Written by Katja Boehm and the CAM-Cancer Consortium.
Updated February 8, 2017


Is it safe?

There is no literature regarding the safety of Essiac. The above review from the Natural Standard Collaboration notes that there is a lack of safety data for Essiac and the other preparations that are marketed under the exact formula12. However, it cannot be assumed that Essiac is safe as it is a product with an unknown safety profile particularly with regards to use during pregnancy and lactation and concomitant use with other drugs.

Patients are also at risk as they are advised that no other treatment, including chemotherapy and radiotherapy, should be used while taking Essiac.

Adverse effects associated with its use have not been reported. The constituent herbs may cause allergic dermatitis and have a laxative effect29,30.


None currently known


None currently known.

Adverse effects and interactions

The following information regarding safety, adverse effects and interactions is available from Natural Medicines Comprehensive Database 31 for the individual plants Essiac contains:

Burdock root (Arctium lappa L.) Orally, burdock can cause an allergic reaction. Rarely, it has caused anaphylaxis32. Theoretically, taking burdock with anticoagulant or antiplatelet drugs might increase the risk of bleeding due to decreased platelet aggregation.
Indian rhubarb root (Rheum palmatum) Orally, rhubarb can cause cramp-like or spasmodic gastrointestinal discomfort, watery diarrhoea, and uterine contractions; there is also one report of anaphylaxis with short-term use33. Chronic use or abuse of rhubarb can cause electrolyte loss (especially potassium), hyperaldosteronism, accelerated bone deterioration, albuminuria, hematuria, dehydration, inhibition of gastric motility, pseudomelanosis coli (pigment spots in intestinal mucosa), arrhythmias, muscular weakness, nephropathies, and edema34.

Sorrel (Rumex acetosa L.). Orally, excessive amounts of sorrel can cause diarrhoea, nausea, polyuria, dermatitis and gastrointestinal symptoms. Theoretically, concomitant oral administration may cause precipitation of some drugs due to the high tannin content of sorrel.35.

Slippery elm bark (Ulmus rubra Muhl.) Orally, the whole bark is an abortifacient36. Topically, slippery elm extracts can cause contact dermatitis and the pollen is an allergen. In theory, the consumption of slippery elm bark when taken with other drugs may slow the absorption and reduce serum levels of orally administered drugs due to mucilage content35.

Watercress (Nasturtium officinale). Orally, large amounts of watercress can cause gastrointestinal irritation33. Theoretically, excessive or prolonged use might cause kidney damage35. Consuming large amounts of watercress with high vitamin K content might theoretically antagonize the anticoagulant effects of warfarin37.

Blessed thistle (Centaurea = Cnicus benedictus). When administered orally and used in doses greater than 5g/cup of tea, it can cause stomach irritation and vomiting34.

Red clover (Trifolium pratense). The oral administration can cause rash-like reactions, myalgia, headache, nausea, and vaginal spotting38. Concomitant use with drugs that have constituents that might affect platelet aggregation could theoretically increase the risk of bleeding in some people. Concomitant use of large amounts of red clover can theoretically increase the anticoagulant effects and bleeding risk of these drugs due to its coumarin content37. There is some concern that red clover might interfere with the effects of tamoxifen because of its potential estrogenic effects38.

Kelp (Laminaria digitata). Orally, kelp can induce or exacerbate hyperthyroidism39,40. The iodine in kelp can cause idiosyncratic reactions. Prolonged high intake of dietary iodine is associated with goitre and an increased risk of thyroid cancer41. Kelp seems to have anticoagulant effects and therefore, theoretically, taking kelp with antiplatelet or anticoagulant drugs might increase the risk of bruising and bleeding42.

Quality issues

The quality of the mixture depends on the quality of each individual ingredient used in preparing the mixture.


Katja Boehm, CAM-Cancer Consortium. Essiac [online document]. http://cam-cancer.org/The-Summaries/Herbal-products/Essiac. February 8, 2017.

Document history

Assessed as up to date in February 2017 by Barbara Wider.
Assessed as up to date in April 2016 by Barbara Wider.
Assessed as up to date in January 2015 by Barbara Wider.
Assessed as up to date in February 2013 by Katja Boehm.
Fully revised and updated in December 2011 by Katja Boehm.
Fully revised and updated in August 2009 by Katja Boehm.
Summary first published in May 2005, authored by Katja Boehm and Edzard Ernst.


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