Herbs to Know: Slippery Elm

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Slippery elm bark, a traditional herb used to treat irritated mucous membranes, is also listed as an over-the-counter drug in the United States
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Slippery elm bark contains ­numerous carbohydrates, ­especially mucilage

In the mid 1960s, Hall of Fame San Francisco Giants pitcher Gaylord Perry threw pitches that some baseball fans identified as the outlawed spitball. Decades before, pitchers had tried a little of everything to make the ball roll, bounce, and jump to confound the batter, but old-timers agreed that slippery elm bark, chewed as tablets or little slivers, worked best. Perry’s pitches, however, were excellent sinkers–not spitballs.

Slippery elm, still available in drugstores and natural product stores today, may also confound herb consumers. As an herb, it is often sold as a dietary supplement. Yet it is also approved by the U.S. FDA as an over-the-counter drug for soothing sore throats, tickly coughs, and other irritations of the mucous membranes of the mouth and throat.

Slippery elm’s classification as a drug recognizes its long ­tradition of usefulness in the United States, but only a few brief scientific papers address its effectiveness, and no clinical studies have been conducted. At the same time, extensive scientific research has documented the effectiveness of other medicinal herbs such as ginkgo, saw palmetto, and echinacea, but these remain rele­gated to the realm of dietary supplements, and their manufacturers can make no claim as to their medicinal effects.

What is slippery elm?
The Pennsylvania botanist Henry Ludwig Muhlenberg (1756-1817) first drew attention to the slippery elm tree in a 1793 publication, in which he named it Ulmus rubra. Later, the eminent French botanist Andre Michaux (1746-1802) named it Ulmus fulva; his was the first book on the flora of North America. Today Muhlenberg’s name is ­accepted as the correct one, although many herb books continue to use the obsolete U. fulva.

Ulmus is the classical name for elms. The species name rubra, meaning red, refers to the rust color of the tree’s buds before it leafs out in spring. Our common name “elm” survives unchanged from Anglo-Saxon, Celtic, Gothic, and Teutonic dialects.

Knowing a plant’s current scientific name can be essential when seeking information about it. I once visited Harvard University’s Arnold Arboretum in Jamaica Plains, Massachusetts, hoping to photograph a slippery elm tree. The afternoon passed as I searched a splendid elm grove for a tree tagged Ulmus fulva, the name I had in my head as the correct one for slippery elm. When I looked the tree up in a botanical manual, I found that I had passed by the slippery elm several times–it was correctly labeled U. rubra.

Several features distinguish slippery elm from other eastern North American elms. Its leaves look much like those of American elm (U. americana), but the leaves of slippery elm are sandpapery on the upper surface; those of American elm are smooth. Slippery elm’s silky waferlike fruits are smooth-edged and hairless along the edges; the fruits of other eastern North American elms have a hairy fringe. Slippery elm thrives in dry upland soils as well as moist, alkaline stream banks from Maine west through the St. Lawrence Valley to the Dakotas, south to Texas, and east to Florida.

Slippery elm was once harvested for domestic use and export. In the past century, so much slippery elm bark was harvested that the tree’s survival was threatened. In 1837, the legislature of Massachusetts commissioned distinguished Boston schoolmaster George B. Emerson to study the state’s woody plants. The result was A Report of the Trees and Shrubs Growing Naturally in Massachusetts (1846). In the 1875 revised edition, Emerson decried the tree’s decimation in eastern Massachusetts through overharvest of the bark.

In many places I have found it dead or dying, from having been stripped of its bark. . . . It is much to be regretted that the slippery elm has become so rare. The inner bark is one of the best applications known for affections of the throat and lungs. Flour prepared from the bark by drying perfectly and grinding, and mixed with milk, like arrow-root, is a wholesome and nutritious food for infants and invalids.

Slippery elm’s importance in history
The tawny or buff inner bark lends its highly mucilaginous or “slippery” qualities to many herbal products. It has a faint but distinctive fenugreek-like scent and a bland taste.

European settlers learned of its uses from Native Americans. Midwestern tribes used the fresh inner bark to make a soothing laxative. The Omaha rendered the tallow from fat mixed with slippery elm to prevent rancidity. In 1852, Dr. C. W. Wright reported in a pharmacy journal that when fatty substances and slippery elm bark at a ratio of 128:1 are heated for several minutes, the fat can be easily separated by straining and remains fresh.

