As of 2015, there is no clear evidence that Essiac herbal tea provides any cancer-fighting benefits, according to the National Cancer Institute. The U.S. Food and Drug Administration does not approve Essiac herbal tea for treating cancer patients.
The multiple animal tests conducted to see if any benefits occur from taking Essiac herbal tea yielded mixed results, explains the National Cancer Institute. A 1970 experiment concluded that the test subjects did not experience a boost in their immune systems to fight cancer. Another test in 1983 revealed similar results but noted that the animals died when given high doses of the substance. The results indicated that the tumor cells in animals taking the Essiac herbal tea grew larger than before taking the substance. There are no reports of clinical trials in any peer-reviewed journals regarding the efficacy of Essiac herbal tea in treating cancer, so Essiac herbal tea sellers cannot claim that it fights cancer.
Since the safety of Essiac lacks a thorough scientific study, side effects are theoretical and are based on reactions that occur with some of its components, such as burdock root, sheep sorrel and slippery elm bark, notes the Susan G. Komen Foundation. Some of these side effects may include heightened urine flow and low potassium blood levels.