Slippery elm

Slippery Elm (Ulmus rubra): A Comprehensive Reference

1. Identity and Botanical Description

Nomenclature and Taxonomy

Slippery elm (Ulmus rubra) is a species of elm native to eastern North America. Other common names include red elm, gray elm, soft elm, moose elm, and Indian elm. The tree was first named as part of Ulmus americana in 1753, but was identified as a separate species, U. rubra, in 1793 by Pennsylvania botanist Gotthilf Muhlenberg. The slightly later name U. fulva, published by French botanist André Michaux in 1803, is still widely used in information related to dietary supplements and alternative medicine. Taxonomically, it belongs to the family Ulmaceae, and is closely related to American elm (U. americana) but distinguished by its pubescence and heartwood color.

The currently accepted scientific name for slippery elm is Ulmus rubra Muhl. There are no recognized subspecies, varieties, or forms.

Morphology and Habitat

Slippery elm is a medium-sized deciduous tree with a spreading head of branches, commonly growing to 12–19 metres (39–62 feet), very occasionally over 30 m (98 ft) in height. Leaves are oblong to obovate, 10–20 cm long, rough on top and velvety below, with double-serrate margins and oblique bases. The bark is reddish-brown, and the inner bark is mucilaginous — slippery when chewed — giving the tree its name.

The species is native to eastern North America, ranging from southeast North Dakota, east to Maine and southern Quebec, south to northernmost Florida, and west to eastern Texas, where it thrives in moist uplands, although it will also grow in dry, intermediate soils.

Medicinal Part Used

The inner bark of slippery elm, when stripped of the outer bark, can be used as a lozenge to treat sore throat, as a pill for gastrointestinal upset, and as a cream or ointment for skin rash and wound healing. Slippery elm gets its common name from the mucilaginous substance produced by its inner bark.

Common Forms and Preparations

Slippery elm is known by various common names including gray elm, Indian elm, red elm, sweet elm, Ulmus fulva, and Ulmus rubra. The inner bark of the tree is used to make tea, lozenges, and dietary supplements. Slippery elm is available in several forms, including as a supplement in tablet or capsule form. Slippery elm bark can be dried and pounded into a coarse powder, which, when mixed with water, becomes a paste that can be applied to the skin. Lozenges containing slippery elm are used to treat sore throats and also as a way to swallow slippery elm for stomach upset.

2. Traditional and Historical Use

Native American Use

The dried inner bark of the slippery elm tree was a favorite medicinal substance of many Indigenous American tribes and was subsequently adopted by European colonists. Like marshmallow and mullein, slippery elm was used as a treatment for sore throat, coughs, dryness of the lungs, skin inflammation, wounds, and digestive tract irritation. It was also made into a porridge to be taken by weaned infants and during recovery from illness.

Slippery elm preparations were used in Native American traditional medicine for gastrointestinal and urinary tract disorders and topically for skin diseases. The Cherokee, Iroquois, and other indigenous communities utilized the bark for its soothing and healing properties. One notable application was in the form of a poultice, where the powdered bark was mixed with water to create a thick paste. This poultice was then applied externally to wounds, burns, and other skin irritations.

U. rubra was used historically as a laxative; for coughs, colds and sore throats; and was given to women in labor to help ease the process of childbirth. The wood was also used to craft a variety of tools, such as mortars and pestles, baskets, and floor mats.

American Indians and early North American settlers used the inner bark of slippery elm not only as a material for constructing canoes, shelters, and baskets, but also as a poultice and as an ingredient in a soothing drink. Upon contact with water, the inner bark yields a thick mucilage or demulcent that was used as an ointment or salve to treat urinary tract inflammation.

Adoption by European Settlers and Colonial-Era Medicine

Although similar species grow in Europe and were used to a limited degree by ancient Greek physicians, slippery elm is closely identified with Native American herbalism. Traditionally, the sticky, mucilage-rich inner bark (the medicinal portion of the plant) was dried, then ground and prepared as a salve for burns and wounds and as a base for poultices. First Nations herbalists long ago discovered that the mucilage had a soothing effect on skin and mucous membranes. It was also used in preparations for colds, sore throats, coughs, and digestive disorders.

