Slippery elm is a species of the elm tree family. It is commonly used for respiratory conditions (bronchitis, sore throat, cough, fever, and inflammation), gastrointestinal disease (peptic ulcers and diarrhea), dermatological conditions (skin abscesses and skin ulcers), and even cancer treatment.
Unlike many other herbal folk remedies, slippery elm has the unique distinction of having FDA approval for certain conditions. Let’s look at the evidence for the use of slippery elm and which conditions get approval from the FDA.
What Is Slippery Elm?
Slippery elm is also known as Ulmus rubra (family Ulmaceae), Indian elm, red elm, and gray elm. It is a species of elm tree that is native to North America and Canada. It has a red-brown bark and grows up to 18 to 20 meters tall.
It was used by Native Americans and the early settlers for a variety of reasons, including making canoes and fires but also for healing. The leaves of the slippery elm were used in the American Revolution to heal gunshot wounds. With the passing of time, slippery elm has continued to be used right up to the current day. Nowadays, the main interest in the healing properties of slippery elm relates to the bark of the tree and not the leaves.
The bark of the slippery elm tree contains mucopolysaccharides, hexoses, pentoses, and polyuronides. The plant also has phytosterols, sesquiterpenes, calcium oxalate, cholesterol, and tannins.
There are 3,000 slippery elm products for sale on Amazon, including powder, capsules, lozenges, oil, tea, and even pet formulas. These products cost on average $3.50 per oz and $10/fluid oz.
Is There Any Research?
There are 430 published research studies on slippery elm, including just 4 human clinical trials/reports. To put this into context, there are almost 2,000 published studies and 63 clinical trials on cinnamon. Cinnamon is a valid comparison as another tree whose bark is of medicinal interest.
What Are Demulcents?
The bark of the slippery tree produces a slime (think of oysters) once it comes in contact with water. The slime (medically called mucilage) acts as a mechanical barrier to protect the skin and body tissues.
Demulcents are agents that soothe and protect the underlying tissues.
Slippery elm has FDA approval as a demulcent for sore throats (1). It is worth noting that this is the only FDA-approved indication for slippery elm.
Slippery elm is used by herbalists to soothe the mouth, throat, upper airways, and upper gastrointestinal tract. Slippery elm is used as a cough suppressant, as it is believed to coat the cough receptors in the upper airway. Equally, it is believed to coat the upper gastrointestinal tract and help with symptoms of heartburn.
There are two theories about the use of slippery elm when it comes to the lower gastrointestinal tract.
Some herbalists feel that the mucilage is inactivated as it passes through the stomach. As such, this limits the benefits of slippery elm to the mouth, upper airway, and esophagus.
Other herbalists believe that slippery elm causes reflex activation of mucus-secreting glands along the entire length of the gastrointestinal tract, which offers preventive and therapeutic benefits beyond the stomach.
At this time, neither theory is substantiated by science.
Slippery elm has FDA approval as a demulcent for sore throats, although there are no clinical trials to support this indication.
Does Slippery Elm Improve IBS, Bloating, or Diarrhea?
An Australian study compared two natural medicine formulations for irritable bowel syndrome (2). A total of 31 patients were assigned to either a formulation containing a mixture of dried powdered bilberry fruit, slippery elm bark, agrimony aerial parts, and cinnamon quill (for diarrhea-dominant irritable bowel disease) or a formulation containing slippery elm bark, lactulose, oat bran, and licorice root (for constipation-dominant disease).
The study showed that the two formulations had different effects depending on whether the study participants had diarrhea- or constipation-dominant irritable bowel symptoms.
The diarrhea-directed formula did not help with bowel habit but did improve abdominal pain, straining, and bloating. The constipation-directed formula improved bowel habit, abdominal pain, and bloating.
This is one of the four human clinical studies looking at slippery elm.
From the perspective of understanding the clinical benefits of slippery elm, this study has a number of major limitations:
- Only 31 patients were enrolled in the study, including patients with different types of symptoms, e.g. diarrhea and constipation. Moreover, the study looked at a wide range of variables in these two patient populations (bowel habit, pain, bloating). This makes it very difficult to draw any conclusions. The study was over-ambitious.
