Sometime prior to 1922, Rene Caisse was given the recipe by an English miner's wife who said it came from an old medicine man. The original formula had 8 herbs but Rene refined it to the 4 herbs and named it "Essiac". Treating terminal cancer patients with Essiac, she gained physician support and operated her own Bracebridge Cancer Clinic from 1935 to 1941. However, Rene Caisse finally had to close her Clinic after endless hassles with Canadian health laws and Health officials.

Rene Caisse kept her formula a secret most of her life, concerned that lay people would make it incorrectly or it would be commercially exploited. She even refused to reveal it to interested research centers in the US, like Memorial Sloan-Kettering Cancer Center and the Brusch Medical Clinic.

When she was 89 years old, Rene Caisse signed over her Essiac recipe to Resperin Corporation Limited of Toronto, Ontario on October 26, 1977, because Resperin promised to do clinical trials to prove Essiac could cure cancer. Rene died 14 months after she signed the Resperin Agreement.

Resperin clinical trials were poorly conducted and in 1982, Health Canada concluded there was no evidence to support claims that Essiac was an effective cancer treatment. However, Essiac could be obtained by physician request under Canadian Emergency Drug Release Program for many years.

The Essiac formula and trademark was purchased from Resperin Corporation by David Dobbie in 1995 and his Essiac® Products Inc. of New Brunswick became the manufacturer of Essiac®. The allied Essiac® International of Ontario owned by Terry Maloney was formed to market the Essiac®. Resperin Corporation dissolved itself in 1998 and the Resperin rights were sold (but not to Essiac®).

"From Resperin Corporation" was the Canadian Essiac® promotion used to connect their formula to Rene Caisse, letting people think Resperin Corporation still made the product (despite Resperin protests about that use of its name). Essiac® promotion in 2000 became "From Resperin Canada", which usurped Resperin rights of real "Resperin Canada" company in Canada who owned the rights.

More confusion, two Essiac® trademarks exist, an unrelated company owned by Dr. Pierre Gaulin
of Florida holds the legal Essiac® trademark in the US. He sells all of the Rene Caisse formulas.

More controversy, Dr. Charles Brusch started claiming (after Rene died) that she had revealed her formula to him during her brief time at Brusch Medical Center in 1959-1960 (contradicted by evidence in a recent Snow/Klein book). Dr. Brusch got together with Elaine Alexander (Canadian broadcaster enthusiastic about essiac) to have Flor-Essence, his 8 herb tea, manufactured by Flora Inc. in 1993 (and Linda Paulhus of MA claims Brusch gave her a version of his 8 herb formula in 1986).

A few people knew Rene's Essiac formula. Rene became disappointed with Resperin and gave the recipe to Gilbert Blondin. Her close friend and helper Mary McPherson knew it and continued making Essiac for Rene's patients after she died. Dr. Gary Glum's 1988 book "Calling of An Angel" about Rene Caisse had a $79.95 video offer revealing her Essiac formula (he got it from Pat Judson, Detroit patient of Rene's). After the recipe became public, the essiac bandwagon started rolling with dozens of essiac entrepreneurs claiming to have "genuine" essiac or an "improved version".

The recipe was confirmed as the "real thing" by Mary McPherson, who helped Rene write out the formula for Resperin, and generic essiac marketers on Prices page claim they use this recipe.