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

There are no controlled clinical trials available but only a retrospective cohort study and a case series.

Anticancer treatment

  • Tumour burden: Reports from one case series (n=87) did not suggest that Essiac had an effect on tumour burden.

Supportive care

  • Quality of life:  One uncontrolled retrospective cohort study (n=510) concluded that Essiac did not appear to improve health-related quality of life or mood states.

The safety profile of Essiac is largely unknown but some of its ingredients are associated with possibly considerable adverse effects. An indirect risk is that patients using Essiac are advised to cease conventional cancer treatments including chemo-or radiotherapy.


Wider B, Mora D, CAM-Cancer Collaboration. Essiac [online document], Aug 31, 2023

Document history

Assessed as up to date in August 2023 by Dana Mora and revised by Barbara Wider. Assessed as up to date in August 2020, January 2019, February 2017, April 2016 and January 2015 by Barbara Wider. Revised and updated in February 2013, December 2011 by Katja Boehm, August 2009 by Katja Boehm. Summary first published in May 2005, authored by Katja Boehm and Edzard Ernst. Next update: August 2026

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) (Kaegi 2020, Boon 2004, Tai 2004). 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 emerged (Thomas 1993, Meehan 1997). 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 cancer (NIH, 2020).

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.

Alleged indication

According to the proponents, Essiac can be used to strengthen the immune system and as an anti-cancer remedy. Essiac’s original developer Renée Caisse documents her view of how it 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 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.

These claims are not supported by good evidence, nor are they deemed a possible and sufficient explanation by current scientific standards.

Mechanisms of action

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 1976 (Hutchinson 1988, Glun 1991) . 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) (Tai 2004).  Most of Essiac’s identifiable components have shown anti-cancer properties individually (Foldeak 1964, Dombradi 1966, Itokawa 1982, Woo 1977, Morita 1984, US Congress 1990, Belkin 1952, Kupchan 2000, Pettit 1977) .

In a Canadian animal lab study Essiac was administered orally to rats (Leonard 2006). 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 tumors (Kulp 2020) . 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 activity (Seely 2020). 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 effect (Eberding 2007).

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 patients (Henderson, 1982). In a Canadian survey from 2000 among women with breast cancer 15% reported using Essiac (ResperinTM, Canada Limited) (Boon, 2020). 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 cancer (Low, 2001, Tamayo, 1999). 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 Essiac (Morita, 2020).

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.

There are no controlled clinical trials available in the peer-reviewed scientific literature. One uncontrolled retrospective cohort study assessing quality of life in breast cancer patients and one case series in patients with advanced cancer

Anticancer treatment

  • Tumour burden: Reports from one case series (n=87) did not suggest that Essiac had an effect on tumour burden.

Supportive care

  • Quality of life:  One uncontrolled retrospective cohort study (n=510) concluded that Essiac did not appear to improve health-related quality of life or mood states.

Description of included 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 survey (Zick 2006). 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.

A Canadian study collected case reports submitted voluntarily by physicians. This case series included 86 patients with advanced cancers who had been treated with Essiac (Henderson 1982). 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.

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 formula (Ulbricht 2009). 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 effect (Rodriguez 1995, Schulz 2020).


None currently known


None currently known.

Adverse effects and interactions

The following information regarding safety, adverse effects and interactions is available from NatMed Database 2023) for the individual plants Essiac contains:

Burdock root (Arctium lappa L.) Orally, burdock can cause an allergic reaction. Rarely, it has caused anaphylaxis (Sasaki 2003). 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 use (Gruenwald 1998). 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 edema (McGuffin 1997).

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 (Brinker 1998).

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 content (Brinker 1998).

Watercress (Nasturtium officinale). Orally, large amounts of watercress can cause gastrointestinal irritation (Gruenwald 1998). Theoretically, excessive or prolonged use might cause kidney damage (Brinker 1998). Consuming large amounts of watercress with high vitamin K content might theoretically antagonize the anticoagulant effects of warfarin (Bolton-Smith 2020).

Blessed thistle (Centaurea = Cnicus benedictus). When administered orally and used in doses greater than 5g/cup of tea, it can cause stomach irritation and vomiting (McGuffin 1997).

Red clover (Trifolium pratense). The oral administration can cause rash-like reactions, myalgia, headache, nausea, and vaginal spotting (Tice 2001). 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 content (Bolton-Smith 2020). There is some concern that red clover might interfere with the effects of tamoxifen because of its potential estrogenic effects (Tice 2001).

Kelp (Laminaria digitata). Orally, kelp can induce or exacerbate hyperthyroidism (Nelsen 2002, This 2001). The iodine in kelp can cause idiosyncratic reactions. Prolonged high intake of dietary iodine is associated with goitre and an increased risk of thyroid cancer (Baker 2020). Kelp seems to have anticoagulant effects and therefore, theoretically, taking kelp with antiplatelet or anticoagulant drugs might increase the risk of bruising and bleeding (Phaneuf 2020).

Quality issues

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

Baker DH. Iodine toxicity and its amelioration. Exp Biol Med (Maywood) 2004;229:473-8. Accessed 7th of September 2020.

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Bolton-Smith C, Price RJ, Fenton ST, et al. Compilation of a provisional UK database for the phylloquinone (vitamin K1) content of foods. Br J Nutr 2000;83:389-99. Accessed 7th of September 2020.

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Dombradi CA, Foldeak S. Screening Report on the Antitumor Activity of Purified Arctium Lappa Extracts. Tumori 1966;52:173.

Eberding A, Madera C, Xie S, Wood CA, Brown PN, Guns ES: Evaluation of the antiproliferative effects of Essiac on in vitro and in vivo models of prostate cancer compared to paclitaxel. Nutr Cancer 2007; 58(2):188-196. Accessed 7th of September 2020.

Foldeak S, Dombradi GA. Tumor-Growth Inhibiting Substances of Plant Origin. I. Isolation of the Active Principle of Arctium lappa. Acta Phys Chem 1964;10:91- 93. Accessed 7th of September 2020.

Glun GL. Essiac. Nature’s cure for cancer. Wildfire 1991:6:48-55.

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