Can slippery elm cause cancer? What the research does and doesn't show

No evidence connects slippery elm bark, taken by mouth, to causing cancer. There's also no clinical evidence that it treats cancer — including in Essiac, the four-herb tea that contains slippery elm bark and is sometimes used by people with a cancer diagnosis, where reviewers have found a lack of high-quality human trials.

What the evidence doesn't support

It doesn't support the idea that oral slippery elm bark causes cancer — no toxicology or safety review identified for this page finds a cancer risk from it. It also doesn't support slippery elm, or the herbal blend Essiac that includes it, as something that treats cancer. Essiac is a mixture of slippery elm bark, burdock root, sheep sorrel and Indian rhubarb, marketed since the 1920s to people with cancer; a systematic review of the published and unpublished literature on it found a lack of high-quality clinical trials substantiating any of its traditional uses, and called the preclinical evidence "inconclusive."

What the trials found

A systematic review by the Natural Standard Research Collaboration searched 10 databases, 20 additional journals, and the bibliographies of 50 secondary sources for evidence on Essiac. It found weak evidence from preclinical, animal and laboratory studies, no well-designed human trials, and a general lack of both safety and efficacy data — concluding that well-designed trials of Essiac or its individual herbs, slippery elm bark among them, are needed before any firm recommendation can be made.

A 2007 laboratory study tested a diluted Essiac preparation across a battery of assays: antioxidant activity, immune markers, and toxicity to several cell lines grown in a dish. The preparation showed antioxidant activity and some immune-modulating effects, and was toxic to one line of ovarian cancer cells (A2780) in the dish; it also inhibited two liver enzymes involved in drug metabolism (CYP1A2 and CYP2C19) and slowed blood-clot breakdown. None of this was tested in an animal or a person, and the results describe the four-herb Essiac mixture, not slippery elm bark on its own.

A separate review of herb–cancer-drug interactions named Essiac, alongside garlic, mistletoe and other herbs commonly used by cancer patients, as a supplement whose effect on drug-metabolizing enzymes creates a real potential to interact with cancer drugs — even though almost none of these herbs have been tested in a rigorous clinical trial.

Questions people ask

Can slippery elm cause cancer?

No evidence found for this page supports that. No toxicology study or safety review of slippery elm identifies a cancer risk from oral use.

Does slippery elm, or Essiac, treat cancer?

No. The only systematic review of Essiac — the herbal tea that includes slippery elm bark — found a lack of high-quality clinical trials and called the evidence inconclusive.

When to talk to a doctor

Slippery elm and Essiac are not a treatment for cancer, and nothing above should delay or replace care from an oncologist. If you have a cancer diagnosis or are undergoing treatment, ask your oncologist before adding any herbal supplement — including slippery elm or Essiac — since herbs that affect drug-metabolizing enzymes can change how well a cancer treatment works. See who should not take slippery elm and slippery elm and medications for more.