The formula for the herbal remedy was given to Caisse in 1922 by a hospital patient whose breast cancer had been healed by an Ontario Indian medicine man. Essiac came within just three votes of being legalized by the Canadian parliament in 1938. Over the years, many prominent physicians voiced their support for the efficacy of Caisse's medicine. For example, Dr. Charles Brusch-a founder of the prestigious Brusch Medical Center in Cambridge, Massachusetts, and a former physician to President John F. Kennedy-declared that "Essiac has merit in the treatment of cancer" and revealed that he cured his own cancer with it. In a notarized statement made on April 6, 1990, Dr. Brusch testified, "I endorse this therapy even today for I have in fact cured my own cancer, the original site of which was the lower bowels, through Essiac alone."

Despite such support, Rene Caisse lived under the constant threat of persecution and harassment by Canadian authorities. Today, Essiac is unapproved for marketing in the United States and Canada. However, Resperin Corporation of Ontario provides Essiac to patients in Canada under a special agreement with the Canadian Health and Welfare department, which permits "emergency releases of Essiac on compassionate grounds" while still deeming it "an ineffective cancer treatment." Another company reportedly has the authentic formula for the herbal remedy in Caisse's handwriting, plus eight of her formula variations for specific cancers, including cancer of the prostate. It recently made Essiac available through various distributors. A number of herbal distributors claim to sell the original Essiac tea. Prospective users should carefully weigh the background of all vendors and examine all claims with caution.

Rene Caisse refused to publicly divulge the precise Essiac formula during her lifetime, fearing that a monopolistic medical establishment would either try to discredit the formula or use it to reap enormous profits. Also, she wanted Essiac safe for immediate use on suffering cancer patients, but medical experts demanded prior testing on lab mice. Caisse repeatedly offered to reveal the exact formula and method of preparation if the Canadian medical authorities would first admit that Essiac had merit in the treatment of cancer. But the doctors and politicians argued that they realistically couldn't give any such endorsement until they first knew what was in the herbal mixture. The result was a stand-off.

The principal herbs in Essiac include burdock root, turkey rhubarb root (Indian rhubarb), sheep sorrel, and slippery elm bark. Burdock root, a key active ingredient, is also a major ingredient of the Hoxsey herbal remedy. As discussed in the chapter on the Hoxsey therapy, two Hungarian scientists in 1966 reported "considerable antitumor activity. in a purified fraction of burdock.1 In addition, as also discussed, Japanese scientists at Nagoya University in 1984 discovered burdock contains a new type of desmutagen, a substance uniquely capable of reducing cell mutation either in the absence or in the presence of metabolic activation. So important is this property, the Japanese researchers named it the B-factor, for "burdock factor."2 Another herb in Essiac, turkey rhubarb root, was demonstrated to have antitumor activity in the sarcoma-37 animal test system. Herbalists, however, believe that the synergistic interaction of herbal ingredients contributes to their therapeutic effects. They point out that laboratory tests on a single, isolated compound from one herbal formula fail to address this synergistic potency.