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


Abstract and key points

  • Essiac is a herbal mixture mainly administered as tea.
  • There is no evidence for Essiac as an effective and safe cancer treatment.

Essiac is a herbal mixture usually administered as tea. It is promoted mostly via the internet as an alternative cancer cure.

There is no evidence from clinical trials to indicate that it is effective. No clinical trial has been carried out to assess its efficacy and the only published uncontrolled clinical investigation did not suggest that Essiac has an effect on tumour burden.

The safety profile of Essiac is largely unknown but some of its ingredients are associated with possibly considerable adverse effects. Patients are advised not to use any other cancer treatments including chemo- or radiotherapy.

Read about the regulation, supervision and reimbursement of herbal medicine at NAFKAMs website CAM Regulation.

What is it?

Scientific name / brand name / common name

Essiac tea has been used for over 70 years as a remedy for the adverse effects caused by conventional cancer treatments and supposedly for curing cancer itself. The name ‘Essiac’ was created by the Canadian nurse Renée M. Caisse (‘Essiac’ is ‘Caisse’ spelled backwards)1-3. Other Essiac products are known as Flor-Essence®.


The four herbs contained in Essiac® are:
• Burdock root (Arctium lappa L.),
• Indian rhubarb root (Rheum officinale L.),
• Sorrel (Rumex acetosa L.)
• Slippery elm bark (Ulmus rubra/fulva Muhl.)

A modified Essiac product (Flor-Essence®) also includes the following four additional herbs:
• Watercress (Nasturtium officinale L.),
• Blessed thistle (Centaurea = Cnicus benedictus L.),
• Red clover (Trifolium pratense L.) and
• Kelp (Laminaria digitata).

History / providers

According to Renée Caisse, an English miner’s wife had received the recipe for Essiac from a Native Ojibwa Indian medicine man, and had cured her breast cancer with this treatment. Renée Caisse, who worked at the Bracebridge Cancer Clinic in Ontario, Canada from 1935 to 1941, treated cancer patients with Essiac herbal tea for 50 years.

In 1938, concerns about the use of Essiac were raised, after evidence of one reported death and one report of toxicity after Essiac tea injections emerged4,5. In 1941, the Bracebridge Cancer Clinic was closed following a request by the Canadian authorities. Between 1959 and 1978 Caisse worked with Dr Charles Armao Brusch, director of the Brusch Medical Clinic in Cambridge, Massachusetts, in the US, to modify the original recipe and promote the use of Essiac. After carrying out some laboratory studies on mice, four further herbs were added to the recipe (see above) to improve the healing action and taste of Essiac. In 1977 Mrs Caisse sold the original Essiac recipe to Resperin Corporation Ltd of Toronto, Canada.

In 1982 the Resperin Corporation Ltd carried out some poorly designed trials in which physicians using the product were asked to submit case reports. The Canadian Department of National Health and Welfare terminated the tests, claiming that Resperin had conducted a poorly conceived and executed investigation. Health Canada concluded that the evidence was unconvincing and that there was no scientific evidence to support claims that Essiac could cure cancer6. However, under the Canadian Emergency Drug Release Programme, Essiac could be obtained on physician’s request. In 1995 the Essiac formula and its trademark were purchased from Resperin Corporation Ltd by David Dobbie. Thus, Essiac® Products Inc of New Brunswick became the manufacturer of Essiac®. Another Canadian product, Flor-Essence®, is manufactured in British Columbia, where Charles Armao Brusch is involved in using the eight herbs of the modified Essiac formula. Nowadays, more than 40 different formulas of Essiac are available globally.

Claims of efficacy / mechanisms of action / alleged indication

Renée Caisse documents her view of how Essiac affects the cancer process as follows: after enlarging and hardening of the tumour following the first few treatments, tumour softens and, if the tumour was located near an exterior route, the patient discharges large amounts of pus and fleshy material. She believed that somehow Essiac would cause cancerous cells to retreat to the site of the original tumour where they would then shrink and vanish.

Charles A Brusch claimed that Essiac works by identifying toxins, gathering them, breaking them down and discharging them. He also suggested that in an unpublished double-blinded study carried out by his institute, positive results were observed including pain cessation, increased appetite, improved sleep, well-being and energy, decreased depression, anxiety and fear and a decrease in nodular masses.

The explanations put forward for a mechanism of the therapy are not supported by good evidence, nor are they deemed a possible and sufficient explanation by current scientific standards.

Application and dosage

The tea is usually taken 1-3 times before meals to minimise possible adverse effects such as nausea, vomiting and diarrhoea. Initially, Caisse administered one of the herbs by injection and gave the others as tea. Nowadays, most products are in tea form but other products also exist in the form of drops, capsules, liquids and dry versions. The patient is supposed to boil the mixture and then drink the tea. The patient information also advises that no other treatment, including chemotherapy and radiotherapy, should be used while taking Essiac.

