. J., et al. (2022). KCNQ5 activation by tannins mediates vasorelaxant effects of barks used in Native American botanical medicine — in vitro. FASEB J. https://pubmed.ncbi.nlm.nih.gov/35997997/
10. Ahuja, A., & Ahuja, N. K. (2019). Popular remedies for esophageal symptoms: a critical appraisal — review. Curr Gastroenterol Rep. https://pubmed.ncbi.nlm.nih.gov/31289950/
11. Leonard, S. S., Keil, D., Mehlman, T., Proper, S., Shi, X., & Harris, G. K. (2006). Essiac tea: scavenging of reactive oxygen species and effects on DNA damage — in vitro. J Ethnopharmacol. https://pubmed.ncbi.nlm.nih.gov/16226859/
12. Cheung, S., Lim, K. T., & Tai, J. (2005). Antioxidant and anti-inflammatory properties of ESSIAC and Flor-Essence — in vitro. Oncol Rep. https://pubmed.ncbi.nlm.nih.gov/16211307/
13. Ottenweller, J., Putt, K., Blumenthal, E. J., Dhawale, S., & Dhawale, S. W. (2004). Inhibition of prostate cancer-cell proliferation by Essiac — in vitro. J Altern Complement Med. https://pubmed.ncbi.nlm.nih.gov/15353028/
14. Eberding, A., Madera, C., Xie, S., Wood, C. A., Brown, P. N., & Guns, E. S. (2007). Evaluation of the antiproliferative effects of Essiac on in vitro and in vivo (mouse) models of prostate cancer compared to paclitaxel. Nutr Cancer. https://pubmed.ncbi.nlm.nih.gov/17640165/
15. Tamayo, C., Richardson, M. A., Diamond, S., & Skoda, I. (2000). The chemistry and biological activity of herbs used in Flor-Essence herbal tonic and Essiac — review. Phytother Res. https://pubmed.ncbi.nlm.nih.gov/10641040/
16. Zick, S. M., Sen, A., Feng, Y., Green, J., Olatunde, S., & Boon, H. (2006). Trial of Essiac to ascertain its effect in women with breast cancer (TEA-BC) — observational study. J Altern Complement Med. https://pubmed.ncbi.nlm.nih.gov/17212569/
17. Gill, R. E., Hirst, E. L., & Jones, J. K. N. (1946). Constitution of the mucilage from the bark of Ulmus fulva (slippery elm mucilage) — chemistry. Journal of the Chemical Society. https://pubmed.ncbi.nlm.nih.gov/20282480/
18. Hough, L., Jones, J. K. N., & Hirst, E. L. (1950). Chemical constitution of slippery elm mucilage; isolation of 3-methyl-D-galactose from the hydrolysis products — chemistry. Nature. https://pubmed.ncbi.nlm.nih.gov/15400433/
19. Rahman, H., Kim, M., Leung, G., Green, J. A., & Katz, S. (2017). Drug-herb interactions in the elderly patient with IBD: a growing concern — review. Curr Treat Options Gastroenterol. https://pubmed.ncbi.nlm.nih.gov/28918484/
20. Tinsley, G. M., Urbina, S., Santos, E., Villa, K., et al. (2019). A purported detoxification supplement does not improve body composition, waist circumference, blood markers, or gastrointestinal symptoms in healthy adult females — randomised, double-blind, placebo-controlled trial. J Diet Suppl. https://pubmed.ncbi.nlm.nih.gov/29958034/
21. Williams, B. (1954). Two cases of slippery elm bladder calculus in pregnancy — case report. Journal of Obstetrics and Gynaecology of the British Empire. https://pubmed.ncbi.nlm.nih.gov/13192523/
22. Beveridge, R. J., Stoddart, J. F., Szarek, W. A., & Jones, J. K. N. (1969). Some structural features of the mucilage from the bark of Ulmus fulva — chemistry. Carbohydrate Research, 9, 429–439. doi:10.1016/S0008-6215(00)80033-1
23. Braun, L., & Cohen, M. (2010). Herbs & Natural Supplements: An Evidence-Based Guide (Vol. 2). Sydney: Elsevier Australia. (Pp. 916–919.)
24. Grieve, M. (1931). A Modern Herbal — “Elm, Slippery” (historical source). https://www.botanical.com/botanical/mgmh/e/elmsli09.html
25. Hoffmann, D. (2003). Medical Herbalism: The Science and Practice of Herbal Medicine. Rochester, VT: Healing Arts Press. (P. 591.)
26. Coladonato, M. (1993). Ulmus rubra, slippery elm. In Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. https://research.fs.usda.gov/feis/species-reviews/ulmrub
27. Duke, J. A. (2016). Dr. Duke’s Phytochemical and Ethnobotanical Databases — Ulmus rubra. USDA. https://phytochem.nal.usda.gov/
28. Bean, W. J. (1970). Trees & Shrubs Hardy in the British Isles (8th ed., p. 656). London: John Murray.
29. Sherman-Broyles, S. L., Barker, W. T., & Schulz, L. M. (1997). Ulmus rubra Muhlenberg — species description, habitat, distribution and uses — flora. In Flora of North America Editorial Committee (eds.), Flora of North America North of Mexico, Vol. 3 (Ulmaceae). http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233501329
30. United Plant Savers. Slippery Elm (Ulmus rubra) — species at-risk profile. https://unitedplantsavers.org/slippery-elm-ulmus-rubra/
31. United Plant Savers (2026). Species At-Risk List (updated 26 August 2026). https://unitedplantsavers.org/species-at-risk-list/
32. Fugh-Berman, A. (2000). Herb-drug interactions — review. The Lancet, 355(9198), 134–138. https://pubmed.ncbi.nlm.nih.gov/10675182/

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