When starvation loomed, slippery elm bark could even be used as a survival food, chopped or ground and boiled much like oatmeal. European settlers called the tree Indian elm and quickly adopted the herb. Its use was well established by the 1600s.

Role in American Military History

Various heroes of the American Civil War are said to have credited slippery elm with their recovery from war wounds. One unique use for slippery elm was the chewing of slippery elm tablets by baseball pitchers to enhance saliva production for the famous spitball, a practice that was banned in 1920.

Pharmacopeial History

Slippery elm was included in the US Pharmacopeia from 1820 to 1960, based largely on its historical use in soothing skin and digestive irritations and as a cough suppressant.

3. Key Constituents and Active Compounds

Mucilage Polysaccharides

Slippery elm inner bark is predominantly composed of dietary fibre including celluloses, lignin, mucilage, and gums. The mucilage consists of long-chain polysaccharides which combine with water to form a viscous, semi-solid mass, and is regarded as the main active constituent. The polysaccharides are composed of D-galactose, L-rhamnose, and D-galacturonic acid and their methylated derivatives and are highly branched. Other constituents include phytosterols, starch, minerals, and oleic and palmitic acids.

Water-soluble polysaccharides are found in a linear chain of alternating D-galacturonic acid and L-rhamnose residues joined by alpha linkages with side branches of galactose or 3-O-methyl-galactose. Mucilage forms a gelatinous solution when mixed with water and will swell 50–140 times its original volume when mixed with water.

Tannins and Astringent Compounds

Slippery elm preparations were used in Native American traditional medicine for gastrointestinal and urinary tract disorders and topically for skin diseases. The active ingredients appear to be mucilages, but the inner bark is also rich in tannins and resins which are astringents and may account for some of its effects. Slippery elm contains mucilage, which is a complex, sticky substance that can help reduce swelling (inflammation). It also contains chemicals called tannins, which can reduce inflammation by acting as astringents.

Additional Phytochemicals

The inner bark is rich in mucilage (complex polysaccharides including pentoses, hexoses, polyuronides, and methyl-pentoses), forming a viscous gel in water. Other constituents include tannins, sesquiterpenes, calcium oxalate, phytosterols (e.g., beta-sitosterol), beta-carotene, essential fatty acids, and starches.

Flavonoids present in slippery elm have antioxidant and anti-inflammatory effects through reduced expression of iNOS and COX-2 enzymes.

4. Established Mechanisms of Action

Demulcent and Mucosal Coating

Mucilage forms a gelatinous solution when mixed with water and swells considerably upon hydration. This may provide a direct soothing effect and create a protective barrier against gastric acid on the digestive mucosa. Mucilage in slippery elm is responsible for its demulcent, emollient, and antitussive properties. Insoluble polysaccharides in mucilage (hexose, pentose, methylpentose) form a viscous material following oral administration or when prepared for topical use. The fiber content is thought to reduce gastrointestinal transit time, act as a bulk-forming laxative, and adsorb toxins.

Reflex Mucus Stimulation

The mechanism of action in the upper stomach and esophagus appears to be reflex stimulation of the nerve endings in the lining, which causes increased mucous secretion, increasing the protective coating. Its medicinal effects appear to be due to stimulation of mucous and saliva, which may alleviate sore or dry throat and coat irritated or ulcerated esophageal or gastric mucosa.

Prebiotic Activity

Beyond coating, the complex carbohydrates in slippery elm slow intestinal transit time and influence how substances move through the gut. The mucilage binds to lipids, reduces the absorption rate of sugars and other digestible contents, and may support beneficial gut bacteria. This combination of effects helps explain why it appears in formulas targeting bowel irregularity.

