Essiac
Also called: Flor Essence, Essiac tea.
Last reviewed 2026-09-16. How this works.
Treating cancer Grade D
No human evidence of benefit, or none that survived testing.
Nobody has shown this tea helps, and in animals and in the dish it made breast tumours grow more.
No human benefit data, and animal and cell work suggesting tumour promotion.
The claim
The claim is that Essiac, a herbal tonic, treats cancer. It is among the best known alternative preparations in North America.
What it does
No mechanism of benefit is established. What the laboratory work found runs the other way.
The evidence
The National Cancer Institute records that no controlled human data are available to suggest Essiac or Flor Essence can be effective in treating cancer.1
In 112 rats, mammary tumour incidence was 82.5 percent in the water group against 90 percent and 97.3 percent in the two groups given the tonic, a dose-dependent increase. In the laboratory, both tonics stimulated the growth of human breast cancer cells, through both oestrogen receptor-mediated and independent routes.12
One human trial exists. Its citation is in this register and its result is not, because it has not been read. That trial determines whether this entry stays where it is.3
The studies this rests on
-
Flor-Essence herbal tonic in Sprague Dawley rats1
An animal study, not in people, measured a clinical outcome, 112 animals.
dose-dependent increase in mammary tumour incidence.
The harm
This D carries a warning no other D in the register carries. This is not a compound nobody examined. It is one that was examined, in animals and in cell culture, and showed tumour promotion.12
It stays at D rather than moving to E for a reason the book is strict about. Every harm signal here is animal or cell culture. This book spends twenty-seven chapters insisting that laboratory findings do not establish what happens in a person, and that rule cannot be suspended for a compound the author disapproves of. An E requires human evidence pointing the wrong way.1
What is absent
No controlled human data suggest Essiac is effective. One human trial exists and its result has not been read into this register.
Scope: controlled human data on effectiveness.
Established by regulatory statement, National Cancer Institute PDQ summary, checked 2026-09-16. Result: no controlled data available from human studies to suggest effectiveness.13
What to ask
If something has only ever been tested in animals, what does that tell us about what it does in me?
The dish-to-person gap
The register holds no human pharmacokinetic measurement for Essiac against any laboratory concentration.
When to call your team — no warning signs are recorded
Whatever you are taking or thinking of taking, the people treating you can only weigh it if they know about it. That is true when nothing has been written down here, and it is most true then.
The register records no warning signs for Essiac. That is not a statement that nothing can go wrong.
Interactions
The register holds no measured interaction between Essiac and a cancer treatment class. An empty list means nobody has measured it.
Nobody having looked is not the same as nothing being there. That is what this line says and all it says.
The whole interaction list, and how to turn it into a pharmacy review request.
Find a trial instead
One human trial exists and its result has not been read into this register.
Search ClinicalTrials.gov for recruiting studies of Essiac OR Flor Essence
A trial is the same decision with monitoring, a known preparation and a doctor who knows what else you are taking.
References
Essiac/Flor Essence, National Cancer Institute PDQ summary, health professional version. The animal study is Bennett LM, Montgomery JL, Steinberg SM, et al. Flor-Essence herbal tonic does not inhibit mammary tumor development in Sprague Dawley rats. Breast Cancer Research and Treatment 2004;88(1):87-93.
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 18 note 12. The author string is abbreviated in the source that was read and has not been expanded.
Kulp KS, Montgomery JL, Nelson DO, et al. Essiac and Flor-Essence herbal tonics stimulate the in vitro growth of human breast cancer cells. Breast Cancer Research and Treatment 2006;98(3):249-259.
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 18 note 13. The author string is abbreviated in the source that was read and has not been expanded.
Zick SM, Sen A, et al. Trial of Essiac to ascertain its effect in women with breast cancer, known as TEA-BC. Journal of Alternative and Complementary Medicine 2006;12(10):971-980.
No persistent identifier recorded.
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 18 note 14. The author string is abbreviated in the source that was read and has not been expanded.