In Colonial America, slippery elm emerged as an important domestic remedy, and in some cases as a food; it was sometimes used as a pudding base. The first work on ­American medicinal plants, J. Schoepf’s Materia Medica Americana (1787), listed it as “salve bark.” Surgeons during the American Revolution used slippery elm poultices as a field treatment for gunshot wounds, and one soldier, separated from his company, survived in the wilderness for ten days by eating the barks of slippery elm and sassafras. During the War of 1812, U. S. Army soldiers stationed on the Canadian frontier during a bitter winter fed their horses the inner bark of slippery elm after their stores of hay ran out.

Nineteenth-century physicians and herbalists recommended slippery elm for a plethora of ills. Pneumonia, consumption, pleurisy, and other lung afflictions were treated with slippery elm tea; a large dose of the tea was thought to literally slide parasitic tapeworms out of the digestive tract. Skin ulcers, abscesses, inflammations, fresh burns, chilblains, boils, carbuncles, and the sores of herpes, syphilis, and leprosy were treated with bark poultices, which tended to dry out and harden unless kept moist.

When a patient could not keep food down, early-nineteenth-century physicians recommended a broth made from the bark. One writer suggests that slippery elm bark made a good “formula” for weaning infants. A tablespoonful of the bark powder, cooked in a pint of milk, affords a nourishing diet for infants weaned from the breast, preventing the bowel complaints to which they are subject, and rendering them fat and healthy, wrote H. W. Felter and J. U. Lloyd in King’s American Dispensatory (1905).

Once an ingredient in cough syrups, slippery elm probably served more as a thickener for the syrup than as a cough suppressant, and it is no longer approved for this purpose.

Slippery elm throat lozenges
For over a century, drugstore shelves have held slippery elm throat lozenges made by the Henry Thayer Company. The firm, now located in Lincoln Center, Massachusetts, con­tinues to manufacture the lozenges, as do others.

I use slippery elm lozenges to soothe sore throats and coughs. Sometimes I make my own by mixing powdered slippery elm bark and honey into a thick paste. I roll generous pinches of the paste into marble-sized balls and dust each with a coat of dry slippery elm powder or powdered sugar. I freeze the lozenges in a sealed container until needed.

Modern use
Curiously, one of the few herbs approved as a nonprescription drug in the United States is rarely used in Europe, a center of herbal tradition and research. German regulatory texts do not mention slippery elm, although many British herbal works do.

Slippery elm’s soothing action results from its carbohydrate constituents, especially mucilage. It also contains a number of sugarlike compounds. In both England and the United States, after soaking a sliver of the bark in water to make it slippery, desperate women inserted the bark into the cervix to mechanically induce abortion. Fatal hemorrhage or infection sometimes followed, and consequently the sale of whole bark was banned.

Slippery elm bark, both powdered and in formulas, serves a useful purpose in treating minor mucous-membrane irritations. The herb has stood the test of time and remains appreciated today.

Further Reading
Emerson, G. B. A Report on the Trees and Shrubs Growing Naturally in the Forests of Massachusetts. 2nd ed. 2 vols. Boston: Little, Brown and Company, 1875.
Felter, H. W., and J. U. Lloyd. King’s American Dispensatory. 18th ed., 3rd rev. 2 vols. Reprint of 1905 edition. Portland, Oregon: Eclectic Medical Publications, 1983.
Foster, S. 101 Medicinal Herbs-An Illustrated Guide. Loveland, Colorado: Interweave Press, 1998.
Foster, S., and V. Tyler. Tyler’s Honest Herbal. 4th ed. Binghamton, New York: Haworth Press, 1999.
Newall, C. A., L. .A. Anderson, and J. D. Phillipson. Herbal Medicines: A Guide for Health-Care Professionals. London: Pharmaceutical Press, 1996.
Tyler, V., and S. Foster. “Herbs and Phytomedicinal Products.” In Handbook of Nonprescription Drugs. 11th ed. Washington, D.C.: American Pharmaceutical Association, 1996.

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