Physical Drug Absorption Barrier

Because slippery elm coats the lining of the digestive tract, it can physically block the absorption of other medications taken by mouth. The same gel that protects tissue also creates a barrier that oral drugs must pass through, potentially reducing how much of the medication reaches the bloodstream.

5. Scientific Evidence by Area of Use

5.1 Sore Throat and Pharyngeal Conditions

In the United States, slippery elm is marketed commercially to treat upper airway inflammatory conditions, and its reported benefits in treating these conditions are ubiquitous in anecdotal contexts. Individuals with voice disorders and other inflammatory conditions of the upper airway (e.g., laryngitis) are increasingly seeking information related to the use of herbal medications such as slippery elm, although most clinicians are unfamiliar with these medications and do not understand their biological actions and purported benefits.

The most widely cited human clinical trial relevant to slippery elm and throat conditions is the "Throat Coat" study. Patients were given either Throat Coat (n = 30) or placebo (n = 30). Throat Coat was found to be significantly superior to placebo in providing rapid, temporary relief from sore throat pain in patients with pharyngitis (Brinckmann et al. 2003). However, it is not possible to attribute any perceived benefits of the treatment to a particular ingredient in the formulation — as Throat Coat is a multi-ingredient herbal tea also containing licorice root and marshmallow.

Although limited scientific research exists specifically on slippery elm's benefits for sore throats, there is evidence to suggest it may help reduce throat discomfort. In a randomized controlled trial, individuals with sore throats who consumed tea containing slippery elm bark reported a reduction in throat discomfort.

No scientific evidence is available to support the validity of slippery elm's use specifically in treating upper airway inflammatory conditions such as laryngitis. Although both safety and affordability seem good, the overall evidence base is still moderate to low. Standardized preparations and good multicenter randomized controlled trials should be studied further to aid clinical utilization.

Evidence strength: Weak to preliminary for slippery elm specifically. The multi-ingredient Throat Coat RCT provides indirect clinical support for the demulcent class, but isolating the contribution of slippery elm is not possible from existing data.

5.2 Gastrointestinal Conditions — IBS and Digestive Upset

In a small pilot study of eight women with constipation-predominant irritable bowel syndrome, a daily formula containing 14 grams of slippery elm (along with lactulose, licorice, and oat bran) led to significant improvements over three weeks. Participants experienced better bowel movement frequency, softer stool consistency, less straining, and reduced severity of abdominal pain and bloating. No side effects were reported.

A clinical trial found that a formula consisting of powdered slippery elm bark, lactulose, oat bran, and licorice root may help improve irritable bowel syndrome (IBS) symptoms, especially in patients with predominant constipation-type IBS. Participants taking the formula experienced increased bowel movement frequency, improved stool consistency with reduced straining, and less abdominal discomfort.

The aim of each formula in Hawrelak and Myers (2010) was to normalize stool frequency and stool consistency. Ingestion of the formula was associated with a small, but significant increase in bowel movement frequency (p = 0.027).

A network meta-analysis of 51 IBS RCTs confirms soluble fiber has RCT-grade support; the American Gastroenterological Association (AGA) Clinical Practice Update formally endorses soluble fiber for IBS symptoms without endorsing slippery elm specifically.

Evidence strength: Weak overall. The clinical data comes exclusively from small pilot studies of multi-ingredient formulas; slippery elm's individual contribution cannot be isolated. Larger, well-controlled RCTs with slippery elm as a single intervention are lacking.

5.3 Gastroesophageal Reflux Disease (GERD)

Some patients take slippery elm, marshmallow root, D-limonene, and other herbs as part of herbal and naturopathic medicine traditions for GERD treatment; however, there are no rigorous studies evaluating their efficacy.

One study found that a formula containing slippery elm, curcumin, aloe vera, guar gum, pectin, peppermint oil, and glutamine may help manage heartburn associated with GERD, indigestion, nausea, constipation, and diarrhea by 60–80% after one month of use. Again, this was a multi-ingredient formula study, not specific to slippery elm.

