Essiac was popularized in Canada during the 1920s, when the developer, a nurse from Ontario, began to advocate its use as a cancer treatment. In 1922, the developer obtained an herbal tea formula from a female breast cancer patient who claimed the mixture had cured her disease. Reviewed in [1-6] The patient reportedly received the formula from an Ontario Ojibwa Native American medicine man. The developer subsequently modified the formula, producing both injectable and oral forms of treatment. Reviewed in [2-9]
From 1934 to 1942, the developer operated a cancer clinic in Bracebridge, Ontario, and dispensed Essiac free of charge. Reviewed in  In 1938, members of the Royal Cancer Commission of Canada visited the clinic and heard testimonials from patients who had been treated with the mixture. Reviewed in [4,8] The Cancer Commission concluded there was only limited evidence for the effectiveness of Essiac. After years of controversy, the developer closed the clinic in 1942 but continued to provide Essiac to patients until the late 1970s. Reviewed in [4,5] (Refer to the Human/Clinical Studies section of this summary for more information.)
From 1959 until the late 1970s, the developer collaborated with an American physician to conduct clinical and laboratory studies of Essiac and to promote its use. Reviewed in [4,8] This collaboration led to the development of the eight-herb formula now marketed as Flor Essence. None of the results of these collaborative studies were reported in peer-reviewed scientific journals.
In 1977, the developer provided a four-herb recipe for Essiac to a Canadian corporation. Reviewed in [6,8] In 1978, the corporation filed a preclinical new drug submission with the Canadian Department of National Health and Welfare (Health Protection Branch) and was given permission to conduct clinical studies of Essiac’s safety and effectiveness in cancer patients. Reviewed in [4-6,8,9] In 1982, this permission was withdrawn when it was determined that the corporation had not fulfilled commitments to adequately control the manufacturing consistency of Essiac, to isolate and characterize active substances in the mixture, and to design and execute appropriate clinical trials. Reviewed in [4-6] During this period, restrictions were imposed on the promotion of Essiac as a cancer treatment, but the corporation was allowed to distribute it to cancer patients through their physicians under Canada’s Emergency Drug Release Program (also called Health Canada’s Special Access Programme). Reviewed in  While the preclinical new drug submission was in effect in Canada, the corporation filed an unsuccessful New Drug Application (NDA) with the U.S. Food and Drug Administration, seeking permission to market Essiac in the United States. Details of the NDA submission, which can be disclosed only by the corporation, have not been made public. Reviewed in  (Refer to the Human/Clinical Studies section of this summary for more information.)
In the early 1980s, the Canadian Department of National Health and Welfare (Bureau of Human Prescription Drugs) conducted a retrospective review of case summaries submitted by physicians whose patients had obtained Essiac under the Emergency Drug Release Program. Reviewed in [2,5,8] The Department found little evidence to suggest that Essiac was effective as a cancer treatment. (Refer to the Human/Clinical Studies section of this summary for more information.)
Also in the 1980s, the manufacturers of Essiac-like products began to market their formulations as health tonics and to avoid making claims of effectiveness in treating disease. Consequently, the mixtures were no longer subject to regulation as drugs. Reviewed in  Essiac is not currently available under Canada’s Emergency Drug Release Program.
In 1995, the corporation that acquired the four-herb recipe for Essiac from the developer dissolved voluntarily. Later that year, a new company was formed to manufacture and distribute this proprietary herbal mixture. Reviewed in 
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