- Formulations were used in the study (as opposed to single agent preparations), which makes it difficult to attribute any specific outcome to any one component of the formulation.
- Either way, this study is unlikely to help us understand slippery elm bark, as both formulations used in this study contained slippery elm.
There is no convincing clinical evidence to support a role for slippery elm in irritable bowel disease.
Does It Aid in Weight Loss?
A study from New York Chiropractic College in 49 healthy volunteers showed that the study subjects lost weight and had improvements in total cholesterol and low-density lipoprotein cholesterol following a complex dietary intervention which included supplementation with multiple agents, including slippery elm (3).
The supplementation contained over 12 other bio-active compounds and was only taken during week 2 of the 3-week study. There are too many variables to attribute the weight loss in this study to slippery elm.
There is no proof that slippery elm aids in weight loss.
Does It Help With Psoriasis?
A group of researchers in Hawaii enrolled five patients with chronic psoriasis in a ten-day residential nutritional program, followed by a six-month dietary intervention (4). The diet consisted of fresh fruit and vegetables with a minimal amount of processed food (essentially an anti-inflammatory diet). Saffron tea and slippery elm bark water were also consumed daily.
All five patients were noted to have improvements in their psoriatic skin plaques at the end of the study. It is hard to take this as proof that slippery elm helps psoriasis, given the fact that the sample size was very small and the slippery elm was just part of a larger dietary intervention.
There is no convincing evidence that slippery elm can help psoriasis.
Does It Help Prevent Breast Cancer?
Slippery elm is part of a popular alternative breast cancer treatment called Essiac, which was developed in the 1920s by Rene Caisse (5). (Essiac is Caisse spelled backwards). Essiac contains burdock (Arctium lappa), sheep sorrel (Rumex acetosella), slippery elm bark (Ulmus rubra), and Indian rhubarb (Rheum officinale) or turkey rhubarb (Rheum palmatum).
Flor-Essence® is an eight-herb formula derivative of Essiac that is sold in health food shops and contains Essiac plus red clover, blessed thistle herb, kelp, watercress, and citric acid.
There are conflicting results from in vitro studies about the effect of Essiac on breast cancer (6).
One study from Canada showed that Essiac can inhibit breast cancer cell growth (7).
However, another in vitro study (also from Canada) showed that Essiac can promote cell growth in breast cancer tumor cell lines (8).
A retrospective cohort study was carried out in 510 women with breast cancer who were randomly chosen from the Ontario Cancer Tumour Registry (9).
The aim of the study was to determine differences in health-related quality of life between users and non-users of Essiac. The study found that Essiac neither improved the quality of life nor mood in these women.
There is no proof that Essiac is an effective treatment for breast cancer.
Does It Lower Stress and Anxiety?
There are no studies looking at slippery elm in stress or anxiety.
There is nothing to draw on to support a role for slippery elm in stress or anxiety.
Is Slippery Elm Safe?
Slippery elm has been reported to cause contact dermatitis and abortions, and the pollen is allergenic in some people (1). As a demulcent, slippery elm may impair the absorption of other drugs by physically blocking it.
There is a case report that dates back to 1932, in which a surgeon reports finding a piece of slippery elm in the bladder of a pregnant woman (10). The slippery elm had been mistakenly placed in the urethra instead of the vagina during an attempted abortion. The slippery elm was removed, and the baby was successfully delivered.
Two further case reports of slippery elm bladder stones in pregnancy were published in the 1950s (11).
Slippery elm is one of the very few herbs that come with an FDA endorsement. This endorsement is as a demulcent for sore throats and not for any other indication.
Yet, we have seen that there are only four human clinical studies to guide us. None of them relate to sore throats. How then did slippery elm get FDA approval?
It seems that slippery elm was initially grandfathered in as an “old drug.” Subsequently, the leading manufacturer of the slippery elm lozenge provided data to the FDA, which allowed slippery elm to maintain the FDA seal of approval for sore throats.
True to its name, slippery elm may have “slipped” past the FDA reviewers but not past the more discerning #HBS readership who know that there is no science to support a medicinal or health-promoting role for slippery elm.