The mucosal-coating proof-of-concept for GERD is preclinical and comes from analog mucilages, not from human trials of slippery elm. Models using alginate, cashew gum, and lemon gum establish that mucilage-class polysaccharides can physically protect the esophageal epithelium from acid exposure, but none of those studies used slippery elm. The mechanism is plausible, the analog data are encouraging, and slippery-elm-specific human GERD trials have not been conducted.

Evidence strength: Insufficient. No slippery-elm-specific human GERD trials exist. The mechanism of action (mucosal coating) is biologically plausible but unconfirmed for this indication.

5.4 Inflammatory Bowel Disease (IBD)

Few studies on slippery elm have been reported. An in vitro study investigated the antioxidant effects (in cell-free oxidant-generating systems and inflamed human colorectal biopsies) of six herbal therapies used to treat inflammatory bowel disease (IBD). Slippery elm, like the positive control 5-aminosalicylate (and most of the other herbal remedies tested), was found to have a dose-dependent antioxidant effect and was the most potent of the herbs tested in the biopsy study. The authors concluded that it was a promising candidate for formal evaluation of its therapeutic potential.

In one study, inflamed colon tissue from ulcerative colitis patients exposed to slippery elm extract produced fewer oxygen free radicals — suggesting a mild antioxidant effect. However, this was an in vitro study, not a patient trial.

No randomised controlled human trials have shown that slippery elm induces or maintains remission in Crohn's or ulcerative colitis. Neither ECCO (European Crohn's and Colitis Organisation) nor the British Society of Gastroenterology list slippery elm as a treatment.

Recently, the bark of slippery elm was suggested to be effective for treating IBD patients owing to its antioxidant effects; however, further studies are needed to confirm its efficacy.

Evidence strength: Preclinical only (in vitro). The antioxidant findings are promising but have not been validated in human trials. No clinical recommendation exists from major gastroenterological bodies.

5.5 Skin and Wound Healing (Topical Use)

Externally, slippery elm was applied as a salve to heal wounds, boils, ulcers, burns, and for the reduction of skin inflammation. Traditionally, the sticky, mucilage-rich inner bark was dried, then ground and prepared as a salve for burns and wounds and as a base for poultices.

Contemporary clinical evidence specifically for topical slippery elm use in wound or skin healing is absent from the scientific literature. The rationale rests on the well-characterized demulcent and emollient properties of its mucilage, which create a moist protective environment over damaged tissue.

Evidence strength: Traditional use well documented; modern clinical evidence absent.

5.6 Cough and Respiratory Conditions

While slippery elm remains a popular ingredient in cough lozenges, the scientific research supporting these uses is limited. Some small-scale studies suggest its effectiveness for cough relief, but overall, there is a lack of substantial evidence backing its efficacy for other claims.

Slippery elm contains mucilage, which is a complex, sticky substance that can help reduce swelling (inflammation). It also contains chemicals called tannins, which can reduce inflammation by acting as astringents. This has led to interest in sucking on slippery elm lozenges to help reduce cough or sore throat.

Evidence strength: Weak. Interest is based primarily on the well-known demulcent mechanism of action and traditional use. Dedicated clinical trials for cough are lacking.

5.7 Urinary Tract

Slippery elm has been noted for its potential benefits in conditions like irritable bowel syndrome, inflammatory bowel disease, gastritis, and esophageal reflux. Additionally, slippery elm has been used to support skin health, promote lactation in nursing mothers, and aid urinary tract health.

No controlled human trials have examined slippery elm for urinary tract conditions. Its use for this indication is derived entirely from traditional and historical reports.

Evidence strength: Traditional use only; no clinical data available.