Prevalence of use

In 1982 when Canadian health officials conducted a retrospective review of Canadian patients treated with Essiac they found that about 150 physicians in Canada had at that stage reportedly requested supplies of Essiac on behalf of their cancer patients7. In a Canadian survey from 2000 among women with breast cancer 15% reported using Essiac (ResperinTM, Canada Limited)8. Two further surveys were carried out in the USA and targeted specifically at Flor-Essence® users in order to quantify its use, it was found that among the 5051 respondents 22% were diagnosed with breast cancer9,10. Finally, in a survey at the Royal Marsden Hospital in London, UK 318 cancer patients were asked about their use of Essiac and 6% reported using Essiac11.

Legal issues

Essiac cannot be marketed as a drug because it has no licence. It is therefore usually sold as a nutritional supplement. In Canada, Essiac is currently unapproved for marketing and cannot be used in clinical trials without a valid preclinical new drug submission. However, the Canadian government allows Essiac to be manufactured and sold. Manufacturers are not allowed to make any medical claims, instead Essiac is promoted as a health-enhancing herbal tea. Patients who wish to obtain Essiac must ask their physician to make a request to the Canadian Bureau of Human Prescription Drugs, which relays the order to the company and the company then ships it directly to the patient.


Essiac products vary in price from €4.15 to hundreds of Euros per month for pre-made bottled blends. A pre-fabricated Essiac tea can range from €15.00 to €24.00 per ounce bottle. A higher price does not necessarily indicate higher quality of the product.

Does it work?


Three reviews exist in the peer-reviewed literature1,2,12, which did not identify a single published clinical trial. The first review, by Kaegi et al.1 discusses the history and safety of Essiac along with laboratory and clinical evidence. The second review by Boon et al.2 reviews the efficacy and safety of various botanical medicines (including Essiac). The third is a systematic review carried out in the USA by researchers at Natural Standard (an international multidisciplinary collaboration including contributors from more than 100 academic institutions) showed a lack of high-quality clinical trials to substantiate any of Essiac's traditional uses12. The results are inconclusive despite indications from preclinical, animal and laboratory data suggesting possible positive effects caused by Essiac application.

Controlled trials

No controlled studies are available.

Epidemiological studies

In a retrospective cohort study of Essiac to ascertain its effects in women with breast cancer in Canada, 510 women with a positive breast cancer pathology report who were diagnosed between 2001 and 2003 responded to a mail survey13. The survey packet included a) the Functional Assessment of Cancer Therapy Breast Cancer Version (FACT-B), b) the Profile of Mood States (POMS), c) the Yale Social Support Index (YALE), d) Patterns of use of Essiac and e) prevalence of general use of complementary and alternative medicine. Overall, 8.1% of the surveyed women were using Essiac. Results showed that there were differences on one of the subscales regarding health-related quality of life (physical well-being) as assessed by the FACT-B scale (p<0.02) between Essiac users and non-users for which Essiac users seemed to score better. However, on all other subscales, women who reported Essiac use consistently had higher scores compared to non-users, meaning that scores for health-related quality of life and mood were generally worse in Essiac users. Furthermore, Essiac seemed to have a negative effect on users as those reported scores indicating a higher burden due to their disease. Dose, frequency of use and brand of Essiac product did not affect disease-specific QoL or various mood states on the POMS. However, the authors of the survey put forward the likely explanation that Essiac use is a marker of physical distress. Only two adverse events were reported in this survey, involving mild gastrointestinal upset and an unpleasant taste.

Case series/reports

A Canadian study collected case reports submitted voluntarily by physicians. This case series included 86 patients with advanced cancers who had been treated with Essiac7. Forty-seven patients received “no benefits”, eight of the reports were impossible to evaluate, 17 patients died, one patient experienced ‘subjective improvement’, five required fewer analgesics, four had an ‘objective response’, and four were in ‘stable condition’. All of the patients also received conventional treatment, which could have explained their improvement.

Pre-clinical studies

Essiac was tested in a mouse sarcoma model in the US by the Memorial Sloan Kettering Laboratories, New York, in 1959 and again from 1973 to 197614,15. Some unpublished preliminary reports suggested some evidence of biological activity. The results of six immunotherapy tests and two chemotherapy tests of Essiac samples as tested on the mouse sarcoma model, showed no activity.

An in-vitro study comparing Essiac® and Flor-Essence® in human breast cancer cells found that both of the teas demonstrated antiproliferative and differentiation inducing properties, but this effect was only observed at high concentrations (1/10 and 1/100)3.
Most of Essiac’s identifiable components have shown anti-cancer properties individually16-24.

In a Canadian animal lab study Essiac was administered orally to rats25. The administration demonstrated a modest gastric protective effect. In 2006 a U.S. study wanted to assess the effect of Flor-Essence® and Essiac® on cell proliferation. Herbal tonics were tested in various types of cancer cells isolated from human breast tumors26. It was found that Flor-Essence® and Essiac® herbal tonics can stimulate the growth of human breast cancer cells in vitro through estrogen receptors mediated as well as estrogen receptors independent mechanisms of action.

A Canadian-Australian research team carried out another in vitro analysis of Essiac® by measuring its activity27. The in vitro analysis showed significant antioxidant and immuno-modulatory properties as well as neoplastic, cell specific cytotoxicity,.
Another Canadian research team evaluated the anti-proliferative effects of Essiac TM on in vitro and in vivo models of prostate cancer compared to Paclitaxel. The investigations showed no marked anti-proliferative effect28.

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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