6. Body Systems and Health Areas Associated with Slippery Elm

• Gastrointestinal system: Traditionally used to relieve the symptoms of indigestion, heartburn, flatulence, colic, irritable bowel syndrome (IBS), and to treat diarrhoea.
• Respiratory system / upper airway: Used as a treatment for sore throat, coughs, and dryness of the lungs.
• Skin and integumentary system: Historically appreciated for its demulcent properties, useful in the treatment of a wide range of inflammatory conditions including digestive, respiratory and urinary disorders. It has also been widely used externally for skin diseases and wound healing.
• Urinary system: Used in Native American traditional medicine for gastrointestinal and urinary tract disorders.
• Immune / antioxidant activity: Slippery elm is thought to have antioxidant and anti-inflammatory properties.
• Gut microbiome (prebiotic): The soluble fiber of slippery elm acts as a prebiotic which feeds probiotics, the beneficial bacteria of the intestines. Through a natural fermentation process, the soluble fiber is broken down, nourishing and encouraging the proliferation of these probiotic bacteria.

7. Dosage Forms and Reported Dosages

There is no established dosage for slippery elm. Research on how quickly effects are felt, or whether any benefit will be seen at all, is limited.

No clinical studies exist to provide dosage guidelines. Traditional use suggests a dosage of 1 to 3 teaspoons of slippery elm powder in 240 mL of water up to 3 times a day.

Powdered bark is typically taken in 1-tablespoon doses, up to 3 times daily, mixed with water or tea.

In a small pilot study of eight women with constipation-predominant IBS, a daily formula containing 14 grams of slippery elm (along with lactulose, licorice, and oat bran) was used over three weeks.

Mucilages taken in capsule or tablet form should be taken with plenty of water to reduce the risk of esophageal obstruction.

8. Safety Considerations and Drug Interactions

General Safety and Regulatory Status

There is no reliable data on adverse events from slippery elm and it is designated as "generally recognized as safe" (GRAS). There have been no large-scale clinical trials that have reported on adverse events associated with use of slippery elm preparations.

Slippery elm (Ulmus rubra) is used orally to treat sore throat and gastrointestinal upset, and topically for skin rash and irritation. Slippery elm preparations are generally recognized as safe and there is no evidence that it can cause elevations in liver-related enzymes or clinically apparent liver injury.

While not approved as therapy for any disease or condition, over-the-counter preparations are sold as demulcents and for gastrointestinal upset.

Drug Interactions (Oral Absorption Interference)

Due to its mucilaginous property, slippery elm may decrease absorption rates of other medicines; if taken concomitantly, it may be beneficial to separate slippery elm doses from those of other medicines by 1 to several hours.

Because slippery elm coats the lining of the digestive tract, it can physically block the absorption of other medications taken by mouth. The same gel that protects tissue also creates a barrier that oral drugs must pass through, potentially reducing how much of the medication reaches the bloodstream. To avoid this, slippery elm should be taken at least one hour after any oral medications. This gives other drugs enough time to be absorbed before the mucilage layer forms. This interaction applies broadly to any oral medication, not just specific drug classes. It is a physical effect of the coating rather than a chemical interaction, which means the timing rule is the same regardless of what is being taken.

Slippery elm may affect the absorption of some medicines. The interactions between slippery elm and medicines are not fully understood.

Pregnancy and Lactation

Use during pregnancy should be avoided. Abortifacient effects have been described, possibly related to vaginal use of whole bark pieces to induce abortion. This generally ineffective practice has also resulted in reports of serious urinary tract calculi when bark pieces have migrated into the bladder. Information regarding safety and efficacy of oral use in pregnancy and lactation is lacking.

Slippery elm may cause miscarriage, although it is not clear whether this is from taking it orally or from insertion of the bark into the cervix during pregnancy. Avoiding slippery elm while pregnant is advised. There is no information on the safety of slippery elm use by nursing mothers.

Allergic Reactions and Contact Dermatitis

Oleoresins from several Ulmus species have been reported to cause contact dermatitis, and the pollen of slippery elm is a known allergen. Common side effects of slippery elm include allergic reaction and contact dermatitis.

Potential Contraindications

Use should be avoided in cases of excessive mucus congestion of the bronchioles or bowels. Slippery elm is contraindicated in intestinal obstruction.

9. Conservation Status and Sustainability

Due to Dutch elm disease, there are very few mature slippery elm trees left in nature. Harvesting currently healthy trees for lumber or bark could remove disease resistance from the gene pool.

Dutch elm disease (DED), caused by an introduced fungal pathogen (Ophiostoma ulmi), devastated North American elm populations, including slippery elm, beginning in the 1930s. Estimates of the numbers of elms lost to DED are unknown but range into the hundreds of millions of trees given their former abundance.

Slippery elm has "at-risk" status on the United Plant Savers' list. It is considered endangered due to overharvesting and to Dutch elm disease, which has taken out many of the once very prolific elm species. Since the inner bark of slippery elm is used, harvesting the tree can kill it, and slippery elm should not be used from wild-harvested sources.

Ulmus rubra is listed as being of "Special Concern" in Rhode Island, and "Possibly Extirpated" in Maine. Ulmus rubra is of "Least Concern" globally, according to the IUCN Red List.

10. Overall Assessment of the Evidence Base

Limited studies have investigated the antioxidant and anti-inflammatory potential of slippery elm. However, no large clinical studies exist, and data are lacking to support use of slippery elm for any specific indication.

The claims behind slippery elm span the sore-throat demulcent role, IBS symptoms, GERD or reflux, and IBD (Crohn's and ulcerative colitis). The demulcent effect on the oropharynx has the strongest direct human-trial evidence in the slippery-elm-adjacent literature.

The most clearly demonstrated property of slippery elm — its formation of a viscous, mucilaginous gel upon contact with water — is both well-established chemically and underpins the biological plausibility of most of its claimed applications. However, for nearly all therapeutic indications, available evidence consists of: (1) traditional and ethnohistorical accounts; (2) in vitro studies; and (3) small pilot clinical trials of multi-ingredient formulas in which slippery elm is one of several active components. No large, well-designed randomized controlled trials have been conducted in which slippery elm is administered as the sole intervention. The overall scientific evidence base should therefore be characterized as preliminary and largely insufficient to confirm clinical efficacy for any indication, even as biological plausibility remains strong.

References

• LiverTox® (NCBI/NIH): Slippery Elm — National Institute of Diabetes and Digestive and Kidney Diseases (2024)
• Slippery Elm — PubMed (LiverTox entry, 2024)
• Integrative Therapies and Pediatric Inflammatory Bowel Disease: The Current Evidence — PMC (2016)
• Natural Product-Derived Drugs for the Treatment of Inflammatory Bowel Diseases — PMC (2014)
• Integrative Medicine for Gastrointestinal Disease — PMC (2017)
• Slippery Elm — Memorial Sloan Kettering Cancer Center Integrative Medicine
• Slippery Elm (Chapter) — Phytopharmacy: An Evidence-Based Guide to Herbal Medicinal Products, Wiley (2015), via ResearchGate
• Slippery Elm, its Biochemistry, and Use as a Complementary and Alternative Treatment for Laryngeal Irritation — ResearchGate / Journal of Voice (2012)
• Brinckmann et al. (2003): Safety and Efficacy of Throat Coat® in Acute Pharyngitis — Journal of Alternative and Complementary Medicine
• Ulmus rubra — Wikipedia (botanical overview)
• Ulmus rubra — USDA Forest Service Fire Effects Information System
• Slippery Elm Plant Guide — USDA Natural Resources Conservation Service
• Slippery Elm — United Plant Savers
• Slippery Elm Uses, Benefits & Dosage — Drugs.com
• Slippery Elm's Therapeutic Uses — EBSCO Research Starters
• Conservation of Genetic Diversity in Slippery Elm Despite Dutch Elm Disease — Conservation Genetics, Springer (2016)
• Ulmus rubra (Slippery Elm) — Go Botany, Native Plant Trust
• Slippery Elm: An Effective Anti-Inflammatory Agent — Clinical Advisor
• Slippery Elm, Its Biochemistry, and Use as a CAM for Laryngeal Irritation — American Journal of Plant Biology and Pharmacology
• Slippery Elm — USDA Southern Research Station